Manually add user defined maximize button except system defined form property button on top of the Windows Form using c#

Let me add to OriginalGriff's and Orcun's wise answers, that ... if font-scaling in response to form re-size is NOT an issue ... then you can exploit the Anchor or Dock properties of Controls so their size will change as the Form size changes.

You can also, by use of Margin, and Padding properties, control the spacing between a Control and its "container," and the distances between Controls, but please note that Dock will over-ride Margin and Padding property settings.

best, Bill

About the Button: let me ask you:

1. is the reason you want a customized Button to switch between two sizes because you are using a Form whose 'FormBorderStyle property is set to 'none:

Or:

You are using a Form whose 'FormBorderStyle property is set to 'FixedToolWindow and its 'Text property is not set: in which case, Maximize and Minimize Buttons will not appear in the TitleBar: whether or not you have them "on" in the design-time UI.

Or:

You just do not wish the standard WinForms Window TitleBar adornments to appear ?

2. Do you realize that by using the design-time MaximumSize and MinimumSize design-time Properties of a WinForm you can control the resizing triggered by using the standard TitleBar adornments ?

3. Do you realize you could, via code, use the standard adornments, and by creating an EventHandler for the Form SizeChanged Event, you could detect and change the ultimate size setting : note: I would NOT recommend this approach for several reasons, including the need to prevent recursion.

... okay ... now: let's assume, for whatever reason, the standard Minimize/Maximize thing is not used ...

4. is there a reason why you don't wish to have two buttons, one to Minimize, and one to Maximize: note: I am not saying that you should have two buttons.

5. is it an absolute requirement that your (assume single) Button-whatever looks exactly like the standard one ?

~

Whatever you choose to use as your Custom Control to switch back and forth between two Window Sizes ... you could use a Button, a Label, a PictureBox, maybe even, perhaps, an Icon:

You are going to end up with some code that may work like this example:

... edit Jan. 22nd. changed code to use a boolean flag to switch states ...

// you'll need to set proper values for the 'original' character in the Button
// and the Form Size somewhere: either at Design-Time ... 
// or, in code, in an EventHandler like: Form Load, or Form Shown

private Size MinSize = new Size(784, 517);
private Size MaxSize = new Size(784, 593);
private bool IsSizeMax = true;

private void CustomMaxMinButton_Click_1(object sender, EventArgs e)
{
    // negate the boolean value here
    IsSizeMax = ! IsSizeMax;

    if (IsSizeMax)
    {
        // using 0xA3 to represent minimize
        CustomMaxMinButton.Text = "£";
        this.Size = MaxSize;
    }
    else
    {
        // using 0xB3 to represent maximize
        CustomMaxMinButton.Text = "³";
        this.Size = MinSize;
    }
}

In this example, I took the "easy way out," and just used a Button which:

1. has AutoSize set to 'false

2. has the Font set to the Symbol font, at 12 points size or so.

3. has its Anchor property set to Top and Right: that's really not a concern here if you make the Form not re-sizable is it ?

4. I used this in a Form with its FormBorderStyle set to 'FixedToolWindow, and "empty" Text: I left the 'ControlBox adornment visible, so the user has a the standard 'Close Button available.

Since this is not a "real pretty" solution: if I wanted to make it better looking, I'd probably be swapping two graphic images in and out of a PictureBox or even a Button's 'BackGroundImage Property ... rather than doing what's shown here.

That is not necessarily easy to do, particularly if you expect the controls and so forth to resize in a nice way so it all looks good. Winforms is not really very good at that kind of thing - fonts do not scale automatically when buttons grow and shrink, and so forth. If you really need that kind of feature, you need to move to WPF - otherwise pick a useful size and stick with it, or go to a plan like VS with dockable control holders surrounding a central area the central area expands and contracts, the controls and their holders remain the same size.