WPF DependencyProperty and data binding

Question

I am working on WPF project. I create a usercontrol containing a combobox; which represent boolean value(True or false). And I register a DependencyProperty Value for my usercontrol.

Whenever combobox selection was changed, I will update the Value property and also when Value property is update I will update combobox.

But I found the problem when I use my usercontrol in MVVM. I bind the Value property with my IsEnable property in my viewModel. I set binding mode as TwoWay binding. But when I changed selection in comboBox, IsEnable property is never set.

My usercontrol:

public bool Value
{
    get { return (bool)GetValue(ValueProperty); }
    set { SetValue(ValueProperty, value); }
}

public static readonly DependencyProperty ValueProperty =
        DependencyProperty.Register("Value", typeof(bool), 
        typeof(BooleanComboBox),
        new UIPropertyMetadata(true, OnValuePropertyChanged));

private void Cmb_Selection_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
    ComboBox cmb = sender as ComboBox;
    object selectedValue = cmb.SelectedValue;
    if (selectedValue == null)
    {
        this.Value = false;
    }
    else
    {
        if (selectedValue.GetType() == typeof(bool))
        {
            this.Value = (bool)selectedValue;
        }
        else
        {
            this.Value = false;
        }
    }

    if (this.OnValueChange != null)
        this.OnValueChange(this, this.Value);
}

private static void OnValuePropertyChanged(DependencyObject sender, DependencyPropertyChangedEventArgs args)
{
    BooleanComboBox self = sender as BooleanComboBox;
    self.Cmb_Selection.SelectedValue = (bool)args.NewValue;
}

In window, where I place my usercontrol (I already set usercontrol's datacontext to my viewModel):

<tibsExtControl:BooleanComboBox Grid.Row="4" 
                                Grid.Column="1" 
                                VerticalAlignment="Center"
                                Value="{Binding Path=NewTemporaryZone.IsEnable, 
                                                Mode=TwoWay, 
                                                UpdateSourceTrigger=PropertyChanged}"
                                x:Name="Cmb_AllowNonLBILogon"/>

In my model class I declare an IsEnable property:

private bool _isEnable;
public bool IsEnable
{
    get { return _isEnable; }
    set 
    { 
        _isEnable= value;
        OnPropertyChanged("IsEnable");
    }
}

What's going on with my usercontrol. I miss something ? Please help me. TT

Answer 1

请检查VS的输出窗口中是否存在任何绑定错误。

Answer 2

Try refreshing your binding in Cmb_Selection_SelectionChanged . Something like:

BindingExpression b = cmb.GetBindingExpression(MyNamespace.ValueProperty);
b.UpdateSource();

Answer 3

I've had the same problem; with boolean dependency properties! Try switching the bool to a INullable<bool> ( bool? ) and apply the appropriate type conversions. This worked for me. Don't know if this is a bug or if value types are handled somewhat different compared to reference types when creating dependency properties? Maybe someone else could verify that.