Envisage ZK 6.0: Rendering List and Tree Model with Templates
Tom Yeh, Potix Corporation
July 20, 2011
ZK 6.0
The Story
Before ZK 6.0, the custom renderer must be implemented through Java. Although Java is very powerful and anything can be achieved with it, it is still tedious and not always the most feasible solution having to create and maintain an additional Java class every single time. Speaking in terms of the MVC concept, in many cases, it makes much more sense to place ZUL as it is closer to "View" rather than the "Control" in the Java code.
With ZK 6.0, a new concept called "template" is introduced. It allow UI designers to specify templates right in a ZUML page, the model can then be rendered based on the template without any Java code.
What Is a Template
A template is a segment of a ZUML page enclosed with the template element as shown below.
<window>
<template name="foo">
<textbox/>
<grid>
<columns/>
</grid>
</template>
...
The template can contain any ZUML elements users desire, including other templates. When ZK interprets a template, it does not interpret its content immediately, rather, it first stores it as an instance of org.zkoss.zk.ui.util.Template into the component, such that it can be retrieved later to create components by the application or the component to create its child component(s).
Listbox Model Rendering with Template
With 6.0, the custom renderer can be done with a template without any Java code. For example, when wanting to render a two-dimensional array, the follow can be done to achieve the desired outcome
<?variable-resolver class="foo.FruitProvider"?>
<listbox model="${fruits}">
<listhead>
<listheader label="Name" sort="auto"/>
<listheader label="Weight" sort="auto"/>
</listhead>
<template name="model">
<listitem>
<listcell label="${each[0]}"/>
<listcell label="${each[1]}"/>
</listitem>
</template>
</listbox>
where fruits is a two-dimensional array that can be retrieved by use of a variable resolver (VariableResolver)[1] called foo.FruitProvider as shown below.
public class FruitProvider implements VariableResolver {
public Object resolveVariable(String name) {
if ("fruits".equals(name))
return new ListModelArray(
new String[][] {
{"Apple", "10kg"},
{"Orange", "20kg"},
{"Mango", "12kg"}
});
return null;
}
}
As illustrated above, custom rendering is defined by a template called model. The template's name is important because users are allowed to associate multiple templates to one component. Furthermore, when the template is rendered, a variable called each is assigned with the data being rendered.
Additionally, if value="${each}" is not specified to the listitem (Listitem.setValue(Object)) in the template, the renderer will automatically assign the data being rendered to the listitem in order for users to conveniently retrieve back the data when necessary.
- ↑ There are several ways to assign a model to a UI component. Please refer to ZK Developer's Reference for detailed information.
Nested Listboxes
The template can be applied recursively. Here is an example of a listbox-in-listbox:
<zk>
<zscript><![CDATA[
ListModel quarters = new ListModelArray(new String[] {"Q1", "Q2", "Q3", "Q4"});
Map months = new HashMap();
months.put("Q1", new ListModelArray(new String[] {"Jan", "Feb", "Mar"}));
months.put("Q2", new ListModelArray(new String[] {"Apr", "May", "Jun"}));
months.put("Q3", new ListModelArray(new String[] {"Jul", "Aug", "Sep"}));
months.put("Q4", new ListModelArray(new String[] {"Oct", "Nov", "Dec"}));
ListModel qs = (quarters);
]]></zscript>
<listbox model="${quarters}">
<template name="model">
<listitem>
<listcell>${each}</listcell>
<listcell>
<listbox model="${months[each]}">
<template name="model">
<listitem label="${each}"/>
</template>
</listbox>
</listcell>
</listitem>
</template>
</listbox>
</zk>
To access the data of the outer template from the inner template, use the parent listitem's Listitem.getValue() where the data is stored by default. Please look at line 8 of the following example, data can be retrieved from the outer model by travelling the component tree
<listbox model="${quarters}">
<template name="model">
<listitem>
<listcell>
<listbox model="${months[each]}">
<template name="model">
<listitem>
<listcell label="${forEachStatus.index}" />
<listcell>${self.parent.parent.parent.parent.parent.value}</listcell>
<listcell>${each}</listcell>
</listitem>
</template>
</listbox>
</listcell>
</listitem>
</template>
</listbox>
Notice that, unlike the forEach attribute, the forEachStatus is only available in the near template scope when the nested listbox is about to render.
Grid Model Rendering with Template
Similarly, users can define a customer rendering with a template for a grid:
<grid model="${books}">
<columns>
<column label="ISBN" sort="auto"/>
<column label="Name" sort="auto"/>
<column label="Description"/>
</columns>
<template name="model">
<row>
<label value="${each.isbn}"/>
<label value="${each.name}"/>
<label value="${each.description}"/>
</row>
</template>
</grid>
where books is assumed as an instance of ListModel that contains a list of the Book instances while each Book instances has at least three getter methods: getIsbn, getName and getDescription.
Notice that the template named model must be associated with the grid, i.e., it must be a direct child element of the grid element as shown above. A common mistake is to put it under the rows element. Remember the template is a ZUML fragment telling the grid how to render a row, and the template itself is not a component.
Tree Model Rendering with Template
Similarly, users can also define a customer rendering with a template for a tree:
<tree model="${files}">
<treecols>
<treecol label="Path"/>
<treecol label="Description"/>
</treecols>
<template name="model">
<treeitem context="menupopup">
<treerow>
<treecell label="${each.data.path}"/>
<treecell label="${each.data.description}"/>
</treerow>
</treeitem>
</template>
</tree>
assume files is an instance of DefaultTreeModel. Notice since DefaultTreeModel is used, each references an instance of DefaultTreeNode. Thus, to retrieve the real data, use DefaultTreeNode.getData()
Combobox Model Rendering with Template
Here is an example of how to render a combobox with a template:
<window>
ListModel infos = new ListModelArray(
new String[][] {
{"Apple", "10kg"},
{"Orange", "20kg"},
{"Mango", "12kg"}
});
</zscript>
<combobox model="${infos}">
<template name="model">
<comboitem label="${each[0]}: ${each[1]}"/>
</template>
</combobox>
</window>
Using Template in Application
"Template" is a generic feature and its use is not limited to custom model rendering. Users are able to use "template" in ZK applications too.
Each template is stored as part of a component and can be retrieved it by invoking the getTemplate method. To create the component tree defined in the template, just invoke the Template.create(Component parent, Component insertBefore, VariableResolver resolver) method. For example,
comp.getTemplate("foo").create(comp, null, null, null);
The third argument of the create method is a variable resolver (VariableResolver). Depending on the requirement, you could pass any implementation you like. For example, the implementation of a listbox actually utilizes it to return the data being rendered; the code is similar to the following (for easy understanding, the code has been simplified).
For more detailed information about the variable resolver, please refer to ZUML Reference.
public class TemplateBasedRenderer implements ListitemRenderer {
public void render(Listitem item, final Object data) {
final Listbox listbox = (Listbox)item.getParent();
final Component[] items = listbox.getTemplate("model").create(listbox, item,
new VariableResolver() {
public Object resolveVariable(String name) {
return "each".equals(name) ? data: null;
}
}, null);
final Listitem nli = (Listitem)items[0];
if (nli.getValue() == null) //template might set it
nli.setValue(data);
item.detach();
}
}
In addition, the template allow users to specify any number of parameters with any name, and these parameters can be retrieved back by the getParameters method of the Template interface:
<template name="foo" var1="value1" var2="${el2}">
...
</template>
If a template is located elsewhere as a separated file, to reference it, specify it in the src attribute as follows.
<template name="foo" src="foo.zul">
...
</template>
Download
To test drive, please download a freshly release of 6.0.0.
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