根据字体和文字来计算 UILable 的长度和大小

根据要显示的文字以及UILable本身的字体，来计算能够完全显示所有文字的label所需要的大小，从而进行调整。

//Calculate the size necessary for the UILable
NSString *theText = @"Texting";
CGSize theStringSize = [theText sizeWithFont:font 
    constrainedToSize:theLabel.frame.size
    lineBreakMode:theLabel.lineBreakMode];

//Adjust the size of the UILable
theLable.frame = CGRectMake(theLable.frame.origin.x, 
    theLable.frame.origin.y, 
    theStringSize.width, theStringSize.height);
theLable.text = theText;