What are the best practices with Databinding and ObservableCollections in WPF?

I am using LinqToSql as my datasource, let’s say I query a list of programmers from a table and then loop through that data populating an ObservableCollection. (First question, is this part wrong? It just seems weird to query data into a list and then loop through it to populate another list)

Next, when I databind my ObservableCollection of programmers to a ListBox. Then I bind the selectedItem of the Listbox to a TextBox. I understand that when I select an item in the ListBox the textbox will be updated and when I make a change in the textbox, the ListBox will get updated and as a result the ObservableCollection that the listbox is bound to will also be updated.

What I don’t completely understand is what the best practice is to get the data from the OC back 开发者_如何转开发into my original datasource. Do I just loop through the observable collection commiting my changes by updating each record? That doesn’t seem terribly efficient.

Thanks so much for your help! -Josh

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This is purely a view-model issue. You have complete control over all the objects and properties on the data side of the fence. Sometimes you have a simple arrangement where the user can only edit a single record, databinding does all the work, and you just write it back to the database when the user clicks save.

If you have a lot more data being displayed and any one piece of it can be modified by the user, then it is probably wise for you to keep a dirty flag in the object itself that records whether any of the properties have been changed. That way, you can efficiently save back just the modified entries.

Since your objects probably support INotifyPropertyChanged and your collections are observable, you can even automatically detect and manage the dirty flag. Or it might be simpler to just set dirty to true in all of your setters.

In any case, this information can even be useful to the user. For example, a user-interface can show unsaved records in bold or with some other convention.

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The ObservableCollection is not the only one collection which you could use in wpf. But it is standard collection allows wpf to automatically update ui item containers like ListBox on collection changes like addition or removal of an item. You can't do it with List.

When the user modifies a textbox in ListBoxItem the ObservableCollection is not updated cause you don't add or remove or reorder items in the collection. You change the property in one of the items.

The ListBox contains a list of ListBoxItem containers, one for each item in collection specified as an ItemsSource. The DataContext of each ListBoxItem is set to the corresponding item stored in ObservableCollection. So, if you change the text in TextBox in code, the binding engine will change the property of that item specified for TextBox.Text in binding. Nothing to change or update for the ObservableCollection object.

In the setter of such item's property the PropertChanged event of INotifyPropertyChanged interface are usually raised. That is also the usual the place to set up a dirty flag. Then you could also commit changes immediately from there, keep some list of dirty objects or search for them on commit like:

items.Where(item => item.IsDirty)

Also there are good tools like Snoop and WPFInspector, which greatly help you to understand the wpf app visual tree and datacontexts for each element