org.apache.tapestry5.annotations

## Annotation Type Parameter

-     @Target(value=FIELD)
       @Documented
       @Retention(value=RUNTIME)
       @UseWith(value={COMPONENT,MIXIN})
      public @interface Parameter

  Annotation placed on a field to indicate that it is, in fact, a component parameter. Parameters may be optional or required. Required parameters must be bound.

- - ### Optional Element Summary

    Optional Elements
    Modifier and Type | Optional Element and Description
    --- | ---
    `boolean` | `allowNull` If false, and the parameter is bound, then the value for the parameter must not be null.
    `boolean` | `autoconnect` Used to create a default binding, connecting the parameter to a property of the container whose property name matches the id of the component.
    `boolean` | `cache` If true (the default), then the value for the parameter is cached while the component is, itself, rendering.
    `String` | `defaultPrefix` The default binding prefix for the parameter, if no specific binding prefix is provided with the binding.
    `String` | `name` The name of the parameter.
    `boolean` | `principal` Used to mark a parameter as requiring earlier initialization than other parameters.
    `boolean` | `required` If true, the parameter is required and and must be bound.
    `String` | `value` The default value for the parameter if not bound.

- - ### Element Detail

    - #### name

          public abstract String name

      The name of the parameter. If not specified, the name of the parameter is derived from the name of the field (after stripping off leading and trailing punctuation).
      Default:
        ""

  - - #### required

          public abstract boolean required

      If true, the parameter is required and and must be bound. If false (the default), then the parameter is optional.
      Default:
        false

  - - #### allowNull

          public abstract boolean allowNull

      If false, and the parameter is bound, then the value for the parameter must not be null. The default is true, to allow nulls. This is different than required, in that the parameter may be bound, but bound to a null value.
      Default:
        true

  - - #### cache

          public abstract boolean cache

      If true (the default), then the value for the parameter is cached while the component is, itself, rendering. Values from invariant bindings (such as literal strings) are always cached, regardless of this setting. Set this attribute to false to force the parameter to be re-read every time the field is accessed, even while the component is rendering.
      Default:
        true

  - - #### value

          public abstract String value

      The default value for the parameter if not bound. This is a binding expression, typically the name of a property of the component to bind. The default value for this attribute is the empty string, indicating that there is no default default binding.
      Default:
        ""

  - - #### defaultPrefix

          public abstract String defaultPrefix

      The default binding prefix for the parameter, if no specific binding prefix is provided with the binding. There is rarely a reason to override this. Typically, non-standard default binding prefixes are paired with specific `BindingFactory` implementations, and used with parameters whose name reflects the binding prefix.
      See Also:
        `BindingConstants`
      Default:
        "prop"

  - - #### principal

          public abstract boolean principal

      Used to mark a parameter as requiring earlier initialization than other parameters. This is used when default bindings for secondary parameters rely on a principal parameter, which itself may have a default value. This ensures that the binding for the principal parameter(s) are initialized, possibly involving a defaulter method, before the secondary parameters are initialized (as they may need to know if the principal parameter is bound, and what type of value it is bound to). This is rarely used, and it is highly unlikely a single component would have more than a single principal parameter.
      Default:
        false

  - - #### autoconnect

          public abstract boolean autoconnect

      Used to create a default binding, connecting the parameter to a property of the container whose property name matches the id of the component. This is frequently used for form element components. This default binding is only used if there is no matching container property.
      See Also:
        `ComponentDefaultProvider.defaultBinding(String, org.apache.tapestry5.ComponentResources)`
      Default:
        false

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