Question

I have a Winforms Application with a TabStrip Control. During runtime, UserControls are to be loaded into different tabs dynamically.

I want to present a “User Control xyz is loading” message to the user (setting an existing label to visible and changing its text) before the UserControl is loaded and until the loading is completely finished.

My approaches so far:

1. Trying to load the User Control in a BackgroundWorker thread. This fails, because I have to access Gui-Controls during the load of the UserControl
2. Trying to show the message in a BackgroundWorker thread. This obviously fails because the BackgroundWorker thread is not the UI thread 😉
3. Show the Message, call DoEvents(), load the UserControl. This leads to different behaviour (flickering, …) everytime I load a UserControl, and I can not control when and how to set it to invisible again.

To sum it up, I have two questions:

1. How to ensure the message is visible directly, before loading the User control
2. How to ensure the message is set to invisible again, just in the moment the UserControl is completely loaded (including all DataBindings, grid formattings, etc.)

Answer 1

what we use is similar to this:

1. create a new form that has whatever you want to show the user,
2. implement a static method where you can call this form to be created inside itself, to prevent memory leaks
3. create a new thread within this form so that form is running in a seperated thread and stays responsive; we use an ajax control that shows a progress bar filling up.

within the method you use to start the thread set its properties to topmost true to ensure it stays on top.

for instance do this in your main form:

loadingForm.ShowLoadingScreen("usercontrollname");
//do something
loadingform.CloseLoadingScreen();

in the loading form class;

public LoadingScreen()
{
  InitializeComponent();
}

public static void ShowLoadingScreen(string usercontrollname)
{
  // do something with the usercontroll name if desired
  if (_LoadingScreenThread == null)
  {
    _LoadingScreenThread = new Thread(new ThreadStart(DoShowLoadingScreen));
    _LoadingScreenThread.IsBackground = true;
    _LoadingScreenThread.Start();
  }
}

public static void CloseLoadingScreen()
{
  if (_ls.InvokeRequired)
  {
    _ls.Invoke(new MethodInvoker(CloseLoadingScreen));
  }
  else
  {
    Application.ExitThread();
    _ls.Dispose();
    _LoadingScreenThread = null;
  }
}

private static void DoShowLoadingScreen()
{
    _ls = new LoadingScreen();
    _ls.FormBorderStyle = FormBorderStyle.None;
    _ls.MinimizeBox = false;
    _ls.ControlBox = false;
    _ls.MaximizeBox = false;
    _ls.TopMost = true;
    _ls.StartPosition = FormStartPosition.CenterScreen;

  Application.Run(_ls);
}