Hi i am having some troube with DataTables. So What i need is to detect whenever i change any cell in the DataGrid of the DataTable that is binded.
How to do it? With INotifyPropertyChanged or with INotifyCollectionChanged?
Note: I am trying with INotifyPropertyChanged but it only detects when i set some value in the DataTable, and never when i change any value of any cell in the DataGrid, i already have tried OneWay and TwoWay but nothing happens.
Thanks in advance!
The datagrid would be bound to a list of objects. If you want the grid to update when individual object properties change, than each contained object must implement the INotifyPropertyChanged interface.
The INotifyCollectionChanged is an interface that the collection should implement, and are for notifications of addition and removal events.
See the section "How to implement collections" on this page.
Here's a way to approach your problem:
Create a new class that exposes the properties currently held in each DataRow. On this class implement INotifyPropertyChanged.
Instead of a DataTable, use an ObservableCollection<T> or your new class.
ObservableCollection already implements INotifyCollectionChanged, so this saves you the effort of implementing it yourself.
if you set the itemssource of your datagrid to a datatable then wpf create a IBindingListView wich is bound to the datagrid.
what you can do now is edit,add and delete items to your datatable via datagrid. if you wanna know when a cell in your datatable is changed you can subscribe to DataTable.ColumnChanged event.
why do you want do know when a cell is changed?
The answer to the title of your question is : Neither. Actually you do not need to bind a DataTable to a DataGrid. You bind a DataView. "The ADO.NET DataView implements the IBindingList interface, which provides change notifications that the binding engine listens for."(Binding Sources Overview)
One answer to your question is :
You modify the datagrid cell with a TextBox (usually). Do this with a new textbox inheriting from TextBox and override the OnGotFocus and OnLostFocus methods of it.
Related
I used the List<Person> collection as the ItemsSource for the DataGrid control.
But it did not update the View if i remove the item from the List collection. I was struggling for a long time for the solution.
Then Instead of the List<Person> collection in my ViewModel. I changed this into ObservableCollection<Person> collection. Now it updates the view when ever there is a change in the collection.
I am not sure why it updates only for ObservableCollection<Person> ? Anyone ?
Well its in the name. A simple List doesn't tell the ui to update, in other words "the view can't observe the list". There is no weird magic behind Databinding. WPF and DataBinding needs the Data model to tell them "this is new" or "this is changed", you propably already saw INotifyPropertyChanged, INotifyCollectionChanged is the same but for collections, and the List<> doesn't implement it, ObservableCollection does.
Because List does not implement INotifyCollectionChanged
Because the update of a databinding is not a kind of magic, there are several requirements to make databinding working correctly. If you have a single property to bind on this property must be either a dependency property or its parent class must implement the INotifyPropertyChanged interface to notify the wpf binding system about changes of the property value.
For a collection there is a simelar mechanism: it must implement INotifyPropertyChanged to inform the wpf binding system about removed/moved/added items.
See here for more details: http://msdn.microsoft.com/en-us/library/system.collections.specialized.inotifycollectionchanged.aspx
ObservableCollection<T> fires change events every time you change the items in the collection. List<T> doesn't. That's the reason.
DataBinding is lazy. If you don't tell your view that something has changed, it won't bother updating. Under the hoods, WPF DataBinding registers for change notifications, so that your ViewModel can tell the view when it has changed. It does this with interfaces like INotifyPropertyChanged and INotifyCollectionChanged.
ObservableCollection<T> implements the interface INotifyCollectionChanged. This interface defines the event CollectionChanged, which your View basically attaches its own event handler to. That handler will update the view when the event is raised by the collection.
I have a View with a dataGrid. This datagrid bind a property in the ViewModel that is an ObservableCollection.
I edit some data in the dataGrid, and a field is updated by code, because it depends on some operations. Well, if I check the item in the observable collection, I can see that all the data is correct, but the info in the dataGrid is no refresh.
I want to force the refresh because I know that the observableCollection only raise the change property event when I add o remove items, but not if I edit one of them.
Because I am use Entity Framework 4.1, really the ItemsSource of the dataGrid is the local of the DbSet, so I don't know how to implement the notifyPorpertyChanged in the classes of the model edmx, and I am looking for an alternative, like to force refresh the dataGrid.
Because the property of the ViewModel that I use to bing the ItemsSource of the dataGrid is a reference to the local, I mean that to set the property I do myProperty = myContext.MyTable.Local and that raise the event PropertyChanged that I implement in my ViewModel, I try to do myProperty = myContext.MyTable.Local again to try to raise the event and force the refresh of the dataGrid, but it does not work.
What alternatives do I have?
Make sure that you have the Binding Mode set to TwoWay. Implement in the set portion of your property OnPropertyChanged and the rest should take care of itself.
I have an object which has a property of type ObservableCollection<bool>. It is bound to a list of checkboxes on a form using TwoWay bindings. I would like to add a PropertyChanged notification to this so that if certain values are selected, some other ones get automatically deselected. Is there a way to do this?
The ObservableCollection.PropertyChanged event doesn't get triggered when a value in the collection gets changed and I'm using the MVVM design pattern.
You would need to use your own class that implements the INotifyPropertyChanged interface. You won't be able to use bool, but you can have a single property in your class that is that bool that you want.
I'm just getting started with silverlight.
Basically I have a silverlight user control that has various dataGrids and a combobox, their item sources set to the properties of a custom plain c# object.
My problem is that I have a dropdown list that when a user selects an item from the list a new row should appear in one of the grids.
All I'm doing is handling the SelectionChanged event and adding a new item to to a list in my custom object and setting the itemsource for the grid again. This doesnt seem to work; no row is added to the dataGrid
I have no idea how to force my grid to "rebind" to this property.
I've been reading about dependency properties, are these what I need?
Any pointers would be really appreciated.
The list you are binding against should be of the type ObservableCollection. Then the datagrid should display the new item automatically .
The problem is that when you assign the same List to the ItemsSource the DataGrid knows its the same List so it does nothing.
As Henrik points out you should expose an Observable<T> not a List<T> for properties that are to be bound to ItemsSource properties of multi-item controls such as DataGrid, ListBox etc.
In addition your "plain c# objects" should implement the INotifyPropertyChanged interface if you want changes made by code to these properties to automatically appear in the UI.
What you probably want to do is update the binding source - which is relatively easily done.
private void ComboBox_SelectionChanged(object sender, RoutedEventArgs e)
{
this.dataGrid.GetBindingExpression(DataGrid.ItemsSource).UpdateSource();
}
This is a tad hack-y but will do what you need it to do. Implementing INotifyPropertyChanged is another great suggestion.
Silverlight show have some great info on INotifyPropertyChanged here
I have user control to which I bind a viewmodel, this implements the INotifyPropertyChanged, thru the datacontext, this has a property that is a IList that I bind to the itemsdatasource of a grid, then on the code, in another class I add some values to the list, but the UI doesn't reflect this change although in debug I can see that the datagrid has this items added but they don't appear in the UI, can anybody help me, I can't see what is the problem.
ObservableCollection<T> is your friend. It implements INotifyCollectionChanged, saving you the trouble.