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Answer 1

A:

I believe the problem is that in the constructor you do not have this line:

Customers = new ObservableCollection<Customer>(res.Result);

before you attempt to set the DataContext to that value.

Luis Miguel 2010-10-09 03:14:43

Answer 2

+1 A:

The reason that it didn't work when you put it in the constructor is that there is not yet any value in the customers field at that moment.

You will only get the value when MainPage_Loaded is triggered, which will not happen because of the following line in your XAML:

Loaded="UserControl_Loaded"

That will execute UserControl_Loaded and not MainPage_Loaded. What you can do is call MainPage_Loaded from UserControl_Loaded, which probably is not what you intend to do. So in that case you should change your XAML instead to:

Loaded="MainPage_Loaded"

And you can delete UserControl_Loaded altogether since you are not using it anymore.

And as for the assigning of the result to the DataGrid, you can actually do it directly by assigning the result straight to the DataContext instead of going through the Customers property.

But if you insist to assign it to the Customers property and have the DataGrid updated accordingly, then the next easiest solution would be to include the following line somewhere in your Customers set method:

DataContext = value;

If you really, really insist that the DataGrid should update itself when the PropertyChanged event is triggered, without having you to code the DataContext = Customers row, then what you want is data binding. By binding the DataContext property to your Customers property, then the DataGrid will be updated when it receive the PropertyChanged event.

To declare the data binding in XAML, you would need to assign a name to your UserControl tag. Then you would assign the binding to the DataContext, something along this line:

DataContext="{Binding Path=Customers, ElementName=theUserControlName}"

And if I were you, instead of having to implement the INotifyPropertyChanged interface, I would instead use Dependency Properties instead. Converting your example to use Dependency Property, I would have:

public static DependencyProperty CustomersProperty =
    DependencyProperty.Register("Customers", typeof(ObservableCollection<Customer>), typeof(MainPage), null);

public ObservableCollection<Customer> Customers
{
    get { return (ObservableCollection<Customer>) GetValue(CustomersProperty); }
    set { SetValue(CustomersProperty, value); }
}

Just that, the property change notification will be handled by the framework.

Amry 2010-10-09 06:08:01

@Amry :- I've used `INotifyPropertyChanged` to update the grid as soon as the content of `ObservableCollection` changes. I've resolved the error just by setting `this.DataContext = this` instead of `this.DataContext = Customers` and according changed DataGrid's binding to `{Binding Path=Customers}` instead of `{Binding}`.

Ankit Rathod 2010-10-09 06:25:13

@Nitesh: You don't need to implement `INotifyPropertyChanged` to update the grid when the content of `ObservableCollection` changes, that is done automatically by the `ObservableCollection` itself. You implement `INotifyPropertyChanged` to let the grid knows that you assigned a totally new instance of `ObservableCollection`. And yes, you can also set `this.DataContext = this`, that's another way of doing it. It would be better if you understand why it works the way it works.

Amry 2010-10-09 15:08:58

@Amry :- Thanks for being so kind. Now my concepts are getting clearer. However there are few more doubts. I hope you don't mind answering them. 1) When we add new row from UI(data grid), will the row be added in code behind's `ObservableCollection`? 2) Should i make a `DependencyProperty` or implement `INotifyPropertyChanged`? Which is the best practise? Isn't `INotifyPropertyChanged` more effecient?

Ankit Rathod 2010-10-10 03:37:10

@Nitesh, answering your questions:1) Sorry, I'm not really sure about that. But I am pretty sure that if you add a new row in the code behind's `ObservableCollection`, then the `DataGrid` will be updated accordingly.2) I can't say which one is the best practise, but for WPF / Silverlight related stuff, Microsoft is implementing most of their properties as Dependency Properties and by doing that, it automatically provides change notifications, binding support etc. Does that say anything? :)

Amry 2010-10-10 23:39:41

@Amry :- Yes it said everything and i have voted and checked your answer :)

Ankit Rathod 2010-10-12 17:33:48

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