Reusing Components with a Template

In ZK 8, <template> is our recommended form for reusing a view pattern composed by a group of components. Putting components into <template> can make them reusable easily by <apply>. It usually involves 2 steps:

1. Define a template
2. Apply a template

Defining a template

With ZK 8, you can put a <template> inside any component. Defining a template will not create any component until you apply it. You can define a template like this:

<div>
    <template name="layout">
    <!-- UI components or shadow components -->
    </template>
</div>

or a path of a zul

<div>
    <template name="layout" src="/mytemplate.zul"/>
</div>

The usage is the same as what we mentioned in previous chapters. But we can also use the following tags to describe a component creation logic based on certain conditions.

Applying a Template

When we apply a template, ZK will create the components inside the template upon its logic and insert those components into the position of <apply> tag. Therefore, we also call it Template Injection.

We usually apply a template with its name like:

<apply template="layout"/>

Or apply with a path of a zul like:

<apply templateURI="/chapter1/banner.zul"/>

Turning Components into Templates

To reuse the <forEach>, we turn it into a template named iterate first.

<navbar id="navbar" orient="horizontal" collapsed="false" onSelect="@command('navigate')" >
    <apply template="iterate" menuItems="@ref(vm.menuHierarchy)"/>
</navbar>
<template name="iterate">
    <forEach items="@load(vm.menuHierarchy)">
        <choose>
            <when test="@load(empty each.subMenus)">
                <navitem label="@load(each.label)" />
            </when>
            <otherwise>
                <nav label="@load(each.label)" iconSclass="@load(each.iconSclass)"/>
            </otherwise>
        </choose>
    </forEach>
</template>

• Line 2: We pass a parameter by menuItems="@ref(vm.menuHierarchy)". Therefore, we can access the menu list in <forEach> by items="@load(menuItems)".

In this simple case (just 2 choices), we can re-write it in a simpler way by creating 2 templates for menu and menuitem respectively.

<template name="menu">
    <nav label="@load(menuItem.label)" iconSclass="@load(menuItem.iconSclass)"/>
</template>

<template name="menuitem" >
    <navitem label="@load(menuItem.label)" />
</template>

Then replace <choose>/<when>/<otherwise> with ternary operator ? like:

<template name="iterate">
    <forEach items="@load(menuItems)">
        <apply template="@load(empty each.subMenus?'menuitem':'menu')" menuItem="@ref(each)"/>
    </forEach>
</template>

Applying a Template Inside a Template

Everything is fine so far except for the fact those sub-menus are not rendered. That's because in template menu, we only render the menu node itself to a <nav> and don't render its sub-menu. A node in a sub-menu is also a menu node, and it can also have a sub-menu. We still need to render a sub-menu node like what we do for a menu node, by using a control structure. The best thing is: we don't need to repeat ourselves in template menu. We can just apply the template iterate to iterate a collection of menu nodes recursively.

All 3 templates are used in this example

<template name="menu">
    <nav label="@load(menuItem.label)" iconSclass="@load(menuItem.iconSclass)">
        <apply template="iterate" menuItems="@ref(menuItem.subMenus)"/>
    </nav>
</template>
<template name="iterate">
    <forEach items="@load(menuItems)">
        <apply template="@load(empty each.subMenus?'menuitem':'menu')" menuItem="@ref(each)"/>
    </forEach>
</template>
<template name="menuitem" >
    <navitem label="@load(menuItem.label)" />
</template>

• Line 3: Apply the previous template iterate here to traverse each menu node and render them.