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How to make your custom component accept and pass on all unknown parameters to the underlying HTML element |
Supporting Informal Parameters
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Informal parameters are any additional parameters beyond the parameters explicitly defined for a component using the Parameter annotation.
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| style | float:right |
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| class | aui-label |
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| showLabels | false |
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| showSpace | false |
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| title | Related Articles |
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| cql | label = "parameters" and space = currentSpace() |
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Any component that closely emulates a particular HTML element should support informal parameters. You'll find that many of the built-in Tapestry components, such as Form, Label and TextField, do exactly that.
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In the example below we create an Img component, a custom replacement for the <img> tag. Its src parameter will be an asset. We'll use the @SupportsInformalParameters annotation to tell Tapestry that the component should support informal parameters.
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@SupportsInformalParameters
public class Img
{
@Parameter(required=true, allowNull=false, defaultPrefix=BindingConstants.ASSET)
private Asset src;
@Inject
private ComponentResources resources;
boolean beginRender(MarkupWriter writer)
{
writer.element("img", "src", src);
resources.renderInformalParameters(writer);
writer.end();
return false;
}
}
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Another, equivalent, approach is to use the RenderInformals mixin:
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public class Img
{
@Parameter(required=true, allowNull=false, defaultPrefix=BindingConstants.ASSET)
private Asset src;
@Mixin
private RenderInformals renderInformals;
void beginRender(MarkupWriter writer)
{
writer.element("img", "src", src);
}
boolean beforeRenderBody(MarkupWriter writer)
{
writer.end();
return false;
}
}
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