THIS IS A TEST INSTANCE. ALL YOUR CHANGES WILL BE LOST!!!!
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The component listed below is a looping component; it renders its body a number of times, defined by its start and end parameters (which set the boundaries of the loop). The component can update a value result parameter bound to a property of its container, ; it will automatically count up or down depending on whether start or end is larger.
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package org.example.app.components;
import org.apache.tapestry5.annotations.AfterRender;
import org.apache.tapestry5.annotations.Parameter;
import org.apache.tapestry5.annotations.SetupRender;
public class Count
{
@Parameter (value="1")
private int start = 1;
@Parameter(required = true)
private int end;
@Parameter
private int valueresult;
private boolean increment;
@SetupRender
void initializeValueinitializeValues()
{
valueresult = start;
increment = start < end;
}
@AfterRender
boolean next()
{
if (increment)
{
int newValuenewResult = value + 1;
if (newValuenewResult <= end)
{
valueresult = newValuenewResult;
return false;
}
}
else
{
int newValue newResult= value - 1;
if (newValue >newResult>= end)
{
valueresult = newValuenewResult;
return false;
}
}
return true;
}
}
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The name of the parameter is derived from the same as field name (by stripping except with leading "_" and "$" characters, if any, removed). Here, the parameter names are "start", "end" and "valueresult".
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Prefix | Description |
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 value 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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<t:layout xmlns:t="http://tapestry.apache.org/schema/tapestry_5_1_0.xsd">
<p> Countdown:
<t:count start="5" end="1" valueresult="index">
${index} ...
</t:count>
</p>
</t:layout>
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Because the Count component updates its value result parameter (the _value result field), the index property of the containing component is updated. Inside the Count's body, we output the current value of the index property, using the expansion ${index}. The resulting output will look something like:
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You may set a default value for optional parameters as you would for any other fieldusing the value element of the @Parameter annotation. In the Count component above, the min start parameter has a default value of 1. That value is used unless the min start parameter is bound, in which case, the bound value supersedes the default.
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The @Parameter annotation's value() attribute element can be used to specify a binding expression that will be the default binding for the parameter is if otherwise left unbound. Typically, this is the name of a property that that will compute the value on the fly.
Example:
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@Parameter(value="defaultMessage") // or, equivalently, @Parameter("defaultMessage") private String message; @Parameter(required=true) private int maxLength; public String getDefaultMessage() { return String.format("Maximum field length is %d.", _maxLength); } |
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