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
</div>