UWP Webview 只为最后一次请求触发 NavigationCompleted 事件 [英] UWP Webview only triggers NavigationCompleted event for the last request

问题描述

我有一个 foreach 循环可以多次调用 _webView.NavigateToLocalStreamUri(url[index], resolver).据我所知，每次导航到特定 URL 时，都会触发事件 NavigationStarting 和 NavigationCompleted.但就我而言，NavigationStarting 会为每个请求调用，但 NavigationCompleted 仅在最后一个请求时触发.我想知道有没有办法确保为每个请求调用 NavigationCompleted.我搜索了但没有符合我目的的答案.

I have a foreach loop to call _webView.NavigateToLocalStreamUri(url[index], resolver) many times. As I know each time I navigate to a specific URL, the events NavigationStarting and NavigationCompleted are triggered. But in my case, NavigationStarting is called for every request but NavigationCompleted only trigger for the last request. I want to know Is there a way to make sure NavigationCompleted is called for every request. I searched but there is no answer meet my purpose.

for (int i = 0; i < 3; i++){
// here I raise event to call `NavigateToLocalStreamUri` of _webview
}

_webview 有 2 个事件 NavigationStarting 和 NavigationCompleted

_webview have 2 events NavigationStarting and NavigationCompleted

//当 i = 0 or 1程序只调用NavigationStarting的事件处理程序，不调用NavigationCompleted

// when i = 0 or 1 the program only calls event handler of NavigationStarting, but not call event handler of NavigationCompleted

//当i = 2(总是for循环的最后一次迭代)程序调用 NavigationStarting 和 NavigationCompleted

// when i = 2 (always, the last iteration of for loop) the program calls event handler of both events NavigationStarting and NavigationCompleted

//有没有办法确保当 i = 0 或 1 时，NavigationCompleted 处理程序被调用?

// Is there any solution to make sure when i = 0 or 1, NavigationCompleted handler is called?

推荐答案

我复制了您的问题.该问题是由 for 循环在上一个导航完成之前继续引起的.

I reproduced your issue. The issue is caused by the for loop continue before the previous navigation completed.

解决这个问题的关键是等待前面的 NavigationCompleted 事件句柄发生.你可以使用 AutoResetEvent 通知等待线程发生了事件.例如:

The key point to resolve this is to wait for the previous NavigationCompleted event handle occurred.You could use AutoResetEvent which notifies a waiting thread that an event has occurred. For example:

public MainPage()
{
    this.InitializeComponent();        
    urls = new List<Uri>();
    waitForNavComplete = new AutoResetEvent(false);
    urls.Add(...); 
}

List<Uri> urls;
AutoResetEvent waitForNavComplete;
private async void btnnavigate_Click(object sender, RoutedEventArgs e)
{
    for (int i = 0; i < 3; i++)
    {
        mywebview.Navigate(urls[i]);
        await Task.Run(() => { waitForNavComplete.WaitOne(); });
    }
}
private void mywebview_NavigationCompleted(WebView sender, WebViewNavigationCompletedEventArgs args)
{
    System.Diagnostics.Debug.WriteLine(args.Uri.ToString());
    waitForNavComplete.Set();
}

使用 Set 方法将完成事件的状态设置为已发出信号，以便 for 循环将停止等待并继续.

Using Set method to set the state of the completed event to signaled so that for loop will stop waiting and continue.

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