iOS开发中图片拉伸的三个方法介绍

第一个方法:

- (UIImage *)resizableImageWithCapInsets:(UIEdgeInsets)capInsets NS_AVAILABLE_IOS(5_0); // create a resizable version of this image. the interior is tiled when drawn.

这个方法是从iOS5开始的, 参数UIEdgeInset是指定拉伸区域用的,  也就是说被拉伸区域距离上下左右的间距,  方法的返回值是被拉伸后的图片,下面为应用示例

- (void)test {
    UIImage *iconView = [[UIImage alloc] init];
    CGFloat top = iconView.size.width * 0.5;
    CGFloat left = iconView.size.height * 0.5;
    CGFloat bottom = iconView.size.width * 0.5;
    CGFloat right = iconView.size.height * 0.5;
    UIImage *newIconView = [iconView resizableImageWithCapInsets:UIEdgeInsetsMake(top, left, bottom, right)];
}

第二个方法:

- (UIImage *)resizableImageWithCapInsets:(UIEdgeInsets)capInsets resizingMode:(UIImageResizingMode)resizingMode NS_AVAILABLE_IOS(6_0); // the interior is resized according to the resizingMode

此方法和第一个基本上一样,  多出一个参数拉伸模式的参数,  系统设定两种拉伸模式:第一种 UIImageResizingModeTile,瓦片拉伸, 也就是说用指定区域去平铺拉伸的空隙,  第二种  UIImageResizingModeStretch直接拉伸指定的区域,  应用示例如下:

- (void)test1 {
    UIImage *iconView = [[UIImage alloc] init];
    CGFloat top = iconView.size.width * 0.5;
    CGFloat left = iconView.size.height * 0.5;
    CGFloat bottom = iconView.size.width * 0.5;
    CGFloat right = iconView.size.height * 0.5;
    UIImage *newIconView = [iconView resizableImageWithCapInsets:UIEdgeInsetsMake(top, left, bottom, right)resizingMode:UIImageResizingModeTile];
}

第三个方法:

- (UIImage *)stretchableImageWithLeftCapWidth:(NSInteger)leftCapWidth topCapHeight:(NSInteger)topCapHeight __TVOS_PROHIBITED;

这个方法和上面两个不太一样,  需要指定两个参数, topCapHeight和leftCapWidth; 实际上也是四个参数, 只不过下面的和右面的两个间距系统自动计算了.  两个参数的含义如下:

@property(nonatomic,readonly) NSInteger leftCapWidth __TVOS_PROHIBITED;   // default is 0. if non-zero, horiz. stretchable. right cap is calculated as width - leftCapWidth - 1
@property(nonatomic,readonly) NSInteger topCapHeight __TVOS_PROHIBITED;   // default is 0. if non-zero, vert. stretchable. bottom cap is calculated as height - topCapWidth - 1

该方法的示例代码如下:

- (void)test2 {
    UIImage *iconView = [[UIImage alloc] init];
    NSInteger leftCapWidth = iconView.size.width * 0.5;
    NSInteger topCapHeight  = iconView.size.height * 0.5;
    
    UIImage *newIconView = [iconView stretchableImageWithLeftCapWidth:leftCapWidth topCapHeight:topCapHeight];
}

以上三种方法都可以实现对一个小图片的拉伸, 自己根据书写习惯进行选择,  如果是TV系统的话貌似不能用第三种,  这个我也不太确定, 因为没有开发过TV上的应用!