Question

I have text box,i binded its Text property to MainTxtBoxTxt property in ModalView of Window.When MainTxtBoxTxt changes it affects to TextBox,but when Text property of TextBox changes it doesnt affect to MainTxtBoxTxt in ModelView.What is the problem?

<cstmTxtBox:CustomTextBox Grid.Row="0" TextWrapping="Wrap" FontSize="16" x:Name="TxtBox" cstmTxtBox:CustomTextBox.CaretIndex="{Binding Path=CaretIndex, Mode=TwoWay}" Text="{Binding Path=MainTxtBoxText,Mode=TwoWay}"   >

CustomTxtBox

public class CustomTextBox : TextBox
    {

        public CustomTextBox()
        {

        }
        public static  DependencyProperty CaretIndexProperty =DependencyProperty.RegisterAttached( "CaretIndex",typeof(int),typeof(CustomTextBox),new FrameworkPropertyMetadata(0, FrameworkPropertyMetadataOptions.AffectsRender));
        public static void SetCaretIndex(UIElement element, int value)
        {
            element.SetValue(CaretIndexProperty, value);
        }
        public static int GetCaretIndex(UIElement element)
        {
            return (int)element.GetValue(CaretIndexProperty);
        }
    }

Answer 1

Try this

Text="{Binding Path=MainTxtBoxText,Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"