C#•2y ago

Move Line Up in C# TextBox like in VS

I am working on a Notepad clone and I want to create the move line up/down feature that is so common in editors. I believe in VS it is Alt+Up/Alt+Down. I was wondering how can I do this, or if someone has done it before, if you don't mind sharing your code. I might probably have to remove the current line's content and then insert it at a higher line index but what if there is already a non-empty line above? Would appreciate help on this.

2 Replies

Anton•2y ago

split by new line, move the lines, join back

mario12136OP•2y ago

private void MoveLine(int direction)
{
    int currentLineIndex = LineIndex - 1;
    if ((currentLineIndex <= 0 && direction < 0) || (currentLineIndex == LineCount - 1 && direction > 0)) return;

    int caretLine = GetLineIndexFromCharacterIndex(CaretIndex);
    int caretChar = CaretIndex - GetCharacterIndexFromLineIndex(caretLine);
    string[] lines = Text.Split(Environment.NewLine);
    (lines[currentLineIndex], lines[currentLineIndex + direction]) =
        (lines[currentLineIndex + direction], lines[currentLineIndex]);
    Text = string.Join(Environment.NewLine, lines);
    CaretIndex = GetCharacterIndexFromLineIndex(caretLine + direction) + caretChar;
}

private void OnPreviewKeyDown(object sender, KeyEventArgs e)
{
    Key key = (e.Key == Key.System ? e.SystemKey : e.Key);

    if (Keyboard.IsKeyDown(Key.LeftAlt))
    {
        if (key == Key.Up)
        {
            MoveLine(-1);
            e.Handled = true;
        }
        else if (key == Key.Down)
        {
            MoveLine(1);
            e.Handled = true;
        }
    }
}

private void MoveLine(int direction)
{
    int currentLineIndex = LineIndex - 1;
    if ((currentLineIndex <= 0 && direction < 0) || (currentLineIndex == LineCount - 1 && direction > 0)) return;

    int caretLine = GetLineIndexFromCharacterIndex(CaretIndex);
    int caretChar = CaretIndex - GetCharacterIndexFromLineIndex(caretLine);
    string[] lines = Text.Split(Environment.NewLine);
    (lines[currentLineIndex], lines[currentLineIndex + direction]) =
        (lines[currentLineIndex + direction], lines[currentLineIndex]);
    Text = string.Join(Environment.NewLine, lines);
    CaretIndex = GetCharacterIndexFromLineIndex(caretLine + direction) + caretChar;
}

private void OnPreviewKeyDown(object sender, KeyEventArgs e)
{
    Key key = (e.Key == Key.System ? e.SystemKey : e.Key);

    if (Keyboard.IsKeyDown(Key.LeftAlt))
    {
        if (key == Key.Up)
        {
            MoveLine(-1);
            e.Handled = true;
        }
        else if (key == Key.Down)
        {
            MoveLine(1);
            e.Handled = true;
        }
    }
}

What do you think code-wise? I tested and it works. One annoying thing is that the caret visibly, even if ever so quickly, changes position. I took care of that with BeginChange() and EndChange()

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Move Line Up in C# TextBox like in VS