Composition

Composition is one of the built-in templating implementations. The concept is simple:

1. Define a template (a ZUML document representing a complete UI)
2. Define a ZUML document that contains a collections of fragments that a template might reference

Notice that the user shall visit the ZUML document with a collection of fragments rather than the template document.

The advantage of Composition is that you don't need additional configuration file.

Defines a Template

A template document is a ZUML document that defines how to assemble the fragments. For example,

<!-- /WEB-INF/layout/template.zul -->
<vbox>
  <hbox self="@{insert(content)}"/>
  <hbox self="@{insert(detail)}"/>
</vbox>

As shown, the anchor (i.e., the component that a fragment will insert as children) is defined by specify an annotation as @{insert(name)}. Then, when Composition is applied to a ZUML document with a collections of fragments, the matched fragment will become the child of the annotated component (such as hbox in the above example).

Define Fragments

To apply a template to a ZUML document that an user visits, you have to defined a collection of fragments that a template might use, and then specify Composition as one of the initiators of the document:

<!-- foo/index.zul -->
<?init class="org.zkoss.zk.ui.util.Composition"
arg0="/WEB-INF/layout/template.zul"?>
<zk>
  <window self="@{define(content)}" title="window1" width="100px"/>
  <window self="@{define(content)}" title="window2" width="200px"/>
  <grid self="@{define(detail)}" width="300px" height="100px"/>
</zk>

As shown, a fragment is defined by specify an annotation as self="@{define(name)}. Furthermore, the template is specified in the init directive.

Then, when the user visits this page (foo/index.zul in the above example), Composition will do:

1. Load the template, and render it as the root components of this page(foo/index.zul)
2. Move the fragments specified in this page to become the children of the anchor component with the same annotation name

Thus, here is the result

<vbox>
  <hbox>
    <window title="window1" width="100px"/>
    <window title="window2" width="200px"/>
  </hbox>
  <hbox>
    <grid width="300px" height="100px"/>
  </hbox>
</vbox>

Multiple Templates

You could apply multiple templates to a single page too:

<?init class="org.zkoss.zk.ui.util.Composition"
arg0="/WEB-INF/layout/template0.zul" arg1="/WEB-INF/layout/template1.zul"?>

The templates specified in arg0 and arg1 (etc.) will be loaded and rendered one-by-one.

Grouping Fragments into Separated Files

In a complex templating environment, it might not be appropriate to put fragments in the target page (e.g., foo/index.zul in the above example), since you might want to use the same collection of fragments in several target pages. It can be easily by use of the include component as follows.

<!-- foo/index.zul -->
<?init class="org.zkoss.zk.ui.util.Composition"
arg0="/WEB-INF/layout/template.zul"?>
<include src="/WEB-INF/layout/fragments.zul"/>

Then, you could group fragments into one or multiple individual ZUL documents, such as

<!-- /WEB-INF/layout/fragments.zul -->
<zk>
  <window self="@{define(content)}" title="window1" width="100px"/>
  <window self="@{define(content)}" title="window2" width="200px"/>
  <grid self="@{define(detail)}" width="300px" height="100px"/>
</zk>

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