如何在RichTextBox中设置一行的MaxLength？

Question

I wonder if there's anyway i can set a maximum number of characters for a line in a RichTextBox. I know I can set a general MaxLength for the whole Box, but not for the line itself.

• I was thinking that the only solution, or at least a viable one, would be to select the line in a TextRange, count the chars and check if it's greater than the max number I manually set. Then, create a new line with:

   myRichTextBox.AppendText(Environment.NewLine); 

  and also set the caret position to the end of the selection with something similar to that:

   myRichTextBox.CaretPosition = myRichTextBox.Selection.End; 

Would that be the best approach for my problem, or is there an simpler way to do that?

Answer 1

您可以设置一个按键事件，在触发该事件时，验证按键和所需的长度，并在需要时附加Environment.NewLine。

Answer 2

This is a tricky one I think and his code can pretty much do the trick:

private void myRichTextBox_TextChanged(object sender, EventArgs e)
{
    int maxLen = 10;
    int CursorIndex = myRichTextBox.SelectionStart;



    var text = myRichTextBox.Text;

    int startIndex = text.Substring(0, CursorIndex).LastIndexOf("\n") + 1;
    int endIndex = text.IndexOf("\n", CursorIndex, text.Length - CursorIndex);

    // if (startIndex < 0) startIndex = 0;
    if (endIndex < 0) endIndex = text.Length;


    string line = text.Substring(startIndex, endIndex - startIndex).Trim();

    if (line.Length > maxLen)
    {
        int insertionPoint = startIndex + maxLen;
        text = text.Insert(insertionPoint, "\n");
        CursorIndex += (insertionPoint < CursorIndex) ? 1 : 0;
        myRichTextBox.Text = text;
        myRichTextBox.SelectionStart = CursorIndex;
    }

}

however I think there should be a better way to do this.