CheckBox binding not updating source

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?

Try "{Binding Check1, Mode=TwoWay]"

Haim Katz
– Haim Katz

2016-08-03 06:11:26 +00:00
Commented Aug 3, 2016 at 6:11 — Haim Katz
– Haim Katz, Commented Aug 3, 2016 at 6:11

ViVi · Accepted Answer · 2016-08-03 06:33:41Z

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>

Devin · Accepted Answer · 2020-07-09 22:24:29Z

2

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.

answered Jul 9, 2020 at 22:24

Devin

1007 bronze badges

Comments

Karina K. · Accepted Answer · 2016-08-03 06:09:42Z

1

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(); 
        }
 }

answered Aug 3, 2016 at 6:09

Karina K.

19010 bronze badges

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