从事件处理程序更改属性

Question

I want a progressbar to be visible until a download is finished.

In order to do that, I bind the "Visibility" property with an attribute called "loadBarVisibility".

XAML Code :

<ProgressBar Visibility="{Binding loadBarVisibility}" IsIndeterminate="True"/>

ViewModel Code :

public class MainViewModel : ViewModelBase
{
    public static Visibility loadBarVisibility { get; set; }
    private const String URL = "myurl";


    public MainViewModel()
    {

        loadFlux();


        if (IsInDesignMode)
        {
            // Code runs in Blend --> create design time data.
        }
        else
        {
            // Code runs "for real"
        }
    }


    public static void loadFlux()
    {
        loadBarVisibility = Visibility.Visible;

        WebClient client = new WebClient();
        client.DownloadStringAsync(new Uri(URL));
        client.DownloadStringCompleted += new DownloadStringCompletedEventHandler(test_downloadFinished);



    }


    public static void test_downloadFinished(object sender, DownloadStringCompletedEventArgs e)
    {
        if (e.Error == null)
        {

            loadBarVisibility = Visibility.Collapsed;

        }

    }

}

But the code above doesn't work : the progressbar is still visible.

Otherwise, when I put "loadBarVisibility = Visibility.Collapsed;" just after "client.DownloadStringCompleted += new DownloadStringCompletedEventHandler(test_downloadFinished);", it works.

Is there a way to solve my problem ?

Thanks a lot.

Answer 1

您的ViewModel需要实现接口INotifyPropertyChanged以通知您查看属性visiblilty已更改（http://msdn.microsoft.com/en-us/library/system.componentmodel.inotifypropertychanged.aspx）