How do I make a WinForms app go Full Screen

To the base question, the following will do the trick (hiding the taskbar)

private void Form1_Load(object sender, EventArgs e)
{
    this.TopMost = true;
    this.FormBorderStyle = FormBorderStyle.None;
    this.WindowState = FormWindowState.Maximized;
}

But, interestingly, if you swap those last two lines the Taskbar remains visible. I think the sequence of these actions will be hard to control with the properties window.

And for the menustrip-question, try set

MenuStrip1.Parent = Nothing

when in fullscreen mode, it should then disapear.

And when exiting fullscreenmode, reset the menustrip1.parent to the form again and the menustrip will be normal again.

I recently made a Mediaplayer application and I used API calls to make sure the taskbar was hidden when the program was running fullscreen and then restored the taskbar when the program was not in fullscreen or not had the focus or was exited.

Private Declare Function FindWindow Lib "user32" Alias "FindWindowA" (ByVal lpClassName As String, ByVal lpWindowName As String) As Integer
Private Declare Function FindWindowEx Lib "user32" Alias "FindWindowExA" (ByVal hWnd1 As Integer, ByVal hWnd2 As Integer, ByVal lpsz1 As String, ByVal lpsz2 As String) As Integer
Private Declare Function ShowWindow Lib "user32" (ByVal hwnd As Integer, ByVal nCmdShow As Integer) As Integer

Sub HideTrayBar()
    Try


        Dim tWnd As Integer = 0
        Dim bWnd As Integer = 0
        tWnd = FindWindow("Shell_TrayWnd", vbNullString)
        bWnd = FindWindowEx(tWnd, bWnd, "BUTTON", vbNullString)
        ShowWindow(tWnd, 0)
        ShowWindow(bWnd, 0)
    Catch ex As Exception
        'Error hiding the taskbar, do what you want here..'
    End Try
End Sub
Sub ShowTraybar()
    Try
        Dim tWnd As Integer = 0
        Dim bWnd As Integer = 0
        tWnd = FindWindow("Shell_TrayWnd", vbNullString)
        bWnd = FindWindowEx(tWnd, bWnd, "BUTTON", vbNullString)
        ShowWindow(bWnd, 1)
        ShowWindow(tWnd, 1)
    Catch ex As Exception
        'Error showing the taskbar, do what you want here..'
    End Try


End Sub

I worked on Zingd idea and made it simpler to use.

I also added the standard F11 key to toggle fullscreen mode.

Setup

Everything is now in the FullScreen class, so you don't have to declare a bunch of variables in your Form. You just instanciate a FullScreen object in your form's constructor :

FullScreen fullScreen;

public Form1()
{
    InitializeComponent();
    fullScreen = new FullScreen(this);
}

Please note this assumes the form is not maximized when you create the FullScreen object.

Usage

You just use one of the classe's functions to toggle the fullscreen mode :

fullScreen.Toggle();

or if you need to handle it explicitly :

fullScreen.Enter();
fullScreen.Leave();

Code

using System.Windows.Forms;


class FullScreen
{ 
    Form TargetForm;

    FormWindowState PreviousWindowState;

    public FullScreen(Form targetForm)
    {
        TargetForm = targetForm;
        TargetForm.KeyPreview = true;
        TargetForm.KeyDown += TargetForm_KeyDown;
    }

    private void TargetForm_KeyDown(object sender, KeyEventArgs e)
    {
        if (e.KeyData == Keys.F11)
        {
            Toggle();
        }
    }

    public void Toggle()
    {
        if (TargetForm.WindowState == FormWindowState.Maximized)
        {
            Leave();
        }
        else
        {
            Enter();
        }
    }
        
    public void Enter()
    {
        if (TargetForm.WindowState != FormWindowState.Maximized)
        {
            PreviousWindowState = TargetForm.WindowState;
            TargetForm.WindowState = FormWindowState.Normal;
            TargetForm.FormBorderStyle = FormBorderStyle.None;
            TargetForm.WindowState = FormWindowState.Maximized;
        }
    }
      
    public void Leave()
    {
        TargetForm.FormBorderStyle = FormBorderStyle.Sizable;
        TargetForm.WindowState = PreviousWindowState;
    }
}

You need to set your window to be topmost.

On the Form Move Event add this:

private void Frm_Move (object sender, EventArgs e)
{
    Top = 0; Left = 0;
    Size = new System.Drawing.Size(Screen.PrimaryScreen.Bounds.Width, Screen.PrimaryScreen.Bounds.Height);
}

If you want to keep the border of the form and have it cover the task bar, use the following:

Set FormBoarderStyle to either FixedSingle or Fixed3D

Set MaximizeBox to False

Set WindowState to Maximized