In my Silverlight project I am creating textboxes which are two-way databound to some Context during runtime. The binding in one direction (from the source to the target) seems to work fine, but the other direction (from the target back to the source) is not showing any effect.
This is the data-context:
public class Leg : INotifyPropertyChanged {
private string passengers;
public string Passengers {
get { return passengers; }
set {
// here I have a breakpoint.
passengers = value;
FirePropertyChanged("Passengers");
}
}
private void FirePropertyChanged (string property) {
if (PropertyChanged != null) {
PropertyChanged(this, new PropertyChangedEventArgs(property));
}
}
public event PropertyChangedEventHandler PropertyChanged;
}
Then on another place I am creating a new TextBox control together with a binding for it:
Binding passengersBinding = new Binding();
// viewModelLeg is an instance of the class Leg from above
passengersBinding.Source = viewModelLeg;
passengersBinding.Path = new PropertyPath("Passengers");
passengersBinding.Mode = BindingMode.TwoWay;
legItem.paxTextBox.SetBinding(TextBox.TextProperty, passengersBinding);
Now when I am altering the value of the Passengers string the corresponding textbox that is bound to it is updating its text correctly. So here's everthing fine.
But when i change the text of a textbox manually and then make the textbox lose its focus, nothing happens - i.e. there is no two-way binding taking place - no down propagation of the new text-value of the textbox to the source !
I have a breakpoint at the setter of the passengers-attribute (marked with the breakpoint-comment above). When I am getting all this right the binding engine also uses this public setter when the target-value of a binding has changed to update the source - so when this happens the breakpoint must be hit. But he doesn't ! So it seems that i can do what I want with my textbox (play with the focus or press enter) it is never updating its source.
Am I overseeing something ? There must be a capital error either in my code or in my thinking.. i would be really thankful for any ideas ...
EDIT:
In the following I try to demonstrate how i create my XAML objects and my DataContext objects. Because I am creating XAML controls and their bindings at runtime I haven't found a good solution to implement the MVVM approach very well. So I am doing the following (which is maybe not the best way to do it):
The situation I am modelling is that I have a UserControl (called LegItem) which is comprised (primarely) of textboxes. At runtime the user can create as much of these userControls as hew wishes to (one after the other).
On my ViewModel side I have a class (called Leg) that serves as a ViewModel for exactly one LegItem. So when I have say n (XAML-) LegItems then I also have n Leg instances. I store these Leg objects in a List.
So I am doing the following everytime the user clicks the 'add a new leg' button:
// here we are inside the applications view in an .xaml.cs file
public void AddLeg () {
// this is going to serve as the ViewModel for the new LegItem
// I am about to create.
Leg leg = viewModel.insertLeg();
// here I am starting to create the visual LegItem. The ViewModel object
// I have created in the previous step is getting along with.
createLegItem(leg);
}
// the primary job here is to bind each contained textbox to its DataContext.
private LegItem createLeg (Leg viewModelLeg) {
// create the visual leg item control element
// which is defined as a XAML UserControl.
LegItem legItem = new LegItem();
Binding passengersBinding = new Binding();
// viewModelLeg is an instance of the class Leg from above
passengersBinding.Source = viewModelLeg;
passengersBinding.Path = new PropertyPath("Passengers");
passengersBinding.Mode = BindingMode.TwoWay;
legItem.paxTextBox.SetBinding(TextBox.TextProperty, passengersBinding);
}
// on the viewModel side there is this simple method that creates one Leg object
// for each LegItem the View is creating and stores inside a simple list.
public Leg InsertLeg () {
Leg leg = new Leg();
legList.add(leg)
return leg;
}
SomeTextBox.Text = "SomeValue"? Because the 2nd way is overwriting the binding, so theTextBox.Textproperty is no longer bound. - RachelLegItem, particularlypaxTextBox? - Rachel