Get element after item click on collectionview via mvvm

Question

I am trying to get the clicked item on my collection view (what a noble idea).

I am happy with the inner workings of my view:

<CollectionView SelectionChangedCommand="{Binding ClickCommand}" SelectionMode="Single"  SelectionChangedCommandParameter="{Binding SelectedItem}" VerticalOptions="FillAndExpand" ItemsSource="{Binding WifiHotSpots}">
    <CollectionView.ItemTemplate>
        <DataTemplate>
            <Grid Padding="10">
                <Label Text="{Binding .}" FontAttributes="Bold" />
            </Grid>
        </DataTemplate>
    </CollectionView.ItemTemplate>
</CollectionView>

I am also happy with having the click being registered inside my command:

[RelayCommand]
public void Click(object obj)
{

}

... however, I am unhappy with my obj not containing anything. It is null.
How can I return the clicked item?

EDIT: The selected Item (which was just a test I believe):

    private object _selectedItem;
    public object SelectedItem
    {
        get { return _selectedItem; }
        set
        {
            if (_selectedItem != value)
            {
                _selectedItem = value;
                OnPropertyChanged(nameof(SelectedItem));
            }
        }
    }

Please show where SelectedItem is defined and how you set it. — Julian
– Julian, Commented May 13, 2024 at 14:17

innom · Accepted Answer · 2024-05-14 12:12:32Z

1

I solved it myself eventually doing this:

                        <Grid.GestureRecognizers>
                            <TapGestureRecognizer Command="{Binding BindingContext.ClickCommand, Source={x:Reference WifiPageViewPage}}" CommandParameter="{Binding .}"/>
                        </Grid.GestureRecognizers>

it takes an x:name on the page for the reference,.

answered May 14, 2024 at 12:12

innom

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1 Comment

H.A.H. Over a year ago

Close enough...

halfer · Accepted Answer · 2024-08-25 18:55:15Z

0

I am answering this:

I am trying to get the clicked item on my collection view

First, specifying your Model class in your DataTemplate is mandatory:

<DataTemplate x:DataType="model:MyModel">

(Julian pointed out, that it is not mandatory, if you never specified your ViewModel, never skipped it myself, because I do not get binding typo warnings, TODO: test)

Second, I advise you to use tap gesture, let's say I have Grid in the DataTemplate:

<Grid.GestureRecognizers>
    <TapGestureRecognizer...

Third, the way you go get to the ViewModel, and execute the command is with:

<TapGestureRecognizer CommandParameter="{Binding .}"
                      Command="{Binding Source={RelativeSource AncestorType= 
{x:Type viewmodel:MyViewModel}}, Path=MyCommand}"/>

It is the most basic way to get the clicked item.

Edit

When you see "model:MyModel" and "local:MainPage", "viewmodel:MyViewModel", you have to understand that MyModel, MainPage, MyViewModel are classes. And model, local, viewmodel are name spaces.

And let's say we have MainViewModel, that is at the top-level namespace of my application.

To use it for binding, you do this:

xmlns:local="clr-namespace:MyApp"

And after that you set your view model as DataType:

x:DataType="local:MyViewModel"

The same way you can add your model namespace as XML namespace and use it when setting DataType of the collection. And also the same way, you can specify your view model as type for the command binding. By declaring "viewmodel" name space.

You can pick any words, not just "model", "viewmodel" etc. It is just an example.

edited Aug 25, 2024 at 18:55

halfer

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answered May 13, 2024 at 13:27

H.A.H.

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13 Comments

Julian Over a year ago

Actually, specifying the x:DataType on the DataTemplate is only mandatory, when you also have specified the x:DataType anywhere higher up in the hierarchy of the ContentPage/ContentView up to where the BindingContext is set.

H.A.H. Over a year ago

@Julian and what is he doing with "{Binding .}" ? I mean, he is doing some binding. There is set DataType, its not part of the code sample...

Julian Over a year ago

If the x:DataType is not specified on the root element or lower down in the hierarchy, the "{Binding .}" will still work. This is only a problem with compiled bindings.

H.A.H. Over a year ago

@Julian I do not see everything, but leaving DataTemplates empty, without specifying the DataType is the main cause of empty CollectionViews in Release mode.

Julian Over a year ago

But under which conditions? Normally, that only happens when the type cannot be inferred and that's usually the case when there's a mismatch between the compiled binding and the actual type. Now, I'm always in favor of specifying x:DataType wherever possible, because it not only speed up the binding resolution, but it also makes it easier to read and navigate the code and assists tools and IDEs.

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