How do I update an ObservableCollection item's property from change in a WPF DataGrid?

c# wpf binding wpfdatagrid observablecollection

24,797

Solution 1

CollectionChanged is for Insert and Delete. NotifyPropertyChanged is for update of an items. In the posted code you don't actually implement INotifyPropertyChanged.

   public event PropertyChangedEventHandler PropertyChanged;
    private void NotifyPropertyChanged(String info)
    {
        if (PropertyChanged != null)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(info));
        }
    }

And I think it is cleaner to bind to a public property where you return _itemDataCol

Otherwise the TwoWay answer of celopez3

Solution 2

An ObservableCollection doesn't listen to its items' INotifyPropertyChanged events; use a BindingList instead.

In other words, [an ObservableCollection] only notices when items are added or removed, not when the values of its items change, even if those items implement INotifyPropertyChanged. In comparison, a BindingList DOES listen to INotifyPropertyChanged, and therefore, if its items are modified, the changes will be reflected in the grid. As a result grouping, sorting, and statistical functions will be updated.

http://xceed.com/CS/blogs/dontpanic/archive/2009/04/01/i-notify-we-notify-we-all-wait-no-we-don-t.aspx

24,797

Author by

K J

Updated on July 09, 2022

Comments

K J almost 2 years
I have a WPF DataGrid who's data source is an ObservableCollection. It is set up loosely as the following:
```
public class ItemDataCollection : ObservableCollection<ItemData>
{
}

public class ItemData : INotifyPropertyChanged
{
    private bool _selected = true;
    public bool Selected 
    { 
        get
        {
            return _selected;
        }
        set
        {
            if (value != _selected)
            {
                _selected = value;
                NotifyPropertyChanged("Selected");
            }
        }
    }
    }


    _itemDataCol = new ItemDataCollection();
        <... fill the _itemDataCol with data here ...>
    dataGrid1.ItemsSource = _itemDataCol;
```
When the collection is updated, a dataGrid1.Items.Refresh() updates dataGrid1 nicely. However when I modify the "Selected" property of a row by checking or unchecking the checkbox in the row corresponding to that property, the item in the collection does not get updated. I looked into the CollectionChanged event of the ObeservableCollection, but that is not appearing to get triggerd. What wiring do I need to get the dataGrid1 to update the collection.

Update

All I was doing was setting the ItemSource property to the ObservableCollection and letting the columns auto-generate. I have since changed to bind directly, and found more detail to the problem. When I simply check the box - no notification is triggerd. However if I hit after checking the box, then the collection is updated. Here is the binding:
```
<DataGridCheckBoxColumn Binding="{Binding Path=Selected, Mode=TwoWay}" Header="Selected"></DataGridCheckBoxColumn>
```
So I guess the question is how do I get the update with having to hit after checking or unchecking the box?

Update #2 (I cannot answer as my rep is not high enough yet) OK - I think I have the solution. If I include "UpdateSourceTrigger=PropertyChanged" in the binding everything seems to work.
```
<DataGridCheckBoxColumn Binding="{Binding Path=Selected, Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}" Header="Selected"></DataGridCheckBoxColumn>
```
Please leave comments if there are any negative affects of this that I may be missing. Thanks for the help!
K J about 12 years

Sorry - I omitted the implementation of NotifyPropertyChanged to keep the post short. It is implemented correctly in my actual code.
paparazzo about 12 years

Does it get called? Does set get called? Please try binding to a public property. If all that fails try bypassing you ItemDataCollection and supply a ObservableCollection<ItemData> directly (for testing).
K J about 12 years

All I was doing was setting the ItemSource property to the ObservableCollection and letting the columns auto-generate. I have since changed to bind directly, and found more detail to the problem. When I simply check the box - no notification is triggerd. However if I hit <enter> after checking the box, then the collection is updated. Here is the binding: <DataGridCheckBoxColumn Binding="{Binding Path=Selected, Mode=TwoWay}" Header="Selected"></DataGridCheckBoxColumn> Any ideas?
K J about 12 years

I tried the following: <DataGridCheckBoxColumn Binding="{Binding Path=Selected, Mode=TwoWay}" Header="Selected"></DataGridCheckBoxColumn> Selected is public. The problem turns out that if I hit <enter> after checking or unchecking the box, the ObservableCollection is updated. Simply checking the box does is not enough to trigger the update however.
paparazzo about 12 years

You need to set the UpdateSourceTrigger to PropertyChanged msdn.microsoft.com/en-us/library/…
K J about 12 years

I was messing with the site - still new to posting on it. When I noticed it unchecked yours, I re-accepted but it didn't take. It was not my intention - you earned the accepted answer.
paparazzo about 12 years

That is strange as it shows you both accepted and unaccepted today. The answer shows a check mark but I did not get credit. Please try a single click on the check mark. And if I don't get credit then no problem. Good you got it working.
K J about 12 years

Hmm. I tried unaccepting and accepting again. It does show your post as the accepted answer - at least in my browser on different machines. My apologies - you were the first to post and the credit should be yours. That is what I get for playing with something that was not broken...
paparazzo about 12 years

Did you try to accept your answer? I bet that is what killed my answer.