WPF双向数据绑定到可观察集合中的自定义数据类型

Question

I'm trying to data bind to a custom data type property FormulaField in WPF. I don't understand if there's something I've missed or if what I'm trying to do can't be done?

I've followed the convention of how I've bound to a primitive and found that hasn't worked, there's not update on the FormulaField property. I've also noticed that the custom data type set method is never hit. I'm using MVVM.

A model:

 public class OBQModel : NotificationObject
    {    
        private FormulaField _tovLitres;
        public FormulaField TOVLitres
        {
            get
            {
                if (_tovLitres.UsesFormula)
                {
                    _tovLitres.Value = ConversionHelper.USBarrelsToLitres(_tovBarrels);
                }
                return _tovLitres;
            }
            set
            {
                _tovLitres = value;
                RaisePropertyChanged("TOVLitres");
            }
        }
}

The NotificationObject implements INotifyPropertyChanged :

public abstract class NotificationObject : DependencyObject, INotifyPropertyChanged
    {
        public event PropertyChangedEventHandler PropertyChanged;

        protected void RaisePropertyChanged<T>(Expression<Func<T>> action)
        {
            var propertyName = GetPropertyName(action);
            RaisePropertyChanged(propertyName);
        }

        private static string GetPropertyName<T>(Expression<Func<T>> action)
        {
            var expression = (MemberExpression)action.Body;
            var propertyName = expression.Member.Name;
            return propertyName;
        }

        protected internal void RaisePropertyChanged(string propertyName)
        {
            if (PropertyChanged != null)
                PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }

FormulaField looks like this:

public class FormulaField
{
    public bool UsesFormula { get; set; }
    public double Value { get; set; }
}

EDIT Implementing INotifyPropertyChanged in FormulaField goes stack overflow...

public class FormulaField : INotifyPropertyChanged
    {
        public bool UsesFormula { get; set; }
        public double Value
        {
            get
            {
                return Value;
            }
            set
            {
                Value = value;
            }
        }

        public event PropertyChangedEventHandler PropertyChanged;

        // Create the OnPropertyChanged method to raise the event 
        protected void OnPropertyChanged(string name)
        {
            PropertyChangedEventHandler handler = PropertyChanged;
            if (handler != null)
            {
                handler(this, new PropertyChangedEventArgs(name));
            }
        }
    }

The Models sit inside an ObservableCollection in a ViewModel.

An illustration of the View:

<StackPanel>
    <DataGrid ItemsSource="{Binding OBQModelCollection}">    
     <DataGrid.Columns>
      <DataGridTemplateColumn Header="new TOV (L)" Width="100">
       <DataGridTemplateColumn.CellTemplate>
        <DataTemplate>
         <TextBox BorderThickness="0" 
                  Text="{Binding TOVLitres.Value, UpdateSourceTrigger=PropertyChanged, Mode=TwoWay}"/>
        </DataTemplate>
       </DataGridTemplateColumn.CellTemplate>
      </DataGridTemplateColumn>
     </DataGrid.Columns>
    </DataGrid>
</StackPanel>

Answer 1

Based upon what you wrote, you are raising INPC on "LiquidGOVLitres", which doesn't seem to appear in your code listing, but you are binding to "TOVLitres".

Fixing this inconsistency will help, but you will also need to implement INPC on the FormulaField if you want changes to its members to be part of your UI.

ETA: After the clarifying edit to your code listing, the remaining task is to implement INPC on your FormulaField class and raise the event accordingly.

Also, if you are using 4.5 you can investigate the new Member Info class which helps avoid the use of magic strings in INPC.

Finally, for semantic clarity, it wouldn't hurt to rename "Value" to "FormulaValue"...

To avoid recursion, try this model...

    private double _value;
    public double Value
    {
        [DebuggerStepThrough]
        get { return _value; }
        [DebuggerStepThrough]
        set
        {
            if (Math.Abs(value - _value) > Double.Epsilon)
            {
                _value = value;
                OnPropertyChanged("Value");
            }
        }
    }