Event when a window gets maximized/un-maximized

Question

Is there an event that is fired when you maximize a Form or un-maximize it?

Before you say Resize or SizeChanged: Those get only fired if t

Answer 1

A complete solution with maximize, minimize, restore and correct remove of the lower bits which are used for internal purposes only.

protected override void WndProc(ref Message m)
{
    const int WM_SYSCOMMAND = 0x0112;
    const int SC_MAXIMIZE = 0xF030;
    const int SC_MINIMIZE = 0xF020;
    const int SC_RESTORE = 0xF120;

    // dependig on the needs may be called before, after or even never (see below)
    // base.WndProc(ref m);

    if (m.Msg == WM_SYSCOMMAND)
    {
        /// <see cref="https://docs.microsoft.com/en-us/windows/win32/menurc/wm-syscommand"/>
        /// Quote:
        /// In WM_SYSCOMMAND messages, the four low - order bits of the wParam parameter 
        /// are used internally by the system.To obtain the correct result when testing 
        /// the value of wParam, an application must combine the value 0xFFF0 with the 
        /// wParam value by using the bitwise AND operator.
        int wParam = (m.WParam.ToInt32() & 0xFFF0);

        Debug.WriteLine($"Received param: { Convert.ToString(wParam, 16) } ");

        if (wParam == SC_MAXIMIZE)
        {

        }

        if (wParam == SC_MINIMIZE)
        {

        }

        if (wParam == SC_RESTORE)
        {

        }
    }

    // don't use when above call is uncommented
    base.WndProc(ref m);
}

Answer 2

Suprising that no one mentioned the inbuilt .NET method.

This way you don't need to override the Window Message Processing handler.

It even captures maximize/restore events caused by double-clicking the window titlebar, which the WndProc method does not.

Copy this in and link it to the "Resize" event handler on the form.

    FormWindowState LastWindowState = FormWindowState.Minimized;
    private void Form1_Resize(object sender, EventArgs e) {

        // When window state changes
        if (WindowState != LastWindowState) {
            LastWindowState = WindowState;


            if (WindowState == FormWindowState.Maximized) {

                // Maximized!
            }
            if (WindowState == FormWindowState.Normal) {

                // Restored!
            }
        }

    }

Answer 3

Another little addition in order to check for the restore to the original dimension and position after the maximization:

protected override void WndProc(ref Message m)
{
    base.WndProc(ref m);

    // WM_SYSCOMMAND
    if (m.Msg == 0x0112)
    {
        if (m.WParam == new IntPtr(0xF030) // Maximize event - SC_MAXIMIZE from Winuser.h
            || m.WParam == new IntPtr(0xF120)) // Restore event - SC_RESTORE from Winuser.h
        {
            UpdateYourUI();
        }
    }
}

Hope this help.

Answer 4

' Great tip. So if it helps to VisualBasic In Code
Private Const WM_SYSCOMMAND As Integer = &H112
Private Const SC_MAXIMIZE As Integer = &HF030
' # WndProcess 루프함수
Protected Overrides Sub WndProc(ByRef m As Message)
    If m.Msg.Equals(WM_SYSCOMMAND) Then
        If (m.WParam.ToInt32.Equals(SC_MAXIMIZE)) Then
            Me.p_FullScreen()
            Return
        End If
    End If

    MyBase.WndProc(m)
End Sub

Answer 5

I believe the code is even simpler than that. You don't need to save the lastState because the WindowState is checked anytime when the event is fired.

 private void MainForm_Resize(object sender, EventArgs e)
    {
        if (WindowState == FormWindowState.Maximized)
        {
            spContainer.SplitterDistance = 1000;
        }
        if (WindowState == FormWindowState.Normal)
            spContainer.SplitterDistance = 500;
    }

Answer 6

I'm a newbie here so comments not allowed, but this IS a comment to the clean answer by GeoTarget:

The first line OUGHT to be slightly changed to nullable, to catch if the form is started Minimized:

FormWindowState? LastWindowState = null;

And a banal suggestion: Move the assignment of LastWindowState to after the "if"s, so the user can easily check not only what you go to, but also what it came from:

FormWindowState? LastWindowState = null;
private void Form1_Resize(object sender, EventArgs e) {
    // When window state changes
    if (WindowState != LastWindowState) {
        if (WindowState == FormWindowState.Maximized) {
            // Maximized!
        }
        if (WindowState == FormWindowState.Normal) {
            // Restored!
        }
        LastWindowState = WindowState;
    }
}