Resizing the content of a ScrollViewer

Question

Hi all,

I've got a program in which I want to display rendered content inside a Scrollviewer that allows zoom. What I do when the user zooms is that I resize the content of the ScrollViewer and then I want to change the view position and zoom factor so that it looks like I'm at the same position as I just was. Basically, I want the zoom factor to always be 1 (except during zoom, since the system takes care of that).

So, I created a small sample where I have a ScrollViewer (mMainScroller) and a Canvas (mMainCanvas) as the content of the ScrollViewer. So, when the ScrollViewer finishes it's manipulation, I want to resize the canvas and then set the zoom factor back to 1 (the reason is that I'm using rendered content, so when you zoom in I want to re-render at this larger scale and then replace the content). The reason I do it this way is because the zoom limits of the ScrollViewer isn't large enough for my app, and also I found that when using really high zoom levels, it doesn't work smoothly anymore (http://social.msdn.microsoft.com/Forums/windowsapps/en-US/d9d3f1b6-89cb-4b15-a891-5c98fafe5bc9/scrollviewer-jumps-around-on-high-zoom-levels#d9d3f1b6-89cb-4b15-a891-5c98fafe5bc9).

Either way, here's the code I've added to mMainScroller's viewChanedHandler:

        private void ViewChangedHandler(object sender, ScrollViewerViewChangedEventArgs e)
        {
            if (e.IsIntermediate)
            {
                System.Diagnostics.Debug.WriteLine("intermediate");
            }
            else
            {
                System.Diagnostics.Debug.WriteLine("Finished");
                double zoomValue = mMainScroller.ZoomFactor;
                double newWidth = mMainCanvas.Width * zoomValue;
                double newHeight = mMainCanvas.Height * zoomValue;
                double newXPos = mMainScroller.HorizontalOffset;
                double newYPos = mMainScroller.VerticalOffset;

                mMainCanvas.Width = newWidth;
                mMainCanvas.Height = newHeight;
                mMainScroller.ChangeView(newXPos, newYPos, 1, true);
            }
        }

mMainCanvas is basically just a 5000 x 5000 canvas.

I hope that gives you an idea of what I am trying to accomplish. I find that it "almost" works. However, there is a jump by the scroll bar, and with content that was more varied in it's appearance, you might see the content of the scroll viewer "flash" whatever's at that other position.

I will note that this is the same approach as I've used on Windows 8.0, but when trying to post it I am trying to use the new ChangeView function as opposed to ScrollToVerticalOffset and so on, which are all deprecated.

I would really appreciate some suggestions.

Thanks,

Tomas Hofmann

Answer 1

Hi Tomas,

Is this thread based on what you saw in your previous thread? If so, can you check whether the recommendation I suggested on the other thread applies to you? If not, I will take a look at this thread and we can investigate further.

Thanks,

Prashant.

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Answer 2

Hi Prashant,

I would still very much appreciate some help with this. The other option was something I was considering to use as a backup solution, and now it might be more viable. However, if we can solve this it would be better for me. This way, I don't have to re-implement anything.

Currently, I just left it with the old deprecated functions, and it's working fine, so I will just continue with that for now. Still, an upgrade to use the new function would be good to have.

So, I would appreciate if you could look into this.

Thanks for your help,

Tomas Hofmann