Problem with DockStyle.Fill and Scroll bars

Posted on Tuesday, September 17, 2013

I am in the middle of doing a rewrite of some code for a client, fixing up some poorly written code (that I wrote L  … the code is correct, it does the job but in its current state it will be very hard to maintain in the future).

As part of the rewrite I am separating a lot of the interface into smaller pieces of code.  I am making several UserControls  (System.Windows.Controls.UserControl ).  I am adding this controls to a Form by placing a Panel on the form and adding the control to the panel. 

As an example

    public partial class OrderMiddleControl : UserControl {

        private OrderSignaturePanelControl orderSignaturePanelControl =
                       new OrderSignaturePanelControl();

        public OrderMiddleControl() {

        public OrderMiddleControl() {

            //Add the orderSignaturePanelControl
            orderSignaturePanelControl.Dock = DockStyle.Fill;

I have a UserControl called OrderSignaturePanelControl this control has its Dock set to DockStyle.Fill and added as a control to a Panel called signaturePanel.
Setting the DockStyle.Fill allows the control to respond to a SizeChanged event when the Panel that it has been added to changes its size.

This control also is usually larger than the Panel and has auto scroll bars.

This is the behavior I want.    When the panel changes its size the Control can respond and change its size (as long as its Dock is set to DockStyle.Fill).

The problems I am having are the following

·         I have to click on the Control before I can scroll with my wheel on my mouse
·         When the Control gains focus it always scrolls to the top.  (I want it to remain where it is)

Here is the Control, as you can see it has scroll bars

Fix the gain focus issue

My case is simple; I want the Control to gain focus when the mouse pointer is over it.

To do that I did the following.

From the Design view of my Control I added a MouseEnter Event.

        private void OrderIsolationSequenceControl_MouseEnter(
                                    object sender, EventArgs e) {

Now when the mouse enters the control it gains the focus and I can use my scroll wheel just fine.

Fix it to not scroll to the top when it regains focus

I found this article, written by Nick Olsen, that fixed my problem [1]

In my UserControl code I added the following method

        protected override System.Drawing.Point  
                                                    activeControl) {
            // Returning the current location prevents the panel from
            // scrolling to the active control when the panel loses
            //and regains focus
            return this.DisplayRectangle.Location;

This fixed my problem.

I also found this short article [2] that seemed to explain a little more of the why it does this.


[1]  C#: Panel Resets Scroll Position after Focus is Lost and Regained
       Visited 9/2013
[2]  ScrollToControl (.NET C#)
       Visited 9/2013

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