选取截图

效果如下

图片截屏实现思路.

• 1、手指在屏幕上移动的时，添加一个半透明的UIView（作为遮盖）
• 2、然后开启一个上下文把UIView的frame设置成裁剪区域.把图片显示的图片绘制到上下文当中,生成一张新的图片
• 3、再把生成的图片再赋值给原来的UImageView.

代码实现如下：

#import "ViewController.h"

@interface ViewController ()
@property (weak, nonatomic) IBOutlet UIImageView *imageView;
/** 开始点*/
@property (assign, nonatomic) CGPoint startP;
/** 当前点*/
@property (assign, nonatomic) CGPoint currP;
/** 遮盖view*/
@property (weak, nonatomic) UIView *coverView;
@end

@implementation ViewController

- (UIView *)coverView {
    if (_coverView == nil) {
        UIView *cV = [[UIView alloc] init];
        _coverView = cV;
        _coverView.backgroundColor = [UIColor grayColor];
        _coverView.alpha = 0.7;
        [self.view addSubview:_coverView];
    }
    return _coverView;
}

- (void)viewDidLoad {
    [super viewDidLoad];
    self.imageView.userInteractionEnabled = YES;
    // 给imageview添加手势
    UIPanGestureRecognizer *panGest = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(panHandle:)];
    [self.imageView addGestureRecognizer:panGest];
}

- (void)panHandle:(UIPanGestureRecognizer *)panGest {
//    NSLog(@"%s", __func__);
    CGFloat coverX = 0;
    CGFloat coverY = 0;
    CGFloat coverW = 0;
    CGFloat coverH = 0;
    if (panGest.state == UIGestureRecognizerStateBegan) {
        // 获取起点
        self.startP = [panGest locationInView:self.view];
        
    } else if(panGest.state == UIGestureRecognizerStateChanged) {
        // 获取当前点
        self.currP = [panGest locationInView:self.view];
        coverX = self.startP.x;
        coverY = self.startP.y;
        coverW = self.currP.x - coverX;
        coverH = self.currP.y - coverY;
        // 显示遮盖层
        self.coverView.frame = CGRectMake(coverX, coverY, coverW, coverH);
        NSLog(@"%@", NSStringFromCGRect(CGRectMake(coverX, coverY, coverW, coverH)));
        
    } else if(panGest.state == UIGestureRecognizerStateEnded) {
        // 开起一个位图上下文
        UIGraphicsBeginImageContextWithOptions(self.imageView.bounds.size,NO,0.0);
        CGContextRef ctx = UIGraphicsGetCurrentContext();
        // 设置一个截取path
        UIBezierPath *path = [UIBezierPath bezierPathWithRect:self.coverView.frame];
        [path addClip];
        // 把imageview的内容渲染到当前上下文
        [self.imageView.layer renderInContext:ctx];
        // 生成新图片
        UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
        UIGraphicsEndPDFContext();
        self.imageView.image = newImage;
        
        [self.coverView removeFromSuperview];
        
    }
}

@end