ios中图片拉伸的几种方式

1. UIImageView整体拉伸

UIImageView-contentMode

typedef NS_ENUM(NSInteger, UIViewContentMode) {
UIViewContentModeScaleToFill, // 默认 拉伸（会变形）
UIViewContentModeScaleAspectFit, // 等比例拉伸
UIViewContentModeScaleAspectFill, // 等比例填充
UIViewContentModeRedraw, // redraw on bounds change (这个不清楚)
UIViewContentModeCenter, // 下面的就是不拉伸按位置显示了
UIViewContentModeTop,
UIViewContentModeBottom,
UIViewContentModeLeft,
UIViewContentModeRight,
UIViewContentModeTopLeft,
UIViewContentModeTopRight,
UIViewContentModeBottomLeft,
UIViewContentModeBottomRight,
};

2. UIImage局部拉伸

// 按4边间距显示不拉伸的区域

• (UIImage *)resizableImageWithCapInsets:(UIEdgeInsets)capInsets NS_AVAILABLE_IOS(5_0);
  // 按2点拉伸
• (UIImage *)stretchableImageWithLeftCapWidth:(NSInteger)leftCapWidth topCapHeight:(NSInteger)topCapHeight;
• (UIImage *)resizableImageWithCapInsets:(UIEdgeInsets)capInsets resizingMode:(UIImageResizingMode)resizingMode;
  // 拉伸模式
  typedef NS_ENUM(NSInteger, UIImageResizingMode) {
  UIImageResizingModeTile,//进行区域复制模式拉伸
  UIImageResizingModeStretch,//进行渐变复制模式拉伸
  };

3.UIImage修改大小

//内缩放，一条变等于最长边，另外一条小于等于最长边

• (UIImage *)scaleToSize:(CGSize)newSize {
  CGFloat width = self.size.width;
  CGFloat height= self.size.height;
  CGFloat newSizeWidth = newSize.width;
  CGFloat newSizeHeight= newSize.height;
  if (width <= newSizeWidth &&
  height <= newSizeHeight) {
  return self;
  }

  if (width == 0 || height == 0 || newSizeHeight == 0 || newSizeWidth == 0) {
  return nil;
  }
  CGSize size;
  if (width / height > newSizeWidth / newSizeHeight) {
  size = CGSizeMake(newSizeWidth, newSizeWidth * height / width);
  } else {
  size = CGSizeMake(newSizeHeight * width / height, newSizeHeight);
  }
  return [self drawImageWithSize:size];
  }

• (UIImage *)drawImageWithSize: (CGSize)size {
  CGSize drawSize = CGSizeMake(floor(size.width), floor(size.height));
  UIGraphicsBeginImageContext(drawSize);

  [self drawInRect:CGRectMake(0, 0, drawSize.width, drawSize.height)];
  UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
  UIGraphicsEndImageContext();
  return newImage;
  }