Maximize another process' Window in .NET

Question

I have a handle on another process' main window in .net (proc.MainWindowHandle). How do I maximize the window inside of .net?

Answer 1

You can pinvoke to ShowWindow with SW_SHOWMAXIMIZED to maximize the window.

Pinvoke.net has an entry for ShowWindow here.

For example,

// Pinvoke declaration for ShowWindow
private const int SW_SHOWMAXIMIZED = 3;

[DllImport("user32.dll")]
static extern bool ShowWindow(IntPtr hWnd, int nCmdShow);

// Sample usage
ShowWindow(proc.MainWindowHandle, SW_SHOWMAXIMIZED);

Answer 2

I had some problems with this and finally managed to solve it. In my case I had a WinForm application that needed to maximize or minimize a WPF application.

Firstly, we need to import InteropServices

using System.Runtime.InteropServices;

Then we need methods for the actions that we require:

[DllImport("user32.dll")]
private static extern bool SetWindowPlacement(IntPtr hWnd, [In] ref WINDOWPLACEMENT lpwndpl);

[DllImport("user32.dll")]
[return: MarshalAs(UnmanagedType.Bool)]
static extern bool GetWindowPlacement(IntPtr hWnd, ref WINDOWPLACEMENT lpwndpl);

Next, we can check the process by its name, get its window placement, and then update its window placement:

/// <summary>
/// WINDOWPLACEMENT showCmd - 1 for normal, 2 for minimized, 3 for maximized, 0 for hide 
/// </summary>
public static void MaximizeProcessWindow(string processName)
{ 
    foreach (Process proc in Process.GetProcesses())
    {
        if (proc.ProcessName.Equals(processName))
        {
            try
            { 
                WINDOWPLACEMENT wp = new WINDOWPLACEMENT();
                GetWindowPlacement(proc.MainWindowHandle, ref wp); 

                // Maximize window if it is in a normal state
                // You can also do the reverse by simply checking and setting 
                // the value of wp.showCmd
                if (wp.showCmd == 1)
                {
                    wp.showCmd = 3; 
                } 
                SetWindowPlacement(proc.MainWindowHandle, ref wp);                         
                break;
            }
            catch(Exception ex)
            {
                // log exception here and do something
            }
        }
    }
}

You may also get the process by the window title:

if (proc.MainWindowTitle.Equals(processTitle))

Depending on the process, your application may need to be executed under administrator privileges. This can be done by adding a manifest file and then adding the following administrator privilege:

<requestedExecutionLevel  level="requireAdministrator" uiAccess="false" />

Answer 3

You could also use SetWindowPlacement. There's further info about it on Pinvoke.net.