IOS拉伸圆角图片

 UIImage *buttonImageNormal = [UIImage imageNamed:@"whiteButton.png"];
 UIImage *stretchableButtonImageNormal = [buttonImageNormal
 stretchableImageWithLeftCapWidth:12 topCapHeight:0];\\设置帽端为12px,也是就左边的12个像素不参与拉伸,有助于圆角图片美观
 [doSomethingButton setBackgroundImage:stretchableButtonImageNormal
 forState:UIControlStateNormal];

 UIImage *buttonImagePressed = [UIImage imageNamed:@"blueButton.png"];
 UIImage *stretchableButtonImagePressed = [buttonImagePressed
 stretchableImageWithLeftCapWidth:12 topCapHeight:0];
 [doSomethingButton setBackgroundImage:stretchableButtonImagePressed
 forState:UIControlStateHighlighted];