If (Tapestry API Documentation)

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org.apache.tapestry5.corelib.components
Class If

java.lang.Object
  org.apache.tapestry5.corelib.base.AbstractConditional
      org.apache.tapestry5.corelib.components.If

public class If extends AbstractConditional
extends AbstractConditional

Conditionally renders its body. May render its tag and any informal parameters.

Parameters:

Name	Type	Flags	Default Prefix	Description
else	org.apache.tapestry5.Block		literal	An alternate org.apache.tapestry5.Block to render if org.apache.tapestry5.corelib.base.AbstractConditional#test() is false. The default, null, means render nothing in that situation.
negate	boolean		prop	Optional parameter to invert the test. If true, then the body is rendered when the test parameter is false (not true).
test	boolean	Required	prop	If true, then the body of the If component is rendered. If false, the body is omitted.

Examples:

Start.tml

<html xmlns:t="http://tapestry.apache.org/schema/tapestry_5_1_0.xsd" xmlns:p="tapestry:parameter">
    <body>
        <h1>Welcome!</h1>

        <t:if test="user">
            Welcome back, ${user.firstName}
            <p:else>
                <t:pagelink name="login">Login</t:pagelink> /
                <t:pagelink name="register">Register</t:pagelink>
            </p:else>
        </t:if>
        
        . . .

</html>

Here, the main text is rendered if the user is logged in (the user property will be non-null after the user logs in). Otherwise, links to a login and register page are rendered.

Note the use of the p: namespace (new in Tapestry 5.1). In 5.0, this would be .

Notes:

Tapestry has many built in coercions to boolean:

String: True if non-blank and not the literal string "false" (case insensitive)
Number: True if non-zero
Collection: True if non-empty
Object: True (as long as its not null)

Constructor Summary
`If()`

Method Summary
`protected boolean`	`test()` Performs the test via the parameters; return true to render the body of the component, false to render the else block (or nothing).

Methods inherited from class java.lang.Object
`clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

Constructor Detail

If

public If()

Method Detail

test

protected boolean test()

Description copied from class: AbstractConditional

Performs the test via the parameters; return true to render the body of the component, false to render the else block (or nothing).

Specified by:: test in class AbstractConditional

Returns:: test parameter (if negate is false), or test parameter inverted (if negate is true)