I remember you demoing this (or some variation of this) at MIX08 with some version of the Newegg website search. Is that available for public viewing? If not, do you have a video of it that we could see? I’m trying to describe it to some co-workers of mine and the visual is worth a thousand words in this case.

I don’t know how performant it is but the following code seems to be working to calculate the Size on MeasureOverride method:

protected override Size MeasureOverride(Size availableSize)
{
Size s = new Size(this.CellWidth, this.CellHeight);

foreach (UIElement element in this.Children)
{
element.Measure(s);
}

double width = availableSize.Width;

int elsPerRow = (int)(width / this.CellWidth);
double rowCount = Math.Ceiling((double)this.Children.Count / elsPerRow);

return new Size(width, rowCount * this.CellHeight);
}

The scrolling issue is a result of the “simplicity” vs. “completeness” tradeoff that I mentioned in the post. Basically, I took the easy way out in the MeasureOverride method. That method is supposed to return a Size that represents the amount of space that the panel needs to “lay out” all of its children. Scrollviewer, for example, depends on that size to know whether or not scrolling is needed.

In UniformWrapPanel, I don’t keep that part of the contract. Instead, I just return a new Size() ojbect (which is a size of 0×0). Other panels do this (like Canvas), but a solid implementation of WrapPanel should be more robust.

So, to fix it, you need to use the MeasureOverride method to calculate the amount of space needed to lay out all of the panels children and then return that instead of the new Size(). This should not be difficult code to write, but can be tough to optimize because a lot of times you end up doing the same calculations in both MeasureOverride and ArrangeOverride.