iOS开发image背景图片拉伸问题解决分析

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

   UIImage *image = [UIImage imageNamed:@"圆角矩形-7-拷贝"];
    //原始图片样式添加
    self.originalImageView.image = image;
    //没处理好的图片
    self.badImageView.image = image;
//图片处理后的 将被弃用 方法一：
//这个函数是UIImage的一个实例函数，它的功能是创建一个内容可拉伸，而边角不拉伸的图片，需要两个参数，第一个是左边不拉伸区域的宽度，第二个参数是上面不拉伸的高度。
//根据设置的宽度和高度，将接下来的一个像素进行左右扩展和上下拉伸。
    [self.textImageView setImage:[image stretchableImageWithLeftCapWidth:image.size.width*0.5 topCapHeight:image.size.height*0.5]];
//注意：可拉伸的范围都是距离leftCapWidth后的1竖排像素，和距离topCapHeight后的1横排像素。

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

   UIImage *image = [UIImage imageNamed:@"圆角矩形-7-拷贝"];
    //原始图片样式添加
    self.originalImageView.image = image;
    //没处理好的图片
    self.badImageView.image = image;
//处理图片 iOS 5 方法三：
            CGFloat width = image.size.width;
            CGFloat height = image.size.height;
            CGFloat top = height/2.0f - 0.5f; // 顶端盖高度
            CGFloat bottom = height/2.0f - 0.5f ; // 底端盖高度
            CGFloat left = width/2.0f - 0.5f; // 左端盖宽度
            CGFloat right = width/2.0f - 0.5f; // 右端盖宽度
            UIEdgeInsets insets = UIEdgeInsetsMake(top, left, bottom, right);
            //创建 一个可变的image版本，内部平铺，类：UIImageResizingModeTile模式；
            self.textImageView.image = [image resizableImageWithCapInsets:insets];

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

   UIImage *image = [UIImage imageNamed:@"圆角矩形-7-拷贝"];
    //原始图片样式添加
    self.originalImageView.image = image;
    //没处理好的图片
    self.badImageView.image = image;
            //处理图片 iOS 6 方法二：
            CGFloat width = image.size.width;
            CGFloat height = image.size.height;
            CGFloat top = height/2.0f - 0.5f; // 顶端盖高度
            CGFloat bottom = height/2.0f - 0.5f ; // 底端盖高度
            CGFloat left = width/2.0f - 0.5f; // 左端盖宽度
            CGFloat right = width/2.0f - 0.5f; // 右端盖宽度
            UIEdgeInsets insets = UIEdgeInsetsMake(top, left, bottom, right);
            // 指定为拉伸模式，伸缩后重新赋值
            //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
            _textImageView.image = [image resizableImageWithCapInsets:insets resizingMode:UIImageResizingModeTile];
// Swift
let image = UIImage(named: "rounded_rectangle_7_copy")
if image != nil {  
    self.originalImageView.image = image  
    self.badImageView.image = image  
} else {  
    self.originalImageView.image = image  
    self.badImageView.image = image  
}
let width = image?.size.width ?? 0  
let height = image?.size.height ?? 0
let top = height / 2 - 0.5  
let bottom = height / 2 - 0.5  
let left = width / 2 - 0.5  
let right = width / 2 - 0.5
let insets = UIEdgeInsets(top: top, left: left, bottom: bottom, right: right)
if image != nil {  
    let resizingMode = UIImage.resizableImageResizingMode.tile  
    self.textImageView.image = UIImage(resizableImageWithCapInsets: insets, resizingMode: resizingMode)  
} else {  
    self.textImageView.image = UIImage(resizableImageWithCapInsets: insets, resizingMode: resizingMode)  
}

typedef NS_ENUM(NSInteger, UIViewContentMode) {
    UIViewContentModeScaleToFill,
    UIViewContentModeScaleAspectFit,      
// contents scaled to fit with fixed aspect. remainder is transparent
    UIViewContentModeScaleAspectFill,    
 // contents scaled to fill with fixed aspect. some portion of content may be clipped.
    UIViewContentModeRedraw,             
 // redraw on bounds change (calls -setNeedsDisplay)
    UIViewContentModeCenter,             
 // contents remain same size. positioned adjusted.
    UIViewContentModeTop,
    UIViewContentModeBottom,
    UIViewContentModeLeft,
    UIViewContentModeRight,
    UIViewContentModeTopLeft,
    UIViewContentModeTopRight,
    UIViewContentModeBottomLeft,
    UIViewContentModeBottomRight,
};

//使用方法
[ImageView setContentMode:UIViewContentModeScaleAspectFit];
//OR
ImageView.contentMode = UIViewContentModeScaleAspectFit;
//以下方法，图片保持原有大小比例的情况下，展示在ImageView的上下左右等位置；如果视图大小小于图片的尺寸，则图片会超出视图边界；
    UIViewContentModeTop,
    UIViewContentModeBottom,
    UIViewContentModeLeft,
    UIViewContentModeRight,
    UIViewContentModeTopLeft,
    UIViewContentModeTopRight,
    UIViewContentModeBottomLeft,
    UIViewContentModeBottomRight,
    UIViewContentModeCenter,  
    UIViewContentModeScaleToFill,  //根据视图的比例去拉伸图片内容。图片可能变形；
    UIViewContentModeScaleAspectFit,  //保持图片内容的纵横比例，来适应视图的大小。
    UIViewContentModeScaleAspectFill,   //用图片内容来填充视图的大小，多余得部分可以被修剪掉来填充整个视图边界。 
    UIViewContentModeRedraw,     //这个选项是单视图的尺寸位置发生变化的时候通过调用setNeedsDisplay方法来重新显示。