Why is my form being resized when it is displayed?

Question

I have a form that appears as a modal dialog. The form looks like this in the designer:

(width = 360, height = 215)

When it is shown in the application, it gets 10 pixels taller and wider than is defined, leaving a wide margin around the bottom and left edges:

(width = 370, height = 225)

The form is explicitly set to be 360x215 pixels in dimension, has a border style of FixedDialog, inherits from System.Windows.Forms.Form, and has no code in it to manipulate the dimensions (with the exception of the auto-generated designer file). If I change the border style to FixedSingle or FixedToolWindow it appears the correct size (but I want it styled as FixedDialog).

Any idea what is causing this?

---

I've fixed this by removing the MinimumSize setting on the form. It appears that if it is set to the same size (or near, but I haven't quite found the threshold yet) as the Size property, the margins are introduced. As the form is not resizable, I don't need the MinimumSize set so it can be removed.

I still don't understand why this is the case though.

Answer 1

Why don't you brute force the issue with the code:

protected override void SetClientSizeCore(int x, int y)
{
    base.SetClientSizeCore(360, 215);
}

which sets the client area. You need to calculate what values you want.

Answer 2

First, your form seems to have AutoScaleMode set to Font. This causes a form resize depending on the used font.

Second, ensure to have the following lines before creating the main form:

Application.EnableVisualStyles();
Application.SetCompatibleTextRenderingDefault(false);  // Not using this - or using true - will cause a different font rendering
...
Application.Run(new Form1());                          // this creates your main form

(Usually this is part of the static Main method in Program.cs)

Not using those lines causes the usage of a different font rendering (have a look at your screenshots - the letters don't look exacly identical!)