WPF CheckBox TwoWay Binding not working

You need to raise the PropertyChanged event when you set Foo in your DataContext. Normally, it would look something like:

public class ViewModel : INotifyPropertyChanged{    private bool _foo;    public bool Foo    {        get { return _foo; }        set        {            _foo = value;            OnPropertyChanged("Foo");        }    }    public event PropertyChangedEventHandler PropertyChanged;    protected void OnPropertyChanged(string propertyName)    {        var propertyChanged = PropertyChanged;        if (propertyChanged != null)        {            propertyChanged(this, new PropertyChangedEventArgs(propertyName));        }    }}

If you call Foo = someNewvalue, the PropertyChanged event will be raised and your UI should be updated

I spent hours looking for a complete answer to this issue. I guess some people assume that other people searching this issue know the basics - sometimes we don't. A very important part about setting the form's data context was usually missing:

    public YourFormConstructor()    {        InitializeComponent();        DataContext = this;                 // <-- critical!!    }

My checkbox control was set up in the xaml file like this:

<CheckBox x:Name="chkSelectAll" IsChecked="{Binding chkSelectAllProp, Mode=TwoWay}" HorizontalAlignment="Left"/>

The "Path=" and "UpdateSourceTrigger=..." parts appear to be optional, so I left them out.

I am using this checkbox in a ListView header column. When someone checks or unchecks the checkbox, I want all the items in the ListView to also be checked or unchecked (select/unselect all functionality). I left that code in the example (as "optional logic") but your checkbox value logic (if any) would replace this.

The ListView contents are set by browsing for a file, and when a new file is selected, code sets the ListView ItemsSource and the CheckBox is checked (selecting all the new ListView items), which is why this two-way operation is required. That portion of the code is not present in this example.

The code in the xaml.cs file to handle the CheckBox looks like this:

    // backing value    private bool chkSelectAllVal;    // property interchange    public bool chkSelectAllProp    {        get { return chkSelectAllVal; }        set        {            // if not changed, return            if (value == chkSelectAllVal)            {                return;            }            // optional logic            if (value)            {                listViewLocations.SelectAll();            }            else            {                listViewLocations.UnselectAll();            }            // end optional logic            // set backing value            chkSelectAllVal = value;            // notify control of change            OnPropertyChanged("chkSelectAllProp");        }    }    // object to handle raising event    public event PropertyChangedEventHandler PropertyChanged;    // Create the OnPropertyChanged method to raise the event    protected void OnPropertyChanged(string name)    {        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(name));    }