UI线程/调度程序问题（BeginInvoke）

Question

In a previous question I asked how to get access to UI elements in a callback thread. I got a lot of good answers, one of which was to implement a wrapper class such as this:

public static class UIThread
{
    private static readonly Dispatcher Dispatcher;

    static UIThread()
    {
        Dispatcher = Deployment.Current.Dispatcher;
    }

    public static void Invoke(Action action)
    {
        if (Dispatcher.CheckAccess())
        {
            action.Invoke();
        }
        else
        {
            Dispatcher.BeginInvoke(action);
        }
    }
}

And you can call this using

UIThread.Invoke(() => TwitterPost.Text = "hello there");

However I tried extending this by calling the following in my callback function

UIThread.Invoke(() => loadUserController(jsonObject));

with the following method:

private void loadUserController(JObject jsonObject)
{
    string profile_image_url = (string)jsonObject["profile_image_url"];
    string screen_name = (string)jsonObject["screen_name"];
    string name = (string)jsonObject["name"];
    string location = (string)jsonObject["location"];
    int statuses_count = (int)jsonObject["statuses_count"];

    if (!string.IsNullOrEmpty(profile_image_url))
    {
        ProfileImage.Source = new BitmapImage(new Uri("blahblahbalhb.jpg", UriKind.Absolute));
    }

    // Set the screen name and display name if it differs
    if (!string.IsNullOrEmpty(name) && !string.IsNullOrEmpty(screen_name))
    {
        ScreenName.Text = screen_name;

        if (!screen_name.Equals(name))
        {
            _Name.Text = name;
        }
    }

    if (!string.IsNullOrEmpty(location))
    {
        Location.Text = location;
    }

    Tweets.Text = statuses_count.ToString() + " Tweets";
}

then the image will not render until another action forces a redraw (clicking a button) but the text controls will be updated. If within my callback function I call setImageFile(string imageFile) which is implemented as:

private void setImageFile(string imageFile)
{
    if (this.Dispatcher.CheckAccess())
    {
        ProfileImage.Source = new BitmapImage(new Uri("fdsfdfdsf.jpg", UriKind.Absolute));
    }
    else
    {
        this.Dispatcher.BeginInvoke(new Action<string>(setImageFile), imageFile);
    }
}

then the image will be rendered immediately. Why is this happening? What properties of the Dispatcher am I not fully understanding?

Answer 1

I strongly recommend that you not do this. SynchronizationObject was designed to handle this kind of scenario, along with AsyncOperation and AsyncOperationManager .

The only disadvantage to SynchronizationObject is that there isn't the ability to test whether the code is already running on the correct thread. That shouldn't be a problem, since business logic code should always be aware of its thread context.