Application stuck in full screen?

Question

To reproduce my problem please do the following:

1. Create a new Windows Form Application in C#.
2. In the Properties window of Form1 set FormBorderSt

Answer 1

Check this solution - it removes Maximize/Minimize/Titlebar/Border by API calls.

public partial class Form1 : Form
{
    // import necessary API functions to get and set Windows styles for P/Invoke
    [DllImport("user32.dll")]
    internal extern static int SetWindowLong(IntPtr hwnd, int index, int value);

    [DllImport("user32.dll")]
    internal extern static int GetWindowLong(IntPtr hwnd, int index);

    // define constants like they are named in SDK in order to make source more readable
    const int GWL_STYLE = -16;
    const int GWL_EXSTYLE = -20;
    const int WS_MINIMIZEBOX = 0x00020000;
    const int WS_MAXIMIZEBOX = 0x00010000;
    const int WS_CAPTION = 0x00C00000;
    const int WS_THICKFRAME = 0x00040000;
    const int WS_EX_DLGMODALFRAME = 0x00000001;
    const int WS_EX_CLIENTEDGE = 0x00000200;
    const int WS_EX_STATICEDGE = 0x00020000;

    // this replaces MinimizeBox=false and MaximizeBox=false
    void HideMinimizeAndMaximizeButtons()
    {
        // read current style
        int style = GetWindowLong(Handle, GWL_STYLE);
        Debug.WriteLine("0x{0:X}", style);
        // update style - remove flags for MinimizeBox and MaximizeBox
        style = style & ~WS_MINIMIZEBOX & ~WS_MAXIMIZEBOX;
        Debug.WriteLine("0x{0:X}", style);
        SetWindowLong(Handle, GWL_STYLE, style);
    }

    // part of removing the whole border
    void HideTitleBar()
    {
        // read current style
        int style = GetWindowLong(Handle, GWL_STYLE);
        Debug.WriteLine("0x{0:X}", style);
        // update style - remove flag for caption
        style = style & ~WS_CAPTION;
        Debug.WriteLine("0x{0:X}", style);
        SetWindowLong(Handle, GWL_STYLE, style);
    }

    // hide the border
    void HideBorder()
    {
        // read current style
        int style = GetWindowLong(Handle, GWL_STYLE);
        Debug.WriteLine("0x{0:X}", style);
        // update style - remove flag for border (could use WS_SIZEBOX which is the very same flag (see MSDN)
        style = style & ~WS_THICKFRAME;
        Debug.WriteLine("0x{0:X}", style);
        SetWindowLong(Handle, GWL_STYLE, style);

        // read current extended style
        style = GetWindowLong(Handle, GWL_EXSTYLE);
        Debug.WriteLine("0x{0:X}", style);
        // update style by removing some additional border styles -
        // may not be necessary, when current border style is not something exotic,
        // i.e. as long as it "normal"
        style = style & ~WS_EX_DLGMODALFRAME & ~WS_EX_CLIENTEDGE & ~WS_EX_STATICEDGE;
        Debug.WriteLine("0x{0:X}", style);
        SetWindowLong(Handle, GWL_EXSTYLE, style);
    }

    public Form1()
    {
        InitializeComponent();

        // hide those unwanted properties - you can try to leave out one or another to see what it does
        HideMinimizeAndMaximizeButtons();
        HideTitleBar();
        HideBorder();
    }
}

This works as intended. Maximizing/minimizing by setting WindowState works as well.

One could analyze in sources what the framework does and what it does "wrong" (or not quite correct).

Edit: I added debug output of the style values. Please try this sequence of commands in Form1 constructor:

MaximizeBox = false;
FormBorderStyle = FormBorderStyle.Sizable;
HideMinimizeAndMaximizeButtons();
FormBorderStyle = FormBorderStyle.None;
MaximizeBox = true;
MaximizeBox = false;
HideMinimizeAndMaximizeButtons();
FormBorderStyle = FormBorderStyle.None;
HideMinimizeAndMaximizeButtons();

You'll see, that setting FormBorderStyle.None enables the WS_MAXIMIZEBOX style. This cannot be "corrected" by another MaximizeBox = false. It seems it's necessary to call API functions.