WPF dependency binding could not find source

Question

I bound the ischecked property of the checkbox before loading the component

public FileControl()
        {
            RelativeSource relativeSource = new RelativeSource();
            relativeSource.Mode = RelativeSourceMode.FindAncestor;
            relativeSource.AncestorType = typeof(FileControl);
            Binding bind = new Binding() { RelativeSource=relativeSource };
            checkBox.SetBinding(FileIsCheckedIsCheckedProperty,bind);
            InitializeComponent();

        }

Custom dependencies:

public Nullable<bool> FileIsChecked
        {
            get { return (Nullable<bool>)GetValue(FileIsCheckedIsCheckedProperty); }
            set { SetValue(FileIsCheckedIsCheckedProperty, value); }
        }

        // Using a DependencyProperty as the backing store for ChcckBoxIsChecked.  This enables animation, styling, binding, etc...
        public static readonly DependencyProperty FileIsCheckedIsCheckedProperty =
            DependencyProperty.Register("FileIsChecked", typeof(Nullable<bool>), typeof(FileControl), new FrameworkPropertyMetadata(false));

Then run in MainWindow with an error:

CheckBox.FileIsChecked Nullable`1 Source not found: RelativeSource FindAncestor, AncestorType='FileOperator.FileControl', AncestorLevel='1'。

I have no problem binding XAML in the foreground and can access it normally:

<CheckBox Name="checkBox" IsChecked="{Binding IsChecked, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type local:FileControl}}}">
                </CheckBox>

Answer 1

Try moving the InitializeComponent( ) line to the beginning.