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异步web请求回调中未更新UI

windows-phone-7

John Sheehan · 技术社区 · 15 年前

我用它来做一个网络请求并下载一些数据:

public partial class MainPage : PhoneApplicationPage
{
    public MainPage()
    {
        InitializeComponent();

        var client = new WebClient();

        client.DownloadStringCompleted += (s, e) => {
            textBlock1.Text = e.Result;
        };

        client.DownloadStringAsync(new Uri("http://example.com"));
    }
}

的文本 textBlock1 e.Result 有正确的数据。如何从回调中更新?

编辑: 如果我加上 MessageBox.Show(e.Result);

再次编辑:

6 回复 | 直到 15 年前

Sergey Zwezdin 15 年前

Jacob 15 年前

在更新来自不同调度器的UI时,我也遇到了一些问题。我最后做的是使用TextBlock(或其他UI元素)自己的dispatcher,这对我很有用。我认为phone框架可能在app和UI元素之间使用了不同的调度器。注意从dispatcher.BeginInvoke到textbox1.dispatcher的更改。。。

void MainPage_Loaded(object sender, RoutedEventArgs e)
{
    var dispatcher = Deployment.Current.Dispatcher;

    var client = new WebClient();

    client.DownloadStringCompleted += (s, e) =>
    {
        var result = e.Result;
        textBlock1.Dispatcher.BeginInvoke(
            ()=> textBlock1.Text = result
            );
    };

    client.DownloadStringAsync(new Uri("http://example.com"));
}

John Sheehan 15 年前

TheTodd 15 年前

client.DownloadStringAsync需要如下Uri:

client.DownloadStringAsync(new Uri("http://example.com"));

另外,您不应该通过Dispatcher.BeginInvoke更新TextBlock吗

    client.DownloadStringCompleted += (s, e) => 
    { 
        if (null == e.Error) 
            Dispatcher.BeginInvoke(() => UpdateStatus(e.Result)); 
        else 
            Dispatcher.BeginInvoke(() => UpdateStatus("Operation failed: " + e.Error.Message)); 
    };

Daniel Crenna 15 年前

public partial class MainPage : PhoneApplicationPage
{
    public MainPage()
    {
        InitializeComponent();

        Loaded += MainPage_Loaded;
    }

    void MainPage_Loaded(object sender, RoutedEventArgs e)
    {
        var dispatcher = Deployment.Current.Dispatcher;

        var client = new WebClient();

        client.DownloadStringCompleted += (s, e) =>
        {
            var result = e.Result;
            dispatcher.BeginInvoke(
                ()=> textBlock1.Text = result
                );
        };

        client.DownloadStringAsync(new Uri("http://example.com"));
    }
}

Ben Gracewood 15 年前

public void BeginDownload(bool doWorkAfterDownload)
{
    DownloadStatus = "Starting ...";

    _doExtraWork = doWorkAfterDownload;
    var webClient = new WebClient();

    string auth = "Basic " + Convert.ToBase64String(System.Text.Encoding.UTF8.GetBytes("test:password"));
    webClient.Headers["Authorization"] = auth;

    webClient.DownloadProgressChanged += new DownloadProgressChangedEventHandler(webClient_DownloadProgressChanged);
    webClient.OpenReadCompleted += new OpenReadCompletedEventHandler(webClient_OpenReadCompleted);

    webClient.OpenReadAsync(new Uri("http://www.ben.geek.nz/samsung1.jpg"));
}

void webClient_OpenReadCompleted(object sender, OpenReadCompletedEventArgs e)
{
    if (e.Error != null)
    {
        DownloadStatus = e.Error.Message;
        return;
    }

    DownloadStatus = "Completed. Idle.";

    if(_doExtraWork)
    {
        Thread t = new Thread(DoWork);
        t.Start(e.Result);
    }

}

void DoWork(object param)
{
    InvokeDownloadCompleted(new EventArgs());

    // just do some updating
    for (int i = 1; i <= 10; i++)
    {
        DownloadStatus = string.Format("Doing work {0}/10", i);
        Thread.Sleep(500);
    }
    DownloadStatus = "Completed extra work. Idle.";
    InvokeExtraWorkCompleted(new EventArgs());
}