CSS: centering an elemenent vertically and horizontally

I had already written an article about this quite some time ago. The problem with this approach is that it only works with elements having a fix size. So I’ve written an article specific to the horizontal centering of variable width DIVs last year. The problem with this approach is that although it works I have no clue why and feel it might break some time in the future. Also this approach only works for centering horizontally. Luckily, since then, I’ve able to use another approach which seems cleaner and also doesn’t require my components to have a fix size and works both vertically and horizontally, without using any strange hacks.

First let’s start with a non-centered element:

<html>
	<body>
		<div style="background-color:green;width:35%;height:35%">
	</body>
</html>

It’s green and it has a height and width of 35% (so no fixed size). As expected, it’s displayed in the upper left corner:

not centered

Obviously, the first thing you’d try and is giving it a top and left margin of 50% to center it:

<html>
	<head>
		<style>
		.centered {
			margin-left: 50%;
			margin-top: 50%;
		}
		</style>
	</head>
	<body>
		<div class="centered" style="background-color:green;width:35%;height:35%">
	</body>
</html>

Unfortunately, this will move the element past the center. You’ll also notice that it’s off by a lot vertically but less horizontally:

margins 50 percent

This is because margin-top doesn’t use the height of the container to compute percentages to pixels but just like margin-left, it uses the width. So if your container is square, you won’t see a difference but otherwise, it’s a problem. So using margin-top is no option. Instead, we’ll set the position to relative and set top to 50%. Ok, we’d implement it without hacks but this one not really a bad one…

<html>
	<head>
		<style>
		.centered {
			margin-left: 50%;
			top: 50%;
			position: relative;
		}
		</style>
	</head>
	<body>
		<div class="centered" style="background-color:green;width:35%;height:35%">
	</body>
</html>

This now looks better but it’s still not properly centered:

better 50 percent

As you can probably guess now, the problem is that the upper left corner of the element is centered both vertically and horizontally. Not the center of the element. In order to correct this, we need some CSS properties which unlike the margin-xxx or top do not take into account the dimensions of the container but the dimensions of the element. Actually there aren’t so many properties like this. Luckily CSS transformations do work with the dimensions of the element. So a translation of -50% both vertically and horizontally will center the element:

<html>
	<head>
		<style>
		.centered {
			margin-left: 50%;
			top: 50%;
			position: relative;
			-webkit-transform: translate(-50%, -50%);
			-moz-transform: translate(-50%, -50%);
			-o-transform: translate(-50%, -50%);
			-ms-transform: translate(-50%, -50%);
			transform: translate(-50%, -50%);
		}
		</style>
	</head>
	<body>
		<div class="centered" style="background-color:green;width:35%;height:35%">
	</body>
</html>

Now it looks exactly the way it’s supposed to:

centered

AngularJS: Running a directive after data has been fetched

In one of my AngularJS projects, I am using the angular-split-pane directive which is basically wrapping the split-pane JQuery plugin. This directive finds out how to split the panes and position the slider by reading the height and width attributes of the HTML tag.

I needed to add a functionality to my application so that the position of the slider is written to some session file on the server and reused next time the application is started to reposition the sliders at the same position, basically setting the height of the lower pane in percentage.

The previous position is fetched using $http. The problem is that it runs asynchronously and by the time the results are there, the directive has already been processed and changing the height tag has no effect anymore.

You can define the order in which directives are run by setting the priority property. But I needed a way to have the directive processed after the results from the server were available, not after or before another directive is processed.

After searching for a solution for quite some time, I finally find a way of implementing it late at night. This is actually pretty simple but for some reason it took me forever to think about such a solution.

When I fetch the data from the server I set some variable in my scope e.g.:

$http.get("../api/Config/").success(function(data) {
	sessionModel.ui = data;
});

Since I only want to execute the directive once the data is fetched, this means I want to have it executed once sessionModel.ui has a value. So all I need to do is add an ng-if attribute to my tag. Since the variable is initially not set, AngularJS will remove the element from the DOM and once the value is set, it will recreate it having the directive executed. So my tag would now look like this:

<split-pane ng-if="sessionModel.ui">

Of course the small disadvantage of this solution is that my UI is first shortly rendered without the split pane and when the data has been fetched, the split-pane is also rendered. In order not to have a partial rendering of the UI, you could of course move the ng-if attribute higher in your HTML code so that the whole UI is only rendered once the data from the server is available.

If your directive is not replacing the DOM element but just manipulating them, another solution would be to have the logic run asynchronously using $timeout and repeat until the data from the server is available. Or having it applied once the data is available by using $watch.

C#: WPF / Console Hybrid Application

I am working on a WPF application which needs to also provide a command line interface running as a console application. This means that depending on how it is started, it should either work as a console application or start with a GUI.

In my case I already had a WPF application by the time this requirement came in. So I had to adapt my existing application to make it an hybrid application.

First I created a new class Program with a Main method:

using System;

namespace HybridApp
{
    public class Program
    {
        public static void Main(string[] args)
        {
        }
    }
}

You might get an error saying that there are two Main methods, so you will have to select this new class as Startup object in the project properties.

Then you need to set the output type to “Console Application” in the project properties:

Output Type Console Application

This is required so that your application doesn’t automatically start with a GUI.

Now we’ll need either keep running as a Console application or start the WPF application depending on how the application was started.

First in order to be able to start the WPF application, you’ll need to add the STAThread attribute to your main method:

using System;

namespace HybridApp
{
    public class Program
    {
        [STAThread]
        public static void Main(string[] args)
        {
        }
    }
}

We’ll now assume that in order to start the UI, we’ll call the application with the -g argument. In order to start the GUI, all you need is to call the Main method of your WPF application:

using System;

namespace HybridApp
{
    public class Program
    {
        [STAThread]
        public static void Main(string[] args)
        {
			if (args.Length > 0 && args[0] == "-g") {
				// GUI mode
				App.Main();
			}
			else {
				// console mode
			}
        }
    }
}

Now, you’ll notice that when starting in GUI mode, you will still have a Console window displayed. This doesn’t look good. I did not find a way to completely get rid of it but at least managed to hide it before starting the UI so that you only see the console window for a very short time. In order to do this, you need to use GetConsoleWindow from kernel32.dll in order to get the handle of the console window and ShowWindow from user32.dll in order to hide it:

using System;
using System.Runtime.InteropServices;

namespace HybridApp
{
    public class Program
    {
        [DllImport("kernel32.dll")]
        private static extern IntPtr GetConsoleWindow();

        [DllImport("user32.dll")]
        private static extern bool ShowWindow(IntPtr hWnd, int nCmdShow);

        [STAThread]
        public static void Main(string[] args)
        {
			if (args.Length > 0 && args[0] == "-g") {
				// GUI mode
				ShowWindow(GetConsoleWindow(), 0 /*SW_HIDE*/);
				App.Main();
			}
			else {
				// console mode
			}
        }
    }
}

Now all you need is to implement the logic for the console mode and you’re done !

AngularJS: binding HTML code with ng-bind-html and $sce.trustAsHtml

I am working on a project in which based on some user interactions I am calling a service on the server and receive some pieces of HTML code which I need to display in the UI.

Of course I could just inject them in the DOM but to keep it clean I wanted to just store the HTML in the scope and bind it to an HTML tag. Basically doing something like this:

<!DOCTYPE html>
<html>

<head>
  <script src="https://code.angularjs.org/1.4.0-beta.6/angular.js" data-semver="1.4.0-beta.6" data-require="angular.js@*"></script>
  <link href="style.css" rel="stylesheet" />
  <script src="script.js"></script>
</head>

<body ng-app="myApp" ng-controller="myCtrl">
  <div ng-bind-html="myHtmlVar"></div>
</body>

</html>

The JavaScript code being:

var app = angular.module('myApp', []);

app.controller('myCtrl', function($scope) {
    $scope.myHtmlVar= "<a href='http://benohead.com'>benohead.com</a>";
});

This will unfortunately not work and you will get the following error message in the JavaScript console:

Error: [$sce:unsafe] Attempting to use an unsafe value in a safe context.

This basically means that the value we provided to ng-bind-html is not inherently safe and is also not marked as safe. So we need to mark it as trustworthy. This can be done by using $sce.trustAsHtml. An easy fix to the problem is to use the following:

app.controller('myCtrl', function($scope, $sce) {
    $scope.myHtmlVar= $sce.trustAsHtml("<a href='http://benohead.com'>benohead.com</a>");
});

If you do not want to add the calls to trustAsHtml everywhere in your code, you can also introduce a function in your scope and reference it in your page:

app.controller('myCtrl', function($scope, $sce) {
    $scope.myHtmlVar= "<a href='http://benohead.com'>benohead.com</a>";
    
    $scope.trustAsHtml = function(html) {
      return $sce.trustAsHtml(html);
    }
});

This function can then be called in the ng-bind-html attribute:

<div ng-bind-html="trustAsHtml(myHtmlVar)"></div>

Another way to do it is to define a filter which works in exactly the same way as the trustAsHtml function above:

app.filter('trustAsHtml', function($sce) {
  return function(html) {
    return $sce.trustAsHtml(html);
  };
});

app.controller('myCtrl', function($scope, $sce) {
  $scope.myHtmlVar = "<a href='http://benohead.com'>benohead.com</a>";
});

And use it like this:

<div ng-bind-html="myHtmlVar | trustAsHtml"></div>

Also note that if you want to set the HTML to the scope variable and then perform some DOM manipulation on this HTML code, you’ll run into a problem, because as long as your code is running, the data binding won’t be reflected until you return. Here is such an example:

app.controller('myCtrl', function($scope, $sce, $http) {
	$scope.myHtmlVar = "<a href='http://benohead.com'>benohead.com</a>";

	$scope.getHtmlCode = function (serviceParameter) {
		var responsePromise = $http.post("my-service-url", JSON.stringify(serviceParameter));
		responsePromise.success(function (data) {
			$scope.myHtmlVar = data;
			$scope.manipulateDom();
		});
	};
	
	$scope.manipulateDom = function () {
		//do some DOM manipulation on the retrieved HTML code...
	});
});

In order to execute some additional code, you’ll have to wrap it using $timeout:

app.controller('myCtrl', function($scope, $sce, $http, $timeout) {
	$scope.myHtmlVar = "<a href='http://benohead.com'>benohead.com</a>";

	$scope.getHtmlCode = function (serviceParameter) {
		var responsePromise = $http.post("my-service-url", JSON.stringify(serviceParameter));
		responsePromise.success(function (data) {
			$scope.myHtmlVar = data;
			$timeout(function() {
				$scope.manipulateDom();
			});			
		});
	};
	
	$scope.manipulateDom = function () {
		//do some DOM manipulation on the retrieved HTML code...
	});
});

 

Getting a file extension with JavaScript

For a current project, I needed to get the extension of a file being given it’s full path. In C#, you’d do something like this:

var extension = Path.GetExtension(path);

Unfortunately, we have no such possibility in JavaScript. Fortunately, writing a function returning the extension in JavaScript is not that difficult.

First you need to get the file name from the full path (basically getting rid of all parent directories in the path). In order to do this you have to also consider that you could either have a slash or a backslash as separator in the path.

The file name is basically, the last part of the path when you split it with the file path separator. This means you just need to use a split and a pop:

var filename = path.split('/').pop(); // when using slash as a file path separator

var filename = path.split('\\').pop(); // when using backslash as a file path separator

In order to handle both, you just need to do it twice:

var filename = path.split('\\').pop().split('/').pop();

It doesn’t really matter in which order you do it. If you use slashes, the first split/pop combination will not do anything. If you use backslashes, the second one will not do anything.

Getting the file name without path information is important because we’ll be searching for the extension based on dots in the path. If one of the parent directories does contain a dot, it will return a wrong results, so it’s safer to first get the file name without path information and then get the file extension.

Now we have the file name (without full path information), we need to extract the extension.

Let’s first look at which results we expect in different cases:

  • if the input name is an empty string, the returned extension should be an empty string as well
  • if the input name is does not contain any dots, the returned extension should be an empty string
  • if the input name contains only one dot and it’s the first character of the file name (e.g. .htpasswd), the returned extension should be an empty string
  • if the input name starts with a dot but contains another dot (e.g. .htpasswd.sav), the returned extension should be the part after the last dot
  • in general if the name contains any dots which are not at the beginning of the file, the returned extension should be the part after the last dot

You can get the index of the last dot in the file name using:

filename.lastIndexOf(".")

This will return -1 if no dot is present in the name. In this case, there is no extension and we can return an empty string:

var lastIndex = filename.lastIndexOf(".");
if (lastIndex < 0) return "";

Actually, even if it returns 0, it means that the file name starts with a dot and contains no further dots. In this case we also want to return an empty string:

var lastIndex = filename.lastIndexOf(".");
if (lastIndex < 1) return "";

In other cases (i.e. when we have at least one dot which is not at the beginning of the name), we want to exclude everything until the dot (including it) and return the rest:

var lastIndex = filename.lastIndexOf(".");
if (lastIndex < 1) return "";
return filename.substr(lastIndex + 1);

So the complete function to get the file extension from an arbitrary file path is:

function getFilePathExtension(path) {
	var filename = path.split('\\').pop().split('/').pop();
	var lastIndex = filename.lastIndexOf(".");
	if (lastIndex < 1) return "";
	return filename.substr(lastIndex + 1);
}

Now let’s test it a little bit and check that we do get the expected results:

console.log(getFilePathExtension(""));
console.log(getFilePathExtension("name"));
console.log(getFilePathExtension("name.ext"));
console.log(getFilePathExtension(".name"));
console.log(getFilePathExtension(".name.ext"));
console.log(getFilePathExtension("name.with.a.few.dots.ext"));
console.log(getFilePathExtension("/path/with/.a/few/dots"));
console.log(getFilePathExtension("/path/with/.a/few/.dots"));
console.log(getFilePathExtension("/path/with/.a/few/.dots/name.with.a.few.dots.ext"));

As expected the 4 tests where the name ends with “.ext” will return ext. The others will return an empty string.

You can make the function above even a little bit compacter (but less readable) by using Infinity as index in case the index returned is 0 or less. This is done by using:

  1. the Math.max function so that we get 0 whether lastIndexOf returns -1 or 0
  2. the fact that 0 is evaluated as false
  3. the fact that substr will return an empty string if the provided index is higher than the index of the last character
  4. the fact that Infinity + 1 is still higher than the index of the last character

So the compacter code looks like this:

function getFilePathExtension(path) {
	var filename = path.split('\\').pop().split('/').pop();
	return filename.substr(( Math.max(0, filename.lastIndexOf(".")) || Infinity) + 1);
}

 

AngularJS: Using Plupload in a dialog

Plupload is a very configurable JavaScript library you can use to allow your users to upload images. I’ve already used it in a few projects. I now wanted to use it in my current AngularJS project. Integrating Plupload in an AngularJS project is not especially difficult. There are already a few articles showing how this can be done. But it gets more difficult, when you try to integrate it into a dialog.

When initialized, Plupload puts an overlay above the browse button. This unfortunately only works if this element is displayed. If it is not displayed, the Plupload initialization will fail.

When working with dialogs, this means you need to execute the initialization of Plupload once the dialog is already displayed.

Let’s assume you have the use the following method to open a dialog using ngDialog:

$scope.uploadFile = function(){
	ngDialog.open({
		template: '/template/fileUploadDialog.html',
		controller: 'FileUploadController'
	});
};

and your controller looks like this:

app.controller('FileUploadController', function($scope){
	$scope.uploader = new plupload.Uploader({
		browse_button: 'browse',
		url: 'upload.php'
	});

	$scope.uploader.init();
});

Or if you are using angular-dialog-service:

$scope.uploadFile = function () {
	dialogs.create('/template/fileUploadDialog.html', 'FileUploadController', {}, {
		'backdrop': false,
		'size': 'sm',
		'copy': false,
		'windowClass': 'dialog-type-primary'
	});
};

and the same controller.

You will see that although you do not get any kind of error, nothing will happen when you click on the browse button. This is because no overlay was added by Plupload. If you put a breakpoint in the controller code, you will see that the dialog is not yet displayed when the code runs.

This is because Plupload has issues rendering inside elements which are hidden at initialization time You need to “refresh” Plupload after the dialog has been displayed:

$scope.uploader.refresh();

Now we know the root cause of the problem, all we need to do is either call the refresh method after displaying the dialog or just initialize Plupload after displaying the dialog. The problem is that I never found out how to provide a callback to get triggered after the dialog has been displayed.

After googling for it with no result, I decided to do it with a hack (won’t win a design price with this one but it works). Assuming the dialog will never take more than 300 milliseconds to display and the user will need at least 300 milliseconds to find the browse button, you can just solve it by executing some code asynchronously using setTimeout or $timeout (since we work with AngularJS):

app.controller('FileUploadController', function($scope, $timeout){
	$scope.uploader = new plupload.Uploader({
		browse_button: 'browse',
		url: 'upload.php'
	});

	$timeout(function () {
		$scope.uploader.init();
	}, 300);
});

Now your browse button should be working.

Plupload: previewing images and getting Data URI

I am working on a project where users can be created and assigned an image. The natural choice to upload images is to use Plupload. Plupload is a well-known JavaScript library to upload images using a variaty of uploader runtimes. It provides an HTML4 and an HTML5 runtime but also a Flash and a Silverlight runtime. You can configure a list of runtimes. Plupload will check for you which one is available on the particular client.

The usual way to use Plupload is to let the user select files with a native dialog or using drag&drop. You then upload the file to some server side business logic and display the progress. In my case, I wanted something different. First I want to show the selected image to the user and second I want to store the image not on the server but in a model on the client (which contains other data and will eventually be stored somewhere).

In this article, I will describe how to display a preview of the image in a canvas and how to convert the image to a Data URI.

First you need to deploy Plupload on your web server and reference it’s JavaScript file e.g.:

<script src="vendor/plupload/plupload.full.min.js"></script>

Then you need to have some HTML code to define a button which will be clicked by the user to open the file browser and a tag to display the image preview:

<a href="" type="button" id="selectfiles">Select</a>
<div id="preview"></div>

Now you’ll have to write some JavaScript code to initialize Plupload:

var uploader = new plupload.Uploader({
	runtimes: 'html5,flash,silverlight',
	browse_button: 'selectfiles',
	multi_selection: false,
	url: "about:blank",
	flash_swf_url: 'vendor/plupload/Moxie.swf',
	silverlight_xap_url: 'vendor/plupload/Moxie.xap',
	filters: [{title: "Image files", extensions: "jpg,gif,png"}]
});

uploader.init();

We’ve defined that Plupload should use the selectfiles element to let the user open the file browser. If you use the Flash and/or Silverlight runtimes, you have to point Plupload to the URL of those SWF and XAP files. And we define that a user can only choose one file and that it needs to be a GIF, JPEG or PNG file. This all pretty standard.

The only special trick is that we use “about:blank” as URL for the upload. Actually, you can specify whatever you want. It just needs to be a non-empty string. Otherwise Plupload will not initialize successfully. But since we won’t use Plupload to actually upload the file, we do not care about the value of this option, as long as it is defined.

Then we’ll want to be notified when the user as selected a file. So we need to register for an event:

uploader.bind("FilesAdded", filesAdded);

function filesAdded (uploader, files) {}

Now we’ll implement the filesAdded function. It will get the selected file and will need to embed that image in canvas in our preview element. Luckily, Plupload provides us with an Image class which provides us with all we need to do this:

function filesAdded (uploader, files) {
	$.each(files, function () {
		var img = new mOxie.Image();
		img.onload = function () {
			$('#preview').empty();
			this.embed($('#preview').get(0), {
				width: 100,
				height: 100
			});
		};
		img.onembedded = function () {
			this.destroy();
		};
		img.onerror = function () {
			this.destroy();
		};
		img.load(this.getSource());
	});
};

Now once the user select a file, it will be displayed as a preview. Now once the user decides to save, we can use this preview to save the image (note that this works in my case because I only want to store a 100×100 image and do not need the original image):

var dataURI = $("#preview canvas")[0].toDataURL();

Now you can store the data URI however you want.

Additionally, if you have a previously stored data URI and want to display it in the preview area, you can use the following code:

$('#preview').empty();
var $canvas = $("<canvas></canvas>");
$('#preview').append($canvas);
var context = $canvas.get(0).getContext('2d');
$canvas.attr('width', '100');
$canvas.attr('height', '100');
$('#preview').append($canvas);
var image = new Image();
image.onload = function () {
	context.drawImage(image, 0, 0, 100, 100);
};
image.src = $scope.data.user.image;

It just creates a canvas, loads the data URI in an Image object and has it drawn in the canvas’ 2D context.

Drag&Drop with AngularJS

I am working on a project where I have a board containing different lanes (a kind of grid) on which you can place cards and move them according to their completion status. In order to implement the drag&drop functionality, I am using the angular-dragdrop module.

It is a wrapper for jQueryUI draggable/droppable components which makes it easy to implement drag and drop functionality in AngularJS.

In order to install the module, just run the following in your terminal:

bower install angular-dragdrop

Then in order to load it, you need to reference its JavaScript file, just after the reference to angular.js (and also a reference to jQuery and jQuery UI which are used by this module):

<script src="//ajax.googleapis.com/ajax/libs/jquery/1.9.0/jquery.min.js"></script>
<script src="//ajax.googleapis.com/ajax/libs/jqueryui/1/jquery-ui.min.js"></script>
<script src="bower_components/angular/angular.js"></script>
<script src="bower_components/angular-dragdrop/src/angular-dragdrop.min.js"></script>

And add a dependency in your main module e.g.:

angular.module('myapp', [ 'ngDragDrop' ]);

Now, you’re ready to define draggable elements and droppable areas.

First, let’s make the card elements draggable. My elements looked like this before the change:

<div class="card">
	...
</div>

You need to add three custom attributes to this element:

<div class="card"
	 data-drag="true"
	 data-jqyoui-options="{revert: revertCard,
							helper: 'clone',
							appendTo: 'body',
							zIndex: 350}"
	 jqyoui-draggable="{index: 0,
						placeholder:true,
						animate:true,
						onStart: 'startCallback'}">
	...
</div>

jqyoui-draggable contain options passed to hte angular-dragdrop module. data-jqyoui-options contains the options passed to jQuery UI Draggable.

I’ve just copied the index, placeholder and animate options from some example, so you’ll have to use Google to find more info on them.

revertCard and startCallBack are functions on my controller which are used to control the way the draggable element react.

The zIndex is set so that the element is on top of all other elements while dragged. In my first try, I hadn’t set the appendTo and helper options. Since my draggable elements where contained in a container on which the overflow property was set, I could not move it out of its container. That’s because the element being dragged still had the same parent as the original element.

So you need to attach the element being dragged to the body of the page so that it can be moved anywhere. Unfortunately, attachTo with the “body” value only works if the helper option is set to “clone” i.e. it will not detach the element from its current container and attach it to the body but needs to work with a clone of the element which can be attached to the body.

The drawback is that the original element is still displayed. This is fine if you are writing an editor with some toolbox and want to use drag&drop to create new instances of this element. But if you actually want to move the element, it just doesn’t look good. So you need to additionally hide the original element while its clone is being dragged. That’s what is done in the startCallback of my controller:

$scope.startCallback = function (event, ui) {
	var $draggable = $(event.target);
	ui.helper.width($draggable.width());
	ui.helper.height($draggable.height());
	$draggable.css('opacity', '0');
};

This callback does two things:

  1. It makes sure that the clone element doesn’t grow to take up the whole screen (because its size is not limited by its parent anymore).
  2. It hides it by setting its opacity to 0.

In one of my early tries, I had hidden the original element by using display:none. The problem is that all other elements in this container would then move because this element was not displayed anymore. But setting its opacity to 0, it works as an empty placeholder.

Later on, once the dragging is stopped, I’ll make it visible again if required (only if it is not dropped at a valid location).

Usually, you will find that most example will set the revert option to “invalid”. This means that if you drop the component outside of a valid drop area, the helper will just come back to the original location and disappear. The problem is that since we’ve hidden the original element, you will end up with no element displayed at all. Thankfully, revert can also take a function as value. This is our second callback:

$scope.revertCard = function (valid) {
	if (!valid) {
		var that = this;
		setTimeout(function () {
			$(that).css('opacity', 'inherit');
		}, 500);
	}
	return !valid;
};

Returning false will cause the helper to return to the original location. The default duration of the animation is 500 milliseconds. Before returning true of false, we check whether the drop location was valid and if yes, we make the original element visible again. If we set the opacity to “inherit” immediately, the original element would be visible while the helper is moving back to the original location. That’s why we make the CSS change with a timeout of 500 milliseconds so that the original element is made visible as soon as the revert animation is finished.

Now we have a working draggable element and just need to define droppable areas where we can drop it:

<div class="lane"
	 data-drop="true"
	 jqyoui-droppable="{multiple: true,
						onDrop: 'dropCallback'}"
	 data-jqyoui-options="{hoverClass: 'ui-state-active',
							tolerance: 'pointer'}">
	...
</div>

The hoverClass is just used so that we can display the droppable area below the mouse pointer differently.

The tolerance option is used so that the element is dropped on the area below the mouse pointer and not on the area below the corner of the dragged element. This is useful when the dragged element is larger than the droppable areas.

We also define an additional callback in the controller:

$scope.dropCallback = function (event, ui) {
	var $lane = $(event.target);
	var $card = ui.draggable;
	if ($card.scope().card.lane != $lane.scope().lane.id) {
		$card.scope().card.lane = $lane.scope().lane.id;
	}
	else {
		$card.css('opacity', 'inherit');
		return false;
	}
};

This callback does two things:

  1. It updates the model so that the card is displayed on the lane it was dropped on.
  2. It prevents dropping the card on the lane it was on before dragging.

The first part is pretty straightforward. The second one just involves checking the original lane ID and the lane ID on which the drop operation is being performed. If they do not match we allow the drop. Otherwise we return false which is similar to a revert. Unfortunately, returning false doesn’t cause the revert callback to be called. So I have to change the opacity of the original element before returning false.

You’ll also notice that I do not set a timeout of 500 milliseconds. This is because returning false in the drop callback doesn’t cause a revert animation to be executed. I haven’t yet found out how to do this. So the helper just immediately disappears and I have to make the original element visible immediately.

That’s it ! It was actually pretty easy. Since you can set any draggable and droppable options without limitation, having this angular module between you and jQuery UI doesn’t seem to introduce any additional limitation. And since all references to event handler all point to callback in your controller, everything stays clean.

Update: I’ve also come accross an issue with a button on the card. I’m using the angular dialog service to display a dialog when a button on the card is clicked (using ng-click to trigger a function in my controller). At first, nothing happened when clicking on the button. This is because the mouse click didn’t go to the button. The solution was to increase the z-index of the button to 500 i.e. higher than the 350 configured for the draggable card.

Update: I’ve created a Plunker to show a working example.

WP Prism Syntax Highlighter not working on archive pages

Prism is a is a lightweight and extensible syntax highlighter written in JavaScript and CSS by Lea Verou. It’s fast and the rendered code looks great.

WP Prism Syntax Highlighter is one of the WordPress plugins integrating the Prism syntax highlighter. It is relatively new and I didn’t see much updating done but it works well.

Until now, I’ve only found one real problem with this plugin: althought it does work fine on individual posts, it just doesn’t work on archive pages and on the home page. So basically it fails to work on all pages showing lists of posts. It’s not an issue if you only display excerpts on those pages. But if you display full posts on them, all you see is the standard appearance of <pre> tags. This is because Prism will not be loaded on such pages.

The problem is that the plugin tries to limit the pages on which it loads Prism to those pages which actually do display some code. It does it with the following code:

private function decide_load_prism() {
	if ( strstr( get_post()->post_content, '<code class="language-' ) !== false ) {
		$this->load_pjsh = true;
	}
}

It basically gets the content of the current post and checks whether a Prism code tag is there. Only then will it load prism. This ensures that you do not load Prism on pages where you don’t need it in the first place e.g. posts without code, disclaimers, about me pages…

The problem is that this piece of code actually only works on single posts, not on archive pages or on the home page. Anyway for such pages, you’d need to check whether the whole post is displayed, if yes go through the posts being displayed and check whether code is present there. That’s kind of complex and probably the reason why it was implemented this way.

So to solve this you could delete the “if” line and the corresponding closing bracket. But then you’d load Prism on all pages including the ones where you definitely do not need it. After loading on all pages displaying code no matter whether a single post or a list of posts, the second best solution would be to make sure that single post pages only load Prism if required and on archives / on the home page, Prism is always loaded.

To implement it, open wp-prism-syntax-highlighter.php (http://YOURSITE/wp-admin/plugin-editor.php?file=wp-prism-syntax-highlighter/wp-prism-syntax-highlighter.php&a=te), search for “decide_load_prism” and replace this function by this one:

private function decide_load_prism() {
	if ( !is_single() || strstr( get_post()->post_content, '<code class="language-' ) !== false ) {
		$this->load_pjsh = true;
	}
}

This is almost the same as the previous one. The only difference is that it also loads Prism if is_single() is false i.e. we’re displaying a list of posts.

Now, the code displayed in my category archives and on my homepage also looks great !! Of course, if you don’t have a problem in the first place e.g. because you only display excerpts on these pages, then there is no point in implementing this since it will unnecessarily load Prism on these pages.

Please note that when the changes you make in a plugin will be overwritten after every update of the plugin. So until this issue is fixed in the plugin, you will need to reapply it after every update.

Update: There are no support requests on the plugin page on wordpress.org but I’ve just seen that there is a bug report on github.

WordPress: Menu items combining multiple categories

On one of the websites I am administrating, posts are assigned two kinds of categories:

  • the age of children
  • for boys or for girls

In the navigation menu, you need to be able to select menu items corresponding to the following types of criteria:

  • Display all posts for boys or all posts for girls
  • Display all posts for children in a specific age category
  • Display all posts for boys in a specific age category or for girls in a specific age category

The first two requirements are easy. You just need to add the corresponding category archives to the menu. For the last one, there is no way to select a combination of categories in the WordPress menu builder.

So you need to add links to the menu and point to the results of a query for a combination of categories. Fortunately, you do not need to write any code to have such a list of post displayed. This can all be done by providing the appropriate parameters in the URL e.g.:

http://mysite.com/?cat=for-boys,6-12-months

for-boys and 6-12-months are the slugs of the corresponding categories.

If you have pretty URLs, it’d look like this:

http://mysite.com/category/for-boys,6-12-months

This will show you posts belonging to either category. What we actually want are posts belonging to both categories. In order to get this result, you need to replace the comma by a plus sign:

http://mysite.com/?cat=for-boys+6-12-months

If you have pretty URLs, it’d look like this:

http://mysite.com/category/for-boys+6-12-months

Instead of “category” you can use “tag” for post tags or “author” for post authors.