UIImage *image2 = [UIImage imageNamed:imgName];

                    CGFloat top = ; // 顶端盖高度

                    CGFloat bottom =  ; // 底端盖高度

                    CGFloat left = ; // 左端盖宽度

                    CGFloat right = ; // 右端盖宽度

                    UIEdgeInsets insets = UIEdgeInsetsMake(top, left, bottom, right);

                    image2 = [image2 resizableImageWithCapInsets:insets resizingMode:UIImageResizingModeStretch];

                    //    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

//                    [btn setImage:image2 forState:UIControlStateNormal];//[UIImage imageNamed:imgName]

                    [btn setBackgroundImage:image2 forState:UIControlStateNormal];