Dynamic Item Size

[Ross-Patterson]

Version Info
Package Version: 2.0.0 Preview 4

Describe your issue
Is there support for a dynamic item size? i.e. user can choose the item width/height.

As far as I can see if you bind to ItemSize, it doesn't update when the size changes, or some max limit is reached.

I also tried implementing IItemSizeProvider, but it seems to only calculate initially, any way to force a recalculation?

Thanks!

[sbaeumlisberger]

Hi, binding to the ItemSize property should work fine (I just tested it). The interface ItemSizeProvider is only intended for use if the property AllowDifferentSizedItems is enabled.

If you still have an issue with the ItemSize property, let me know how to reproduce it. Thank you.

[Ross-Patterson]

Take a look at the attached test project & video.

As you move the height slider, it seems to me that the size is not being reflected/recalculated, as the scrollbar size is wrong.

This is using AllowDifferentSizedItems True and implementing IItemSizeProvider.

Video.mp4

VirtualizingWrapPanelTest.zip

[Ross-Patterson]

Update:
So using AllowDifferentSizedItems = False and not using IItemSizeProvider but instead binding to ItemSize works but the default ListViewItem template seems to cause issues (this seems to be consistent with other implementations of VirtualizingWrapPanel i.e. BinaryMission), where the content (ItemTemplate) doesn't size correctly within the ListViewItem when the size is changed.

I had to re-implement the ListViewItem template from scratch - then bind to ItemSize, when it works as I expect.

Using Default ListViewItem template:

DefaultTemplate.mp4

Using Re-Implemented ListViewItem Template (just a Border with a ContentPresenter inside):

NewTemplate.mp4

[sbaeumlisberger]

Right you need to remove the AllowDifferentSizedItems property or set it to false, because if the property is enabled, the item sizes will be cached.

Then you can use the ItemSize property or just bind to the Width and Height properties inside your ItemTemplate. I actually noticed a problem when decreasing the ItemSize property, so for the moment it might be better to bind to the Width and Height properties.

Indeed the default container template has some issues, but it should be sufficient to add the following properties to your ItemContainerStyle:

<ListView.ItemContainerStyle>
  <Style TargetType="ListViewItem">
    <Setter Property="HorizontalContentAlignment" Value="Stretch"/>
    <Setter Property="VerticalContentAlignment" Value="Stretch"/>
    ...
   <Style TargetType="ListViewItem">
<ListView.ItemContainerStyle>

[Ross-Patterson]

It worked a treat by doing as you said - also removing the default padding that the ListViewItem has:

<ListView.ItemContainerStyle>
  <Style TargetType="ListViewItem">
    <Setter Property="Padding" Value="0" />
    <Setter Property="HorizontalContentAlignment" Value="Stretch"/>
    <Setter Property="VerticalContentAlignment" Value="Stretch"/>
    ...
   <Style TargetType="ListViewItem">
<ListView.ItemContainerStyle>

Thanks a lot!

[sbaeumlisberger]

Glad we've found a solution.

The problem with decreasing the ItemSize property has also been fixed and will be released soon.