GEEK!mind

How to reload your .zshrc

2011-08-05T11:56:00.001+02:00

Stupid me, after editing my .zshrc I always invoked a new shell to apply those changes. Now I found out, that you can use your shell's built-in source command to reload your zsh settings.

sk@supernova:~/ > source ~/.zshrc

or, even shorter:

sk@supernova:~/ > . ~/.zshrc

Java: Customizing enums

2011-06-08T16:43:00.000+02:00

After reading this you might wonder why I would write about something obvious like that. And I agree. It is quite obvious. Once you know about it. However, first I didn't know and neither did the other Java programmers I've spoken to. So I thought it's worth writing up a quick blog post.

Probably all of you already know about enums and use them as type-safe flags or enumerations:

enum Cardsuit { CLUBS, DIAMONDS, SPADES, HEARTS };

That is pretty basic and probably everyone learned that in Java 101. What was new to me, though, is that you can customize the enum { } pretty much like a class.

So for example, one day I was working on a XML parser implementation, where depending on an attribute value of a XML element I had to make a decision. Since in XML everything is a String I wrote a quick method which compares an enum to a String. But I didn't know where to put it in my code. I figured the best place would be within the enum itself. Not really thinking that it would work, but still curious I tried the following:
I tried to compile it and voilà: it worked! No errors, no warnings.

In my actual XML parser I then would only have to do the following:

if ( Cardsuit.CLUBS.compareToString(xmlString) ) { .... }

Of course there would have been many other ways to do this, but this solution seems quite clean and elegant to me.

Android: Hide your application's media files from the Gallery App

2011-05-09T17:57:00.000+02:00

If you have a media heavy application it is very likely that you store the image, sound or video data on the sd-card, since it gives you a lot more space than bundling everything with the application. Also, it enables you to dynamically add, remove or modify your media data.

However, the problem that comes with it is, that all your media is public now and can be read by other applications, e.g. the Gallery App, which scans the whole sd-card for image files. To prevent other applications from scanning and displaying your media files, you can simply add an empty file called .nomedia in the root folder of your media data.

From the official Android documentation:

Name of the file signaling the media scanner to ignore media in the containing directory and its subdirectories. Developers should use this to avoid application graphics showing up in the Gallery and likewise prevent application sounds and music from showing up in the Music app.

Debugging Client-Server Communication

2011-04-13T11:15:00.003+02:00

Especially in mobile development you most likely have some client-server communication going on, which is often the source of a lot of problems and long debugging sessions. To make the debugging easier it is helpful to see what each side sends or receives. There are two UNIX tools that can come in quite handy in such situations:

netcat - to listen to all TCP and UDP connections on a specific port
cURL - to send 'fake' requests to a server

Both a very powerful tools and you can do a lot of stuff with them (e.g. write your own web server with a shell script). However, in this post we will keep it simple and focus on debugging a HTTP (JSON) communication between a web server and a mobile client (iPhone, Android, but could be pretty much any kind of client).

Listening to incoming requests

We start a listening server with

nc -lk $ip $port

-l: listen
-k: forces nc to stay listening for another connection after its current connection is completed.
$ip: the IP/interface you want to bind to. Use 0.0.0.0 to bind to all interfaces and IPs.
$port: the port you want to bind to. Doesn't really matter which one you use, as long as the client uses the same one to connect to.

In practice it might look like this:

sk@supernova:~/ > nc -lk 0.0.0.0 8080
POST /rpc HTTP/1.1
Accept: application/json
Content-type: application/json
Accept-Encoding: gzip
Host: 192.168.2.3
Content-Length: 152
Connection: Keep-Alive

{"id":3,"jsonrpc":"2.0","method":"sendTestMessage","params":{"clientVersion":"0.11.4-debug","user":"sk@geekmind.net","imei":"32420214181983746","message":"This is a test message :-)"}}

In green the HTTP header and in blue the actual content, in this case a JSON-RPC message. While the header is mostly irrelevant to us, it might in some cases contain useful information to detect the source of the problem. However, more interesting, and in most cases more prone to errors is our own "custom protocol" and its implementation. By evaluating the content section we can now easily compare if there is a difference between what we were expecting to receive and what the client was actually sending out.

Sending "fake" requests to a server

Sometimes the problem may not be in the client's implementation of our communication protocol, but on the server side. The complementary approach to the above example is to send "fake" requests to our server and look at the response we get.

With cURL it is as simply as that:

curl -v -i -X POST -d $data $uri

-v: verbose
-i: include HTTP headers in the output
-X: HTTP request type. Defaults to GET if none given
-d: data

Applied it might look like this:

sk@supernova:~/ > curl -v -i -X POST -d '{"id":1,"jsonrpc":"2.0","method":"sendTestMessage","params":{"clientVersion":"0.11.4-debug","user":"sk@geekmind.net","imei":"1111111111111111111"}}' http://android.geekmind.net/rpc
* About to connect() to android.geekmind.net port 80 (#0)
* Trying 74.125.43.121... connected
* Connected to android.geekmind.net (74.125.43.121) port 80 (#0)
> POST /rpc HTTP/1.1
> User-Agent: curl/7.19.7 (universal-apple-darwin10.0) libcurl/7.19.7 OpenSSL/0.9.8l zlib/1.2.3
> Host: android.geekmind.net
> Accept: */*
> Content-Length: 157
> Content-Type: application/x-www-form-urlencoded
>
< HTTP/1.1 200 OK
HTTP/1.1 200 OK
< Content-Type: text/html; charset=utf-8
Content-Type: text/html; charset=utf-8
< Cache-Control: no-cache
Cache-Control: no-cache
< Expires: Fri, 01 Jan 1990 00:00:00 GMT
Expires: Fri, 01 Jan 1990 00:00:00 GMT
< Date: Fri, 08 Apr 2011 09:19:32 GMT
Date: Fri, 08 Apr 2011 09:19:32 GMT
< Server: Google Frontend
Server: Google Frontend
< Transfer-Encoding: chunked
Transfer-Encoding: chunked
<
* Connection #0 to host android.geekmind.net left intact
* Closing connection #0
{"jsonrpc": "2.0", "id": 1, "error": "1", "message": "ERROR: user and IMEI do not match!"}}

In red the response we got from the server. In this case we used a real username with a wrong IMEI and tested if the server generates the right response. In our case the server correctly produced an error.

If you're interested in reading more about the actual implementation of client-server communication on mobile devices, check out my blog post Android: Simple HttpClient to send/receive JSON Objects. The code is available on GitHub.

If you want to directly monitor a real connection I suggest that you have a look at tools like Wireshark and tcpdump. Wireshark has a GUI and is fairly easy to understand. It also helps to have a server instance running on your local machine (development server), so you don't need to figure out how to tap into your phones WiFi connection.

Visual Life

2011-03-30T17:26:00.000+02:00

A collection of promo videos of Inte's Visual Life contest. Interesting people and inspiring to watch.

Check them out, if you get a chance.

The Age of Fire - Futuristic Interfaces

2011-02-12T20:33:00.001+01:00

Here is a really well-made video about futuristic interfaces in a completely interconnected home environment. It shows the beauty and usefulness that comes with it, but also points out the inherent problems of complete interconnectivity.

Interesting challenges for User Interface Engineers and Designers :-)

Shortcuts to improve your bash & zsh productivity

2011-01-26T00:48:00.004+01:00

So, you hate using a terminal? That might be, because you use the arrow keys to navigate character by character through a long command just to change a paramater at the other end of the line, right? Here's a list of my most-used bash & zsh shortcuts, that will definitely boost your productivity and will help you to improve your command line experience.

Shortcut	Action
`CTRL + A`	Move to the beginning of the line
`CTRL + E`	Move to the end of the line
`CTRL + [left arrow]`	Move one word backward (on some systems this is `ALT + B`)
`CTRL + [right arrow]`	Move one word forward (on some systems this is `ALT + F`)
`CTRL + U` (bash)	Clear the characters on the line before the current cursor position
`CTRL + U` (zsh)	If you're using the zsh, this will clear the entire line
`CTRL + K`	Clear the characters on the line after the current cursor position
`ESC + [backspace]`	Delete the word in front of the cursor
`CTRL + W`	Delete the word in front of the cursor
`ALT + D`	Delete the word after the cursor
`CTRL + R`	Search history
`CTRL + G`	Escape from search mode
`CTRL + _`	Undo the last change
`CTRL + L`	Clear screen
`CTRL + S`	Stop output to screen
`CTRL + Q`	Re-enable screen output
`CTRL + C`	Terminate/kill current foreground process
`CTRL + Z`	Suspend/stop current foreground process

Command	Action
`!!`	Execute last command in history
`!abc`	Execute last command in history beginning with abc
`!abc:p`	Print last command in history beginning with abc

History Search

Press CTRL + R to search through the history. Continue pressing CTRL + R until you find the entry you're looking for. Press [ENTER] to execute the current expression. Press [Right Arrow] to modify the current expression. Press CTRL + G to escape from search mode.

Special setup for Mac OS X

Go to Terminal -> Preferences -> Settings -> Keyboard

To enable the use of the ALT or OPTION key, select use option as meta key
To enable the CTRL + [left arrow] and CTRL + [right arrow] shortcuts, select

control cursor left and set it to \033b and
control cursor right and set it to \033f.

You know of any other important shortcuts that I missed? Please let me know in the comments.

Android: Better Logging Output

2011-01-19T23:31:00.000+01:00

Ever got annoyed by the flood of information in Android's adb logcat output? Luckily Google Engineer Jeff Sharkey put together a Python script to make the output visually more appealing and easier to follow. Below are a few tipps on how to effectively combine coloredlogcat.py with adb logcat's parameters and options.

Colored Logcat Output

Setup

Download coloredlogcat.py from Jeff Sharky's blog
Copy the script to your local ~/bin folder and make it executable

mkdir ~/bin cp ~/Downloads/coloredl chmod +x ~/bin/coloredlogcat.py

Add ~/bin permanently to your $PATH variable. Either in your .bashrc or .zshrc (or whatever shell you use) add or modify this line:

export PATH=$HOME/bin:$PATH

Usage
You can either use it directly, by simply entering coloredlogcat.py, or you can use adb logcat with all it's parameters and just pipe it into coloredlogcat.py

Show only DEBUG output from the MyApp TAG. Everything else is SILENT: *:s (not shown)

adb -d logcat "*:S MyApp:D" | coloredlogcat.py

Show only WARNING, ERROR and FATAL output. Great for checking on exceptions.

adb -d logcat "*:W" | coloredlogcat.py

References

Logcat Reference

Logcat priorities

V — Verbose (lowest priority)
D — Debug
I — Info
W — Warning
E — Error
F — Fatal
S — Silent (highest priority, on which nothing is ever printed)

Special options

adb logcat -c clears the entire log

Linux WiFi: operation not possible due to RF-kill

2011-01-15T16:26:00.003+01:00

Some people have been experiencing WiFi problems with Ubuntu 10.10 since an update that happend just before Christmas 2010. The problem seems to be a bug in a kernel module, which prevents the rfkill's soft and hard block from syncing correctly.

In practice that means you can press your laptop's WiFi button as often as you want, it doesn't change anything. Your wireless adapter will always appear as disabled. If you try to start the wireless interface manually you get the following error message:

sk@ubuntu:~# sudo ifconfig wlan0 up
SIOCSIFFLAGS: Operation not possible due to RF-kill

If you do a rfkill list all you should get an output similar to this:

sk@ubuntu:~$ sudo rfkill list all
0: hp-wifi: Wireless LAN
Soft blocked: yes
Hard blocked: no
1: phy0: Wireless LAN
Soft blocked: yes
Hard blocked: no

Depending on the state of your WiFi button the Hard blocked will either be yes or no. Press the WiFi button and run rfkill list all again to make sure the value for Hard blocked changes.

The actual problem is, that the Soft blocked value is always set to yes, because for some reason the syncing between the hardware block and the software block doesn't work as supposed. To override this behavior, you can just run rfkill unblock wifi and it should work again. Double check by entering rfkill list all again and make sure it looks like this, with all values set to no:

sk@ubuntu:~$ sudo rfkill list all
0: hp-wifi: Wireless LAN
Soft blocked: no
Hard blocked: no
1: phy0: Wireless LAN
Soft blocked: no
Hard blocked: no

If you then run ifconfig wlan0 up (or enable the wireless via your desktop's network manager) you should be able to connect to a wireless network again without any further issues.

The configuration, which I've been using:

Compaq Presario CQ60
Atheros AR5001 Wireless Network Adapter
Ubuntu 10.10

I also read, that some people could fix it, by turning off the WiFi button during the boot process and then switch it on again, once the system is up and running. It seems that the system expects the hard block to be set to off. This is still a bug, but it could explain why then the soft block didn't sync with the hard block any more.

Rapid Prototyping of Web Applications

2010-11-01T00:47:00.005+01:00

Ryan Singer from 37 Signals gave a really interesting talk at the Future of Web Apps in London about the rapid prototyping process of web applications.

For me, the most important insight was to start off with building a really bare-bone HTML framework, which then involves step-by-step by having already right from the beginning a programmer working on the data models and controllers in parallel with a web designer improving the markup and CSS, instead of going the traditional way of letting only a graphic designer spending days (or even weeks) bringing his design ideas to perfection and blocking other people (i.e. programmers) from getting started, to then finally figure out a couple of weeks later that from a UX perspective the whole thing doesn't work.

Kinda obvious and simple once you hear it. However, most people in the industry still have their way of thinking that you have to tinker a design visually to perfection, but don't get the point that a static design is only a small proportion of what makes an application gonna work or not.

UI Design (Photo by Lucas Mascaro)

Something I personally like a lot, is what I call "back to kindergarden" or the pen, paper & scissors approach, which basically means that we draw all pages and UI elements on paper by using different sized pens of various colors and then play around with them and walk through different use cases by moving the small paper snippets around and then discuss our ideas with other team members including developers. Including the developers is very important, because they're the ones who actually have to build the whole thing. They sometimes might restrict the creativity with bringing up all these ambiguous technological limits, but they're quite crucial when it comes down to decision making about feasibility and time estimates.

Tipp: having pre-designed templates, which can be printed out makes it a lot easier to throw away the current ideas and start over without having to completely start all the way from scratch again.

Hissing noise when connecting earbuds to MacBook

2010-10-12T18:53:00.000+02:00

Recently I bought some high quality Sennheiser earbuds, but since using them together with my MacBook I was annoyed by a constant hissing noise when playing back very quiet parts of a song. For a while I didn't bother and just accepted it as it is, but later on I played around with some tools in /Application/Utilities and found an application called Audio Midi Setup.

Luckily I was listening to some calm music while randomly fooling around with these settings and when I changed the bit rate of the Built-In Output from 2ch-16bit to 2ch-24bit all the sudden I got an impressive increase of sound output with almost no hissing noise. It's still not perfect, but definitely much better compared to what I was tortured with before. Although, increasing the bit rate all the way up to 2ch-32bit didn't cause any significant improvement to 24 bit, that's why I went with 2ch-24bit for now.

If someone can explain what the correlation between bit rate and hissing noise is, please let me know in the comments. I'm curious to know :-)

Android: Implementing your own Listener

2010-10-04T10:54:00.000+02:00

In Android development it's quite common to use things like OnClickListener and similar listeners to implement functionality triggered by a click on a button or other state changes. You probably use them all the time, without even knowing how they work. And actually you don't need to know. But it's worthwhile investing some time, because once you got the idea it's quite simple to implement your own listeners, which can come in handy here and there.

Listeners are pretty much callback functions implemented through Java Interfaces:

Interfaces are commonly used in the Java language for callbacks. Java does not allow the passing of methods (procedures) as arguments. Therefore, the practice is to define an interface and use it as the argument and use the method signature knowing that the signature will be later implemented.

I will explain it with a simple example. Lets say we create our own custom view for our new innovative user interface that is a bit more complex so that a normal Android Button just isn't satisfactory enough for our needs. Lets say we want to have something like a color picker in it:

In this case we would have our custom View ColorPicker, which senses for touch events in our color field and then calculates the correct color values. Now we have the option to store that color value within the ColorPicker and add an additional PREVIEW button to our user interface, on which the user has to click to preview the selected color on for example some random text.

If this is a process, which the user is applying a lot it will be pretty annoying to click every time on the PREVIEW button, just to update the text's color attribute and to see whether the color is okay or not. Wouldn't it be much better if the color on the text would update instantly whenever you change the selection in the color picker? This is quite an improvement to the overall user experience of your application. You reduce a step in the user's workflow and you save a button in the interface.

And it can be realized fairly simple by using listeners (or callbacks). First you need to define a new Interface within your ColorPicker class or as a separate interface file (like a class file) for a more generic use:

Now we have the interface definition, but we also need "something" that actually "holds" our interface. Therefor we add these lines to our ColorPicker class:

Now we have the basic framework for our listener. In addition we add a helper method to our ColorPicker class that calculates the correct color value whenever the user touches the color field and calls the onColorChanged method.

The final piece that is missing now is just our control Activity, that will respond to this change. We need to create a new instance of the OnColorChangedListener, assign it to our instance of the ColorView and implement our callback function onColorChanged, which in this case only applies the received color to myText. But you can implement here whatever you feel like.

I hope this tutorial was easy to understand. If there are still some issues that need to be cleared up please let me know in the comments. Interfaces might look like a bit of a hassle in the actual process of writing them down, but they will help you a lot in writing clearer code and designing the architecture of your application in a more structured way.

Android: Display dialogs in fullscreen

2010-07-25T18:41:00.033+02:00

Ever wondered how to maximize a dialog to the screen's full size? The first thing probably everyone would naturally do is to set

android:layout_width="fill_parent" android:layout_height="fill_parent"

in your mydialog.xml layout file. However, that doesn't seem to have any effect at all.

The solution that works is not much more complicated than that, but unfortunately not that easy to think of in the first place. What you have to do is, when you setup your Dialog in code, you have to set (again) your layout (as you do in the .xml file) after you set your content view.
I don't know why it works when set in code and not when set in the .xml file, but for now I just accept that it does. If you know the answer to this please let me know in the comments.

Android: open new Activity as Dialog

2010-06-17T17:44:00.006+02:00

Did you ever have the problem that your pop-up dialog was so complex that it messed its parent's activity's code? There is a very simple solution to that. Just create the whole thing as a new activity class and change them theme to Theme.Dialog in your AndroidManifest.xml for that specific activity:

And the result should looking similar to this:

That's a really quick & dirty hack. However, the most important thing I learned out of this "accident" is, that I now know how I can easily customize the basic look of my activity screens, just by changing the android:theme attribute in the activity element of the AndroidManifest.xml.

iPhone: "abuse" UITabBar to provide simple, good looking buttons

2010-05-15T20:58:00.059+02:00

The iPhone's UITabBar can also be used to provide as a simple, good looking solution adding extra functionality to the current screen. Similar to what Android tries to solve with the menu button, which, when selected pops up a menu providing extra functionality. Since the iPhone doesn't have a menu I thought why not use a UITabBar for that, which saves you a lot of time developing your own custom solution.

UITabBar items "abused" as buttons

Each UITabBar has a UITabBarDelegate, which requires you to implement

(void)tabBar:(UITabBar *)tabBar didSelectItem:(UITabBarItem *)item

for example like this:

However, there is one little annoyance. Whenever you click a button on a UITabBar it stays selected. Which is the right thing to do, when you actually use it as a tab bar. But since we are not, we have to add a little line of code in our UITabBarDelegate method:

[self.localNavigation setSelectedItem:nil];

This line makes sure, that as soon as we select a tab item in the UITabBar it immediately gets deselected again, with the result that it appears to the user like a normal button behavior.

Warning: this solution worked perfectly for me in the past. However, Apple might reject future applications, since you're giving the UITabBar a totally different purpose as it was originally meant for.

Chrome: adding shortcuts to bookmarks

2010-03-25T23:54:00.001+01:00

In Firefox you can associate shortcuts to your bookmarks, which I used to:

quickly open frequently used sites, e.g. Gmail, Facebook, etc. or
to open a page with a specific topic, e.g. the Wikipedia article about "Linux" or
to trigger a custom search or query, e.g. on Google Translate

Now that I recently switched from Firefox to Chrome I imported my Firefox bookmarks and still had the shortcuts available, but when I edited my bookmarks I couldn't find the option to modify the shortcuts, neither could I add new shortcuts.

After playing around a while I finally found something called "Search Engines", which is a bit of a misleading name, but does exactly the same as bookmark shortcuts in Firefox.

You get there by right clicking on the URL bar / search bar and selecting Edit Search Engines...

Now, when you click on Add you get a form like this, where Keyword is the shortcut you use in the address bar, URL the site where you wanna go with %s as a placeholder for your search term.

In this case to get to the Wikipedia article for "Linux" I would just have to enter "wiki Linux" in the address bar and I get directly there.

In case you wanna go to a static URL like Gmail you just don't use the %s placeholder and enter the URL completely.

Andoid: Eclipse error "Conversion to Dalvik format failed"

2010-03-07T17:57:00.002+01:00

If you receive this error in Eclipse when compiling large .java files or using big .jar libraries

[2009-03-30 17:28:14 - Dex Loader] Unable to execute dex: null
[2009-03-30 17:28:14 - MyProject] Conversion to Dalvik format failed: 
Unable to execute dex: null

then add the following to your eclipse.ini and the problem should be fixed:

-Xms128m
-Xmx512m

Still problems? Increase these values and try again.

iPhone: debugging EXC_BAD_ACCESS errors

2010-03-07T15:40:00.005+01:00

After developing for iPhone and Android for quite some time now I consider myself an advanced developer on both these mobile platforms. But even though I left the beginner stage, sometimes things still don't work as they should (or at least as I expected) and I thought sharing some of my learning experiences would help other developers to lessen their pain.

One of the biggest pains (besides Objective-C itself) is definitely the memory management on the iPhone. Luckily we don't have this problems on Android, due to the fact of using Java and garbage collection, which makes programming an ease (almost!) and enables you to focus on creating something rather than wasting a lot of time debugging. However, Apple decided not to include garbage collection for the iPhone, even though it's available within their frameworks and is actually used for Mac development. I won't elaborate much more on the pros and cons of Objective-C's memory management and the object ownership concept, since a lot of other bloggers ranted about that topic already too many times before me, but rather give you some useful tips to reduce the time you spend debugging.

The most common problem you will have is probably an EXC_BAD_ACCESS error, which occurs when you try to release memory that has already been released. This could be the reason if for example you try

to release an object, which you don't own
to release an object, which is in the autorelease pool
to release an object, which has the "assign" property instead of "retain"

The problem with that is, that the error doesn't occur at the point where you accidentally release the object, but when the object gets released somewhere else at a later point in the code, where it is actually supposed to be released. This could be either by another owner or when the autorelease pool is getting cleaned-up. And this "somewhere else" might not be easy to find. In general I recommend to compile and test your code as often as possible, because of the complex way you have to declare variables and allocate memory in Objective-C (declare, @property, @synthesize, eventually retain and release) it's very likely that you forget one of the steps in your code, especially when things need to be done quickly. In the end you will spend more time debugging and finding the problem than what it would have taken with just being more thorough from the beginning on.

You might, for example, get an output like this:

2010-03-07 15:03:11.136 MyProject[58016:207] *** -[UIView setFrame:]: message sent to deallocated instance 0x1b33240
Program received signal: “EXC_BAD_ACCESS”.

Finding the source of that problem is hard by just knowing the object's address in memory: 0x1b33240. Thus we should enable a few options in our executable's settings: under group & files doubleclick on your executable and then under the "Arguments" tab add and enable the following options:

NSDebugEnabled
MallocStackLogging
NSZombieEnabled
MallocStackLoggingNoCompact

Now recompile your code, run it in the simulator and try to reproduce the same error you had before. But this time you will be able to enter the following command in gdb:

shell malloc_history $PID $ADDRESS_OF_OBJECT_IN_MEMORY

In our case that would be (see the pid and address I marked red above):

shell malloc_history 58016 0x1b33240

and results with the following (or similar) output:

ALLOC 0x1b33240-0x1b33267 [size=40]: thread_a02fa500 |start | main | UIApplicationMain | -[UIApplication _run] | CFRunLoopRunInMode | CFRunLoopRunSpecific | PurpleEventCallback | _UIApplicationHandleEvent | -[UIApplication sendEvent:] | -[UIApplication handleEvent:withNewEvent:] | -[UIApplication _reportAppLaunchFinished] | CA::Transaction::commit() | CA::Context::commit_transaction(CA::Transaction*) | CALayerLayoutIfNeeded | -[CALayer layoutSublayers] | -[UILayoutContainerView layoutSubviews] | -[UINavigationController _startDeferredTransitionIfNeeded] | -[UINavigationController _startTransition:fromViewController:toViewController:] | -[UINavigationController _layoutViewController:] | -[UINavigationController _computeAndApplyScrollContentInsetDeltaForViewController:] | -[UIViewController contentScrollView] | -[UIViewController view] | -[CategorySuperViewController loadView] | -[CategoryViewController initWithStyle:] | -[Functionality requestNewAd] | +[AdMobView requestAdWithDelegate:] | +[NSObject alloc] | +[NSObject allocWithZone:] | _internal_class_createInstance | _internal_class_createInstanceFromZone | calloc | malloc_zone_calloc

What we can see is where exactly the error occurs, but we still don't know by what it is caused and where this happens in the code. What we know though, is that it has something to do with an AdMobView object, which we most likely released at some other point in our code where we shouldn't have released it (because we didn't have ownership or because it's on autorelease).

To fix the problem we just check all AdMobView releases. If you're unsure you can just temporarily disable them, recompile and run it again to see if that was the problem. Another thing, that happens to me sometimes, is that I accidentally type dealloc instead of release, which immediately removes the object from memory, while with a release it might keep existing, because it may still be owned by someone else. In general, never use dealloc (unless you really know what you're doing).

I hope this helps you to make iPhone development and debugging a bit easier and please let me know if something is still unclear.

Swype beta for Android

2010-03-07T13:41:00.000+01:00

After having been using the leaked version of Swype for a while, I'm happy to hear that they finally provide an official beta for Android.

If you haven't heard about Swype, yet, it's an innovate new way of rapidly entering text on mobile touch screen devices.

I highly recommend that you give it a try. I cannot image going back to the standard Android or iPhone keyboard, even though they're pretty good themselves. Check out this video comparing Swype with a standard touch keyboard.

Finally convinced? Get it here on Swype's beta page. Unfortunatelly, they made it a bit of a hassle to install. First you have to sign-up for their limited beta program, then you have to download the Swype Installer, install it, run it and log in. Now it will actually download the "real" Swype keyboard application. Need more details and help? Swype provides a step-by-step guide.

Some users, including myself, who had the leaked version of Swype installed before, might have some problems when switching over to the official beta. I got the following message:

"The Swype package you installed is configured for another device and will operate with limited functionality. Please contact Swype about this issue."

and wasn't actually able to swype. Pressing the letters one by one (like on a normal keyboard) worked, though. As a user pointed out on xda-developers.com you have to do the following steps to make it finally work:

1) Long hold your text box.
2) Switch input methods to another keyboard.
3) Type a letter or two. Swap back to Swype.

Android: providing different layout resources for older versions

2010-01-23T20:46:00.001+01:00

To provide backward compatibility with older phones still running on Android 1.5 you might have to provide separate layout resources for Android 1.5 and Android 1.6+. Especially when dealing a lot with RelativeLayout, which was basically crap before Android 1.6.

Instead of having one res/layout folder we will create two new folders:

res/layout-v3 for Android 1.5
res/layout-v4 for Android 1.6 and higher

Now move all your files to res/layout-v3 and test your application on various phones and emulators (which are running different Android versions). Whenever you see that there's a non-acceptable difference in the layout copy the responsible .xml-file to the res/layout-v4 folder and modify the file in both folders so that they work for Android 1.5 and Android 1.6 and higher again. Android will then pick the right layout resource during runtime depending on its current firmware version.

Bug in Android 2.0

There seems to be a bug in Android 2.0. Instead of picking the resource from res/layout-v4 as it should and if it doesn't find it there then from res/layout-v3, it expects the the resource wrongly in the default res/layout folder. To make it work you should rename res/layout-v3 back to res/layout again (or just create a symlink). The second problem or bug that comes with it, is to provide the special resources for Android 2.0 or higher. Instead of providing those in res/layout-v5 Android 2.0 expects wrongly res/layout-v6. So just use this instead for now. The bug is fixed in Android 2.0.1, but there are still quite some Android 2.0 phones out there.

I hope this post is not too confusing ;-)

Android: Custom List Item with nested clickable Button

2009-11-21T20:05:00.004+01:00

This tutorial will show you how to add a button (or any other clickable item) to a customized list view item.

In the screenshot above you can see a ListView with custom built items. Each list item consists of

TextView for the title
TextView for the content
RelativeLayout (clickable) consisting of

TextView: "For more information click here"
ImageView for the arrow icon

We start this tutorial at a point where you should already know how to create your own customized ListViews and Adapters. If you have no clue how to do so please let me know in the comments. If there's a demand I will eventually compile another tutorial about creating custom list items and list adapters in the future.
1) Build custom adapter that extends BaseAdapter and implement all the required inherited abstract methods from the parent class:

2) Implement View getView(int position, View convertView, ViewGroup parent):
This is where you create and manipulate the view that is used for a list item. I highly recommend that you take advantage of a view holder as it is described in this API example to improve speed and efficiency.

The crucial part is now that you, after you have inflated the list item's main layout

you also need to get hold of the sub-layout (bottom part). That's the part you want to be clickable.

3) Create an onClickListener for the bottom layout and associate the data (in this case a web URL) with the current view:

While for a OnItemClickListener, which is associated to each item of a ListView, we always know which item of the list has been selected through the int position paremeter. We don't have this information for our OnClickListener that is used in the bottom layout. So how do we get the neccessary information that is associated to the current list item?

The trick is to use View.setTag() and View.getTag(). The Android documentation states: “Sets the tag associated with this view. A tag can be used to mark a view in its hierarchy and does not have to be unique within the hierarchy. Tags can also be used to store data within a view without resorting to another data structure.”

In this example we use setTag() to store an URL with each sub-layout and getTag() in the onClickListener to extract that URL whenever a sub-layout was clicked. Then we create an Intent for our WebView, pass the URL to it and start a new Activity. And Voilà! You should have a web browser now displaying the website associated to the item you clicked before.

However, there's one little detail that keeps annoying me. Even though I now can click/tap the bar at the bottom via the touch screen interface I'm not able to select it via the trackball. It always selects the whole list item (see screenshot below) and from there goes directly to the next list item ignoring the bottom bar, even though I set .setFocusable(true) and setClickable(true) for the bottom bar's RelativeLayout in getView().

If anyone knows a solution to this please let me know in the comments or respond to my question asked on stackoverflow.

Android: Simple HttpClient to send/receive JSON Objects

2009-11-07T16:02:00.010+01:00

This tutorial is focused on creating a very simple HTTP client for Google's mobile operating system Android, which then can communicate with a web server and exchange JSON information. I won't go too much into detail, since the code is pretty much self-explaining and already has a lot of comments describing the program flow.

1) Create a new Android project

2) Add permission to access the Internet from your application to your AndroidManifest.xml

3) Create a new (static) class called HttpClient.java

4) Add the following code to your MainActivity.java

The full source code is also available on GitHub for download.

Check the official Android documentation for more information about JSONObjects and Apache's HttpClient classes.

I hope this tutorial was helpful for you. If it was too simple for your needs stay tuned. Upcoming tutorials will deal with the following topics:

Creating a separate HttpClient thread to uncouple the hard work happening in the background from the user interface

Dealing with HTTP exceptions: transport exceptions, protocol exceptions, timeouts.

Setting up a BackgroundService and a ServiceInterface, which will be the new home for our HttpClient. This enables many activies to simply connect to the service and to access the resources provided instead of creating a new HttpClient object for each activity

Instead of using a simple HttpClient (as shown in this tutorial), we will utilize ClientConnectionManager to provide us with a connection pool to save resources and improve performance

Android: Custom ListView Selector

2009-10-31T17:25:00.011+01:00

The following tutorial will show you how to create a custom list selector as shown in the image below. I use an orange frame around the selected list item in this example, but you can virtually design anything you like.

To make it easier we use the original files for the list selector and transition from the Android SDK as a draft and modify them instead of starting from scratch.

1) Copy files from the Android SDK:
Go to android-sdk/platforms/android-1.6/data/res/drawable and copy the following .xml files to your project's /res/drawable folder:

list_selector_background.xml
list_selector_background_transition.xml

You also need the following 9-patch images from the same folder, because they're referenced by the above .xml-files. You have to copy them, because within the SDK they're not a public resource, which means you can't just access them through the android: namespace as you could do with other public resources.

list_selector_background_focus.9.png
list_selector_background_longpress.9.png
list_selector_background_pressed.9.png
list_selector_background_disabled.9.png

2) Edit the two xml files and add to all resource values, which are publicly accessible the "android:namespace"

In our case this is only the following item:

All the other elements can point to the local namespace, because we copied the resources (images) into our local project's /res/drawable/ folder.

3) Modify whatever you like

Instead of having the selected list item been overpainted by a transparent orange color (as it is default in Android), I prefered to have a full opaque (non-transparent) border around the selected list item. Therefor I opened up the list_selector_background_focus.9.png file in gimp and removed everything except of a thin orange frame (→ make sure the center is transparent). The black pixels around the image are 9-patch parameters. Don't remove them. If you want to modify them read up on it first here.

4) Creating a new style

Open up your /res/values/styles.xml (create it if it doesn't exist) and add this new style to it:

The @drawable/list_selector_background is a reference to your list_selector_background.xml file in /res/drawable/

5) Applying the new style to your layout

Open up your layout's xml file and add the style attribute.

I also added android:drawSelectorOnTop=“true” so that the orange image frame will be drawn with full opacity (no transparency effects).

How to enable fake GPS on Android

2009-10-31T14:30:00.016+01:00

In order to build a location depend app or to test the behavior of your app at places besides the one you're currently located it is very helpful to use the Android emulator and just set your location manually.

This post will guide you through the steps of setting up fake GPS on the Google Android emulator
.

Set permissions in AndroidManifest.xml:

Find the correct local port for your Android emulator:

$ adb devices
List of devices attached
emulator-5554 device

The port we are looking for is in this case 5554. Now connect via telnet:

$ telnet localhost 5554
Trying ::1...
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
Android Console: type 'help' for a list of commands

Set your preferred location manually: You set the location with the geo fix command:

geo fix $longitude $latitude

For example the city center of Barcelona:

geo fix 2.169919 41.387917
OK

To get the latitude and longitude you want simply go to http://maps.google.com on your computer's web browser, move the desired location to the center of your screen and simply enter this little JavaScript command into the address bar:

CAUTION: the format of the coordinates you get from Google Maps is ($latitude, $longitude) - but the way you enter the geo fix for Android has longitude and latitude switched around.

Make sure everything works properly:

Just launch the Google Maps application in your emulator. It should take you directly to the location you entered and display a blue blinking light.

Access Android's Location Service in your application:

Notes:

I noticed that sometimes the manully entered location dissolves. I haven't looked into that yet, but a workaround for now is to simply re-enter the location via the geo fix command again.
You always mix up latitude and longitude?

Latitude: goes from East<>West, like the rungs of a ladder (→ sounds similar to latitude)
Longitude: runs from North<>South. Think of the globe as a big, fat guy with a long (→ longitude) tie hanging down from the North Pole.

Android: easier click listeners in 1.6

2009-10-26T10:47:00.006+01:00

Romain guy just posted a really cool improvement of button click listeners for the Android SDK 1.6 on the official Android Developers Blog.

Instead of having every time this recurring bunch of code to set up a simple click listener you can now just add

<Button android:onClick="myClickHandler" />

to your button element in your layout's XML file.

Finally the code to handle the click is as simple as that:

class MyActivity extends Activity {
  public void myClickHandler(View target) {
  // Do stuff
  }
}