Combobox binding breaks after button click WPF MVVM

Question

Combobox binding breaks after button click wpf mvvm. I have used interaction trigger to bind combobox selection changed to an ICommand.

 <ComboBox  IsEditable="True" Text="Please Select" IsReadOnly="True" ItemsSource="{Binding Items}" SelectedItem="{Binding SelectedItem}">
                    <i:Interaction.Triggers>
                        <i:EventTrigger EventName="SelectionChanged">
                            <i:InvokeCommandAction Command="{Binding SelectionChangedCommand}" />
                        </i:EventTrigger>
                    </i:Interaction.Triggers>
                </ComboBox>
 <Button Content="Save"  Command="{Binding SaveCommand}" />

Binding works fine till save button's command is fired. Once save command of button is fired, combobox selectionchange command breaks

Edit: Items is a list of string like below

           "A1", "A2", "A3", "A4", "A5", "A6", "A7", "A8", 
           "B1", "B2", "B3", "B4", "B5", "B6", "B7", "B8", 
           "C1", "C2", "C3", "C4", "C5", "C6", "C7", "C8", 
           "D1", "D2", "D3", "D4", "D5", "D6", "D7", "D8"

Selected item is displayed in a readonly textbox and when the alphabet changes, SelectionChangedCommand binding breaks (SelectedItem is no longer updated but, on clicking save, its updated).

Note that Combobox's SelectedItem is bound to below property of ViewModel.

 private string _SelectedItem;
            public string SelectedItem
            {
                get
                {
                    return _SelectedItem;
                }
                set
                {
                    if (_SelectedItem!= value)
                    {
                        _SelectedItem= value;
                        RaisePropertyChanged(() => SelectedItem);
                    }
                }
            }

Its hard to give any answer with just the details provided here. Can you explain what you mean by "breaks"? Do you mean the SelectedItem no longer gets updated? The SelectionChangedCommand no longer executes? The CanExecute no longer returns true? It could be any number of things, I don't think we can tell with the limited information provided. And can you share what your SaveCommand does to the SelectedItem? (doesn't have to be the exact calculation code, but does it change the SelectedItem value? do anything else related to the SelectChangedCommand or its CanExecute? — Rachel
@user2951819, well, the only thing i can suggest is to run your application in the debugger. Monitor (with the help of a breakpoint), whether the SelectionChangedCommand CanExecute/Execute methods are called and what they are doing. If they are not called, look in the debugger output window for some information regarding failed bindings or triggers. — user2819245
@user2951819, set a breakpoint on the setter of that property and debug it! — user2819245

gomi42 gomi42 · Accepted Answer · 2013-12-28T07:26:27

I'm wondering why you want to get both, the notification via "SelectedItem" AND the InvokeCommandAction. In the setter of your SeletedItem you can do what you want and you hold the new selection in your hand.

Combobox binding breaks after button click WPF MVVM

1 Answers