長按UIWebView上的圖片保存到相冊

不知道各位對於這個需求要如何解決？

可能有些人會想到js與原生交互，js監聽圖片點擊事件，而後將圖片的url傳遞給原生App端，而後原生App將圖片保存到相冊，這樣子麻煩嗎？超麻煩。（1）、js監聽圖片長按事件；（2）、js將圖片url傳遞給原生；（3）、原生經過圖片的url生成UIImage；（4）、保存UIImage到系統相冊，巨麻煩啊，大哥，我很懶的好很差

那麼問題跑出來了，怎麼辦最簡單？

• 鑑於我的道行尚淺，我就將本身的想法說出來

• 有個js的api：Document.elementFromPoint()

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

因此根據這個提示，咱們徹底能夠只在App原生端作一些代碼開發，實現這個需求

開發步驟

• 給UIWebView添加長按手勢
• 監聽手勢動做，拿到座標點(x,y)
• UIWebView注入js:Document.elementFromPoint(x,y).src拿到img標籤的src
• 判斷拿到的src是否有值，有值則表明點擊的網頁上的img標籤，此時彈出對話框，是否保存到相冊。若是src爲空，則表明點擊網頁上的非img標籤，則不須要彈出對話框。
• 拿到圖片的url，生成UIImage。再將圖片保存到相冊

有巨坑

• 長按手勢事件不能每次都響應，據我猜想UIWebView自己就有不少事件，因此實現下UIGestureRecognizerDelegate代理方法。長按手勢準確率100%

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

//
//  ViewController.m
//  WebView長按圖片保存到相冊
//
//  Created by 杭城小劉 on 2017/8/2.
//  Copyright © 2017年 杭城小劉. 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]]];
    //給UIWebView添加手勢
    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{
    UIActivityTypeAddToReadingList
    return 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:@"大寶貝兒" message:@"你真的要保存圖片到相冊嗎？" preferredStyle:UIAlertControllerStyleAlert];
    UIAlertAction *okAction = [UIAlertAction actionWithTitle:@"真的啊" style:UIAlertActionStyleDefault handler:^(UIAlertAction * _Nonnull action) {
            [self saveImageToDiskWithUrl:urlToSave];
    }];
    UIAlertAction *cancelAction = [UIAlertAction actionWithTitle:@"大哥，我點錯了，很差意思" 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 保存圖片後的回調
- (void)imageSavedToPhotosAlbum:(UIImage*)image didFinishSavingWithError:  (NSError*)error contextInfo:(id)contextInfo{
    NSString*message =@"嘿嘿";
    if(!error) {
        UIAlertController *alertControl = [UIAlertController alertControllerWithTitle:@"提示" message:@"成功保存到相冊" preferredStyle:UIAlertControllerStyleAlert];
        
        UIAlertAction *action = [UIAlertAction actionWithTitle:@"肯定" 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:@"肯定" style:UIAlertActionStyleCancel handler:nil];
        [alertControl addAction:action];
        [self presentViewController:alertControl animated:YES completion:nil];
    }
}

@end

附上關鍵的js官方文檔：Document.elementFromPoint()

附上Demo：Demo