WPF - Fire comboBox SelectedIndexChanged only from user click

Question

I want to stop the ComboBox_SelectionChanged event from being fired at the UI loading. It should happen only when the user makes some change in the combo box.

To do this, I have written the following in .xam.cs file.

  private void myComboBox_SelectionChanged(object sender,   SelectionChangedEventArgs e)
      {
        ComboBox cb = (ComboBox)sender;
        if (!cb.IsFocused)
        {
            return;
        }
        else
           ViewModel.OnPropertyChanged("MyProperty");
     }

But this does not even fire the event when the user makes the change. Where have I gone wrong ?

I know there is a similar question in stackoverflow. But the solutions in it did not work for me. pls help.

Are you following the MVVM design pattern? If so, why are you handling the SelectionChanged Event. I would recommend binding the Command property if there is one on this combo to a Property in your ViewModel. — David B, May 12 '15 at 09:21
Command property is not available with comboboxes...am I right ? Yes, I checked it , it's not there :( — nidarshani fernando, May 12 '15 at 09:22

score 2 · Answer 1 · edited May 23 '17 at 12:15

2

found the solution. we just need to combine the Selection_Changed event with PreviewMouseDown event.

could the SelectionChanged event in WPF be handled only for user interaction?

edited May 23 '17 at 12:15

Community

1
1

answered May 12 '15 at 11:23

nidarshani fernando

493
4
10
26

score 0 · Answer 2 · answered May 12 '15 at 09:26

0

This is an example XAML:

<av:ComboBox x:Name="cmbChargeUnit" HorizontalAlignment="Left" Margin="548,15,0,0" Width="187" ItemsSource="{av:Binding ChargeUnits}" DisplayMemberPath="ChargeUnitDescription" SelectedValue="{Binding SelectedChargeUnit}" VerticalAlignment="Top" Background="#FFCBCBCB" Height="20" IsSynchronizedWithCurrentItem="True"  SelectedIndex="0"  BorderBrush="#FF7070CB"/>

VM:

public ChargeUnit SelectedChargeUnit
    {
        get { return _selectedChargeUnit; }
        set
        {
            _selectedChargeUnit = value;
            OnPropertyChanged("SelectedChargeUnit");
            if (SelectedAttributeId != null)//Only Load when an attribute is entered
            {
                LoadRates();
            }
        }
    }

answered May 12 '15 at 09:26

David B

889
2
11
29

How can it ever become null ? I have a property like that. But it's always set to some value. It only gets changed when the user changes the items in the combo box – nidarshani fernando May 12 '15 at 09:31
That part is to check for another property on my ViewModel before calling a method to load rates that use that Property, like I said it is just an example, when you select your item in your combobox it will hit the Set accessor, then you can call a method which will be called everytime this value changes. – David B May 12 '15 at 09:33
I have already tried that too. That too does the same. Fires the combobox selection changed event at the page loading – nidarshani fernando May 12 '15 at 09:37
It should not fire an event, as there should not be an event? Just a property? The property should hit its Set accessor when selecting an Item in the combo. It will hit its Get accessor when the window loads. – David B May 12 '15 at 09:50

WPF - Fire comboBox SelectedIndexChanged only from user click

2 Answers2