如何将UIWebView里面的图片保存到相册中

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;

步骤如下：

需要注入的js代码：

@"document.ontouchstart = function (event) {\
x = event.targetTouches[0].clientX;\
y = event.targetTouches[0].clientY;\
document.location = \"myweb:touch:start:\"+x+\":\"+y;};\
document.ontouchmove = function (event) {\
x = event.targetTouches[0].clientX;\
y = event.targetTouches[0].clientY;\
document.location = \"myweb:touch:move\"+x+\":\"+y;};\
document.ontouchcancel = function (event) {\
document.location = \"myweb:touch:cancel\";};\
document.ontouchend=function(event){\
document.location=\"myweb:touch:end\";};";

其中
touchstart，
touchmove，
touchend
用来捕获元素的触摸事件。

第一步：需要将js代码注入到交互的页面中。

-(void)webViewDidFinishLoad:(UIWebView *)webView {
    [self.webView stringByEvaluatingJavaScriptFromString:kTouchJavaScriptString];
}

第二步：
用js来监听触摸图片长按事件，然后在webview的delegate方法里截取resquest就行了：
用到如下的代理方法：

- (BOOL)webView:(UIWebView *)webView shouldStartLoadWithRequest:(NSURLRequest *)request navigationType:(UIWebViewNavigationType)navigationType

然后，根据触摸点x,y的位置，并且通过js
document.elementFromPoint(%f, %f).tagName获取标签，
然后判断是不是图片，
如果是图片的话，提取图片的src
document.elementFromPoint(%f, %f).src

第三步：
将图片的URL经过转换成原生OC可以用的URL
// _imgURL<===>document.elementFromPoint(%f, %f).src
NSString *urlToSave = [self.webView stringByEvaluatingJavaScriptFromString:_imgURL];,
然后生成UIImage

第四步：保存UIImage到系统相册

掘金上面的另一种解决方案：
https://juejin.im/post/5981a278f265da3e260954b1
我自己如下的解决方案：

代码：

#import "ViewController.h"
#import <WebKit/WebKit.h>
#import "WKDelegateController.h"


typedef enum : NSUInteger {
    GESTURE_STATE_START,
    GESTURE_STATE_MOVE,
    GESTURE_STATE_END,
} GESTURE_STATE;

@interface ViewController()<UIWebViewDelegate>
@property (nonatomic, strong) UIWebView *webView;
@property (nonatomic, strong) NSString *imgURL;
@property (nonatomic, strong) NSTimer *timer;
@property (nonatomic, assign) GESTURE_STATE gesState;

@end



static NSString * const kTouchJavaScriptString =

@"document.ontouchstart = function (event) {\
x = event.targetTouches[0].clientX;\
y = event.targetTouches[0].clientY;\
document.location = \"myweb:touch:start:\"+x+\":\"+y;};\
document.ontouchmove = function (event) {\
x = event.targetTouches[0].clientX;\
y = event.targetTouches[0].clientY;\
document.location = \"myweb:touch:move\"+x+\":\"+y;};\
document.ontouchcancel = function (event) {\
document.location = \"myweb:touch:cancel\";};\
document.ontouchend=function(event){\
document.location=\"myweb:touch:end\";};";

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    
    self.webView = [[UIWebView alloc] initWithFrame:self.view.bounds];
    self.webView.delegate = self;
    [self.view addSubview:self.webView];
    
    NSString *urlStr = @"http://politics.people.com.cn/n1/2017/0810/c14562-29463365.html";
    NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:urlStr]];
    [self.webView loadRequest:request];
}

-(void)webViewDidFinishLoad:(UIWebView *)webView {
    [self.webView stringByEvaluatingJavaScriptFromString:kTouchJavaScriptString];
}

- (BOOL)webView:(UIWebView *)webView shouldStartLoadWithRequest:(NSURLRequest *)request navigationType:(UIWebViewNavigationType)navigationType {
    
    NSString *requestString = [[request URL] absoluteString];
    NSLog(@"%s", __func__);
    NSLog(@"requestString = %@", requestString);
    NSLog(@"currentThread = %@", [NSThread currentThread]);
    NSArray *components = [requestString componentsSeparatedByString:@":"];
    if ([components count] > 1 && [(NSString *)[components objectAtIndex:0]
                                   isEqualToString:@"myweb"]) {
        if([(NSString *)[components objectAtIndex:1] isEqualToString:@"touch"]) {
            if ([(NSString *)[components objectAtIndex:2] isEqualToString:@"start"]) {
                
                _gesState = GESTURE_STATE_START;
                NSLog(@"touch start!");
                
                float ptX = [[components objectAtIndex:3] floatValue];
                float ptY = [[components objectAtIndex:4] floatValue];
                NSLog(@"touch point (%f, %f)", ptX, ptY);
                
                NSString *js = [NSString stringWithFormat:@"document.elementFromPoint(%f, %f).tagName", ptX, ptY];
                NSString *tagName = [self.webView stringByEvaluatingJavaScriptFromString:js];
                _imgURL = nil;
                if ([tagName isEqualToString:@"IMG"]) {
                    _imgURL = [NSString stringWithFormat:@"document.elementFromPoint(%f, %f).src", ptX, ptY];
                }
                if (_imgURL) {
                    _timer = [NSTimer scheduledTimerWithTimeInterval:2 target:self selector:@selector(handleLongTouch) userInfo:nil repeats:NO];
                }
            }
            else if ([(NSString *)[components objectAtIndex:2] isEqualToString:@"move"]) {
                //**如果touch动作是滑动，则取消hanleLongTouch动作**//
                _gesState = GESTURE_STATE_MOVE;
                NSLog(@"you are move");
                
            } else if ([(NSString*)[components objectAtIndex:2]isEqualToString:@"end"]) {
                [_timer invalidate];
                _timer = nil;
                _gesState = GESTURE_STATE_END;
                NSLog(@"touch end");
            }
        }
        
        return NO;
    }
    return YES;
}

- (void)handleLongTouch {
    NSLog(@"%@", _imgURL);
    if (_imgURL && _gesState == GESTURE_STATE_START) {
        UIActionSheet* sheet = [[UIActionSheet alloc] initWithTitle:nil delegate:self cancelButtonTitle:@"取消" destructiveButtonTitle:nil otherButtonTitles:@"保存图片", nil];
        sheet.cancelButtonIndex = sheet.numberOfButtons - 1;
        [sheet showInView:[UIApplication sharedApplication].keyWindow];
    }
}

- (void)actionSheet:(UIActionSheet *)actionSheet clickedButtonAtIndex:(NSInteger)buttonIndex {
    if (actionSheet.numberOfButtons - 1 == buttonIndex) {
        return;
    }
    NSString* title = [actionSheet buttonTitleAtIndex:buttonIndex];
    if ([title isEqualToString:@"保存图片"]) {
        if (_imgURL) {
            NSLog(@"imgurl = %@", _imgURL);
        }
        NSString *urlToSave = [self.webView stringByEvaluatingJavaScriptFromString:_imgURL];
        NSLog(@"image url=%@", urlToSave);
        
        NSData* data = [NSData dataWithContentsOfURL:[NSURL URLWithString:urlToSave]];
        UIImage* image = [UIImage imageWithData:data];
                                                      
        
      UIImageWriteToSavedPhotosAlbum(image, self, @selector(image:didFinishSavingWithError:contextInfo:), nil);
    }
}

- (void) dealloc {
    if(self.webView){
        [self.webView stopLoading];
        self.webView.delegate = nil;
    }
}

- (void)image:(UIImage *)image didFinishSavingWithError:(NSError*)error contextInfo:(void*)contextInfo{
    if (error){
        NSLog(@"Error");
//      [self showAlert:@"保存失败"];
    }else {
        NSLog(@"OK");
//      [self showAlert:@"保存成功"];
    }
}