如何显示等待对话框，直到遵循MVVM设计模式的WPF应用程序中的非ui线程正在工作？

Question

I am developing a WPF application that follows MVVM design pattern. For threading I intend to use Backgroundworker. From viewmodels,I need to initiate threads to perform time taking opeartions.Please suggest me how to display an wait dialog until the thread is performing. If possible please provide a sample code. Regards, Anirban

Answer 1

You could add a property to the ViewModel that indicates that the backgroundworker (or other asynchronous action) is busy.

A View can bind bind to this property to show a progressbar or other busy indicator.

Just make sure you set and reset the property correctly.

EDIT

See this question/answer for making a modal dialog in WPF: How do make modal dialog in WPF?

As an alternative you could use this setup (pseudo code):

<Window>
    <Grid>
        <Grid x:Name="regularContent">
        </Grid>
        <Grid x:Name="Overlay" Visibility="Collapsed">
            <StackPanel HorizontalAlignment="Center" VerticalAlignment="Center">
                <Progressbar Value="{Binding Path=Progress}" />
            </StackPanel>
        </Grid>
    </Grid>
</Window>

Code behind:

private void ShowPopup()
{
    RegularContent.IsEnabled = false;
    Overlay.Visibility = Visibility.Visible;
}

private void ClosePopup()
{
    RegularContent.IsEnabled = true;
    Overlay.Visibility = Visibility.Collapsed;
}

Make sure you disable the regular content to prevent the user from tabbing to it.

You can use the same structure to blockout a part of the View instead of blocking it entirely as I have done.

The Progress property on the ViewModel that the ProgressBar is bound to should be modified on the UI thread. If you are using a backgroundworker that will be done automatically because the ReportProgress event is raised on the UI thread.

If you use a different way of creating a worker thread make sure you use the dispatcher to update the Progress property.

Answer 2

I used it in Windows Phone :

private readonly BackgroundWorker worker = new BackgroundWorker();
private PerformanceProgressBar loader = new PerformanceProgressBar();
worker.DoWork += worker_DoWork;
worker.RunWorkerCompleted += worker_RunWorkerCompleted;

private void worker_DoWork(object sender, DoWorkEventArgs e)
{
   bar.IsIndeterminate = true;
   Bar.Enabled = true;
}

private void worker_RunWorkerCompleted(object sender, 
                                       RunWorkerCompletedEventArgs e)
{
   bar.Enabled = false;
}

worker.RunWorkerAsync();

If you want to define a MVVM structure : PerformanceProgressBar "Invalid cross-thread access" exception

Of course an similar user control also exists in WPF : http://wpftoolkit.codeplex.com/wikipage?title=Extended%20WPF%20Toolkit%20Controls

Answer 3

The easiest way is to use wpf busyindicator ( http://elegantcode.com/2011/10/07/extended-wpf-toolkitusing-the-busyindicator/ ).

You can bind it to some thread_is_busy_flag_property in your model model (I prefer it in some singletone accessible through application-wide resource via locator pattern - it's easy to share across xaml and model view/code behind).

Just don't forget about thread safety when setting this flag (or you can use AutoResetEvent/ManualResetEvent to catch background operation ends). And I suggest to use TPL and tasks (more robust way) instead of BackgroundWorker/QueueUserWorkItem.