c# RTB - paste plain text without colours/fonts?

Question

I am using Rich Text object in my C# application. The only issue I am having is that when user pastes formated text from another app, it remains formated which I cannot have. Is

Answer 1

I was searching for a plaintext-only richtextbox but haven't found the solution online.

Why Plaintext-only RichTextBox instead of a TextBox? For example because RichTextBox has usable undo/redo functionality and much more.

Finally I found a perfect solution by digging into the C header files of the richedit control: A RichTextBox can be switched into plaintext mode, after that it doesn't accept formatted text and images and similar things from the clipboard and behaves like a normal TextBox formattingwise. Fancy things like images can not be pasted and it pastes formatted text by removing the formatting.

class PlainRichTextBox : RichTextBox
{
    const int WM_USER = 0x400;
    const int EM_SETTEXTMODE = WM_USER + 89;
    const int EM_GETTEXTMODE = WM_USER + 90;

    // EM_SETTEXTMODE/EM_GETTEXTMODE flags
    const int TM_PLAINTEXT = 1;
    const int TM_RICHTEXT = 2;          // Default behavior 
    const int TM_SINGLELEVELUNDO = 4;
    const int TM_MULTILEVELUNDO = 8;    // Default behavior 
    const int TM_SINGLECODEPAGE = 16;
    const int TM_MULTICODEPAGE = 32;    // Default behavior 

    [DllImport("user32.dll")]
    static extern IntPtr SendMessage(IntPtr hWnd, int wMsg, IntPtr wParam, IntPtr lParam);

    bool m_PlainTextMode;

    // If this property doesn't work for you from the designer for some reason
    // (for example framework version...) then set this property from outside
    // the designer then uncomment the Browsable and DesignerSerializationVisibility
    // attributes and set the Property from your component initializer code
    // that runs after the designer's code.
    [DefaultValue(false)]
    //[Browsable(false)]
    //[DesignerSerializationVisibility(DesignerSerializationVisibility.Hidden)]
    public bool PlainTextMode
    {
        get
        {
            return m_PlainTextMode;
        }
        set
        {
            m_PlainTextMode = value;
            if (IsHandleCreated)
            {
                IntPtr mode = value ? (IntPtr)TM_PLAINTEXT : (IntPtr)TM_RICHTEXT;
                SendMessage(Handle, EM_SETTEXTMODE, mode, IntPtr.Zero);
            }
        }
    }

    protected override void OnHandleCreated(EventArgs e)
    {
        // For some reason it worked for me only if I manipulated the created
        // handle before calling the base method.
        PlainTextMode = m_PlainTextMode;
        base.OnHandleCreated(e);
    }
}