CODEWITHSUNDEEP
c#wpfdatagridobservablecollection
Offer
Offer

Reputation: 630

Datagrid not updating when query is fired

So I have a DataGrid in my UserControl. It is databound to an observable collection in My ViewModel. The ViewModel implements the INotifyPropertyChanged interface and has been appropriately wired up in the view.

In my view:

<DataGrid AutoGenerateColumns="False"
          EnableRowVirtualization="True"
          ItemsSource="{Binding ContributionCollection, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}">

<!-- DataGrid rows -->

/>

And in The ViewModel:

    private ObservableCollection<contribution> _contributionCollection;
    public ObservableCollection<contribution> ContributionCollection
    {
        get
        {
            return _contributionCollection;
        }
        set
        {
            _contributionCollection= value;
            OnPropertyChanged("ContributionCollection");
        }
    }

What is meant to happen, is that; At a click of a specific button, a query fires against the database and brings back some results. Those results are meant to be shown in the Datagrid.

    // Fired by an ICommand Property
    public object Contributions_CommandExecute(object param)                                           
    {
        var queryContributions = context.contributions.Where(c => c.member == Member);
        return _contributionCollection = new ObservableCollection<contribution>(queryContributions);
    }

But the datagrid always comes up empty. The Application freezes for a bit, suggesting something is happening in the background, but nothing is actually conveyed on the view. In fact, the only time it works properly, is if the ViewModel constructor fires the query upon initialization. But then after that, It won't fire again.

Any idea where I'm going wrong?

Upvotes: 0

Views: 59

Answers (3)

Amine
Amine

Reputation: 1336

View

<DataGrid AutoGenerateColumns="False"
          EnableRowVirtualization="True"
          ItemsSource="{Binding ContributionCollection}">

<!-- DataGrid rows -->

/>

ViewModel

public void Contributions_CommandExecute(object param)                                           
    {
        ContributionCollection = new ObservableCollection<contribution>(context.contributions.Where(c => c.member == Member));
    }

Upvotes: 1

FoldFence
FoldFence

Reputation: 2802

you have to update the list with a Dispatcher so that you don´t interupt the GUI like this:

Dispatcher.BeginInvoke(new Action(() => _contributionCollection = new ObservableCollection<contribution>(queryContributions)));

I had an similar Problem:

Update Observable Collection

Upvotes: 0

ASh
ASh

Reputation: 35681

this line

return _contributionCollection = new ObservableCollection<contribution>(queryContributions);

updates only value of field. Since it doesn't use property setter, OnPropertyChanged("ContributionCollection"); is not called

the solution is to work with property (by the way, why method is not void?) 

// Fired by an ICommand Property
public void Contributions_CommandExecute(object param)
{
    var queryContributions = context.contributions.Where(c => c.member == Member);
    ContributionCollection = new ObservableCollection<contribution>(queryContributions);
}

Upvotes: 1

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