http://www.jb51.net/article/74846.htm

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//
// ViewController.m
// XWZoomImageView
//
// Created by xiao on 15/11/13.
// Copyright © 2015年 xiao. All rights reserved.
//

import "ViewController.h"

@interface ViewController ()<UIScrollViewDelegate>
@property (weak, nonatomic) IBOutlet UIImageView *picView;
@property (weak, nonatomic) UIScrollView *scrollView;
@property (weak, nonatomic) UIImageView *lastImageView;
@property (nonatomic, assign)CGRect originalFrame;
@property (nonatomic, assign)BOOL isDoubleTap;
@end

@implementation ViewController

• (void)viewDidLoad {
  [super viewDidLoad];

self.picView.userInteractionEnabled = YES;
//添加单击手势
UITapGestureRecognizer *tap = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(showZoomImageView:)];

[self.picView addGestureRecognizer:tap];

}

-(void)showZoomImageView:(UITapGestureRecognizer *)tap
{
if (![(UIImageView *)tap.view image]) {
return;
}
//scrollView作为背景
UIScrollView *bgView = [[UIScrollView alloc] init];
bgView.frame = [UIScreen mainScreen].bounds;
bgView.backgroundColor = [UIColor blackColor];
UITapGestureRecognizer *tapBg = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(tapBgView:)];
[bgView addGestureRecognizer:tapBg];

UIImageView *picView = (UIImageView *)tap.view;

UIImageView *imageView = [[UIImageView alloc] init];
imageView.image = picView.image;
imageView.frame = [bgView convertRect:picView.frame fromView:self.view];
[bgView addSubview:imageView];

[[[UIApplication sharedApplication] keyWindow] addSubview:bgView];

self.lastImageView = imageView;
self.originalFrame = imageView.frame;
self.scrollView = bgView;
//最大放大比例
self.scrollView.maximumZoomScale = 1.5;
self.scrollView.delegate = self;

[UIView animateWithDuration:0.5 animations:^{
CGRect frame = imageView.frame;
frame.size.width = bgView.frame.size.width;
frame.size.height = frame.size.width * (imageView.image.size.height / imageView.image.size.width);
frame.origin.x = 0;
frame.origin.y = (bgView.frame.size.height - frame.size.height) * 0.5;
imageView.frame = frame;
}];
}

-(void)tapBgView:(UITapGestureRecognizer *)tapBgRecognizer
{
self.scrollView.contentOffset = CGPointZero;
[UIView animateWithDuration:0.5 animations:^{
self.lastImageView.frame = self.originalFrame;
tapBgRecognizer.view.backgroundColor = [UIColor clearColor];
} completion:^(BOOL finished) {
[tapBgRecognizer.view removeFromSuperview];
self.scrollView = nil;
self.lastImageView = nil;
}];
}

//返回可缩放的视图
-(UIView *)viewForZoomingInScrollView:(UIScrollView *)scrollView
{
return self.lastImageView;
}

.h文件-----------------------------------------------------------------

import

@interface ZoomImage : NSObject
/**
*@brief点击图片放大,再次点击缩小

*@param oldImageView 头像所在的imageView
/
+(void)showImage:(UIImageView)avatarImageView;
@end
.m文件-----------------------------------------------------------------

import "ZoomImage.h"

static CGRect oldframe;
@implementation ZoomImage
+(void)showImage:(UIImageView*)avatarImageView
{
UIImage *image =avatarImageView.image;
// 获得根窗口
UIWindow *window =[UIApplication sharedApplication].keyWindow;
UIView *backgroundView =[[UIView alloc]initWithFrame:CGRectMake(0, 0, WIDTH, HEIGHT)];
oldframe =[avatarImageView convertRect:avatarImageView.bounds toView:window];
backgroundView.backgroundColor =[UIColor blackColor];
backgroundView.alpha =0.5;
UIImageView imageView =[[UIImageView alloc]initWithFrame:oldframe];
imageView.image =image;
imageView.tag =1;
[backgroundView addSubview:imageView];
[window addSubview:backgroundView];
//点击图片缩小的手势
UITapGestureRecognizer tap =[[UITapGestureRecognizer alloc]initWithTarget:self action:@selector(hideImage:)];
[backgroundView addGestureRecognizer:tap];
[UIView animateWithDuration:0.3 animations:^{
imageView.frame =CGRectMake(0,([UIScreen mainScreen].bounds.size.height-image.size.height[UIScreen mainScreen].bounds.size.width/image.size.width)/2, [UIScreen mainScreen].bounds.size.width, image.size.height[UIScreen mainScreen].bounds.size.width/image.size.width);
backgroundView.alpha =1;
}];
}
+(void)hideImage:(UITapGestureRecognizer *)tap{
UIView *backgroundView =tap.view;
UIImageView *imageView =(UIImageView *)[tap.view viewWithTag:1];
[UIView animateWithDuration:0.3 animations:^{
imageView.frame =oldframe;
backgroundView.alpha =0;
} completion:^(BOOL finished) {
[backgroundView removeFromSuperview];
}];
}