While working on a software project, I have found I needed a RichTextBox in C# WinForms, that is capable of paragraph spacing. Sadly, all the forums I visited were saying it is “impossible” or “too difficult”. Well … it appears, that there is a lot of hidden capabilities, that RichTextBox does not expose. After some fiddling, I ended with a viable solution, which appears to be very simple. The complete custom control code is below. Enjoy and happy coding!
Custom control
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using System;
using System.Collections.Generic;
using System.Linq;
using System.Runtime.InteropServices;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
namespace ExtendedRTF
{
class RichTextBoxWithParagraphSpacing : RichTextBox
{
private const int PFM_SPACEBEFORE = 64;
private const int PFM_SPACEAFTER = 128;
private const int EM_SETPARAFORMAT = 1095;
private const int SCF_SELECTION = 1;
public int SelectionParagraphSpacingAfter
{
set
{
PARAFORMAT fmt = new PARAFORMAT();
fmt.cbSize = Marshal.SizeOf(fmt);
fmt.dwMask = PFM_SPACEAFTER;
fmt.dySpaceAfter = value;
SendMessage(new HandleRef(this, this.Handle),
EM_SETPARAFORMAT,
SCF_SELECTION,
ref fmt
);
}
}
public int SelectionParagraphSpacingBefore
{
set
{
PARAFORMAT fmt = new PARAFORMAT();
fmt.cbSize = Marshal.SizeOf(fmt);
fmt.dwMask = PFM_SPACEBEFORE;
fmt.dySpaceBefore = value;
SendMessage(new HandleRef(this, this.Handle),
EM_SETPARAFORMAT,
SCF_SELECTION,
ref fmt
);
}
}
[StructLayout(LayoutKind.Sequential)]
private struct PARAFORMAT
{
public int cbSize;
public uint dwMask;
public short wNumbering;
public short wReserved;
public int dxStartIndent;
public int dxRightIndent;
public int dxOffset;
public short wAlignment;
public short cTabCount;
[MarshalAs(UnmanagedType.ByValArray, SizeConst = 32)]
public int[] rgxTabs;
// PARAFORMAT2 from here onwards.
public int dySpaceBefore;
public int dySpaceAfter;
public int dyLineSpacing;
public short sStyle;
public byte bLineSpacingRule;
public byte bOutlineLevel;
public short wShadingWeight;
public short wShadingStyle;
public short wNumberingStart;
public short wNumberingStyle;
public short wNumberingTab;
public short wBorderSpace;
public short wBorderWidth;
public short wBorders;
}
[DllImport("user32", CharSet = CharSet.Auto)]
private static extern int SendMessage(HandleRef hWnd,
int msg,
int wParam,
ref PARAFORMAT lp);
}
}
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How to use it in your project
Tip: in order to make the spaces really visible, you will need to set values in orders of hundreds, e.g. 250.
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RichTextBoxWithParagraphSpacing rtb = new RichTextBoxWithParagraphSpacing();
rtb.Location = new Point(0, 0);
rtb.Text = "First paragraph\r\nSecond paragraph";
rtb.SelectionParagraphSpacingBefore = 100;
rtb.SelectionParagraphSpacingAfter = 300;
this.Controls.Add(rtb);
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The following links may be of interest: