THIS IS A TEST INSTANCE. ALL YOUR CHANGES WILL BE LOST!!!!
Component parameters are the primary means for a component instance and its container to communicate with each other. Parameters are used to configure component instances.
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<html xmlns:t="http://tapestry.apache.org/schema/tapestry_5_34.xsd"> <t:pagelink page="Index">Go Home</t:pagelink> </html> |
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The component above can be referenced in another component or page template, and its parameters bound:
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<html t:type="layout" xmlns:t="http://tapestry.apache.org/schema/tapestry_5_34.xsd"> <p> Merry Christmas: <t:count end="3"> Ho! </t:count> </p> </html> |
The end attribute is used to bind the end parameter of the Count component. Here, it is being bound to the string value "3", which is automatically coerced by Tapestry into the int value, 3.
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Prefix | Description |
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asset: | The relative path to an asset file (which must exist) |
block: | The id of a block within the template |
component: | The id of another component within the same template |
context: | Context asset: path from context root |
literal: | A literal string |
nullfieldstrategy: | Used to locate a pre-defined NullFieldStrategy |
message: | Retrieves a string from the component's message catalog |
prop: | A property expression to read or update |
symbol: | Used to read one of your symbols |
translate: | The name of a configured translator |
validate: | A validator specification used to create some number of field validators |
var: | Allows a render variable of the component to be read or updated |
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Render variable names are case insensitive.
Property: Bindings
Main Article: Property Expressions
The "prop:" binding prefix indicates a property expression binding.
Property expressions are used to link a parameter of a component to a property of its container. Property expressions can navigate a series of properties and/or invoke methods, as well as several other useful patterns. See Component Parameters.
The default binding prefix in most cases is "prop:", which is why it is usually omitted.
Validate: Bindings
Main Article: Component Parameters Forms and Validation
The "validate:" binding prefix is highly specialized. It allows a short string to be used to create and configure the objects that perform input validation for form control components, such as TextField and Checkbox.
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The list of available translators is configured by the TranslatorSource service.
Asset: Bindings
Main Article: Assets
Assets bindings are used to specify Component Parameters, static content served by Tapestry. By default, assets are located relative to the component class in your packaged application or module. This can be overridden by prefixing the path with "context:", in which case, the path is a context path from the root of the web application context. Because accessing context assets is relatively common, a separate "context:" binding prefix for that purpose exists (described below).
Context: Bindings
Main Article: Assets
Context bindings are like asset bindings, but the path is always relative to the root of the web application context. This is intended for use inside templates, i.e.:
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Sometimes a parameter is marked as required, but may still be omitted if the underlying value is provided by some other means. This is the case, for example, with the Select component's value parameter, which may have its underlying value set by contributing a ValueEncoderSource. Be sure to read the component's parameter documentation carefully. Required simply enables checks that the parameter is bound, it does not mean that you must supply the binding in the template (or @Component annotation). |
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Don't use the ${...} syntax!
Main Article: Expansions
You generally should not use the Template Expansion syntax, ${...}, within component parameter bindings. Doing so results in the property inside the braces being converted to an (immutable) string, and will therefore result in a runtime exception if your component needs to update the value (whenever the default or explicit binding prefix is prop: or var:, since such component parameters are two-way bindings).
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Informal Parameters
Main Article: Component Supporting Informal Parameters
Many components support informal parameters, additional parameters beyond the formally defined parameters. Informal parameters will be rendered into the output as additional attributes on the tag rendered by the component. Generally speaking, components that have a 1:1 relationship with a particular HTML tag (such as <TextField> and <input> will support informal parameters.
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If your component should render informal parameters, just inject the ComponentResources for your component and invoke the renderInformalParameters() method. See Component See Supporting Informal Parameters for an example of how to do this.
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<t:layout xmlns:t="http://tapestry.apache.org/schema/tapestry_5_34.xsd"> <p> Countdown: <t:count start="5" end="1" result="index"> ${index} ... </t:count> </p> </t:layout> |
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<html xmlns:t="http://tapestry.apache.org/schema/tapestry_5_34.xsd"> <body> <div t:type="layout" t:menuTitle="literal:The Title"> ... </div> </body> </html> |
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<t:container xmlns:t="http://tapestry.apache.org/schema/tapestry_5_34.xsd"> <div t:type="title" t:title="inherit:menuTitle"></div> <t:body /> </t:container> |
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Parameter Type Coercion
Main Article: Component Parameters Parameter Type Coercion
Tapestry includes a mechanism for coercing types automatically. Most often, this is used to convert literal strings into appropriate values, but in many cases, more complex conversions will occur. This mechanism is used for component parameters, such as when an outer component passes a literal string to an inner component that is expecting an integer.
You can easily contribute new coercions for your own purposes.
Parameter Names
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In rare cases, you may want to take different behaviors based on whether a parameter is bound or not. This can be accomplished by querying the component's resources, which can be injected into the component using the @Inject annotation:
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public class MyComponent
{
@Parameter
private int myParam;
@Inject
private ComponentResources resourcescomponentResources;
@BeginRender
void setup()
{
if (resourcescomponentResources.isBound("myParam"))
{
. . .
}
}
}
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<t:container xmlns:t="http://tapestry.apache.org/schema/tapestry_5_34.xsd"> <t:pageLink t:id="link">Page Link</t:pageLink> </t:container> |
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There are still cases where you want to use the "inherit:" binding prefix. For example, if you have several components that need to share a parameter, then you must do it the Tapestry 5.0 way: a true parameter on the outer component, and "inherit:" bindings on the embedded components. You can follow a similar pattern to rename a parameter in the outer component.
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