UWP WebView await navigate

问题

I'm trying to get some content on a website which is rendered by JavaScript. So I'm running a WebView with Visibility=Collapsed. I want to wait unitl NavigationCompleted and run some JavaScript then return the value.

The code look like:

private async void Foo()
{
    // Want to get value here
    var content = await GetContent();
}

private async Task<string> GetContent()
{
    string content;
    async void handler(WebView sender, WebViewNavigationCompletedEventArgs args)
    {
        content = await webView.InvokeScriptAsync("eval", new string[] { script });
        webView.NavigationCompleted -= handler;
    }
    webView.NavigationCompleted += handler;
    webView.Navigate(uri);
    return content;
}

Since there is no await in GetContent(), the function always returns before NavigationCompleted fired.

回答1:

You could use a SemaphoreSlim to asynchronously wait for the NavigationCompleted to get raised and handled:

private async Task<string> GetContent()
{
    string content;
    using (SemaphoreSlim semaphoreSlim = new SemaphoreSlim(0, 1))
    {
        async void handler(WebView sender, WebViewNavigationCompletedEventArgs args)
        {
            content = await webView.InvokeScriptAsync("eval", new string[] { script });
            webView.NavigationCompleted -= handler;
            semaphoreSlim.Release();
        }
        webView.NavigationCompleted += handler;
        webView.Navigate(uri);
        await semaphoreSlim.WaitAsync().ConfigureAwait(false);
    }
    return content;
}

回答2:

I think you should use TaskCompletionSource. Create a source, and set its result at the end of the event handler, after you execute the script. Before you return the content, await the task of the task completion source.

回答3:

If you want to wait for something, you can use ManualResetEvent. Just ensure that you don't use ManualResetEvent.WaitOne on the UI thread as it would hang the app.

来源：https://stackoverflow.com/questions/55086961/uwp-webview-await-navigate

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uwp