I have a class:
public class A : INotifyPropertyChanged
{
public List<B> bList { get; set; }
public void AddB(B b)
{
bList.Add(b);
NotifyPropertyChanged("bList");
}
public event PropertyChangedEventHandler PropertyChanged;
private void NotifyPropertyChanged(string info)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(info));
}
}
}
And a binding (DataContext of UserControl is an instance of A):
<ListBox ItemsSource="{Binding Path=bList}" />
Elements are shown, the ListBox is not updated after new object is added to List
After changing list to ObservableCollection and removing the NotifyPropertyChanged handler everything works.
Why the list is not working?
Your property has to be public, or the binding engine won't be able to access it.
EDIT:
After changing list to ObservableCollection and removing the NotifyPropertyChanged handler everything works.
That's precisely why the ObservableCollection<T> class was introduced... ObservableCollection<T> implements INotifyCollectionChanged, which allows it to notify the UI when an item is added/removed/replaced. List<T> doesn't trigger any notification, so the UI can't detect when the content of the list has changed.
The fact that you raise the PropertyChanged event does refresh the binding, but then it realizes that it's the same instance of List<T> as before, so it reuses the same ICollectionView as the ItemsSource, and the content of the ListBox isn't refreshed.
First thought is that you're trying to bind to a private member. That certainly doesn't seem right.
I think that the problem is that, although you are notifying the binding framework that the property has changed, the actual value of the property remains the same. That is to say that although the listbox may reevaluate the value of its ItemsSource binding, it will find that it is still the same object instance as previously. For example, imagine that the listbox reacts by to the property changed event somehow similar to the below.
private void OnItemsSourceBindingChanged()
{
var newValue = this.EvaluateItemsSourceBinding();
if (newValue != this.ItemsSource) //it will be equal, as its still the same list
{
this.AddNewItems();
}
}
In your example, this would mean that it would not reevaluate the items.
Note: I do not know how the listbox works with the ItemsSource property - I'm just speculating!
ObservableCollections send CollectionChanged events not PropertyChanged events
By signaling
NotifyPropertyChanged("bList");
you are basically saying you have a new list object, not that the content of the List has changed.
If you Change the type to ObservableCollection, the collections automatically sends
CollectionChanged
notifications that the collection items have changed, which is what you want.
Related
I have a DataGrid that is bound to an ObservableCollection in the ViewModel. This is a search results DataGrid. The problem is that after I update the search results ObservableCollection the actual DataGrid is not updated.
Before I get down voted to nothing, please note this is NOT about data in the columns (that bind works perfectly) it is about clearing and then placing completely new data into ObservableCollection that is not updating the DataGrid. So linking to something like this will not help as my properties are working correctly
Background:
The ObservableCollection is declared in the ViewModel like this;
public ObservableCollection<MyData> SearchCollection { get; set; }
The search DataGrid that is bound to my search ObservableCollection like this;
<DataGrid ItemsSource="{Binding SearchCollection}" />
In the ViewModel I have a search method like this;
var results =
from x in MainCollection
where x.ID.Contains(SearchValue)
select x;
SearchCollection = new ObservableCollection<MyData>(results);
The method fires correctly and produces the desired results. Yet the DataGrid is not updated with the new results. I know the ViewModel has the correct data because if I put a button on the Page and in the click event put this code;
private void selectPromoButton_Click(object sender, System.Windows.RoutedEventArgs e)
{
var vm = (MyViewModel)DataContext;
MyDataGrid.ItemsSource = vm.SearchCollection;
}
The DataGrid now correctly shows the results.
I know I could put some event in the code behind of the Page but wouldn't that defeat MVVM? What is the correct MVVM way to handle this?
Try to implement INotifyPropertyChanged in your modelview
example:
public abstract class ViewModelBase : INotifyPropertyChanged {
public event PropertyChangedEventHandler PropertyChanged;
protected virtual void OnPropertyChanged(string propertyName)
{
OnPropertyChanged(new PropertyChangedEventArgs(propertyName));
}
protected virtual void OnPropertyChanged(PropertyChangedEventArgs args)
{
var handler = PropertyChanged;
handler?.Invoke(this, args);
}
}
public class YourViewModel : ViewModelBase {
private ObservableCollection<MyData> _searchCollection ;
public ObservableCollection<MyData> SearchCollection
{
get { return _searchCollection; }
set { _searchCollection = value; OnPropertyChanged("SearchCollection"); }
}
}
The problem is that your are resetting your SearchCollection property rather than updating the collection. Observable collection raises the correct change events when items in the list are added, deleted, or updated. But not when the collection property itself is changed.
In your SearchCollection setter, you can fire a PropertyChanged event. Just like any other property when it changes. Also make sure your DataGrid ItemsSource binding is one-way not one-time.
<DataGrid ItemsSource="{Binding SearchCollection, Mode=OneWay}" />
Or you can change the members of the collection (clearing the old results and adding new ones). That should also update the DataGrid as you expect.
From your code sample, I would go with the first option.
I have a hierarchy of items like the following:
MainClass
{
List<Configuration> MyList = new List<Configuration>;
}
Configuration
{
CustomObject MyObject = new CustomObject;
string Property = "";
}
CustomObject
{
string InnerProperty = "";
}
If I want that MainClass gets notified from every change made to InnerProperty and Property, am I correct to assume that I have to transform the List into an ObservableCollection and that both Configuration and CustomObject should derive from INotifyPropertyChanged, right?
If I want only to get a notify when InnerProperty gets changed, and NOT Property, should only CustomObject derive from INotifyPropertyChanged or Configuration too (since I would lose the notification transmission to the parent)?
To get notification about InnerProperty and Property you don't need ObservableCollection in general. ObservableCollection is only for notifications about added\removed items. So you need to implement INotifyPropertyChanged on both Configuration and CustomObject. If you are only interested in changes of InnerProperty, INotifyPropertyChanged on Configuration is not necessary in case your MyObject property never changes and assigned in constructor. Otherwise, you need again to implement INotifyPropertyChanged on both. Same story with ObservableCollection by the way - if your list contains fixed list of items - you don't need that to receive notifications from properties. Otherwise you do.
If I want only to get a notify when InnerProperty gets changed, and NOT Property, should only CustomObject derive from INotifyPropertyChanged or CustomObject too (since I would lose the notification transmission to the parent)?
(I assume that for the second CustomObject in that sentence you actually mean Configuration.)
If you only change InnerProperty and MyProperty doesn't change, then you only need to have CustomObject implement INotifyPropertyChanged. There is no sense of changes propagating up the chain.
If you have a binding path:
{Binding Path=A.B.C.D}
Then if any of those properties change and you want the binding to update, then the relevant level must implement INotifyPropertyChanged. If a property is immutable (doesn't change) then there's no need to support notification of changes. You can think that the binding is listening for changes on each object returned through the evaluation of the binding path.
I'll try to answer your conceptual question. But code is nice...
I'll first just point to C#:: When to use events or a collection of objects derived from an event handling Interface?, which I think is quite helpful.
ObservableCollection takes care of raising events when items are added or removed. There is no need for INotifyPropertyChanged, that is automatically there. If you bind to an ObservableCollection in your XAML, then your XAML will register for those events, and you don't need to do anything yourself. However, nothing else is listening to the events, unless you register. You can do that like this:
myObservablecollection.CollectionChanged += myHandler;
But I don't think that is what you want. If you want to now when something is added to, or removed from MainClass.MyList, then making it an ObservableCollection will do that for you. But you want to know when some particular item in your list is modified, and ObservableCollection does not help with that.
Let's suppose you want a Configuration to do something when its CustomObject changes. Perhaps it sets Property (not a good name?) to MyObject.ToString(). Then you make CustomObject implement INotifyPropertyChanged, like this:
Class CustomObject : INotifyPropertyChanged
{
private string _innerProperty;
public string InnerProperty
{get { return _innerProperty; }
{set
{
_innerProperty = value;
OnPropertyChanged("InnerProperty");
}
}
public event PropertyChangedEventHandler PropertyChanged;
public void OnPropertyChanged(PropertyChangedEventArgs e)
{
if (PropertyChanged != null)
{
PropertyChanged(this, e);
}
}
}
Then in Configuration:
Class Configuration
{
...
public Configuration(...)
{
... // set up stuff
MyObject.PropertyChanged += myObjectChanged_DoSomethingAboutIt;
}
private void myObjectChanged_DoSomethingAboutIt()
{
DoSomething();
// for example:
Property = MyObject.ToString();
}
}
I hope this helps a bit.
More here: http://www.codeproject.com/Articles/41817/Implementing-INotifyPropertyChanged
In my windows store app I have a gridview with data source set to Observable collection. When the item is added or removed to the collection everything works fine and view is updated. However when property of item of the collection is changed, the collectionChanged event is not fired and the views is not updated. I found a solution how to use INotifyChanged and propertyChanged event, but I want to fluidly update the view without doing something as reassigning the data source of gridview in propertyChanged Handler.
So I want to ask, if there is any solution to this problem.
Thank You in advance.
Refer the below code snippet, to notify while collection changed.
public class MyClass : INotifyPropertyChanged
{
private ObservableCollection<double> _myCollection;
public ObservableCollection<double> MyCollection
{
get { return _myCollection; }
set
{
_myCollection = value;
RaisedOnPropertyChanged("MyCollection");
}
}
public event PropertyChangedEventHandler PropertyChanged;
public void RaisedOnPropertyChanged(string _PropertyName)
{
if (PropertyChanged!=null)
{
PropertyChanged(this, new PropertyChangedEventArgs(_PropertyName));
}
}
}
Hope it will help you..!
Regards,
Joy Rex
I have a ListBox, I populate it with ItemsSource with List<Control>.
But when I delete or add new control for this List, I need every time reset my ListBox ItemsSource
Have any method for ListBox sync List content?
Instead of using a List<T>, use an ObservableCollection<T>. It is a list that supports change notifications for WPF:
// if this isn't readonly, you need to implement INotifyPropertyChanged, and raise
// PropertyChanged when you set the property to a new instance
private readonly ObservableCollection<Control> items =
new ObservableCollection<Control>();
public IList<Control> Items { get { return items; } }
In your Xaml, use something like this...
<ListBox ItemsSource="{Binding MyItemsSource}"/>
And wire it up like this...
public class ViewModel:INotifyPropertyChanged
{
public ObservableCollection<Control> MyItemsSource { get; set; }
public ViewModel()
{
MyItemsSource = new ObservableCollection<Control> {new ListBox(), new TextBox()};
}
public event PropertyChangedEventHandler PropertyChanged;
private void OnPropertyChanged(string name)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(name));
}
}
}
This will present the items to the ListBox. In the example here, the collection contains a ListBox and a TextBox. You can add/delete from the collection and get the behaviour you are after. Controls themselves are not all that great as ListBox items because they do not have a meaningful way of populating a visual. So you will probably need to run them through an IValueConverter.
Implement INotifyPropertyChanged interface in your viewmodel.
Post that in the setter of this List, call the NotifyPropertyChanged event. This will
result in updating your changes on UI
I have a chart control in XAML, and datapoints that are bind to the control.
The problem is when my ModelView changes the Collection of points the Chart control doesn’t get any notifications. I have tried dp, with ObservableCollection and INotifyPropertyChanged without any luck. I know that there is a difference between changing a field/property and making collection operations such as (add/remove/replace etc.) for the changes to propagate to the Chart control. But I haven’t got it to work. The change event is only triggered when I instance/reinstance the collection.
Does any have link to a working MVVM that works with collections?
Worth too know.
public class ObservableCollection : Collection, INotifyCollectionChanged, INotifyPropertyChanged
public static DependencyProperty WorkModelsProperty = DependencyProperty.Register("WorkModels", typeof(ObservableCollection), typeof(Chart),
new PropertyMetadata(new ObservableCollection { }, new PropertyChangedCallback(
(sender, args) =>
{
Debugger.Break(); //trigged only when collection got new instance
})));
public ObservableCollection WorkModels
{
get { return (ObservableCollection)GetValue(WorkModelsProperty); }
set { SetValue(WorkModelsProperty, value); }
}
The binding is correct and tested.
Code in Window.Resources.
ObjectDataProvider ObjectType="{x:Type vm:ListWorkViewModel}" x:Key="ListWorkViewModel"
The binding of control.
WorkModels="{Binding Source={StaticResource ListWorkViewModel}, Path=WorkModels}"
In the ViewModel I use the following code to rise changes. (When using INotifyPropertyChanged)
WorkModels.Add(workModel);
this.RaisePropertyChanged("WorkModels");
protected void RaisePropertyChanged(string propertyName)
{
VerifyPropertyName(propertyName);
if (PropertyChanged != null)
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
When I use ObservableCollection I only add new data point to the collection.
WorkModels.Add(workModel);
Question on MVVM pattern on WPF?
Needs more code. How do you bind? What type is ObservableCollection of? Are you sure you are notyfing in class that is value of ObservableColletion?
Edit: Also change title of your question. This is little ambiguous and not really problem of your question.
You've got this:
WorkModels="{Binding Source={StaticResource ListWorkViewModel}, Path=WorkModels}"
Why are you binding to a static resource? how is that resource defined? Is it in the XAML itself? Are you sure you're actually updating the same instance of the model that the control is bound to?
Have you tried something like this...
private IEnumerable<DataPoint> _DataPoints;
public IEnumerable<DataPoint> DataPoints
{
get
{
return _DataPoints;
}
set
{
if (_DataPoints != value)
{
_DataPoints = value;
this.OnPropertyChanged("DataPoints");
}
}
}
Then whenever you modify ANY point within the DataPoints collection, you raise a property change event for the entire DataPoints set
/// <summary>
/// Raised when a property on this object has a new value.
/// </summary>
public event PropertyChangedEventHandler PropertyChanged;
/// <summary>
/// Raises this object's PropertyChanged event.
/// </summary>
/// <param name="propertyName">The property that has a new value.</param>
protected virtual void OnPropertyChanged(string propertyName)
{
//this.VerifyPropertyName(propertyName);
PropertyChangedEventHandler handler = this.PropertyChanged;
if (handler != null)
{
var e = new PropertyChangedEventArgs(propertyName);
handler(this, e);
}
}
EDIT:
Try changing the resource type from StaticResource to DynamicResource...
http://msdn.microsoft.com/en-us/library/ms750613.aspx#staticdynamic
The resource could be being loaded with the page/window and never updated. That would explain the lack of event communication
Thank you for answers. I found the solution to the problem here.
http://msdn.microsoft.com/en-us/library/aa970563.aspx
For a dependency property in general, the implementation pattern that you follow is that you define a CLR property wrapper, where that property is backed by a DependencyProperty identifier rather than a field or other construct. You follow this same pattern when you implement a collection-type property. However, a collection-type property introduces some complexity to the pattern whenever the type that is contained within the collection is itself a DependencyObject or Freezable derived class.