how to set UIView background programmatically
<p>in the interface builder,i can find the background tag,and select the color and the opacity.</p>

<p>if I create the UIView programmatically,if I want to change color,I can set the backgroundColor property</p>

<p>the question is if I want to change the opactiy,What is the property should I change?</p>

<p>Thanks a lot.</p>
