WPF Binding in columns not working - wpf

Question

I have a list ob object like this:
public class Device : ObjectBase
{
private int _DeviceNbr;
public int DeviceNbr
{
get { return _DeviceNbr; }
set { _DeviceNbr = value; }
}
private string _DeviceName;
public string DeviceName
{
get { return _DeviceName; }
set { _DeviceName = value; OnPropertyChanged(); }
}
private ObservableCollection<State> _DeviceStates;
public ObservableCollection<State> DeviceStates
{
get { return _DeviceStates; }
set { _DeviceStates = value; OnPropertyChanged(); }
}
}
public class State: ObjectBase
{
public int StateNbr { get; set; }
private string _stateType;
public string StateType
{
get { return _stateType; }
set { _stateType = value; }
}
private int _value;
public int Value
{
get { return _value; }
set { _value = value; OnPropertyChanged(); }
}
}
which I need to bind to a Datagrid.
My approach is to create a customDataGrid which looks like this:
public class CustomGrid : DataGrid
{
public ObservableCollection<ColumnConfig> ColumnConfigs
{
get { return GetValue(ColumnConfigsProperty) as ObservableCollection<ColumnConfig>; }
set { SetValue(ColumnConfigsProperty, value); }
}
public static readonly DependencyProperty ColumnConfigsProperty =
DependencyProperty.Register("ColumnConfigs", typeof(ObservableCollection<ColumnConfig>), typeof(CustomGrid), new PropertyMetadata(new PropertyChangedCallback(OnColumnsChanged)));
static void OnColumnsChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
var dataGrid = d as CustomGrid;
dataGrid.Columns.Clear();
dataGrid.Columns.Add(new DataGridTextColumn() { Header = "Nbr", Binding = new Binding("DeviceNbr") });
dataGrid.Columns.Add(new DataGridTextColumn() { Header = "Device", Binding = new Binding("DeviceName") });
foreach (var columnConfig in dataGrid.ColumnConfigs.Where(c => c.IsVisible))
{
var column = new DataGridTextColumn()
{
Header = columnConfig.ColumnHeader,
Binding = new Binding("DeviceStates")
{
ConverterParameter = columnConfig.ColumnName,
Converter = new DeviceStateConverter(),
UpdateSourceTrigger = UpdateSourceTrigger.PropertyChanged,
Mode =BindingMode.TwoWay
}
};
dataGrid.Columns.Add(column);
}
}
}
public class DeviceStateConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
if (value is ObservableCollection<State> DeviceStates && parameter != null)
{
var DeviceState = DeviceStates.FirstOrDefault(s => s.StateType == parameter.ToString());
if (DeviceState != null)
return DeviceState.Value;
}
return false;
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
throw new NotImplementedException();
}
}
The ViewModel looks like this:
public class MainViewModel : ObjectBase
{
private ObservableCollection<Device> _Devices;
public ObservableCollection<Device> Devices
{
get { return _Devices; }
set { _Devices = value; OnPropertyChanged(); }
}
private ObservableCollection<ColumnConfig> _columnConfigs;
public ObservableCollection<ColumnConfig> ColumnConfigs
{
get { return _columnConfigs; }
set { _columnConfigs = value; OnPropertyChanged(); }
}
public MainViewModel()
{
Devices = new ObservableCollection<Device>();
_columnConfigs = new ObservableCollection<ColumnConfig>()
{
new ColumnConfig(){ ColumnHeader = "On", ColumnName = "On", ColumnWidth= 100, IsVisible= true},
new ColumnConfig(){ ColumnHeader = "Off", ColumnName = "Off", ColumnWidth= 100, IsVisible= true}
};
for ( int i = 0; i <= 100; i++)
{
_Devices.Add(new Device()
{
DeviceNbr = i,
DeviceName = "Device " + i.ToString(),
DeviceStates = new ObservableCollection<State>()
{
new State() { StateType = "On", Value= i},
new State() { StateType = "Off", Value= i+1}
}
});
}
OnPropertyChanged("ColumnConfigs");
OnPropertyChanged("Devices");
}
public void TestStateChange ()
{
Devices[2].DeviceName = "Device X";
Devices[2].DeviceStates[0].Value = 5;
// OnPropertyChanged("Devices");
}
}
And the XAML like this:
<local:CustomGrid
AutoGenerateColumns="False"
ColumnConfigs="{Binding ColumnConfigs}"
ItemsSource="{Binding Devices, UpdateSourceTrigger=PropertyChanged, Mode=OneWay}" />
Here is the result:
Application
Now the problem is that the binding for the Devicesstates does not work.
In the ViewModel is a method called "TestStateChange" where tried to change that state. The state in the DeviceStatesCollection changed like expected but it doesn't reflect to the view. Can someone please provide me some help?
UPDATE
The binding works but PropertyChanged Event when changing the value of a state does not fire.
public void TestStateChange()
{
foreach (var device in Devices)
{
foreach (var state in device.DeviceStates)
{
state.Value = state.Value + 1;
}
device.OnPropertyChanged("DeviceStates");
}
}
So I have to raise the PropertyChangedEvent on the "parent" collection of the state. That's weird.
The only think that I can now think of, is to implement an event in the State class and let the parent collection object subscribe to it.
Does someone has a better idea?

Answer 1

If your State object implements INotifyPropertyChanged (which all your bindable data objects should), and if your datagrid column binds directly to a State object (i.e. via a binding path that contains an index) then your UI will update as you expect.
You could subscribe to the State property change events from the parent Device object and then re-notify from there, but that is a long winded way to do it and means that you have to subscribe to the CollectionChanged event of the ObservableCollection that contains the State objects so that you can attach/unattach from the PropertyChange event on each State object (sometimes this will be the only way, but avoid it if you can).