UIButton实现背景拉伸，即图片两端不拉伸中间拉伸的办法有如下两种：

第一种方法很简单而且使用性更广。做法就是直接拉伸想要setBackgroundImage的image，代码如下： 

UIImage *image = [UIImage imageNamed:@"image.png"];
image = [image stretchableImageWithLeftCapWidth:floorf(image.size.width/2) topCapHeight:floorf(image.size.height/2)];

设置了左端帽之后，rightCapWidth = image.size.width - (image.leftCapWidth + 1); 也就是说图片中间的一像素用来拉伸。垂直方向同上。设置之后无论把image放到什么控件中都可以自动拉伸了。

  

UIImage *buttonImage = [UIImage imageNamed:@"contact.png"];
buttonImage = [buttonImage stretchableImageWithLeftCapWidth:floorf(buttonImage.size.width/2) topCapHeight:floorf(buttonImage.size.height/2)];

UIImage *buttonImageselected = [UIImage imageNamed:@"contactselected.png"];
buttonImage = [buttonImage stretchableImageWithLeftCapWidth:floorf(buttonImage.size.width/2) topCapHeight:floorf(buttonImage.size.height/2)];

UIButton *button = [UIButton buttonWithType:UIButtonTypeCustom];
button.frame = CGRectMake(0, 0, 240, 44);
[button setBackgroundImage:buttonImage forState:UIControlStateNormal];
[button setBackgroundImage:buttonImageselected forState:UIControlStateHighlighted];
button.center = CGPointMake(160, 240);
[button setTitle:@"button" forState:UIControlStateNormal];
[button setTitle:@"buttonClick" forState:UIControlStateHighlighted];
[self.view addSubview:button];

第二种方法是在UIButton中加入一个UIImageView，拉伸imageView，然后将button的背景设为clearColor等等。把imageView放入button中，并且sendToBack，得到效果。代码如下：

 //刚才imageView拉伸的代码  

UIImageView *strechTest = [[UIImageyiView alloc] initWithImage:[UIImage imageNamed:@"contact.png"]];
[strechTest setContentStretch:CGRectMake(0.5f, 0.5f, 0.f, 0.f)];
CGRect frame = strechTest.frame;
frame.size.width += 100;
strechTest.frame = frame;

 

//把imageView放入button中，并设置为back
 UIButton *button = [UIButton buttonWithType:UIButtonTypeCustom];
 button1.frame = frame;
 button1.center = CGPointMake(160, 140);
 [button1 addSubview:strechTest];
 [button1 sendSubviewToBack:strechTest];
 [button1 setBackgroundColor:[UIColor clearColor]];
 [button1 setTitle:@"button" forState:UIControlStateNormal];
 [button1 setTitle:@"buttonClick" forState:UIControlStateHighlighted];
 [self.view addSubview:button];

效果：