不知道各位对于这个需求要如何解决？

可能有些人会想到js与原生交互，js监听图片点击事件，然后将图片的url传递给原生App端，然后原生App将图片保存到相册，这样子麻烦吗？超麻烦。（1）、js监听图片长按事件；（2）、js将图片url传递给原生；（3）、原生通过图片的url生成UIImage；（4）、保存UIImage到系统相册，巨麻烦啊，大哥，我很懒的好不好

那么问题跑出来了，怎么办最简单？

• 鉴于个人道行尚浅，我就将自己的想法说出来

• 有个js的api：Document.elementFromPoint()

TheelementFromPoint()method of theDocumentinterface returns the topmost element at the specified coordinates.

所以根据这个提示，我们完全可以只在App原生端做一些代码开发，实现这个需求

开发步骤

• 给UIWebView添加长按手势
• 监听手势动作，拿到坐标点(x,y)
• UIWebView注入js:Document.elementFromPoint(x,y).src拿到img标签的src
• 判断拿到的src是否有值，有值则代表点击的网页上的img标签，此时弹出对话框，是否保存到相册。如果src为空，则代表点击网页上的非img标签，则不需要弹出对话框。
• 拿到图片的url，生成UIImage。再将图片保存到相册

有巨坑

• 长按手势事件不能每次都响应，据我猜测UIWebView本身就有很多事件，所以实现下UIGestureRecognizerDelegate代理方法。长按手势准确率100%

- (BOOL)gestureRecognizer:(UIGestureRecognizer *)gestureRecognizer shouldRecognizeSimultaneouslyWithGestureRecognizer:(UIGestureRecognizer *)otherGestureRecognizer{return YES;
}复制代码

//
//  ViewController.m
//  WebView长按图片保存到相册
//
//  Created by 杭城小刘 on 2017/8/2.
//  Copyright © 2017年 杭城小刘. All rights reserved.
//#import "ViewController.h"@interface ViewController ()<UIGestureRecognizerDelegate,NSURLSessionDelegate>
@property (weak, nonatomic) IBOutlet UIWebView *webView;@end@implementation ViewController#pragma mark -- life cycle
- (void)viewDidLoad{[super viewDidLoad];NSString *htmlURL = [[NSBundle mainBundle] pathForResource:@"saveImage" ofType:@"html"];[self.webView loadRequest:[NSURLRequest requestWithURL:[NSURL fileURLWithPath:htmlURL]]];//给UIWebView添加手势UILongPressGestureRecognizer* longPressed = [[UILongPressGestureRecognizer alloc] initWithTarget:self action:@selector(longPressed:)];longPressed.delegate = self;[self.webView addGestureRecognizer:longPressed];
}#pragma mark -- UIGestureRecognizerDelegate
- (BOOL)gestureRecognizer:(UIGestureRecognizer *)gestureRecognizer shouldRecognizeSimultaneouslyWithGestureRecognizer:(UIGestureRecognizer *)otherGestureRecognizer{UIActivityTypeAddToReadingListreturn YES;
}- (void)longPressed:(UILongPressGestureRecognizer*)recognizer{if (recognizer.state != UIGestureRecognizerStateBegan) {return;}CGPoint touchPoint = [recognizer locationInView:self.webView];NSString *imgURL = [NSString stringWithFormat:@"document.elementFromPoint(%f, %f).src", touchPoint.x, touchPoint.y];NSString *urlToSave = [self.webView stringByEvaluatingJavaScriptFromString:imgURL];if (urlToSave.length == 0) {return;}UIAlertController *alertVC =  [UIAlertController alertControllerWithTitle:@"大宝贝儿" message:@"你真的要保存图片到相册吗？" preferredStyle:UIAlertControllerStyleAlert];UIAlertAction *okAction = [UIAlertAction actionWithTitle:@"真的啊" style:UIAlertActionStyleDefault handler:^(UIAlertAction * _Nonnull action) {[self saveImageToDiskWithUrl:urlToSave];}];UIAlertAction *cancelAction = [UIAlertAction actionWithTitle:@"大哥，我点错了，不好意思" style:UIAlertActionStyleDefault handler:nil];[alertVC addAction:okAction];[alertVC addAction:cancelAction];[self presentViewController:alertVC animated:YES completion:nil];
}#pragma mark - private method
- (void)saveImageToDiskWithUrl:(NSString *)imageUrl{NSURL *url = [NSURL URLWithString:imageUrl];NSURLSessionConfiguration * configuration = [NSURLSessionConfiguration defaultSessionConfiguration];NSURLSession *session = [NSURLSession sessionWithConfiguration:configuration delegate:self delegateQueue:[NSOperationQueue new]];NSURLRequest *imgRequest = [NSURLRequest requestWithURL:url cachePolicy:NSURLRequestReturnCacheDataElseLoad timeoutInterval:30.0];NSURLSessionDownloadTask  *task = [session downloadTaskWithRequest:imgRequest completionHandler:^(NSURL * _Nullable location, NSURLResponse * _Nullable response, NSError * _Nullable error) {if (error) {return ;}NSData * imageData = [NSData dataWithContentsOfURL:location];dispatch_async(dispatch_get_main_queue(), ^{UIImage * image = [UIImage imageWithData:imageData];UIImageWriteToSavedPhotosAlbum(image, self, @selector(imageSavedToPhotosAlbum:didFinishSavingWithError:contextInfo:), NULL);});}];[task resume];
}#pragma mark 保存图片后的回调
- (void)imageSavedToPhotosAlbum:(UIImage*)image didFinishSavingWithError:  (NSError*)error contextInfo:(id)contextInfo{NSString*message =@"嘿嘿";if(!error) {UIAlertController *alertControl = [UIAlertController alertControllerWithTitle:@"提示" message:@"成功保存到相册" preferredStyle:UIAlertControllerStyleAlert];UIAlertAction *action = [UIAlertAction actionWithTitle:@"确定" style:UIAlertActionStyleDestructive handler:nil];[alertControl addAction:action];[self presentViewController:alertControl animated:YES completion:nil];}else{message = [error description];UIAlertController *alertControl = [UIAlertController alertControllerWithTitle:@"提示" message:message preferredStyle:UIAlertControllerStyleAlert];UIAlertAction *action = [UIAlertAction actionWithTitle:@"确定" style:UIAlertActionStyleCancel handler:nil];[alertControl addAction:action];[self presentViewController:alertControl animated:YES completion:nil];}
}@end复制代码

附上关键的js官方文档：Document.elementFromPoint()

附上Demo：Demo