CODEWITHSUNDEEP
c#scrollscrollbarpanelautoscroll
Hetiwos
Hetiwos

Reputation: 229

How to automatically scroll up or down when nearing the borders of a panel?

Just like in Word, any browser and tons of other applications, how do you make the content of a panel scroll up or down when dragging an object beyond the visible area of that panel?

This is the closest I come to what I'm looking for but it's still not perfect.

private void Werkorders_DragOver(object sender, DragEventArgs e)
{
    grpWerkorders.AutoScrollPosition = grpWerkorders.PointToClient(new Point(e.X, e.Y));
}

Upvotes: 0

Views: 681

Answers (1)

LarsTech
LarsTech

Reputation: 81620

This can be done with a WinForms Timer. Example code:

private Timer scrollTimer = new Timer();
private int scrollJump = 0;

public Form1() {
  InitializeComponent();
  panel1.AllowDrop = true;
  panel1.AutoScroll = false;
  panel1.AutoScrollMinSize = new Size(0, 1000);
  panel1.MouseMove += panel1_MouseMove;
  panel1.DragEnter += panel1_DragEnter;
  panel1.DragOver += panel1_DragOver;
  panel1.QueryContinueDrag += panel1_QueryContinueDrag;
  scrollTimer.Tick += scrollTimer_Tick;
}

The drag events:

void panel1_MouseMove(object sender, MouseEventArgs e) {
  if (e.Button == MouseButtons.Left) {
    panel1.DoDragDrop("test", DragDropEffects.Move);
  }
}

void panel1_DragEnter(object sender, DragEventArgs e) {
  e.Effect = DragDropEffects.Move;
}

void panel1_DragOver(object sender, DragEventArgs e) {
  Point p = panel1.PointToClient(new Point(e.X, e.Y));
  if (p.Y < 16) {
    scrollJump = -20;
    if (!scrollTimer.Enabled) {
      scrollTimer.Start();
    }
  } else if (p.Y > panel1.ClientSize.Height - 16) {
    scrollJump = 20;
    if (!scrollTimer.Enabled) {
      scrollTimer.Start();
    }
  } else {
    if (scrollTimer.Enabled) {
      scrollTimer.Stop();
    }
  }
}

void panel1_QueryContinueDrag(object sender, QueryContinueDragEventArgs e) {
  if (e.Action != DragAction.Continue) {
    scrollTimer.Stop();
  }
}

The timer code:

void scrollTimer_Tick(object sender, EventArgs e) {
  if (panel1.ClientRectangle.Contains(panel1.PointToClient(MousePosition))) {
    Point p = panel1.AutoScrollPosition;
    panel1.AutoScrollPosition = new Point(-p.X, -p.Y + scrollJump);
  } else {
    scrollTimer.Stop();
  }
}

You can adjust the scrollJump value to increase or decrease the amount the scrollbar changes, or adjust the timer's Interval amount, which defaults to 100 ms.

Upvotes: 1

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