iOS-图片拉伸技巧

iOS开发中我们会遇到渐变的背景，内容可变的流式标签，聊天气泡(QQ聊天气泡)，由于内容是可变的，宽度和高度同样可变，这样就是导致每次出现的尺寸与之前不一样。如果是需要设置的比较的多，估计美工会烦死，同样也会额外增加的内存开销，所以这个知道一点图片拉伸的技巧会师我们的能使我们APP更加高效，代码更加简洁，事半功倍~从设置的角度来有四种方法可以实现~

Assets设置

首先我们有一个不规则的气泡按钮，大小是35*30，Slices选中水平和垂直方向的距离，宽高设置为1

  

设置完成之，我们设置Button的背景图片看下加载效果:

    UIButton *button = [[UIButton alloc] initWithFrame:CGRectMake(80, 100, 100, 40)];
    UIImage *buttonImage = [UIImage imageNamed:@"Question"];
    [button setTitle:@"默认" forState:UIControlStateNormal];
    [button addTarget:self action:@selector(buttonPressed:) forControlEvents: UIControlEventTouchUpInside];
    [button setBackgroundImage:buttonImage forState:UIControlStateNormal];
    [self.view addSubview:button];

模拟器加载效果:

第一个图片是我们需要加载效果，如果我们将Slices设置为None,我们看到的效果是这样的:

看到这里是不是感觉有点兴趣了，为什么设置了上面的选项就可以出现平铺的效果，稍微思考一下，我们在下面的一种方式中将找到答案~

iOS5之前的设置

上图的第二个按钮是我们通过代码设置，不是在Assets中设置，我们先来看一下实现代码:

    //35*30
    UIButton *nextButton = [[UIButton alloc] initWithFrame:CGRectMake(80, 180, 100, 40)];
    [nextButton setTitle:@"iOS5之前" forState:UIControlStateNormal];
    nextButton.layer.borderColor=[[UIColor redColor] CGColor];
    nextButton.layer.borderWidth=1.0f;
    UIImage *image = [UIImage imageNamed:@"Question"];
    // 设置左边端盖宽度  rightCap=width - leftCapWidth - 1
    NSInteger leftCapWidth = image.size.width * 0.5;
    // 设置上边端盖高度  bottom=height - topCapWidth - 1
    NSInteger topCapHeight = image.size.height * 0.5;
    UIImage *newImage = [image stretchableImageWithLeftCapWidth:leftCapWidth topCapHeight:topCapHeight];
    [nextButton setBackgroundImage:newImage forState:UIControlStateNormal];
    [self.view addSubview:nextButton];

新建图片，设置按钮的背景图片，与一般设置没有什么区别，不过多了stretchableImageWithLeftCapWidth:方法，我们看一下API说明:

@interface UIImage(UIImageDeprecated)

// use resizableImageWithCapInsets: and capInsets.

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

@end

我们需要设置拉伸区域具体图片的上方和左边的距离:

strechWidth=width-leftCapWidth-(width-leftCapWidth-1)=1

strechHeight=height-rightCaopWidth-(height - topCapWidth - 1)=1

所以我们拉伸的区域是1*1，关于上面的leftCapWidth有人可能心里有疑问，为什么leftCapWidth = image.size.width * 0.5，为什么是0.5？自己最开始随便设置一个距离结果图片丑的要死，比如说我们左边设置0.2，上边设置为0.8，我们看到的效果是这样的:

这是极端情况，默认的情况下不管图片是如何的规则，中间的1*1区域是正方形，如果按照上面设置，我们会发现，上下左右四个点组成的图片是极其不规则，因此建议设置在中间，不过有的是有偏离一些也没有太多问题，比如说0.4，0.6对于比例设置大家如果有兴趣的可以之后下载代码，自行研究~

iOS5设置

stretchableImageWithLeftCapWidth在iOS5之后已经废弃，我们可以通过resizableImageWithCapInsets来设置上下左右边距~

resizableImageWithCapInsets与之前的方法一样，同样是通过重置产生新的图片:

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

UIEdgeInsets基本上UI中比较常见:

typedef struct UIEdgeInsets {
    CGFloat top, left, bottom, right;  // specify amount to inset (positive) for each of the edges. values can be negative to 'outset'
} UIEdgeInsets;

图片效果参考模拟器的第三个按钮，设置代码如下:

     UIImage *image = [UIImage imageNamed:@"Question"];
    UIButton  *resizableButton=[[UIButton alloc]initWithFrame:CGRectMake(80, 250, 100, 40)];
    [resizableButton setTitle:@"iOS5" forState:UIControlStateNormal];
    // 设置端盖的值
    CGFloat top = image.size.height * 0.5;
    CGFloat left = image.size.width * 0.5;
    CGFloat bottom = image.size.height * 0.5;
    CGFloat right = image.size.width * 0.5;
    
    UIEdgeInsets edgeInsets = UIEdgeInsetsMake(top, left, bottom, right);
    //拉伸图片
    UIImage *edgeImage = [image resizableImageWithCapInsets:edgeInsets];
    //背景图片
    [resizableButton setBackgroundImage:edgeImage forState:UIControlStateNormal];
    [self.view addSubview:resizableButton];

iOS6设置

iOS6的设置方法和iOS5差不多，多了一个参数UIImageResizingMode:

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

UIImageResizingMode说明:

typedef NS_ENUM(NSInteger, UIImageResizingMode) {
    UIImageResizingModeTile,平铺模式，通过重复显示UIEdgeInsets指定的矩形区域来填充图片

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

实际效果参考上图中的最后一个按钮:

    UIImage *image = [UIImage imageNamed:@"Question"];
    UIButton  *resizableButtonMode=[[UIButton alloc]initWithFrame:CGRectMake(80, 320, 180, 40)];
    [resizableButtonMode setTitle:@"iOS6" forState:UIControlStateNormal];
    [resizableButtonMode addTarget:self action:@selector(buttonPressed:) forControlEvents:UIControlEventTouchUpInside];
    // 设置上左下右边距
    CGFloat topMode= image.size.height * 0.5;
    CGFloat leftMode= image.size.width * 0.5;
    CGFloat bottomMode= image.size.height * 0.5;
    CGFloat rightMode= image.size.width * 0.5;
    
    UIEdgeInsets edgeInsetsMode= UIEdgeInsetsMake(topMode, leftMode, bottomMode, rightMode);
    
    // 拉伸图片
    UIImage *edgeModeImage = [image resizableImageWithCapInsets:edgeInsetsMode resizingMode:UIImageResizingModeStretch];
//    UIImage *edgeModeImage = [image resizableImageWithCapInsets:edgeInsetsMode resizingMode:UIImageResizingModeTile];
    
    //设置图片
    [resizableButtonMode setBackgroundImage:edgeModeImage forState:UIControlStateNormal];
    [self.view addSubview:resizableButtonMode];

　项目GitHub地址:https://github.com/SmallElephant/iOS-FEImageStrech