THIS IS A TEST INSTANCE. ALL YOUR CHANGES WILL BE LOST!!!!
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Components can have any number of of render variables. Render variables are named values with no specific type (they are ultimately stored in a Map). Render variables are useful for holding simple values, such as loop indices, that need to be passed from one component to another.
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In other words, you don't have to define a property in the Java code. The disadvantage is that render variables don't work with the property expression syntax, so you can pass around a render variable's s value but but you can't reference any of the value's properties.
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Validate: Bindings
Main Article: 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.
The string is a comma-separated list of of validator types. These are short aliases for objects that perform the validation. In many cases, the validation is configurable in some way: for example, a validator that enforces a minimum string length needs to know what that minimum string length is. Such values are specified after an equals sign.
For example: validate:required,minLength=5 would would presumably enforce that a field requires a value, and with at least five characters.
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The "translate:" binding prefix is also related to input validatorvalidation. It is the name of a configured configured Translator, responsible for converting between server-side and client-side representations of data (for instance, between client-side strings and server-side numeric values).
The list of available translators is configured by the the TranslatorSource service service.
Asset: Bindings
Assets bindings are normally used to specify assets, 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).
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Context bindings are like asset bindings, but the path is is always relative relative to the root of the web application context. This is intended for use inside templates, i.e.:
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Required Parameters
Parameters that are required required must be be bound. A runtime exception occurs if a component has unbound required parameters.
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| Tip |
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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 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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You may set a default value for optional parameters using the the value element element of the @Parameter annotation. In the Count component above, the start parameter has a default value of 1. That value is used unless the start parameter is bound, in which case, the bound value supersedes the default.
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The @Parameter annotation's s value element element can be used to specify a a binding expression that that will be the default binding for the parameter if otherwise left unbound. Typically, this is the name of a property that that will compute the value on the fly.
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