在指定文本之前,如何设置动态UITextField的正确宽度?

在Flex3.2中,我创建了一个UITextField,然后测量将要分配给该字段的text属性的文本。然后,我使用这些度量设置字段的大小。但是,计算的宽度不够宽,无法容纳文本。实现正确测量的顺序是否不同,或者我是否发现measureText()函数有问题?我怎样才能得到准确的结果?

// UITextField's default size appears to be 100x100
// Measure the text then set width and height
var tf:UITextFormat = uiTextField.getUITextFormat();
var tlm:TextLineMetrics = tf.measureText(this.labelText);

// Text within the field is clipped unless 'padding' is added to the size
// Flex Documentation specifies there is a 2 px gutter on each side, so
// the expected padding would be 4 px.  However, clipping occurs, for 
// "Hello, World" up to 9 px.
uiTextField.width = tlm.width + 9; 
uiTextField.height = tlm.height + 4;
uiTextField.border = true;
uiTextField.name = "uiTextField";               
uiTextField.text = this.labelText;