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142 lines
6.5 KiB
Markdown
142 lines
6.5 KiB
Markdown
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# 教你实现微信公众号效果：长按图片保存到相册
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> 不知道各位对于这个需求要如何解决？
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>
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> 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
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#### 那么问题跑出来了，怎么办最简单？
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* 鉴于个人道行尚浅，我就将自己的想法说出来
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* 有个js的api：`Document.elementFromPoint()`
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> The`elementFromPoint()`method of the[`Document`](https://developer.mozilla.org/en-US/docs/Web/API/Document)interface returns the topmost element at the specified coordinates.
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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
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#### 开发步骤
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- 给UIWebView添加长按手势
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- 监听手势动作，拿到坐标点(x,y)
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- `UIWebView注入js:Document.elementFromPoint(x,y).src` 拿到 img 标签的 src
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- 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
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- 拿到图片的 url，生成 UIImage,再将图片保存到相册
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#### 有巨坑
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* 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%
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```
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- (BOOL)gestureRecognizer:(UIGestureRecognizer *)gestureRecognizer shouldRecognizeSimultaneouslyWithGestureRecognizer:(UIGestureRecognizer *)otherGestureRecognizer{
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return YES;
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}
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```
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```
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//
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// ViewController.m
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// WebView长按图片保存到相册
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//
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// Created by 杭城小刘 on 2017/8/2.
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// Copyright © 2017年 杭城小刘. All rights reserved.
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//
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#import "ViewController.h"
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@interface ViewController ()<UIGestureRecognizerDelegate,NSURLSessionDelegate>
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@property (weak, nonatomic) IBOutlet UIWebView *webView;
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@end
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@implementation ViewController
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#pragma mark -- life cycle
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- (void)viewDidLoad{
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[super viewDidLoad];
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NSString *htmlURL = [[NSBundle mainBundle] pathForResource:@"saveImage" ofType:@"html"];
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[self.webView loadRequest:[NSURLRequest requestWithURL:[NSURL fileURLWithPath:htmlURL]]];
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//给UIWebView添加手势
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UILongPressGestureRecognizer* longPressed = [[UILongPressGestureRecognizer alloc] initWithTarget:self action:@selector(longPressed:)];
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longPressed.delegate = self;
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[self.webView addGestureRecognizer:longPressed];
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}
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#pragma mark -- UIGestureRecognizerDelegate
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- (BOOL)gestureRecognizer:(UIGestureRecognizer *)gestureRecognizer shouldRecognizeSimultaneouslyWithGestureRecognizer:(UIGestureRecognizer *)otherGestureRecognizer{
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UIActivityTypeAddToReadingList
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return YES;
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}
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- (void)longPressed:(UILongPressGestureRecognizer*)recognizer{
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if (recognizer.state != UIGestureRecognizerStateBegan) {
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return;
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}
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CGPoint touchPoint = [recognizer locationInView:self.webView];
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NSString *imgURL = [NSString stringWithFormat:@"document.elementFromPoint(%f, %f).src", touchPoint.x, touchPoint.y];
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NSString *urlToSave = [self.webView stringByEvaluatingJavaScriptFromString:imgURL];
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if (urlToSave.length == 0) {
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return;
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}
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UIAlertController *alertVC = [UIAlertController alertControllerWithTitle:@"大宝贝儿" message:@"你真的要保存图片到相册吗？" preferredStyle:UIAlertControllerStyleAlert];
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UIAlertAction *okAction = [UIAlertAction actionWithTitle:@"真的啊" style:UIAlertActionStyleDefault handler:^(UIAlertAction * _Nonnull action) {
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[self saveImageToDiskWithUrl:urlToSave];
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}];
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UIAlertAction *cancelAction = [UIAlertAction actionWithTitle:@"大哥，我点错了，不好意思" style:UIAlertActionStyleDefault handler:nil];
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[alertVC addAction:okAction];
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[alertVC addAction:cancelAction];
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[self presentViewController:alertVC animated:YES completion:nil];
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}
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#pragma mark - private method
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- (void)saveImageToDiskWithUrl:(NSString *)imageUrl{
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NSURL *url = [NSURL URLWithString:imageUrl];
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NSURLSessionConfiguration * configuration = [NSURLSessionConfiguration defaultSessionConfiguration];
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NSURLSession *session = [NSURLSession sessionWithConfiguration:configuration delegate:self delegateQueue:[NSOperationQueue new]];
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NSURLRequest *imgRequest = [NSURLRequest requestWithURL:url cachePolicy:NSURLRequestReturnCacheDataElseLoad timeoutInterval:30.0];
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NSURLSessionDownloadTask *task = [session downloadTaskWithRequest:imgRequest completionHandler:^(NSURL * _Nullable location, NSURLResponse * _Nullable response, NSError * _Nullable error) {
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if (error) {
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return ;
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}
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NSData * imageData = [NSData dataWithContentsOfURL:location];
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dispatch_async(dispatch_get_main_queue(), ^{
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UIImage * image = [UIImage imageWithData:imageData];
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UIImageWriteToSavedPhotosAlbum(image, self, @selector(imageSavedToPhotosAlbum:didFinishSavingWithError:contextInfo:), NULL);
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});
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}];
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[task resume];
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}
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#pragma mark 保存图片后的回调
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- (void)imageSavedToPhotosAlbum:(UIImage*)image didFinishSavingWithError: (NSError*)error contextInfo:(id)contextInfo{
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NSString*message =@"嘿嘿";
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if(!error) {
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UIAlertController *alertControl = [UIAlertController alertControllerWithTitle:@"提示" message:@"成功保存到相册" preferredStyle:UIAlertControllerStyleAlert];
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UIAlertAction *action = [UIAlertAction actionWithTitle:@"确定" style:UIAlertActionStyleDestructive handler:nil];
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[alertControl addAction:action];
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[self presentViewController:alertControl animated:YES completion:nil];
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}else{
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message = [error description];
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UIAlertController *alertControl = [UIAlertController alertControllerWithTitle:@"提示" message:message preferredStyle:UIAlertControllerStyleAlert];
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UIAlertAction *action = [UIAlertAction actionWithTitle:@"确定" style:UIAlertActionStyleCancel handler:nil];
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[alertControl addAction:action];
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[self presentViewController:alertControl animated:YES completion:nil];
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}
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}
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@end
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```
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附上关键的js官方文档：[Document.elementFromPoint()](https://developer.mozilla.org/en-US/docs/Web/API/Document/elementFromPoint)
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附上Demo：[Demo](https://github.com/FantasticLBP/BlogDemos)
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