Attribute

出自OpenFace

<attribute>

　　Sets an attribute of the object that contains it.

　　The <attribute> tag has two uses:

　　1.In a class definiiton, the <attribute> tag defines an attribute that can be set in instances of the class.

<canvas height="30">
 <class name="mybutton" extends="text" fontsize="16">
   <attribute name="myattr" type="string" value="after"/>
 </class>
 <mybutton text="before" myattr="after" oninit="setAttribute('text', this.myattr)"/>
</canvas>

　　In an instance, the <attribute> tag attaches an attribute to the instance. The attribute can be accessed from script.

<canvas height="30">
 <class name="mybutton" extends="text" fontsize="16">
     <attribute name="myattr" type="string" value="after"/>
 </class>
 <mybutton text="before" oninit="setAttribute('text', this.myattr)">
   <attribute name="myattr" value="perhaps later"/>
 </mybutton>
</canvas>

See the Guide for a complete discussion.

Also see the documentation for <class> and the general description of LZX attributes. The Classes tutorial describes how to use attributes to define a class.

Attributes

Name　　　　 Usage　　　 Type(Tag)　　　 Type(JS)　　　 Default 　　　Category

name 　　　　Tag only　　　token 　　　　　　　　　　　　　　　　　　　final

　　　　　　　The name of the attribute.

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required 　　Tag only 　　　boolean 　　　　　　　　　　　 false 　　　　　final

　　　　　　　True if this is a required attribute.

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setter　　Tag only script 　　　　　　　　　　　　　　　　　　　　　final　　　

　　　　　　　Code that is executed when setAttribute is used to set the value of this attribute. This code is executed within a context in which the variable with this attribute's name is bound to the value passed to setAttribute.

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type　　　　Tag only boolean | color | expression | number | size | string | text | html expression final

　　　　　　The type of the attribute. This determines how the value is parsed. Attributes of type string are automatically quoted if when="immediate", for any other value of when, a literal string would have to be quoted to be used as a value.

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value 　　　　Tag only string 　　　　　　　　　　　　　　　　　　　　　　　　　　 final

　　　　　　The initial value of the attribute. The type of this value is specified by the value of the type attribute; if that attribute is not present, it's the type of this attribute in this element's tag. The attribute is given this value when the element is created.

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when　　　　　Tag only immediately | once | always 　　　　　　immediately　　　　final

　　　　　　When the initial value expression is to be evaluated. One of:

immediately evaluate when the enclosing element is defined (must be a constant) once evaluate when the enclosing element is initialized always update whenever the value of the expression changes The default is when="immediately".

The setting for when can be overridden when assigning a value to an attribute by using the syntax attribute name=$when value{expression}. The default for when value is always, for example: <view title="$once{computeTitle()}" /> sets the title of the view to a computed value and <view title="${parent.subtitle}" \> will cause the title of the view to track parent.subtitle.

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