Many people want to disable the “revision” function, but WordPress doesn’t provide any option to do it. I see there are some plugins that can turn off the revision function. However, they doesn’t work well. For example, although you have activated the plugin, when you edit a post, autosave can still produce “revisions”. To solve this problem, you can use “disable autosave” plugin to turn off autosave. However, I think autosave is a good feature. I want to find a way to solve the problem: disable revisions but not for autosave. Fortunately, WordPress is an open-source application, so I can know the mechanism of it.

By checking the source code, I found that there can’t be any plugin to satisfy my requirement. So I have to hack WordPress. At last, I found a simple way, only 2 lines need to be changed! Let’s have a look.

Open wp-includes\default-filters.php and find the line

add_action( 'pre_post_update', 'wp_save_post_revision' );

It means the function ‘wp_save_post_revision’ is hooked ‘pre_post’update’. i.e. when you update a post, Wordpress will call ‘wp_save_post_revision’ function and it will save a revision for the current post. Of cource, the revision isn’t useful. So I need to remove or comment it:

// add_action( 'pre_post_update', 'wp_save_post_revision' );

Now when you update a post, it doesn’t produce revisions any more. However, when you edit a published post in WordPress, the autosave function can still generate a revision draft. It is not what I want, so I must to solve the problem.

Open wp-admin\includes\post.php and found the function wp_create_post_autosave (near line 1030). The last 2 lines should be

// Otherwise create the new autosave as a special post revision
return _wp_put_post_revision( $_POST, true );

Through the comment I see it create a new revision from the $_POST array. I changed it to “return edit_post();” and tested in diffent conditions. I found it works well. Now the function wp_create_post_autosave looks like

function wp_create_post_autosave( $post_id ) {
	$translated = _wp_translate_postdata( true );
	if ( is_wp_error( $translated ) )
		return $translated;
 
	// Only store one autosave.  If there is already an autosave, overwrite it.
	if ( $old_autosave = wp_get_post_autosave( $post_id ) ) {
		$new_autosave = _wp_post_revision_fields( $_POST, true );
		$new_autosave['ID'] = $old_autosave->ID;
		return wp_update_post( $new_autosave );
	}
 
	// Otherwise create the new autosave as a special post revision
	// return _wp_put_post_revision( $_POST, true );
	return edit_post();
}

By now, WordPress doesn’t save the annoying revisions and autosave works well. I think the only disadvantage is that it hacks WordPress core code. Once you upgrade WordPress, you have to change the 2 lines.

Above the “UPLOAD” button, there is the link “Show advanced settings…”. Click it and you can select the correct type of the images.

Unfortunately I haven’t found it before. I have uploaded many screenshots (about 40). I have to change the images’ content type one by one. I found how to do it. Its help says:

You can also change the Content Type after you’ve uploaded your screenshot, either using the “Flag your photo” link under Additional Information on a photo page, or in the Organizr.”

So, don’t forget to select the corrent content type before uploading pictures, especially for screenshots.

Text Ad:

<script type="text/javascript"><!--
google_ad_client = "pub-xxxxxxxxxxxx";
google_ad_width = 728;
google_ad_height = 90;
google_ad_format = "728x90_as";
google_ad_type = "text_image";
google_ad_channel = "";
google_color_border = "FFFFFF";
google_color_bg = "FFFFFF";
google_color_link = "FFFFFF";
google_color_text = "FFFFFF";
google_color_url = "FFFFFF";
google_ui_features = "rc:0";
//-->
</script>
<script type="text/javascript"
  src="http://pagead2.googlesyndication.com/pagead/show_ads.js">
</script>

“google_ad_format” indicates the format of the ad. There are 11 options: “720×90_as”, “468×60_as”, “234×60_as”, “120×600_as”, “160×600_as”, “120×240_as”, “336×280_as”, “300×250_as”, “250×250_as”, 180×150_as, 125×125_as.
“google_ad_type” can be one of the three values: “text_image”, “text”, “image”.
“google_ui_features” indicates the coner style: “rc:0″ — Square, “rc:6″ — Slightly rounded, “rc:10″ — Very rounded.

Link Unit:

<script type="text/javascript"><!--
google_ad_client = "pub-xxxxxxxxxxxx";
google_ad_width = 728;
google_ad_height = 15;
google_ad_format = "728x15_0ads_al";
google_ad_channel ="";
google_color_border = "FFFFFF";
google_color_bg = "FFFFFF";
google_color_link = "FFFFFF";
//--></script>
<script type="text/javascript"
  src="http://pagead2.googlesyndication.com/pagead/show_ads.js">
</script>

For link units, there are 6 kinds of ads. “728×15″, “468×15″, “200×90″, “180×90″, “160×90″, “120×90″. “google_ad_width” and “google_ad_height” set the size of the link unit. The “google_ad_format” consists of its “size” and a suffix. Some link units have 4 links while other have 5 links. If a link unit has 4 links, the suffix of the “google_ad_format” is “_0ads_al”, for example, “728×15_0ads_al”. For the ones which have 5 links, the suffix is “_0ads_al_s”, for example, “728×15_0ads_al_s”.

What these strange functions can be used for? Suppose there is an array that contains some integers. For example, $a=array(34,21,58,32,19,6). And we want to use “array_filter” function to retrieve the odd integers. The usage of the array_filter is:
array array_filter(array $input [,callback $callback])
The function iterates each element in $input. The $callback is a function which returns true or false. If it returns true, the current element is pushed into the result array. Using array_filter, it is easy to write the following code:

<?php
function is_odd($n){
	if ($n%2==1)
		return true;
	else
		return false;
}
$a=array(34,21,58,32,19,6);
$result=array_filter($a,'is_odd');
print_r($result);
?>

Its output is:

Array
(
    [1] => 21
    [4] => 19
)

Obviously, there is a small function “is_odd” to check if an integer is an odd number or not. However, it is used only in array_filter function. So if we can define the small function in array_filter’s second argument’s place, it is a better style.

PHP provides “create_function” that can create an anonymous function. The usage:
string create_function(string $args, string $code)
Now use this function to rewrite the example:

<?php
$a=array(34,21,58,32,19,6);
$result=array_filter($a,create_function('$n','return ($n%2==1)?true:false;'));
print_r($result);
?>

Several days ago I read this article in Google Webmaster Central Blog. It shows some method to avoid comment spam. The first thing is using a captcha. Also, it gives a free script which is called “reCAPTCHA“. For WordPress users, reCAPTCHA provides a plugin, so that it is very easy to integrate with WordPress.

I don’t think the captcha code is a good solution to comment spam. It will make difficult to visitors who want to leave some meaningful comments. However, the comment spam is so serious, I have to do so.

Some people thought it should be /usr because in Windows the Java compiler “javac” is in JAVA_HOMEbinjavac. So in Linux it should be JAVA_HOMEbinjavac and JAVA_HOME=/usr. I don’t think it is the best sulotion. Because I found /usr/bin/javac is not the real Java compiler, it is just a link. I used “ls -l /usr/bin/javac” to see what it links to:

/usr/bin/javac -> /etc/alternatives/javac

And /etc/alternatives/javac is also a link. It links to /usr/lib/jvm/java-6-sun/bin/javac. This is the real Java compiler. And the path is similar to that in Windows. So I think JAVA_HOME should be /usr/lib/jvm/java-6-sun in Ubuntu Linux.

I used “sudo apt-get install virtualbox-ose virtualbox-ose-modules-generic” to install VirtualBox. Its version is 1.5.6. However, I found a serious problem. My keyboard doesn’t work in VirtualBox. If a virtual machine is running and I click the window, the mouse is captured by the virtual machine. When I press the right Ctrl key the mouse should be released. However, it doesn’t work. I have to press Ctrl+Alt+Backspace to restart X. Some people said that the problem can be solved by disabling support to complex characters. But I need the multi-language support so that this method is unuseful for me.

Finally I found a good solution. I used “sudo apt-get install scim-bridge-client-qt” to install the scim-bridge-client-qt package and reboot my computer. Then the keyboard can work in VirtualBox. Although the solution is very simple, I don’t know why. It may be a bug in Ubuntu 8.04.1.

I made a month-day selector using two drop lists. After you select a month, the number of the day drop list may change. For example, at first January is selected and the numbers of the day drop list are from 1 to 31. After you select April, the numbers of the day drop list becomes from 1 to 30. It is very easy to understand. I created two files, demo.html for showing page and response.php for calculate how many days a month has.

demo.html:

<html>
<head>
	<script type="text/javascript" src="script/prototype-1.6.0.3.js"></script>
	<script type="text/javascript">
	function send(value){
		var length=$("day").length;
		for (i=0;i<length;i++){
			$("day").remove(0);
		}
		new Ajax.Request(
			'./response.php',{
				method: "get",
				parameters: {month: value},
				onSuccess: function(response){
					var days=response.responseText;
					for (i=1;i<=days;i++){
						$("day").options.add(new Option(i,i));
					}
				},
				onFailure: function(){
					alert('Failed!');
				}
			}
		);
	}
	function init(){
		for (i=1;i<=12;i++){
			$("month").options.add(new Option(i,i));
		}
		for (i=1;i<=31;i++){
			$("day").options.add(new Option(i,i));
		}
	}
	</script>
</head>
<body onload="init();">
<p>
	Month: <select id="month" onChange="send(this.value);"></select>
	Day: <select id="day"></select>
</p>
</body>
</html>

response.php:

<?php
$d=$_GET['month'];
$days=array(31,29,31,30,31,30,31,31,30,31,30,31);
echo $days[$d-1];
?>

Sending an AJAX request with Prototype is using Ajax.Request. The code below is important:

new Ajax.Request(
	'./response.php',{
		method: "get",
		parameters: {month: value},
		onSuccess: function(response){
			var days=response.responseText;
			for (i=1;i<=days;i++){
				$("day").options.add(new Option(i,i));
			}
		},
		onFailure: function(){
			alert('Failed!');
		}
	}
);

The Ajax.Request contructor needs two arguments. The first is the target file and the second is an Ajax.Options object. The second parameter in this example is expressed as a JSON string. “method” indicates using “get” or “post” method. “onSuccess” and “onFailure” indicate the callback functions. With Prototype framework’s help, sending AJAX requests is very easy and intuitive.

Developing with IDE seems impossible. I have to find a powerful text editor. Now I find Notepad++ and Vim for Windows are very excellent. Although many people said that Emacs is the most powerful text editor, however, I think it is very hard to use. Sometimes I need to write Java code. So I have to learn how to use “ant”, an automatically build utility. In fact, using “ant” instead of some IDEs, such as Eclipse or NetBeans, is not very difficult. For C or C++ programming, I installed Cygwin on her computer. Although Cygwin is not only a C/C++ compilers, it seems a Unix shell running on Windows. Since I have been using Ubuntu Linux for about half a year, I like working on Linux and are farmiliar with it.

For most of my tasks, a good text editor is enough. For Notepad++ and Vim, I prefer Notepad++. It runs faster and much easier to learn.