Using XUL, JavaScript, and CSS

Creating Applications with Mozilla

David Boswell, Brian King, Ian Oeschger, Pete Collins & Eric Murphy Creating Applications with Mozilla

David Boswell, Brian King, Ian Oeschger, Pete Collins, and Eric Murphy

Beijing • Cambridge • Farnham • Köln • Paris • Sebastopol • Taipei • Tokyo Chapter 2 CHAPTER 2 Getting Started

To help you start creating applications as quickly as possible, this chapter presents two “Hello World” examples that demonstrate the beginning stages of Mozilla appli- cation development. The first example is a simple XUL file that is loaded into the browser window. This example is then expanded on by adding additional features to the XUL file, such as imported stylesheets and JavaScript functions. The second “Hello World” example shows how to turn files like these into packages, which are the modular, bundled sets of files that fit together to make Mozilla applications or new modules for the Mozilla browser. These examples provide a context for discussing the development of Mozilla applica- tions. The first example focuses on creating and editing the basic file types, and the second focuses on the organization and distribution of applications on the Mozilla platform. Simple XUL Example Like all good “Hello World” applications, Example 2-1 shows one of the simplest possible examples of XUL. Although it is small, it demonstrates some important aspects of XUL programming, including the use of event handlers to add behavior and the use of a box to lay out elements properly within the window. This example also provides a context for discussing more general features of the language, such as the file format, the namespace, and some XUL programming conventions.

Example 2-1. Hello xFly

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This is the Title of the Book, eMatter Edition Copyright © 2002 O’Reilly & Associates, Inc. All rights reserved. Use your text editor to save the code in Example 2-1 in a file called hello.xul and then load the file in Mozilla (you can do this by using File ➝ Open File from the browser window and browsing to where you saved the file). You should see a button in the upper-left corner of the browser window that brings up an alert box when clicked. Figure 2-1 shows an example of the alert pop-up window that appears.

Figure 2-1. The first Hello xFly example

The next few sections describe this sample file in more detail. The covered topics include the file itself, the syntax of the markup, XUL namespaces, and the basic lay- out of a XUL file.

The xFly Examples The best way to understand the possible uses of the Mozilla framework is to look more closely at a number of various existing applications. This book highlights several Mozilla development projects, such as ChatZilla and JSLib, as examples of how some people have already started using Mozilla’s XPFE technologies. Along with these applications, you’ll note the use of the name “xFly” in many exam- ples in this chapter and elsewhere in this book. The xFly examples are used throughout Chapter 2 to Chapter 6 to show how to create and package a simple Mozilla applica- tion. This simple application is useful because it provides a place to start exploring the new information that you will learn about in this book. As you read more about XUL, CSS, JavaScript, and the other parts of Mozilla’s development framework, you can create and edit the xFly files to see how these technologies work in practice.

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This is the Title of the Book, eMatter Edition Copyright © 2002 O’Reilly & Associates, Inc. All rights reserved. Basic XUL Concepts You have already seen many of XUL’s basic features at work. When you load the example in the previous example, the browser identifies it as a XUL file, parses the data, creates a new window and draws the button widget, and executes the function you’ve defined when the button is clicked. These activities are part of the basic and often transparent interaction between your application files and Mozilla. However, the format of your XUL files, their syntax and namespace, the XUL layout, and the windowing system are all basic to success- ful XUL programming.

The XUL File Format A XUL file is a simple text file that contains proper XML syntax and has a .xul file extension. Mozilla expects to draw UI widgets when it encounters a file with a .xul extension or when it encounters the XUL namespace in other markup files that it rec- ognizes, including HTML and XML. The MIME type registered for XUL files is application/vnd.mozilla.xul+xml. When editing and using XUL files locally, you shouldn’t need to worry about setting this on your computer; however, sometimes you may need to set the MIME type, such as when you host XUL files on a server. Chapter 12 provides additional information about how you can set the correct file type for your system.

Conventions XUL has to follow certain conventions (as does XHTML or any other XML-based file) in order to be valid. Mozilla generates an error when it encounters an invalid XUL file. The first thing required in a XUL document is the XML declaration. Any comments used to introduce your file can begin on the line after the declara- tion. Comments in XUL follow the same format used in HTML and XML, delimited by . All tag sets must be closed. Empty tags are allowed for some elements, such as the element, that are used without nested elements or content. Note that a trail- ing slash at the end of the tag is required to denote an empty element. Another thing to remember is that XUL is case-sensitive. Closing a XUL tag with renders it invalid.

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This is the Title of the Book, eMatter Edition Copyright © 2002 O’Reilly & Associates, Inc. All rights reserved. These conventions ensure that the rendering engine can parse the XUL file success- fully and display the elements defined there. Mozilla does not validate XML files, such as XUL, and it does not resolve externally parsed entities, but it does check for document well-formedness. Following the XML specification, Mozilla ignores well-formed tags that it does not recognize, which can give your applications extra flexibility, particularly as you begin to use technologies such as XBL. But it can also make debugging a little more diffi- cult, as when you create an element named and don’t see why your XUL button doesn’t have the typical borders or three-dimensional style. A good practice to follow when creating XUL files is to use comments, copious whitespace, indentations (but not tabbed indentations where you can avoid them), and XUL widgets you are familiar with.

The XUL Namespace Like other markup vocabularies, XUL uses a namespace declaration to define the particular elements that may be included in a valid file. Example 2-2 shows a sample of the required namespace declaration. The namespace is an attribute of the root window element. The lack of any suffix on the XML namespace declaration (i.e., xmlns:xul) indicates that XUL is the default namespace for this file.

Example 2-2. The XUL namespace declaration Illustrating the XUL namespace

If you want to include XUL content in documents that use other types of markup, you need to declare more than one namespace. Common namespace declarations for getting other language elements into your code include HTML and RDF, but you can invent your own as well. If you wanted to put the button from Example 2-1 into a vanilla XML file, for example, you could place it into an XML document by using the xmlns:xul attribute, as shown in Example 2-3.

Example 2-3. Mixed namespaces in an XML document

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This is the Title of the Book, eMatter Edition Copyright © 2002 O’Reilly & Associates, Inc. All rights reserved. This file has three types of content: XUL, HTML, and customized markup called flies. When you use mixed namespaces, you have to prefix the XUL elements with xul: to distinguish them from markup in other namespaces, as with the xul:box and xul:button shown in Example 2-3.

Basic XUL Layout Example 2-1 features some very common XUL elements. In this section, each ele- ment is dissected to show what it does and how it interacts with other elements. The element is the root of individual primary XUL documents (in contrast to dialogs that pop up from windows, which can use

as the root, and XUL documents loaded within other XUL containers, which can use ). As in HTML, the root element defines the document into which all elements are drawn, but in XUL, that document is a piece of an application interface and not a web page. We’ll have more to say about the window and some of its features in the second example. A element that contains a

is inside the window in Example 2-1. Although you can use attributes on the window element to lay out and position win- dow children, it’s never a bad idea to use the as a container, particularly when you add new layout to your document, such as rows of buttons, grids, tabs, or other elements that need to be arranged precisely within the space of the window. The box is the basic element for layout in XUL. The align attribute on the box specifies that the children do not stretch and center themselves in the middle of the available space. If the box was omitted and there were multiple children of the root window, they would be laid out vertically by default, one under the other. This setting can be overridden by adding the orient attribute to and giving it a value of “horizontal.”

Using XUL Windows The foundation of an XPFE application is a window. Each XUL document has to have at least one XUL element, and it must be the root of the document— the surrounding, outermost element in the XML document, set apart from the XML declaration itself and other processing “preambles.” A basic window with no con- tent looks like this: Commonly, an application has more than one window, with a number of dialogs and secondary windows. Each window is also contained within a element

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This is the Title of the Book, eMatter Edition Copyright © 2002 O’Reilly & Associates, Inc. All rights reserved. (though recent additions to the XUL specification include the dialog and page ele- ments, which are derived from window and can be used in its place as root elements in your XUL files). As your application becomes more complex, you need a way to keep track of the windows and ensure that they can communicate with one another. In Mozilla, there is a way to do this by using the type attribute identifier, which allows you to use spe- cial window-opening functions like toOpenWindowByType() to manage particular win- dow types.

As with any existing Mozilla functions referred to in this book, you can look up toOpenWindowByType by using the LXR web-based source code viewer, described in Appendix A and available at http://lxr. mozilla.org/.

Window features An id attribute is present on the element. Using this attribute is not neces- sary to run the windows system, but it is a good idea to give each window a unique identifier because it makes nodes easier to find from script (see the DOMmethod getElementByID in Chapter 5 for information about how to get elements by identi- fier). This is how to set up an ID attribute: id="xflyMain"> Load event handlers such as onload and onunload are useful and necessary if you want to add behavior to a window, pass input to it, or manipulate its content depending on context: When you load a XUL file that begins in this way, the event handler attributes onload and onunload carry out the functions listed as values (startUp() and shutdown()). In addition, Mozilla provides an onclose event handler that intercepts the upcoming window closure to carry out any extra processing you need. The close event is fired before the unload event, so you can stop the window from closing in the onclose event handler if necessary. To stop window closure, the close event must return false. Additional handlers are available for dialog windows. They are listed and their use is outlined in the section “Application Windows” in Chapter 3.

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This is the Title of the Book, eMatter Edition Copyright © 2002 O’Reilly & Associates, Inc. All rights reserved. Window properties The window declaration is expanding, but there is still plenty of room for more fea- tures. In addition to the attributes—the event handlers, the ID, and the namespace that appear within the tag itself—a XUL window also has all of the proper- ties of the DOM window object from HTML. These properties are listed below, along with additional properties for application specific tasks.

Navigator Document window Parent Top Scrollbars name ScrollX ScrollY ScrollTo scrollBy GetSelection ScrollByLines ScrollByPages Size Dump ToContent SetTimeout SetInterval Clear ClearInterval Timeout SetResizable CaptureEvents Release RouteEvent Events Enable DisableExternal prompt Open External Capture Capture OpenDialog Frames find self Screen History content Sidebar Menubar Toolbar Locationbar Personalbar Statusbar Directories closed Crypto pkcs11 Controllers opener Status defaultStatus Location innerWidthInnerHeight outerWidthOuterHeightscreenX ScreenY pageXOffset PageYOffset lengthFullScreen alert Confirm focus Blur back Forward home Stop print MoveTo moveBy ResizeTo resizeBy Scroll close UpdateCommands escape Unescape atob Btoa AddEvent RemoveEvent Dispatch GetComputed Listener Listener Event Style Special properties of the XUL window object include: window.content Using this property is a quick way to access the content area of your window, if one exists. This property is useful only if your window uses one of the content elements, namely