Not showing items with Visibility=Collapsed in Win

问题:

I have a Windows 8.1 application with a GridView bound to a custom (sortable, deduplicated) observable collection. In this collection, I do some heavy filtering and setting an IsHidden flag for every item.

In the data template for the item, there is a condition making the item collapsed if IsHidden flag is set to true.

<Grid Width="160" Height="280" Visibility="{Binding IsHidden, Converter={StaticResource InvertedBooleanToVisibilityConverter}}">

This approach works in Windows Phone 8.1 XAML, making the items disappear from the ListView but it does not work in Windows 8.1 GridView. The problem with Windows 8.1 is that when I set an item in the collection to hidden, id disappears from the GridView but leaves an empty place, so there is a gap in the GridView.

Any ideas on how to solve it? Maybe same XAML style editing?

Here is a minimal solution to reproduce the problem: https://dl.dropboxusercontent.com/u/73642/gv.zip

I tried binding width and height of the items to the hidden flag and setting it to 0 when the item is hidden, but it did not help, still a gap in the GridView.

Update: One workaround would be filtering the actual bound collection, but this is not possible, because of some business requirements.

回答1:

The problem is in the GridView's ItemsPanel.

Both ItemsWrapGrid and WrapGrid are uniform grids. All their child elements will be sharing the same height and width. That's why even if you collapse the ItemTemplate, the space is still reserved.

What you really need here is a WrapPanel. WINRT doesn't have a built-in WrapPanel but Jerry Nixon has built one and you can grab it from here.

After you updated your GridViews ItemsPanel, you still have one more thing to do. You need to also get the GridViewItem that hosts your Itemtemplate and set its Visibility to Collapsed.

    private async void Button_Click(object sender, RoutedEventArgs e)
    {
        ds[5].IsHidden = true;

        await Task.Delay(1000);
        var gridViewItem =(GridViewItem)this.gv.ContainerFromIndex(5);
        gridViewItem.Visibility = Visibility.Collapsed;
    }

I put a little delay above to make the collapsing more obvious.

回答2:

I tried your sample solution and changed it to a ListView instead. It exhibits the same behavior when the grid itself is hidden. I don't have XAML Spy to verify, but it appears that any List based control will allocate a rendered item for each item in the list.

I changed your click handlder to instead ds.RemoveAt(5); instead of hiding the item, and the element is removed from view with a nice animation. This appears to be as expected, and an interesting find.

回答3:

It takes me a lot of time to understand the problem, and the solution right in front of my eyes. You trying to hide the item itself but the container still there, When you add an item to an GridView, the item is wrapped in an item container. from msdn :

" When you add an item to an ItemsControl, the item is wrapped in an item container. For example, an item added to a ListView is wrapped in a ListViewItem. Without UI virtualization, the entire data set is kept in memory and an item container is also created for each item in the data set. A ListView that's bound to a collection of 1000 items will also create 1000 ListViewItem containers that are stored in memory."

You need to disable the container and create two DataTemplate and using DataTemplateSelector you can choose which DataTemplate for disable and active items. Check this useful article .