事先准备一张图片：
UIImage *image = [UIImage imageNamed:@"red.png"];
在iOS 5.0之前能够这么用:
NSInteger leftCapWidth = image.size.width * 0.5f;
NSInteger topCapHeight = image.size.height * 0.5f;
image = [image stretchableImageWithLeftCapWidth:leftCapWidth topCapHeight:topCapHeight];
在iOS 5.0中能够这么用：
CGFloat top = 8;// 顶端盖高度
CGFloat bottom = 8; // 底端盖高度
CGFloat left = 8; // 左端盖宽度
CGFloat right = 8;// 右端盖宽度
UIEdgeInsets insets = UIEdgeInsetsMake(top, left, bottom, right);
// 伸缩后又一次赋值
image = [image resizableImageWithCapInsets:insets];
在iOS6.0中能够这么用：
CGFloat top = 12; // 顶端盖高度
CGFloat bottom = 12 ; // 底端盖高度
CGFloat left = 10; // 左端盖宽度
CGFloat right = 10; // 右端盖宽度
UIEdgeInsets insets = UIEdgeInsetsMake(top, left, bottom, right);
// 指定为拉伸模式，伸缩后又一次赋值
image = [image resizableImageWithCapInsets:insets resizingMode:UIImageResizingModeStretch];