C# - How can I rename a process window that I started?

Question

Is there any way I can rename the window titlebar of an application that I've launched? I.e. if I launched Notepad.exe, I could rename its title bar from "Untitled - Notepad" to "New Notepad Name".

Answer 1

As @Fredrik Mörk thinks, the problem is that there's need to wait for the window to be able to receive messages, before its title can be set. Waiting 100 milliseconds can break the internal message looper of the program and it's just a workaround. To receive a message, the window must have a handle that's used for referencing that window, thus you can simply wait for the window to have a handle, like this:

Process p = Process.Start("notepad.exe");
while (p.MainWindowHandle == IntPtr.Zero)
    Application.DoEvents();
SetWindowText(p.MainWindowHandle, "My Notepad");

Using Application.DoEvents() the program will continue to receive and process system messages, so it won't block (nor crash), although it isn't asynchronous.

You can also think to avoid CPU overhead by replacing the while statement with a SpinWait.SpinUntil call (from System.Threading):

Process p = Process.Start("notepad.exe");
SpinWait.SpinUntil(() => p.MainWindowHandle != IntPtr.Zero);
SetWindowText(p.MainWindowHandle, "My Notepad");

Answer 2

I had to use the following code to get it work:

while (p.MainWindowHandle == IntPtr.Zero)
      Thread.Sleep(100);

Answer 3

I implemented @Davide Cannizo solution and found an issue that is probably also true with other solutions that loop - that the process could have finished before realization that the MainWindowHandle is non-zero. This happened to me when I ran a lot of processes in parallel and one or two were very short-lived. The specific issue was a SystemAggregrationError because the check p.MainWindowHandle != IntPtr.Zero was causing multiple InvalidOperationError's.

The solution was to add a check on whether the process exited. Look for the p.HasExited below.

using System;
using System.Runtime.InteropServices;

class Program
{
  [DllImport("user32.dll")]
  static extern int SetWindowText(IntPtr hWnd, string text);

  static void Main(string[] args)
  {
    using (System.Diagnostics.Process p = new System.Diagnostics.Process())
    {
      p.StartInfo = new System.Diagnostics.ProcessStartInfo()
      {
        FileName = @"notepad.exe",
        Arguments = @""
      };

      string window_title = "notepad demo";
      p.Start();
      System.Threading.SpinWait.SpinUntil(() => p.HasExited || p.MainWindowHandle != IntPtr.Zero);
      if (!p.HasExited)
        SetWindowText(p.MainWindowHandle, window_title);
      p.WaitForExit();
    }
  }
}

Two other things to note:

• in developing this, I first tried to use .NET Core. That failed - p.MainWindowHandler was always 0. I had to switch to .NET Framework.
• I do not believe that SetWindowText(p.MainWindowHandle, window_title) causes an exception if the process has exited. According to the documentation here, it can fail but will only return 0 instead of a non-zero. That means that if we finish the SpinUntil because the MainWindowHandle is non-zero, but between that point and the SetWindowText the process exited, it will not cause an exception. However, in my testing I did have to add the if (!p.HasExited) line.

Answer 4

No.

This would require that the target application allow the window title to be modified at all. Many programs use their titles to show useful information (such as the name of the file open for editing in Notepad, or the <TITLE> of the HTML document open in Firefox).

The one case I am aware of that lets a user set the title text with few restrictions is CMD.EXE running in a console window. CMD supports the TITLE built-in command that sets the window title based on its arguments. But that can't be done by a second window without injecting key strokes into the particular console window, which is generally not recommended.

Edit:

Since the idea is floating that SetWindowText() will do this for you, let me clarify.

That API function does indeed change the title bar of a top level window. It is, in fact, the call that an application like Notepad is likely using to set its own title any time it thinks that the title has changed.

The reason I claim that this is not a solution is that Notepad does indeed change the title when it wants to. An application that supported arbitrary changes to its title would have a mechanism of some kind to remember that the title was changed and not arbitrarily restore its preferred title string.

Answer 5

You can't do it in C#, but you can do it using low level API. Inject a thread into the process, call SetWindowText() from it

Answer 6

You can do it using P/Invoke:

[DllImport("user32.dll")]
static extern int SetWindowText(IntPtr hWnd, string text);



private void StartMyNotepad()
{
    Process p = Process.Start("notepad.exe");
    Thread.Sleep(100);  // <-- ugly hack
    SetWindowText(p.MainWindowHandle, "My Notepad");
}

The background of the ugly hack in the code sample is that it seems as if you call SetWindowText immediately after starting the process, the title will not change. Perhaps the message ends up too early in the message queue of Notepad, so that notepad will set the title again afterwards.

Also note that this is a very brief change; if the user selects File -> New (or does anything else that will cause Notepad to update the window title), the original title will be back...

Answer 7

Actually, I sorted it myself and it works perfectly. Thanks anyway.

[DllImport("user32.dll")]
static extern SetWindowText(IntPtr hWnd, string windowName);

IntPtr handle = p.MainWindowHandle;
SetWindowText(handle, "This is my new title");