Putting a winform in front of another app window progmtcally

Alessandro Ranieri

Hello to everyone.

I'm looking for a solution to the following problem and i hope someone have any good tips for me:

I have inherited a legacy application, written in C with WinAPI, that draws a 2d animation inside a window on the screen. Now I have to develop (in C#) another application that simply draws some winforms with several buttons that have to be ALWAYS in front of the legacy window, i.e. if a user click on the window of the legacy application, my winforms have to remain foreground. I would avoid to modify the legacy application, and I would act only on the new application written in C#. The "topmost" option is only the very last chance.

Thanks in advance for each contribution!

4 Replies

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Vulpes12y ago
I've just thought of an easy way to close the managed form when the legacy window closes.

All we need to do is to handle the Process_Exited event and call: this.Close() from the handler.

Here's the revised code:

public partial class Form1 : Form
{
const int GWL_HWNDPARENT = -8;

[DllImport("user32.dll")]
static extern int SetWindowLong(IntPtr hWnd, int nIndex, IntPtr dwNewLong);

public Form1()
{
InitializeComponent();
}

private void Form1_Load(object sender, EventArgs e)
{
Process[] procs = Process.GetProcessesByName("legacyappname");

if (procs.Length > 0)
{
IntPtr hWnd = procs[0].MainWindowHandle;
procs[0].EnableRaisingEvents = true;
procs[0].Exited += Process_Exited;
SetWindowLong(this.Handle, GWL_HWNDPARENT, hWnd);
}
}

private void Process_Exited(object sender, EventArgs e)
{
// need to marshal back to UI thread as eventhandler called on a separate thread
this.BeginInvoke((Action)(() =>
{
this.Close();
}));
}

// rest of code
}

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Alessandro Ranieri12y ago
Thank you Vulpes. It suits perfectly to what I intended to do! I also will try to find a solution to the missed closure of the managed window, that would be useful to avoid to the managed window to become orphan. I'll post here if I found a solution/workaround.
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Vulpes12y ago
One thing you could try is setting the 'owner' of the managed form to the legacy window.

This will ensure that the managed form is never shown behind the legacy window.

Normally, it would also ensure that when the legacy window is minimized or closed, then the managed form would be minimized or closed as well. However, when the legacy window was closed the managed form remained open when I tried the following code and I haven't been able to find a workaround for that so far:

using System.Diagnostics;
using System.Runtime.InteropServices;

// ....

public partial class Form1 : Form
{
const int GWL_HWNDPARENT = -8;

[DllImport("user32.dll")]
static extern int SetWindowLong(IntPtr hWnd, int nIndex, IntPtr dwNewLong);

public Form1()
{
InitializeComponent();
}

private void Form1_Load(object sender, EventArgs e)
{
Process[] procs = Process.GetProcessesByName("legacyappname");

if (procs.Length > 0)
{
IntPtr hWnd = procs[0].MainWindowHandle;
SetWindowLong(this.Handle, GWL_HWNDPARENT, hWnd);
}
}

// rest of code
}

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R J12y ago
Set the form's .TopMost property to true.

You probably don't want to leave it this way all the time: set it when your external process starts and put it back when it finishes.

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