25期_iOS_WKWebView生命周期解析

WebKit的加载本文从WKWebView网页加载流程、代理方法、代理方法初步了解WKWebView

第三方源码：
WebViewJavascri源码

网页加载流程

• DNS解析【域名-ip】
• 请求握手
• 获取html文件
• 解析html文件，异步加载css或资源。碰到js会挂起html解析，进行js请求。
• 解析完毕html，执行js代码，成型dom树，配合css，展示样式
• 结束链接

WKNavigationDelegate代理方法

    @protocol WKNavigationDelegate <NSObject>
    
    @optional
    // 请求之前，决定是否要跳转:用户点击网页上的链接，需要打开新页面时，将先调用这个方法。
    - (void)webView:(WKWebView *)webView decidePolicyForNavigationAction:(WKNavigationAction *)navigationAction decisionHandler:(void (^)(WKNavigationActionPolicy))decisionHandler; 
    
    // 页面开始加载时调用
    - (void)webView:(WKWebView *)webView didStartProvisionalNavigation:(null_unspecified WKNavigation *)navigation; 

    // 接收到响应数据后，决定是否跳转
    - (void)webView:(WKWebView *)webView decidePolicyForNavigationResponse:(WKNavigationResponse *)navigationResponse decisionHandler:(void (^)(WKNavigationResponsePolicy))decisionHandler; 
    
    // 主机地址被重定向时调用
    - (void)webView:(WKWebView *)webView didReceiveServerRedirectForProvisionalNavigation:(null_unspecified WKNavigation *)navigation; 
    
    // 当开始加载主文档数据失败时调用
    - (void)webView:(WKWebView *)webView didFailProvisionalNavigation:(null_unspecified WKNavigation *)navigation withError:(NSError *)error; 
    
    // 当内容开始返回时调用
    - (void)webView:(WKWebView *)webView didCommitNavigation:(null_unspecified WKNavigation *)navigation; 
    
    // 页面加载完毕时调用
    - (void)webView:(WKWebView *)webView didFinishNavigation:(null_unspecified WKNavigation *)navigation; 
    
    // 当主文档已committed时，如果发生错误将进行调用
    - (void)webView:(WKWebView *)webView didFailNavigation:(null_unspecified WKNavigation *)navigation withError:(NSError *)error; 
    
    // 如果需要证书验证，进行验证，一般使用默认证书策略即可 
    - (void)webView:(WKWebView *)webView didReceiveAuthenticationChallenge:(NSURLAuthenticationChallenge *)challenge completionHandler:(void (^)(NSURLSessionAuthChallengeDisposition disposition, NSURLCredential *__nullable credential))completionHandler; 
    
    // 9.0才能使用，web内容处理中断时会触发，可针对该情况进行reload操作，可解决部分白屏问题 
    - (void)webVididStartProvisionalNavigationewWebContentProcessDidTerminate:(WKWebView *)webView NS_AVAILABLE(10_11, 9_0); 
    
    @end

decidePolicyForNavigationAction

请求之前，决定是否要跳转:用户点击网页上的链接，需要打开新页面时，将先调用这个方法。业务（拨打电话）

当WebContent即将创建DocumentLoader加载器时，会触发此方法。
cancel：那么浏览器内核会完全忽略这已操作，后续不再执行其他操作。
allow：内核代码会判断该链接是否universalLink，为此链接会尝试调起三方app，能调起取消当前请求。否则会走正常的网络请求

- (void)webView:(WKWebView *)webView decidePolicyForNavigationAction:(WKNavigationAction *)navigationAction decisionHandler:(void (^)(WKNavigationActionPolicy))decisionHandler
{
//    NSURL *URL = navigationAction.request.URL;
    NSString *urlString = navigationAction.request.URL.absoluteString;
    if ([urlString hasPrefix:@"tel:"] || [urlString hasPrefix:@"weixin:"]) {
        [[UIApplication sharedApplication] openURL:navigationAction.request.URL];
        decisionHandler(WKNavigationActionPolicyCancel);
    }else {
        if (navigationAction.targetFrame == nil) {
            [webView loadRequest:navigationAction.request];
        }
        decisionHandler(WKNavigationActionPolicyAllow);
    }
    
}

didStartProvisionalNavigation

decidePolicyForNavigationAction选择allow,并且非universalLink会触发didStartProvisionalNavigation，表示开始加载主文档，

// 页面开始加载时调用
-(void)webView:(WKWebView *)webView didStartProvisionalNavigation:(WKNavigation *)navigation{
    if (![webView.URL.absoluteString containsString:@"about:blank"]) {
        [SVProgressHUD show];
    }
    if ([webView.URL.absoluteString containsString:@"voteindex"])
    {
        self.webView.scrollView.bounces = YES;
    }else
    {
        self.webView.scrollView.bounces = NO;
    }
    self.shareUrl = webView.URL.absoluteString;
    
}

decidePolicyForNavigationResponse

页面加载后为了更好区分各个阶段，会将网络加载的初始阶段命名为临时状态，此时页面不会计入历史，decidePolicyForNavigationResponse为收到响应的之后处理，是否允许跳转

// 在收到响应后，决定是否跳转
- (void)webView:(WKWebView *)webView decidePolicyForNavigationResponse:(WKNavigationResponse *)navigationResponse decisionHandler:(void (^)(WKNavigationResponsePolicy))decisionHandler{
    
    NSLog(@"decidePolicyForNavigationResponse：%@",navigationResponse.response.URL.absoluteString);
    //允许跳转
    decisionHandler(WKNavigationResponsePolicyAllow);
    //不允许跳转
    //decisionHandler(WKNavigationResponsePolicyCancel);
}

didCommitNavigation

直到收到首个数据包，才会进行commit提交，执行。通知进程UIProcess，将网络数据交给WebContent进行渲染。此时网络临时状态处理处理果和提交处理结果如果失败，执行下面两种方法

// 当内容开始返回时调用
- (void)webView:(WKWebView *)webView didCommitNavigation:(WKNavigation *)navigation{
    NSLog(@"didCommitNavigation");
}

didFailProvisionalNavigation/didFailNavigation

当NetProcess进程发生网络错误时，错误首先由NSURLSession回调给WebContent层
WebContent判断主文档的加载状态，如果处于临时Provisional状态，则错误回调给didFailProvisionalNavigation，如果是提交commit状态，则错误回调给didFailNavigation

    // 页面加载失败时调用
    - (void)webView:(WKWebView *)webView didFailProvisionalNavigation:(WKNavigation *)navigation withError:(NSError *)error {
        
        NSLog(@"didFailProvisionalNavigation:%@",error);
    }

    - (void)webView:(WKWebView *)webView didFailNavigation:(WKNavigation *)navigation withError:(NSError *)error {
        
        NSLog(@"didFailNavigation:%@",error);
    }

didFinishNavigation

NetworkProcess层也是使用NSURLSession加载主文档，当NSURLSession接收到finish事件，会将该消息通过进程通信传递给WebContent进程，然后传递给UIProcess进程，直到被代理方法响应
因此didFinishNavigation的加载与子界面上屏没有关系，在网络加载结束触发

// 页面加载完成之后调用
- (void)webView:(WKWebView *)webView didFinishNavigation:(WKNavigation *)navigation{
    NSLog(@"加载完毕");
}