页面加载时的进度指示器

Question

I've got a WPF window that takes about 5 seconds to load. I want to inform the user with a user friendly message and wasn't sure the best way to do this. The two things I can think of: 1. Throw up a dialog that shows the message and then it disappears once the main window has loaded. 2. Use a panel on the main window to show the message and load the UI into a hidden panel. When it has loaded, switch the visibility so the load progress panel is hidden and make the UI panel visible.

I've already implemented the application with option 1 but I'm running into the following issues: 1. Occasionally, the application will throw a Thread.Abort exception which gets caught by the application's unhandled exception handler. 2. The user can close the progress dialog but the main window carries on loading anyway.

My implementation of the progress dialog is fairly simple. It's using just a normal dialog with a message and then I've written a helper class to manage this:

public class ProgressWaitDialogHelper : IDisposable
{
    private Thread _thread = null;
    private ProgressWaitDialog _waitDialog;

    public void ShowDialog()
    {
        ThreadStart threadStart = new ThreadStart(ShowDialogAsync);
        _thread = new Thread(threadStart);
        _thread.SetApartmentState(ApartmentState.STA);
        _thread.Start();
    }

    public void Dispose()
    {
        if ((_thread != null) &&
            (_thread.IsAlive))
        {
            _thread.Abort();
            _thread = null;
        }
    }

    private void ShowDialogAsync()
    {
        _waitDialog = new ProgressWaitDialog();
        _waitDialog.ShowDialog();
    }
}

My calling code then does:

using (ProgressWaitDialogHelper waitDialog = new ProgressWaitDialogHelper())
{
    waitDialog.ShowDialog();

    // Do long running UI update loading here.
}

Does anyone know how I can fix the problems I'm seeing? Also, is it better to move over to solution 2? Or, is there some other way of doing this that is more in line with WPF?

TIA

Answer 1

Occasionally, the application will throw a Thread.Abort exception which gets caught by the application's unhandled exception handler.

Thread.Abort is being called on the main UI thread. That is the source of the exception. It is probably happening because there is a race between calling Dispose (via the using construct) in the UI thread and the ProgressWaitDialog exiting out of its ShowDialog method on its own presumably after Close was called from elsewhere in the code.

The user can close the progress dialog but the main window carries on loading anyway.

The progress dialog can be closed without affecting the main window because it is running on separate thread.

I advise against running that ProgressWaitDialog on another thread which, by the way, is only working half-way correctly because ShowDialog pumps messages. Using more than one UI thread is tricky and causes a lot of weird problems some of which you are already observing.

You really need to reconsider how that long operation on the UI thread is taking place. If it involves loading data from database, doing a bunch calculation, or otherwise does not need to touch any UI controls then that part can be executed in a worker thread. If this long operation is doing a lot of UI manipulation then you need to defer some of that to a later time. For example, if your window is populating a grid with 10,000 records then change it so that it loads only 100 at a time and implement some kind of paging strategy to load the next batch only after a user clicks a button or whatever.

Answer 2

This is clean and attractive way of showing a user your form is loading.

var splashScreen = 
    new SplashScreen(System.Reflection.Assembly.GetExecutingAssembly(),
    @"Resources\MyAppsLogo.png");
splashScreen.Show(true);