iOS图片预览、放大缩小

思路

图片预览，优先考虑基础控件UIImageView、UIButton

图片预览中可能需设置不同的mode，优先考虑UIImageView

typedef NS_ENUM(NSInteger, UIViewContentMode) {    UIViewContentModeScaleToFill,    UIViewContentModeScaleAspectFit,          UIViewContentModeScaleAspectFill,         UIViewContentModeRedraw,                 UIViewContentModeCenter,                  UIViewContentModeTop,    UIViewContentModeBottom,    UIViewContentModeLeft,    UIViewContentModeRight,    UIViewContentModeTopLeft,    UIViewContentModeTopRight,    UIViewContentModeBottomLeft,    UIViewContentModeBottomRight,}

图片放大、缩小的思路：1. 手势+frame 2.scrollview的zoomScale

很愉快的决定选择2，不要问为什么，因为我懒，能用系统提供的，坚决不折腾

上菜
- 设置页面属性
```
@property (nonatomic, strong) UIScrollView *mScroll;@property (nonatomic, strong) UIImageView *imgInfo;
```
- 界面初始化
```
self.mScroll = [[UIScrollView alloc] initWithFrame:CGRectZero];self.mScroll.backgroundColor = [UIColor colorWithHexs:0x3f3f3f];self.mScroll.maximumZoomScale = 3.0;self.mScroll.minimumZoomScale = 1;self.mScroll.delegate = self;self.mScroll.showsVerticalScrollIndicator = NO;self.mScroll.showsHorizontalScrollIndicator = NO;[self.view addSubview:self.mScroll];[self.mScroll mas_makeConstraints:^(MASConstraintMaker *make) {make.edges.equalTo(self.preView);}];
```
self.imgInfo = [[UIImageView alloc] initWithFrame:CGRectZero];
self.imgInfo.clipsToBounds = YES;
[self.imgInfo setUserInteractionEnabled:YES];
self.imgInfo.backgroundColor = [UIColor colorWithHexs:0x3f3f3f];
[self.mScroll addSubview:self.imgInfo];
[self.imgInfo mas_makeConstraints:^(MASConstraintMaker *make) {
make.edges.equalTo(self.mScroll);
make.width.equalTo(self.mScroll);
}];
```
其中maximumZoomScale与minimumZoomScale表示可缩放程度- 顺带加个双击手势，比如双击可放大，再放大，再缩小
```
UITapGestureRecognizer *tap = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(tapHandlerTwice)];
tap.numberOfTapsRequired = 2;
[self.imgInfo addGestureRecognizer:tap];
```
- double click直接控制缩放
```
- (void)tapHandlerTwice {
  if (self.mScroll.zoomScale < 2) {
  [self.mScroll setZoomScale:2];
  } else if (self.mScroll.zoomScale < 3) {
  [self.mScroll setZoomScale:3];
  } else {
  [self.mScroll setZoomScale:1];
  }
  }
- UIScrollViewDelegate设置scrollview的Zooming View
```
#pragma mark - UIScrollViewDelegate
```
- (UIView )viewForZoomingInScrollView:(UIScrollView )scrollView {
  return self.imgInfo;
  }
Game Over

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