ControlPaint.DrawReversibleFrame（）会做你想要什么。性能不是一般的问题 - 只要保持小而干净

ControlPaint.DrawReversibleFrame() will do what you want. Performance is not generally a problem - just keep it small and clean.

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编辑：增加了一个代码示例。 ***Exception表明什么是错的 - 但没有看到你的，不能直接回答

-- Added a code sample. ***Exception indicates something is wrong - but without seeing yours, can't answer directly.

private Point? _start;
private Rectangle _previousBounds;

protected override void OnMouseDown(MouseEventArgs e)
{
    _start = e.Location;
    base.OnMouseDown(e);
}

protected override void OnMouseMove(MouseEventArgs e)
{
    if( _start.HasValue ) {
        ReverseFrame();
        DrawFrame(e.Location);
    }

    base.OnMouseMove(e);
}

protected override void OnMouseUp(MouseEventArgs e)
{
    ReverseFrame();
    _start = null;
    base.OnMouseUp(e);
}

private void ReverseFrame()
{
    ControlPaint.DrawReversibleFrame(_previousBounds, Color.Red, FrameStyle.Dashed);

}
private void DrawFrame(Point end)
{
    ReverseFrame();

    var size = new Size(end.X - _start.Value.X, end.Y - _start.Value.Y);
    _previousBounds = new Rectangle(_start.Value, size);
    _previousBounds = this.RectangleToScreen(_previousBounds);
    ControlPaint.DrawReversibleFrame(_previousBounds, Color.Red, FrameStyle.Dashed);
}