Tapestry Core

org.apache.tapestry5.corelib.components.If

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

Component Inheritance

org.apache.tapestry5.corelib.base.AbstractConditional
- org.apache.tapestry5.corelib.components.If

Component Parameters

Name	Type	Flags	Default Prefix	Description
else	Block	NOT Allow Null	literal	An alternate Block to render if AbstractConditional#test() is false. The default, null, means render nothing in that situation.
negate	boolean	NOT Allow Null	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, NOT Allow Null	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 <t:parameter name="else">.

Notes

Tapestry has many builtin 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)