CommandParameter's bound SelectedIndex is returning last selection, or -1

Question

I've implemented MVVM in WPF and have a ListView as follows:

<ListView DockPanel.Dock="Top" Name="ListViewMain" ItemsSource="{Binding Items}">

... GridView in ListView.View ...

    <i:Interaction.Triggers>
        <i:EventTrigger EventName="SelectionChanged">
            <i:InvokeCommandAction Command="{Binding OnSelectionChangedCommand}"
                                   CommandParameter="{Binding SelectedIndex, 
                                       ElementName=ListViewMain}" />
        </i:EventTrigger>
    </i:Interaction.Triggers>
</ListView>

Whenever I change selection by clicking on any item on the ListView, OnSelectionChangedCommand is called with correct SelectedIndex.

But when I change SelectedIndex programatically as follows:

ListViewMain.SelectedIndex = 0;

I get -1 in OnSelectionChangedCommand. How do I get correct SelectedIndex irrespective of selection change method?

Update

The answers in WPF Listview SelectionChanged event don't explain what'll happen when SelectedIndex is set programmatically and how to define the view model's property which is bound do SelectedIndex.

Why are you doing all this, instead of just binding the SelectedIndex or SelectedItem property? — Clemens, Oct 08 '18 at 09:35
@Clemens: I need the index to access the model data around selected index. Like if selected index is 10, I need to access 11 etc. — Donotalo, Oct 08 '18 at 09:36
Then just add a property to your view model that holds the selected index. — Clemens, Oct 08 '18 at 09:37
Why are you typing TableTestCaseView.ListViewMain.SelectedIndex instead of only ListViewMain.SelectedIndex? — Wasif Mahmood Mustafa, Oct 08 '18 at 09:37
@Clemens: My problem is I need to programmatically change current selection, where I have only the index which I'd like to be selected. — Donotalo, Oct 08 '18 at 09:39
@WasifMahmoodMustafa: Because `ListViewMain` is embedded in `TableTestCaseView` in the program I'm writing. — Donotalo, Oct 08 '18 at 09:39
@WasifMahmoodMustafa: I've understood your confusion and removed extra code. Thanks. — Donotalo, Oct 08 '18 at 09:40
"*I need to programmatically change current selection, where I have only the index which I'd like to be selected*" - that is exactly what happens when you bind SelectedIndex. — Clemens, Oct 08 '18 at 09:49
Can you post more code? Like where are you initializing the selectedindex. — Wasif Mahmood Mustafa, Oct 08 '18 at 09:50
Possible duplicate of [WPF Listview SelectionChanged event](https://stackoverflow.com/questions/1367665/wpf-listview-selectionchanged-event) — Troopers, Oct 08 '18 at 10:22
@Clemens: Can you please explain why binding `SelectedIndex` to a property in the view model will achieve what I need? — Donotalo, Oct 09 '18 at 02:39

score 0 · Accepted Answer · answered Oct 09 '18 at 03:19

0

Finally I've got the solution. The ListView should bind SelectedIndex with a property in view model:

<ListView DockPanel.Dock="Top" Name="ListViewMain" ItemsSource="{Binding Items}" 
          SelectedIndex="{Binding SelectedIndex}">

The ListView shouldn't trigger on SelectionChanged event.

The ListView.DataContext.SelectedIndex (the view model's SelectedIndex) property should call SelectionChanged handler:

public int SelectedIndex
{
    get => _selected_index;
    set
    {
        SetProperty(ref _selected_index, value);
        OnSelectionChangedCommand.Execute(_selected_index);
    }
}

answered Oct 09 '18 at 03:19

Donotalo

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Note that you probably don't need a command anymore. Just call the command's Execute handler directly from the property setter. – Clemens Oct 09 '18 at 05:46
Yep. That's true, that's next part. :) – Donotalo Oct 09 '18 at 07:17

CommandParameter's bound SelectedIndex is returning last selection, or -1

1 Answers1