Setting WPF RichTextBox width and height according to the size of a monospace font

Question

I am trying to fit a WPF RichTextBox to exactly accommodate a grid of characters in a particular monospace font. I am currently using FormattedText to determine the width and height of my RichTextBox, but the measurements it is providing me with are too small--specifically two characters in width too small.

Is there a better way to perform this task? This does not seem to be an appropriate way to determine the size of my control.

RichTextBox rtb;
rtb = new RichTextBox();
FontFamily fontFamily = new FontFamily("Consolas");
double fontSize = 16;
char standardizationCharacter = 'X';
String standardizationLine = "";
for(long loop = 0; loop < columns; loop ++) {
    standardizationLine += standardizationCharacter;
}
standardizationLine += Environment.NewLine;
String standardizationString = "";
for(long loop = 0; loop < rows; loop ++) {
    standardizationString += standardizationLine;
}
Typeface typeface = new Typeface(fontFamily, FontStyles.Normal, FontWeights.Normal, FontStretches.Normal);
FormattedText formattedText = new FormattedText(standardizationString, CultureInfo.CurrentCulture, FlowDirection.LeftToRight, typeface, fontSize, Brushes.Black);
rtb.Width = formattedText.Width;
rtb.Height = formattedText.Height;

Answer 1

Assuming you have a very basic RichTextBox with just the standard FlowDocument inside it then you have to take into account all of the extra layout RichTextBox uses.

The Document.PagePadding property defaults to {5,0,5,0}. So you will have to add 10 to the width.

Additionally the RichTextBox has a BorderThickness that defaults to {1, 1, 1, 1}. So you will have to add 2 to the width.

So the code you want could look like:

var pagePadding = rtb.Document.PagePadding;
var borderThickness = rtb.BorderThickness;
rtb.Width = formattedText.Width
    + pagePadding.Left + pagePadding.Right 
    + borderThickness.Left + borderThickness.Right;

If you do that you will still be off by 1 character, but that's a bit misleading. The RichTextBox will wrap even if the text is just a tiny bit to wide not just a whole character width. If you add 2 to the width it works out. I can't figure out exactly where that extra 2 is coming from. I've never tried to get the width to be so exact. I have run into the PagePadding and BorderThickness issues before, but I just can't find the extra 2. It might just be a constant you are stuck with, but I doubt it. It's got to be somewhere.

A small tip on producing the StandardizationLine you can do

string StandardizationLine = new string('X', columns);

to clean up the loop.

Answer 2

I found a solution for the Rich text box height issues.. i have modified it a for general use..

Create following structs in your application....

[StructLayout(LayoutKind.Sequential)]
    public struct RECT {
        public Int32 left;
        public Int32 top;
        public Int32 right;
        public Int32 bottom;
    }

    [StructLayout(LayoutKind.Sequential)]
    public struct SCROLLBARINFO {
        public Int32 cbSize;
        public RECT rcScrollBar;
        public Int32 dxyLineButton;
        public Int32 xyThumbTop;
        public Int32 xyThumbBottom;
        public Int32 reserved;
        [MarshalAs(UnmanagedType.ByValArray, SizeConst = 6)]
        public Int32[] rgstate;
    }

Create following private variables in your class for form (where ever you need to calculate rich text height)

private UInt32 SB_VERT = 1;
        private UInt32 OBJID_VSCROLL = 0xFFFFFFFB;

        [DllImport("user32.dll")]
        private static extern
            Int32 GetScrollRange(IntPtr hWnd, UInt32 nBar, out Int32 lpMinPos, out Int32 lpMaxPos);

        [DllImport("user32.dll")]
        private static extern
            Int32 GetScrollBarInfo(IntPtr hWnd, UInt32 idObject, ref SCROLLBARINFO psbi);

Add following method to your Class for form

private int CalculateRichTextHeight(string richText) {
            int height = 0;
            RichTextBox richTextBox = new RichTextBox();
            richTextBox.Rtf = richText;
            richTextBox.Height = this.Bounds.Height;
            richTextBox.Width = this.Bounds.Width;
            richTextBox.WordWrap = false;
            int nHeight = 0;
            int nMin = 0, nMax = 0;

            SCROLLBARINFO psbi = new SCROLLBARINFO();
            psbi.cbSize = Marshal.SizeOf(psbi);

            richTextBox.Height = 10;
            richTextBox.ScrollBars = RichTextBoxScrollBars.Vertical;

            int nResult = GetScrollBarInfo(richTextBox.Handle, OBJID_VSCROLL, ref psbi);
            if (psbi.rgstate[0] == 0) {
                GetScrollRange(richTextBox.Handle, SB_VERT, out nMin, out nMax);
                height = (nMax - nMin);
            }

            return height;
        }

You may need to modify above method to make it work as per your requirement... Make sure to send Rtf string as parameter to method not normal text and also make sure to assign available width and height to the Richtextbox variable in the method...

You can play with WordWrap depending on your requirement...