What is wrong with data binding?

Question

WPF

Hello!
An error occurred while binding the data.
There are parent and child controls in which the SelectedIndex dependency property is implemented.
Next, in the parent control, I associate this property with the same property of the subordinate:

//this = currentObject; 
//typeof(this) == typeof(Reader);

var indexBinding = new Binding();
indexBinding.Mode = BindingMode.TwoWay;
//указываю подчненный контролл как источник данных
indexBinding.Source = epubConrol.SelectedIndex;
//Очищаю свойство зависимостей и создаю привязку 
currentObject.ClearValue(Reader.SelectedIndexProperty);
currentObject.SetBinding(Reader.SelectedIndexProperty, indexBinding);

Then, if you change the SelectedItem of the main controller using the page buttons, everything works fine, the controller scrolls the Item of the slave controller. If I swipe on a child control, then the change notification does not come to the parent control.
What could be the reason?

Answer 1

For TwoWay, you must specify using Path or XPath.
Try like this:

//this = currentObject; 
//typeof(this) == typeof(Reader);

var indexBinding = new Binding();
indexBinding.Mode = BindingMode.TwoWay;
//указываю подчненный контролл как источник данных
indexBinding.ElementName = "epubConrol";
indexBinding.Path = new PropertyPath("SelectedIndex");
//Очищаю свойство зависимостей и создаю привязку 
currentObject.ClearValue(Reader.SelectedIndexProperty);
currentObject.SetBinding(Reader.SelectedIndexProperty, indexBinding);

In Xaml it would look something like this:

<ListBox x:Name="lst1" SelectedIndex="{Binding ElementName=lst2, Path=SelectedIndex, Mode=TwoWay}">
    <system:String>1 строка</system:String>
    <system:String>2 строка</system:String>
</ListBox>
<ListBox Grid.Column="1" x:Name="lst2">
    <system:String>1 строка</system:String>
    <system:String>2 строка</system:String>
</ListBox>