Sending an object with a command parameter

Question

I am using PRISM to develop my Windows Phone app using the MVVM design pattern. I need to pass my SelectedItem object from my LongListSelector through my delegate command into my method.

I can do that. The problem is, I'm passing in the wrong object. I don't know if it's a design problem or I am binding improperly.

I need the object to be an Album object. What I'm getting instead is either null or my ViewModel. (I've changed the code a few times and those are the only things I can get.)

XAML

<phone:LongListSelector x:Name="AlbumList" ItemsSource="{Binding Albums}"
                 Margin="10,0,0,0" LayoutMode="Grid" GridCellSize="200, 200"
                 ItemTemplate="{StaticResource AlbumTemplate}"
                                toolkit:TiltEffect.IsTiltEnabled="True"
                                >
            <i:Interaction.Triggers>
                <i:EventTrigger EventName="SelectionChanged">
                    <i:InvokeCommandAction Command="{Binding DataContext.SelectAlbumCommand, ElementName=ContentPanel}"
                                        CommandParameter="{Binding}"/>   
                </i:EventTrigger>
            </i:Interaction.Triggers>
        </phone:LongListSelector>

ViewModel

private ObservableCollection<Album> _albums;
    public ObservableCollection<Album> Albums
    {
        get { return _albums; }
        set
        {
            if (value != null)
            {
                _albums = value;
                NotifyPropertyChanged();
            }
        }
    }

    private Album _selectedAlbum;
    public Album SelectedAlbum
    {
        get { return _selectedAlbum; }
       // code removed as it is not needed; the object is null when trying to set.
}

        public void AlbumSelected(object p)
    {

        App.Dispatcher.BeginInvoke(() =>
            {
                SelectedAlbum = (Album)p;
            });

        ////Navigate("/Views/PhotosListPage.xaml");
    }

//command that takes an object as parameter.
            _selectAlbumCommand = new DelegateCommand<object>(this.AlbumSelected);

If you want to send multiple properties via CommandParameter see this question stackoverflow.com/questions/1350598/… — Simon_Weaver
– Simon_Weaver, Commented Oct 12, 2024 at 20:57

bit · Accepted Answer · 2014-08-01 06:13:33Z

2

In case you merely want to set the SelectedAlbum by your SelectAlbumCommand, why don't you try binding the SelectedItem to SelectedAlbum instead?

<phone:LongListSelector x:Name="AlbumList" ItemsSource="{Binding Albums}" 
 SelectedItem="{Binding SelectedAlbum}" />

In case you actually want to pass the SelectedItem to the SelectedAlbumCommand (for some other reason), you should bind the CommandParameter to the SelectedItem of the LongListSelector

 <i:InvokeCommandAction Command="{Binding DataContext.SelectAlbumCommand, ElementName=ContentPanel}" CommandParameter="{Binding ElementName=AlbumList, Path=SelectedItem}"/>

edited Aug 1, 2014 at 6:13

answered Aug 1, 2014 at 3:31

bit

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3 Comments

McGarnagle Over a year ago

+1, but in your first example, the SelectedItem binding would have to have Mode=TwoWay (?)

bit Over a year ago

Yep.. TwoWay.. I think the default for LongListSelector's SelectedItem property is TwoWay.. No harm in specifying that again though

user3007447 Over a year ago

Thanks, but the object p is still coming up as null with your updated code for the CommandParameter and when I bind SelectedAlbum directly to SelectedItem, nothing happens when I click an item.

Community · Accepted Answer · 2017-05-23 12:20:50Z

0

Apparently, you cannot use LongListSelector for this. I had to change this to a listbox and it worked fine.

Had I searched harder, I would have found this: How to select an item in LongListSelector using the MVVM-pattern?

and this: WP8 LongListSelector SelectedItem not bindable

edited May 23, 2017 at 12:20

CommunityBot

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answered Aug 2, 2014 at 0:25

user3007447

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1 Comment

bit Over a year ago

Good find.. was about to suggest you the same

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