How to bind multiple selection of listview to viewmodel?

Question

I am implementing a listview, and a button next to it. I have to be able that when i select multiple items in a listview, and then click on a button, then the selected items

Answer 1

If you are using Metro/WinRT you may want to look at the WinRTXXAMLToolkit as it offers a bindable SelectedItems dependency property as one of its extensions.

Answer 2

What you can do is you can handle the Button_Click(...) in your code-behind. Then in that code-behind method you can create a List of selected items by iterating over the selected items of the listView.

Since it is allowed to access the ViewModel from the View you can now call a method on your ViewModel and pass the list of selected items as a parameter.

I'm not sure if this would also work with Bindings only, however it is not bad practice to use code-behind as well.

Example Code:

public void Button_Click(object sender, EventArguments arg)
{
  List<ListViewItem> mySelectedItems = new List<ListViewItem>();

  foreach(ListViewItem item in myListView.SelectedItems)
  {
    mySelectedItems.Add(item);
  }

  ViewModel.SomeMethod(mySelectedItems);
}

EDIT

Here is a minimalist example, XAML:

<DataTemplate
            x:Key="CarTemplate"
            DataType="{x:Type Car}">
</DataTemplate>

<ListView x:Name="myListView"
          ItemsSource="{Binding Path=Cars}"
          ItemTemplate="{StaticResource CarTemplate}">
</ListView>

CODE-BEHIND:

public void Button_Click(object sender, EventArguments arg)
    {
      List<Car> mySelectedItems = new List<Car>();

      foreach(Car item in myListView.SelectedItems)
      {
        mySelectedItems.Add(item);
      }

      ViewModel.SomeMethod(mySelectedItems);
    }

Answer 3

It's kind of tricky to do this Mutliple Selection in MVVM, because the SelectedItems property isn't a Dependency Property. However, there are some tricks you can use. I found this triology of blog posts that describe the matter in some details and provide some useful solutions.

• Part I
• Part II
• Part III

Hope this helps

Answer 4

You can't bind, but you can send to Command as an CommandParameter.

Answer 5

I did a solution for this, to me this was simple enough.

<ListBox ItemsSource="{Binding ListOfModel}" x:Name="ModelList"
                                SelectedItem="{Binding SelectedModel, Mode=TwoWay}">
                            <i:Interaction.Triggers>
                                <i:EventTrigger EventName="SelectionChanged">
                                    <i:InvokeCommandAction Command="{Binding ExecuteListBoxSelectionChange}" CommandParameter="{Binding ElementName=ModelList}">
                                    </i:InvokeCommandAction>
                                </i:EventTrigger>
                            </i:Interaction.Triggers>
                        </ListBox>

Then in the viewmodel:

public ICommand ExecuteListBoxSelectionChange { get; private set; }
ExecuteListBoxSelectionChange = DelegatingCommand<ListBox>.For(ListBoxSelectionChnageEvent).AlwaysEnabled();

SelectedModels is the list where I wanted the selection to be filled.

    private void ListBoxSelectionChnageEvent(ListBox modelListBox)
    {
        List<ModelInfo> tempModelInfo = new List<ModelInfo>();
         foreach(ModelInfo a in modelListBox.SelectedItems)
             tempModelInfo.Add(a);

         SelectedModels = tempModelInfo;
    }

Answer 6

Like Doctor has already pointed out, you can bind SelectedItems to XAML CommandParameter

After a lot of digging and googling, I have finally found a simple solution to this common issue.

To make it work you must follow ALL the following rules:

1. Following Ed Ball's suggestion', on you XAML command databinding, define CommandParameter property BEFORE Command property. This a very time-consuming bug.

   

2. Make sure your ICommand's CanExecute and Execute methods have a parameter of object type. This way you can prevent silenced cast exceptions that occurs whenever databinding CommandParameter type does not match your command method's parameter type.

   private bool OnDeleteSelectedItemsCanExecute(object SelectedItems)
   {
       // Your goes here
   }
   
   private bool OnDeleteSelectedItemsExecute(object SelectedItems)
   {
       // Your goes here
   }
   

For example, you can either send a listview/listbox's SelectedItems property to you ICommand methods or the listview/listbox it self. Great, isn't it?

Hope it prevents someone spending the huge amount of time I did to figure out how to receive SelectedItems as CanExecute parameter.