The way to be great programmer

VPN for internal service

2016-11-30T21:57:00.000-08:00

Have to setup VPN for internal service, using AWS as VPN server
----
AWS VPN in 10 mins:
https://www.webdigi.co.uk/blog/2015/how-to-setup-your-own-private-secure-free-vpn-on-the-amazon-aws-cloud-in-10-minutes/
---
but I don't want all traffic go through VPN, I have to setup routes
using Apple script as below:

property version : "2016-12-01"
property theShellScript : "#!/bin/sh
rm /etc/ppp/ip-up
sudo echo '#!/bin/sh' >> /etc/ppp/ip-up
sudo echo '/sbin/route add -net "destination.com" -interface $1' >> /etc/ppp/ip-up
sudo echo '/sbin/route add -net google.com -interface $1' >> /etc/ppp/ip-up
chmod 0755 /etc/ppp/ip-up
cat /etc/ppp/ip-up"
do shell script theShellScript with administrator privileges

What it does is to put a ip-up file in /etc/ppp, when vpn is connect, the ip-up script will be executed, and route for "destination.com" will be route through VPN

Update UITableViewCell from itself

2016-04-13T18:54:00.003-07:00

The code that can update the cell itself.

// update UI on main thread
dispatch_async(dispatch_get_main_queue(), ^{
    //set cell need update
    [self setNeedsUpdateConstraints];
    [self updateConstraintsIfNeeded];
    [self setNeedsLayout];
    [self layoutIfNeeded];
    //trying to get the tableview
    id view = [self superview];
    // different level of UITableView wrapping in different iOS version,
    // for more detail please see:
    //  stackoverflow 
    while (view && [view isKindOfClass:[UITableView class]] == NO) {
        view = [view superview];
    }
    
    if (view) {
        UITableView *tableView = (UITableView *)view;
        NSIndexPath *indexPath = [tableView indexPathForCell:self];
        if (indexPath) {
            [tableView reloadRowsAtIndexPaths:@[indexPath] 
                             withRowAnimation:UITableViewRowAnimationNone];
        }
    }
});

[JavaScript]Get XMLHttpRequest Traffic

2016-04-11T20:30:00.001-07:00

Case: finding network traffic of a website, can't see relevant in the Console->network in Chrome, dig into code, it is XMLHttpRequest and not log in Console->Network

How: In console add hook into XMLHttpRequest

Code:

var rawOpen = XMLHttpRequest.prototype.open;

XMLHttpRequest.prototype.open = function() {
    if (!this._hooked) {
        this._hooked = true;
        setupHook(this);
    }
    rawOpen.apply(this, arguments);
}

function setupHook(xhr) {
    function getter() {
        console.log('get responseText');

        delete xhr.responseText;
        var ret = xhr.responseText;
        setup();
        console.log('url : %s',xhr.responseURL);
        console.log('ret : %s',ret);
        return ret;
    }

    function setter(str) {
        console.log('set responseText: %s', str);
    }

    function setup() {
        Object.defineProperty(xhr, 'responseText', {
            get: getter,
            set: setter,
            configurable: true
        });
    }
    setup();

Source : http://stackoverflow.com/questions/16959359/intercept-xmlhttprequest-and-modify-responsetext

[iOS] UITableView scroll to top when typing in the textfield will scroll to a wrong location

2016-04-04T20:36:00.002-07:00

My case is this:

I have a static table, with hidden cell(height = 0), custom cell that will open keyboard, and a reset button(that will reload table and scroll to top)

What is the problem:

Scroll to top will go to invalid offset.

How to regenerate:

type in the keyboard, reset(which scroll to top and reload the keyboard) and there will be space between my top cell and top of table (just like hidden cell consumed some space)

---

At first I thought it is the hidden cell problem, but it turns out to be problem on [tableView reloadData]

**[tableView reloadData] will interrupt scrolling, so make sure you call [tableView setContentOffset:] or [tableView scrollToRowAtIndexPath:] after all reload is done.

Reference: stackoverflow

Paypal say "Data does not match input character set or default encoding" when WooCommerce Wordpress Checkout with Chinese words

2015-11-17T19:09:00.000-08:00

Recently I am playing with Wordpress and WooCommerce shopping Cart plugin for wordpress to setup a simple E-commerce website, while I am using a plugin to add some extra info to my product ( WooCommerce Extra Fields ) with some chinese character, it randomly give me "Data does not match input character set or default encoding" during checkout.

After some digging on the network call, I found that the product name is in the Paypal link, and the chinese word is trimmed and become weird character.

I found the trim function wc_trim_string is the one to be blamed, and it is using php substr function.

The original wc_trim_string function in "woocommerce/include/wc-formatting-functions.php" contains the line:


 $string = substr( $string, 0, ( $chars - strlen( $suffix ) ) ) . $suffix;

i just replaced it with mb_substr and everything works like charm again. End result will look like:


 $string = mb_substr( $string, 0, ( $chars - strlen( $suffix ) ) ) . $suffix;

The reason is that substr function just trim without handling multiple-byte unicode character, and mb_substr is multi-byte safe.

This workaround should works on other multibyte/unicode character.

Note: Version of my WooCommerce is v2.4.8

[Android] AsyncTask blocking

2013-03-17T23:26:00.000-07:00

In different Android version, there is different handling on AsyncTask, some are in single thread, processed one by one, some are multi-threaded and processed at the same time.

1.0-1.5(API 1-3) single thread.
1.6-2.3.3 (API4-10) multi thread.
3.0+ (API 11 or up) single thread.

but if you want to have AsyncTask run on seperate thread, you can call

    task.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR, params);

instead of

    task.execute(params);

then the task will run on seperate thread, and not blocked by other threads.

[WPF]Background dynamic fill with one direction

2012-11-16T21:19:00.000-08:00

I have a very long and thin image, and I want to use it as a background image in WPF application, which the image should repeat horizontally.
My first code insight is from

WPF: How do i create a background that repeats horizontally without scalling?

But, it fails to repeats properly, the reason is that ViewportUnits="Absolute", so it actually stretch my image to very large. Which is kind of hardcode.

Then I saw this reference TileBrush.Viewport Property
So I use this this code to create the background brush instead

  <imagebrush imagesource="/Resources/Image/pattern.png" 
            tilemode="FlipY" viewport="0,0,0.033,1" 
            viewportunits="RelativeToBoundingBox"
            x:key="BackGroundBrush">

Which 0.033:1 is the width:height ratio of my background. With this brush, the image will be stretch to suitable height.

For repeat horizontally, just change tilemode to FlipX and viewport to "0,0,1,x" where 1:x is the ratio.

p.s. this method is a improved version of the stackoverflow solution on the way that it can show the whole image, but the drawback is the image might be stretched for a little. And seems there is no simple way to do this without binding.

Why Weibo SSO sdk don't jump back to my iOS app

2012-10-21T20:48:00.000-07:00

This question is for those didn't watch the documentation of the SSO-sdk(me as an example).

The callback url is not set in the web. It should be placed when you initiate the SinaWeibo instance. It is provided 2 init method and they are:

-(id) initWithAppKey:(NSString*)_appKey 
           appSecret:(NSString *)_appSecrect 
      appRedirectURI:(NSString *) _appRedirectURI
         andDelegate:(id)_delegate

and

- (id)initWithAppKey:(NSString *)_appKey 
           appSecret:(NSString *)_appSecrect 
      appRedirectURI:(NSString *) _appRedirectURI
   ssoCallbackScheme:(NSString *)_ssoCallbackScheme
         andDelegate:(id)_delegate

We should use the latter one and put the callback Uri as ssoCallbackScheme, then everything will be work fine.

Time to String? Date Format Patterns?

2012-10-18T02:30:00.001-07:00

To convert time to string, we always use formats like "yyyy-MM-dd HH:mm:ss", but sometimes we want something more like "18 Oct 2012" or "Wed 12:34:56", then the reference page can help you.

Date Format Patterns

With the table in the page, you should be good enough to do more tricks on date formats.

[iOS] Why no privacy alerts in simulator?

2012-10-15T22:49:00.002-07:00

This is not a bug. This is the restriction on simulator.
From the iOS6.0 release note, we seen that apple doesn't the privacy alerts in simulator.

Simulator

No privacy alerts are displayed in iOS Simulator for apps that access Photos, Contacts, Calendar, and Reminders.

For this release, iOS Simulator does not support testing In-App Purchase. Please use a device to test your apps that use this feature.

When attempting to play an MP3 sound in Simulator, you will hear a popping sound instead.

Source:iOS6.0 release note

Reset iPhone Privacy

2012-10-15T22:43:00.001-07:00

To clear/reset iPhone Privacy Settings like contacts and location services, you can go to Settings and follow the routine:

Settings -> General -> Reset -> Reset Privacy and Location

Which is useful for developer, as the privacy prompt only prompt once if you never reset.

Toggling Privacy settings in iOS6 will kill the app

2012-10-14T22:59:00.000-07:00

If you played with Location Services in iPhone, you knows that after you changed the location setting in iPhone Settings, you are able to get the change and update your application. While Contact(AddressBook) and Location Services are both packed in Privacy Setting, you would expect there is similar behaviour on Contact.

Sadly, its not true. After you changed the setting of contact, your app will receive a SIGKILL signal and stop.

Source:StackOverflow

Apple iDevice architecture

2012-10-11T22:16:00.001-07:00

Since XCode4.5, apple have drop support to ARM architecture of ARMv6, and set the minimum device version to 4.3, which burden developers that need to support older version.

To understand how it affect developers, one should understand there are 2 fields they need to handle with, they are:

1. ARM Architecture
2. iOS Deployment Target

to know more about architecture, please visit instruction set architecture.

In this article, we mainly focus on the architecture of different apple device.

The first question you may want to ask is, what iDevice is using ARMv6 architecture? The answer is simple, For iPhone, it is iPhone(original) and iPhone 3G. For iPod Touch, it is only 1st generation.
For iPad, none of them are using ARMv6. Here is more detail:

iPhone:

Model	CPU Core	ARM architecture
iPhone	620 MHz (underclocked to 412 MHz) ARM 1176JZ(F)-S	ARMv6
iPhone 3G	620 MHz (underclocked to 412 MHz) ARM 1176JZ(F)-S	ARMv6
iPhone 3GS	833 MHz (underclocked to 600 MHz) ARM Cortex-A8	ARMv7
iPhone 4	1 GHz (underclocked to 800 MHz) Apple A4
iPhone 4S	1 GHz (underclocked to 800 MHz) Dual-core Apple A5
iPhone 5	Apple A6	ARMv7s

iPod Touch:

Model	CPU Core	ARM architecture
1st generation	620 MHz (underclocked to 412 MHz, originally 400 MHz) ARM 1176JZ(F)-S	ARMv6
2nd generation	620 MHz (underclocked to 533 MHz) ARM 1176JZ(F)-S	ARMv7
3rd generation	833 MHz (underclocked to 600 MHz) ARM Cortex-A8 core
4th generation	1 GHz (underclocked to 800 MHz) ARM Cortex-A8
5th generation	ARM Cortex-A9

iPad:

Model	CPU Core	ARM architecture
iPad (original)	1 GHz ARM Cortex-A8	ARMv7
iPad 2	1 GHz dual-core ARM Cortex-A9
iPad (3rd generation)	1 GHz dual-core ARM Cortex-A9

iOS6 permissions [Contacts]

2012-10-08T20:53:00.001-07:00

On iOS6, apple introduce new privacy control, user can control the accessment of contact and calender by each app. So, in the code side, you need to add some way to request the permission. In iOS5 or before, we can always call

ABAddressBookRef addressBook = ABAddressBookCreate();

to get the addressbook without any problem, but in iOS6, if you don't have permission, this call will just return empty pointer. That why we need to change the method to get ABAddressBookRef.

__block BOOL accessGranted = NO;
if (ABAddressBookRequestAccessWithCompletion != NULL) { // we're on iOS 6
    dispatch_semaphore_t sema = dispatch_semaphore_create(0);
    ABAddressBookRequestAccessWithCompletion(addressBook, ^(bool granted, CFErrorRef error) {
        accessGranted = granted;
        dispatch_semaphore_signal(sema);
    });
    dispatch_semaphore_wait(sema, DISPATCH_TIME_FOREVER);
    dispatch_release(sema);
}
else { // we're on iOS 5 or older
    accessGranted = YES;
}

if (accessGranted) {
    // Do whatever you want here.
}

In the code,semaphore is used for blocking until response, while ABAddressBookRequestAccessWithCompletion will ask for permission if the app didn't ask before. Otherwise it will just follow the settings in Settings-Privacy-Contact.

[Windows] Depreciated in C#

2012-05-10T19:44:00.000-07:00

To set a function in .net as depreciated, we can use code like this



        [Obsolete("Reason of depreciate.")]
        public void Your_Function(int parameters)
        {
            Your_Code_Here;
        }

After that, when you reference this function, it will shows as depreciated, and will have a warning saying your call is obsolete.

[Windows] Basic WPF UI template

2012-05-04T21:50:00.001-07:00

When you creating a UI for your application, usually you will make several UI element of same type, it is kind of annoying if you need to copy and paste all attributes to make those object looks the same. So in XAML programming in WPF, you can define a template for your controls.

Code snapshot:

<UserControl>
    <UserControl.Resources>
        <Style x:Key="BaseBtn" TargetType="Button">
            <Setter Property="Width" Value="80px"/>
            <Setter Property="Height" Value="80px"/>
        </Style>
        <Style x:Key="BottomRightBtn" BasedOn="{StaticResource BaseBtn}" 
                TargetType="Button">
            <Setter Property="HorizontalAlignment" Value="Right"/>
            <Setter Property="VerticalAlignment" Value="Bottom"/>
            <Setter Property="Margin" Value="10"/>
        </Style>
        <Style x:Key="BottomLeftBtn" BasedOn="{StaticResource BaseBtn}"
                TargetType="Button">
            <Setter Property="HorizontalAlignment" Value="Left"/>
            <Setter Property="VerticalAlignment" Value="Bottom"/>
            <Setter Property="Margin" Value="10"/>
        </Style>
    </UserControl.Resources> 
    <Grid>
        <Button Content="BaseBtn" Style="{StaticResource BaseBtn}"/>
        <Button Content="BottomLeftBtn"
                Style="{StaticResource BottomLeftBtn}"/>
        <Button Content="BottomRightBtn"
                Style="{StaticResource BottomRightBtn}"/>
    </Grid>
</UserControl>

UserControl.Resources is a nice place to put all your styles.
Note that you need to specify the TargetType in style tag. So your style can be used on this type only.
Each Setter define a single property like width and height, which should also exist in the target type.
To use the style, just use something like Style="{StaticResource ResourceKey}" to reference them.
That how you do simple sytle in WPF XAML, probably will save you some time.

[iOS] Exception catching

2012-04-29T22:05:00.000-07:00

Exception catching is essential in developing application in .net framework and java.
While in Objective-C, it is much less powerful and shouldn't rely on it, as usually it just crash and didn't catch anything. Yet, it is still a plus if you really catch something.

Usage is really simple

@try
{
    Function_You_Want_To_Catch_Exception;
}
@catch (NSException* exception)
{
   Do_Thing_After_Exception_Caught;
}

One example is to put it in main.m, in order to catch any uncaught exception.

int main(int argc, char *argv[]) {
    NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
    int retVal = -1;
    @try {
        retVal = UIApplicationMain(argc, argv, nil, nil);
    }
    @catch (NSException* exception) {
        NSLog(@"Uncaught exception: %@", exception.description);
        NSLog(@"Stack trace: %@", [exception callStackSymbols]);
    }
    [pool release];
    return retVal;
}

which shows how to catch all uncatched exception in the app.

Another usage is when you like "exception programming", you can raise your own exception, by using [NSException raise:format:] and catch it with above code.
Example:


[NSException raise:NSInvalidArgumentException format:@"Foo must not be nil"];

There are several exception name already defined by apple here. but if you want to use your own, put a NSString there is fine.

[iOS] Catch application end

2012-04-29T21:00:00.000-07:00

Sometime we always want to catch the application terminate in mobile platform.

In iDevice, we can use

- (void)applicationWillTerminate:(UIApplication *)application

to catch the terminate action.

But since iOS 4.0, application will goes to background instead of being killed when you press the home button.
If you are doing so,

- (void)applicationWillTerminate:(UIApplication *)application

might not be called.

From apple developer's guide,UIApplicationDelegate Protocol Reference

- (void)applicationDidEnterBackground:(UIApplication *)application

will be called instead.

When you goes to background, and kill the app bu double click the home button and click the red cross,

- (void)applicationWillTerminate:(UIApplication *)application

will still being called. But if it died naturally, then it won't be called.