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Databinding update not changing in GridView

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Chris Kirkman
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Chris Kirkman asked on 22 Jan 2018, 07:55 PM

I've successfully bound data to the grid; however, when the model bound to the grid changes the results don't show up in the grid until I give focus to that row.  For the purposes of this issue, don't worry about the meaning of the "scans" and "_snc" objects as they have nothing to do with the issue.

 

Here is where I successfully bind to a model called "ComparisonScansViewModel" which has a public "List<ComparisonScanViewModel> Scans" property.

 

            await Task.Factory.StartNew(() =>
            {
                // source scans for comparison
                _model = new ComparisonScansViewModel(_snc, scans);
            });
            BatchComparisonGrid.DataSource = _model.Scans;

 

Here is the model code (loads up fine)

 

    public class ComparisonScansViewModel
    {
        public ComparisonScansViewModel(SNC snc, List<Scan> scans)
        {
            Scans = new List<ComparisonScanViewModel>();
            scans.ForEach(s =>
            {
                Scans.Add(new ComparisonScanViewModel()
                {
                    Id = s.ScanId,
                    Type = snc.Values.GetInstance(s.Type).Text,
                    Field = s.FieldSize.ToString(),
                    Energy = s.EnergyForDisplay,
                    Depth = s.Depth,
                });
            });
        }
        public List<ComparisonScanViewModel> Scans;
    }
    public class ComparisonScanViewModel
    {
        public int Id { get; set; }
        public string Type { get; set; }
        public string Field { get; set; }
        public string Energy { get; set; }
        public decimal? Depth { get; set; }
        public decimal Gamma { get; set; }
    }

 

In the code below I am hard coding the value of a property in my model named "Gamma".  When the grid is first shown this value is '0' and when the value changes in a dropdownlist I am going to properly update the "Gamma" value; however, for the purposes of debugging I am simply hard coding for now.

 

        private async void ReferenceProjectDropDownList_SelectedValueChanged(object sender, EventArgs e)
        {
            if (null != _model)
            {
                BatchComparisonWaitingBar.Visibility = Telerik.WinControls.ElementVisibility.Visible;
                BatchComparisonWaitingBar.StartWaiting();
                BatchComparisonStatusLabel.Text = "Calculating gamma...";

                // calculate the passing % (gamma) for each item in the table
                await Task.Factory.StartNew(() =>
                {
                    for (int i = 0; i < _model.Scans.Count; i++)
                    {
                        //Thread.Sleep(500);
                        ComparisonScanViewModel sm = _model.Scans[i];
                        sm.Gamma =250m;
                    }
                });

                BatchComparisonWaitingBar.Visibility = Telerik.WinControls.ElementVisibility.Collapsed;
                BatchComparisonWaitingBar.StopWaiting();
                BatchComparisonStatusLabel.Text = "Ready";
            }
        }

 

When this event above is fired, the values in the model ARE updated; however, the results of this update are NOT reflected in the UI.  I have to scroll through the grid view and/or click on a row to see the value change in the grid.

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Chris Kirkman
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answered on 22 Jan 2018, 08:18 PM

I implemented INotifyPropertyChanged on the model; however, it still doesn't work.  ;(

public class ComparisonScanViewModel : INotifyPropertyChanged
{
    decimal _gamma = 0m;
 
    public int Id { get; set; }
    public string Type { get; set; }
    public string Field { get; set; }
    public string Energy { get; set; }
    public decimal? Depth { get; set; }
    public decimal Gamma
    {
        get { return _gamma; }
        set { _gamma = value; OnPropertyChanged("Gamma"); }
    }
 
    public event PropertyChangedEventHandler PropertyChanged;
    void OnPropertyChanged([CallerMemberName] string propertyName = "")
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }
}
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Chris Kirkman
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answered on 22 Jan 2018, 08:31 PM

Still not working but wanted to show.  Went with a more aggressive option, created a base class that implements INotifyPropertyChanged (I do this in my WPF applications).  Then had the model class derive from the base class.

 

public class ViewModelBase : INotifyPropertyChanged
{
    public ViewModelBase() { }
 
    #region Property changed interface
    public event PropertyChangedEventHandler PropertyChanged;
    protected void OnPropertyChanged([CallerMemberName] string propertyName = "")
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }
    #endregion
}
 
public class ComparisonScansViewModel : ViewModelBase
{
    public ComparisonScansViewModel(SNC snc, List<Scan> scans)
    {
        _scans = new ObservableCollection<ComparisonScanViewModel>();
 
        scans.ForEach(s =>
        {
            Scans.Add(new ComparisonScanViewModel()
            {
                Id = s.ScanId,
                Type = snc.Values.GetInstance(s.Type).Text,
                Field = s.FieldSize.ToString(),
                Energy = s.EnergyForDisplay,
                Depth = s.Depth,
                Gamma = 0m
            });
        });
    }
 
    ObservableCollection<ComparisonScanViewModel> _scans;
    public ObservableCollection<ComparisonScanViewModel> Scans { get { return _scans; } set { _scans = value; } }
}
 
public class ComparisonScanViewModel : ViewModelBase
{
    decimal _gamma = 0m;
 
    public int Id { get; set; }
    public string Type { get; set; }
    public string Field { get; set; }
    public string Energy { get; set; }
    public decimal? Depth { get; set; }
    public decimal Gamma
    {
        get { return _gamma; }
        set { _gamma = value; OnPropertyChanged("Gamma"); }
    }
}
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Dess | Tech Support Engineer, Principal
Telerik team
answered on 23 Jan 2018, 11:12 AM
Hello, Chris,

Thank you for writing.  

RadGridView is capable of fetching bindable properties and data. However, one important issue must be noted: during the data binding process, the grid extracts the data from the data source, but for any later changes in the data source, RadGridView should be notified. Your bindable collection and business objects should follow some standards established in .NET in order to notify RadGridView about the changes:
- The collection that you will bind to RadGridView should implement IBindingList or IBindingListView interfaces. This will allow RadGridView to get notified about insert and delete operations of records.
- Your business objects should implement INotifyPropertyChanged interface (.NET 2.0). This will allow RadGridView to reflect changes which occur to the properties of the business objects

Additional information is available in the following help article: https://docs.telerik.com/devtools/winforms/gridview/populating-with-data/reflecting-custom-object-changes-in-rgv

If you are still experiencing any further difficulties, it would be greatly appreciated if you can provide a sample project demonstrating the undesired behavior. Thus, we would be able to investigate the precise case and assist you further. Thank you in advance.

I hope this information helps. Should you have further questions I would be glad to help. 
 
 Regards,
Dess
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Chris Kirkman
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answered on 23 Jan 2018, 02:05 PM
Dess, thanks again!  Using "BindingList<myobect>" worked whereas using "ObservableCollection<myobject>" did not.  It's nice to see items update right before my eyes one after the other as the values are calculated.
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Chris Kirkman
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Chris Kirkman
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Dess | Tech Support Engineer, Principal
Telerik team
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