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Primer: OpenLayers

Primer: Ext

GeoExt extends Ext JS, a rich library of web UI widgets and helper classes. Using GeoExt requires a working knowledge of Ext’s idioms. This tutorial provides a quick overview of core Ext concepts.

Getting Started

To start using Ext, you will first have to download it. For more complete instructions about how configure a web page to use Ext, you can check the GeoExt QuickStart tutorial.

When you download Ext, you also get their excellent Examples and API Documentation, which you can also look at on-line for education and reference.

In order to get Ext running on a page you will need to have something like the following in the <head> of an HTML page in a directory that is published by your web server.

<script src="ext-3.2.1/adapter/ext/ext-base.js" type="text/javascript"></script>
<script src="ext-3.2.1/ext-all.js"  type="text/javascript"></script>
<link rel="stylesheet" type="text/css" href="ext-3.2.1/resources/css/ext-all.css"></link>

This will load the code and styles for Ext. Change the paths according to where you have put the Ext files.

When writing Ext code, most of what you will be doing is instantiating classes with constructors that takes a single object–its configuration object–as an argument. This snippet demonstrates this coding pattern:

Ext.onReady(function(){
    var myPanel = new Ext.Panel({
        title: 'Hello World!',
        html: '<i>Hello World!</i> Please enjoy this primer on Ext!',
        collapsible: true,
        width:300,
        renderTo: 'panelDiv'
    });
});

There are a few things to note about this example:

  • This code uses Ext’s onReady method to trigger the method when the document’s body is ready. (This is cleaner than using body’s onready event, and with Ext.onReady several functions can be queued for execution before the page loads.)
  • When the page is ready, the Ext.Panel constructor is called with a single configuration object as argument. The Panel’s structure should be familiar from your desktop experience. It has a title which runs across the top, and some content which in this case is html provided in the configuration.
  • Many configuration options (best explored in the Ext examples and API documention) are available. Here, they are represented by the collapsible property, which allows the user to collapse the panel much like you can minimize your browser’s window, and the width of the panel specified in pixels.
  • Lastly, this code assumes that somewhere in the DOM of the page is a div with the id panelDiv. When the Panel is constructed, it will be automatically rendered in this div because of the renderTo option. (This option can be left out and panels rendered manually, if desired.)

Basic Layout

Ext makes it easy to separate out your UI into logical blocks. Most often you will be using one or more nested Containers. The Ext.Panel built above is the most common kind of container. You can nest panels using the items property. For example:

Ext.onReady(function(){
    var myPanel = new Ext.Panel({
        title: 'Top level',
        layout: 'border',
        items: [{
            xtype:'panel',
            title:'Sub1',
            html:'Contents of sub panel 1',
            region: 'east'
        },{
            xtype:'panel',
            title: 'Sub2',
            html:'Contents of sub panel 2',
            region: 'center'
        }],
        width:300,
        height:200,
        renderTo:'panelDiv'
    });
});

This code introduces some new concepts:

  • Each of the objects in the items array is a configuration object for a panel like the one in the earlier example.
  • The Ext.Panel constructor is never called, however. Instead, the xtype option is used. By setting the xtype, you tell Ext what class the configuration is for, and Ext instantiates that class when appropriate.
  • The layout property on the outer container determines the position of the items within it. Here, we have set the layout to be a border layout, which requires that items be given a region property like “center”, “north”, “south”, “east”, or “west”.

Ext provides a variety of other layouts, including a Tab layout and a Wizard layout. The best way to explore these layouts is using the Ext Layout Browser , which demonstrates each layout and provides sample code.

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