初始图片尺寸大小为 25 * 28 pixels

现在我们在根试图上创建两个button

    UIButton *button = [UIButton buttonWithType:UIButtonTypeCustom];

    button.frame = CGRectMake(50, 100, 25, 28);

    [button setBackgroundImage:[UIImage imageNamed:@"btn.png"] forState:UIControlStateNormal];

    [self.view addSubview:button];

    UIButton *button1 = [UIButton buttonWithType:UIButtonTypeCustom];

    button1.frame = CGRectMake(50, 200, 200, 28);

  UIImage *image = [UIImage imageNamed:@"btn.png"];

   [button1 setBackgroundImage:image forState:UIControlStateNormal];

    [self.view addSubview:button1];

 没做拉伸处理前图片效果

在iOS 5.0中，UIImage有一个新方法可以处理图片的拉伸问题 

- (UIImage *)resizableImageWithCapInsets:(UIEdgeInsets)capInsets 

CGFloat left = 12; // 左端宽度  

CGFloat right = 12; // 右端宽度  

UIEdgeInsets insets = UIEdgeInsetsMake(0, left, 0, right);

// 伸缩后重新赋值  

 UIImage *new = [image resizableImageWithCapInsets:insets];

 [button1 setBackgroundImage:new forState:UIControlStateNormal];

 [self.view addSubview:button1];

 在iOS6.0中，UIImage又提供了一个方法处理图片拉伸

- (UIImage *)resizableImageWithCapInsets:(UIEdgeInsets)capInsets resizingMode:(UIImageResizingMode)resizingMode  

对比iOS5.0中的方法，只多了一个UIImageResizingMode参数，用来指定拉伸的模式：

UIImageResizingModeStretch：拉伸模式，通过拉伸UIEdgeInsets指定的矩形区域来填充图片

UIImageResizingModeTile：平铺模式，通过重复显示UIEdgeInsets指定的矩形区域来填充图片

CGFloat left = 12; // 左端宽度  

CGFloat right = 12; // 右端宽度  

UIEdgeInsets insets = UIEdgeInsetsMake(0, left, 0, right); 

// 伸缩后重新赋值  

 UIImage *new = [image resizableImageWithCapInsets:insets resizingMode:UIImageResizingModeStretch];

 [button1 setBackgroundImage:new forState:UIControlStateNormal];

  [self.view addSubview:button1];

下面是拉伸过的图片