Flex TextInput tooltip 当超过组件长度时显示

如标题所说，直接上代码

protected function changeHandler(event:TextOperationEvent){
//通过UIComponent的measureText方法得到TextLineMetrics，它的width就能得到输入框字符所占的真实width
var charsWidth:int = txtInput.measureText(txtInput.text).width;
if (charsWidth > txtInput.width) //与textinput的width进行比较
{
	txtInput.toolTip = txtInput.text;
}
else
{
	txtInput.toolTip = "";
}
}

<s:TextInput id="txtInput" change="changeHandler(event)"/>