CheckBox binding not updating source - wpf

Question

After changing CheckBox.IsChecked by DataTrigger source value to which CheckBox.IsChecked has binding is not changing.
I have simple ViewModel
public class ViewModel : INotifyPropertyChanged
{
private bool check1;
public bool Check1
{
get { return check1; }
set { check1 = value; NotifyPropertyChanged(); }
}
private bool check2;
public bool Check2
{
get { return check2; }
set { check2 = value; NotifyPropertyChanged(); }
}
#region Notify
...
#endregion
}
and simple XAML
<StackPanel Grid.Row="1">
<CheckBox Content="Check1">
<CheckBox.Style >
<Style TargetType="{x:Type CheckBox}">
<Setter Property="IsChecked" Value="{Binding Check1, Mode=TwoWay}"/>
<Style.Triggers>
<DataTrigger Binding="{Binding Check2}" Value="True">
<Setter Property="IsChecked" Value="True"/>
</DataTrigger>
</Style.Triggers>
</Style>
</CheckBox.Style>
</CheckBox>
<CheckBox Content="Check2" IsChecked="{Binding Check2}"/>
<TextBlock Text="{Binding Check1}" Name="uiCheckValue1"/>
<TextBlock Text="{Binding Check2}" Name="uiCheckValue2"/>
</StackPanel>
When I check CheckBox2 the CheckBox1 becomes checked but source is not updated. How to make it update source?

Answer 1

Your code seems to be wrong. You should emit the PropertyChanged event properly to update the view.
Check below code :
public class ViewModel : INotifyPropertyChanged
{
private bool check1;
public bool Check1
{
get { return check1; }
set
{
check1 = value;
PropertyChanged(value, new PropertyChangedEventArgs("Check1"));
}
}
private bool check2;
public bool Check2
{
get { return check2; }
set
{
check2 = value;
PropertyChanged(value, new PropertyChangedEventArgs("Check1"));
}
}
#region Notify
...
#endregion
}
Also change the binding to TwoWay
<<CheckBox Content="Check2" IsChecked="{Binding Check2, Mode=TwoWay}"/>
<DataTrigger Binding="{Binding Check2, Mode=TwoWay}" Value="True">
<Setter Property="IsChecked" Value="True" />
</DataTrigger>

Answer 2

It's easy to say why: You loose the binding if you set IsChecked on True manually.
Delete the DataTrigger and change your ViewModel like this:
public bool Check2{
get { return check2; }
set {
check2 = value;
if (value == true) Check1 = true;
NotifyPropertyChanged();
}
}

Answer 3

A little late, but if you Change
<CheckBox Content="Check2" IsChecked="{Binding Check2}"/>
To
<CheckBox Content="Check2" IsChecked="{Binding Check2, UpdateSourceTrigger=PropertyChanged}"/>
you can get rid of all the code behind. The default for checkboxes is something like LostFocus, which is entirely annoying.