XML Background
Overview
This section provides the most basic concepts of XML to work with ZK. If you are familiar with XML, you could skip this section. If you want to learn more, there are a lot of resources on Internet, such as http://www.w3schools.com/xml/xml_whatis.asp and http://www.xml.com/pub/a/98/10/guide0.html.
XML is a markup language much like HTML but with stricter and cleaner syntax. It has several characteristics worth to notice.
Elements Must Be Well-formed
First, each element must be closed. They are two ways to close an element as depicted below. They are equivalent.
| Close by an end tag: | <window></window>
|
| Close without an end tag: | <window/>
|
Second, elements must be properly nested.
| Correct: | <window>
<groupbox>
Hello World!
</groupbox>
</window>
|
| Wrong: | <window>
<groupbox>
Hello World!
</window>
</groupbox>
|
XML treats every tag as a node in a tree. A node without a parent node is a root component, and it is the root of a tree. In each zul file, only ONE tree is allowed.
For example, for being a whole zul file, the following is allowed, for it has only one root component.
<button/>
And for being a whole zul file, the following is not allowed, for it has more than one root component.
<button/>
<button/>
You can solve the problem by simply adding a tag enclosing the whole zul file to serve as the parent node, so the zul file has one single tree again.
<window>
<button />
<button />
</window>
Special Character Must Be Replaced
XML use <element-name> to denote an element, so you have to replace special characters. For example, you have to use < to represent the < character.
| Required only if use it in a XML attribute's value | ||
| Required only if use it in a XML attribute's value |
Alternatively, you could tell XML parser not to interpret a piece of text by using CDATA as the following.
<zscript>
<![CDATA[
void myfunc(int a, int b) {
if (a < 0 && b > 0) {
//do something
}
]]>
</zscript>
It is suggested to always add <![CDATA[ ]]> inside your <zscript> </zscript>. Thus you don't have to worry about escape sequences for special characters like "&", "<". In addition, the code is much easier to read and maintain.
Attribute Values Must Be Specified and Quoted
| Correct: |
width="100%"
checked="true"
|
| Wrong: |
width=100%
checked
|
Both the single quote (') and the double quote (") can be used, so if the value has double quotes, you could use the single quote to enclose it. For example,
<button onClick='alert("Hello, There")'/>
Comments
A comment is used to leave a note or to temporarily disable a block of XML code. To add a comment in XML, use <!-- and --> to mark the comment body.
<window>
<!-- this is a comment and ignored by ZK -->
</window>
Character Encoding
It is, though optional, a good idea to specify the encoding in your XML such that the XML parser can interpret it correctly. Note: it must be on the first line of the file.
<?xml version="1.0" encoding="UTF-8"?>
In addition to specify the correct encoding, you have to make sure your XML editor supports it as well.