不在UI线程上时的CreateParams

Question

I am trying to prevent the flickering when loading forms. I am loading a form through a new thread and then invoke back to UI. But since I am creating the form on the non UI thread, the override (CreateParams) is not working as intended. Works flawlessly when I create it on the UI thread. How can I make it that it overrides when its back on the UI thread?

// How the loading is done, from UI thread
Thread GetPage = new Thread(() => LoadPage<T>(panel));

public static void LoadPage<T>(Panel Panel)
{ 
  Form form = Activator.CreateInstance(typeof(T)) as Form;

  // Now invoke to UI
   Panel.Invoke((MethodInvoker)delegate
   {
       form.TopLevel = false;
       form.AutoScroll = true;
       Panel.Controls.Add(form);
       form.Show();
   }
}

// Example of a form

public partial class Start : Form
{
    protected override CreateParams CreateParams { get { CreateParams cp =     
             base.CreateParams; cp.ExStyle |= 0x02000000; return cp; } }

    public Start()
    {
    }
 }

Answer 1

It ought to be little obvious that it doesn't have anything to do with threading, considering that you are properly invoking to the UI thread. The value that CreateParams returns does in fact only get used when the native window is created. Which happens at the Controls.Add() call, which runs on the UI thread. Nothing wrong with that aspect of the code. And required, you'll crash the program if you try to set the parent of a window created on the wrong thread.

The real problem is the WS_EX_COMPOSITED style flag you are using. Compositing is only supported for top-level windows. The Form class in Winforms. But you defeated it by setting the TopLevel property to false . The style flag simply stops having an effect, there's no alternative for this for a client window. You'll need to move it to the parent Form that contains this child window.

Answer 2

Don't do this. WinForms controls must be created on the thread on which they'll be used, and they must be used from the thread that created them (the only exceptions being InvokeRequired , Invoke , BeginInvoke and EndInvoke ). Failure to follow these basic rules will result in failures.