Switch to last active application like Alt-Tab

Question

ok, I have found many posts on finding a window by name, etc. What I have not found is how to find and switch the window application focus to last active window. The code I am showing below will give me the list of active applications in the task manager that are active.

What I can not figure out how to do is figure out what application was the last active application, and then switch to it. for example...

I have my custom winform application open.

I click a button

My application switches to the last active window / application.

Here is the working code I have so far. (this is the action on a button, and it expects that the application has a textbox named textbox1. you will also need to add using System.Diagnostics;

    private void button1_Click(object sender, EventArgs e)
    {

        Process[] procs = Process.GetProcesses();
        IntPtr hWnd;
        foreach (Process proc in procs)
        {
            if ((hWnd = proc.MainWindowHandle) != IntPtr.Zero)
            {
                textBox1.Text += (proc.ProcessName.ToString());
                textBox1.Text += "\t";
                textBox1.Text += (hWnd.ToString());
                textBox1.Text += "\r\n";
            }
        }         

    }

Answer 1

Check this article out: http://www.whitebyte.info/programming/how-to-get-main-window-handle-of-the-last-active-window

Specifically, this code:

[DllImport("user32.dll", SetLastError = true)]
static extern IntPtr GetWindow(IntPtr hWnd, uint uCmd);
enum GetWindow_Cmd : uint
{
    GW_HWNDFIRST = 0,
    GW_HWNDLAST = 1,
    GW_HWNDNEXT = 2,
    GW_HWNDPREV = 3,
    GW_OWNER = 4,
    GW_CHILD = 5,
    GW_ENABLEDPOPUP = 6
}
[DllImport("user32.dll", ExactSpelling = true, CharSet = CharSet.Auto)]
public static extern IntPtr GetParent(IntPtr hWnd);
[DllImport("user32.dll")]
[return: MarshalAs(UnmanagedType.Bool)]
static extern bool SetForegroundWindow(IntPtr hWnd);

[...]

IntPtr targetHwnd = GetWindow(Process.GetCurrentProcess().MainWindowHandle, (uint)GetWindow_Cmd.GW_HWNDNEXT);
while (true)
{
    IntPtr temp = GetParent(targetHwnd);
    if (temp.Equals(IntPtr.Zero)) break;
    targetHwnd = temp;
}
SetForegroundWindow(targetHwnd);

Answer 2

Since my comments didn't help you, here's a little resume (didn't test it though):

[DllImport("user32.dll")]
[return: MarshalAs(UnmanagedType.Bool)]
static extern bool IsWindowVisible(IntPtr hWnd);

[DllImport("user32.dll")]
static extern IntPtr GetLastActivePopup(IntPtr hWnd);

[DllImport("user32.dll", ExactSpelling = true)]
static extern IntPtr GetForegroundWindow();

[DllImport("user32.dll")]
[return: MarshalAs(UnmanagedType.Bool)]
static extern bool SetForegroundWindow(IntPtr hWnd);

const uint GA_PARENT = 1;
const uint GA_ROOT = 2;
const uint GA_ROOTOWNER = 3;

public IntPtr GetPreviousWindow()
{
        IntPtr activeAppWindow = GetForegroundWindow();
        if ( activeAppWindow == IntPtr.Zero )
            return IntPtr.Zero;

        IntPtr prevAppWindow = GetLastActivePopup(activeAppWindow);
        return IsWindowVisible(prevAppWindow) ? prevAppWindow : IntPtr.Zero;
 }

 public void FocusToPreviousWindow()
 {
     IntPtr prevWindow = GetPreviousWindow();
     if (  prevWindow != IntPtr.Zero )
         SetForegroundWindow(prevWindow);
 }