I currently have a checkbox that is bound to a property that checks an ObservableCollection for a specific value. If the value exists, then the property returns true.
My property and the property that exposes the ObservableCollection are both readonly.
This approach works fine when I first load my model, but when it add additional items into the ObservableCollection the checkbox that is bound to the property does not update.
Here's the code for my property:
public bool IsMeasure11
{
get //readonly
{
return this.Charges.Any(t => t.IsMeasure11);
}
}
And here's the code for my ObservableCollection:
public ObservableCollection<DACharge> Charges
{
get //readonly
{
if (_charges == null)
{
_charges = new GenericEntityCollection<DACharge>(_DACase.Id).ToList().ToObservableCollection();
}
return _charges;
}
}
And the XAML for the Checkbox:
<CheckBox Content="M11" Name="chkM11" IsChecked="{Binding IsMeasure11, Mode=OneWay}">
Thanks in advance,
Sonny
Your property does not implment INotifyPropertyChanged so there is no way for the binding engine to know to update the bound property.
An ObservableCollection<T> does not update the property which it is being returned within; in this instance the public ObservableCollection<DACharge> Charges property.
You will need to register for the ObservableCollection.CollectionChanged event and when an item is added/removed, etc...fire a PropertyChanged event as displayed in the previous link for the Charges property.
You need to invalidate the binding of IsMeasure11 (i.e. invoke the PropertyChanged event of INotifyPropertyChanged) whenever the Charges collection changes. One way of doing this would be to subscribe to the CollectionChanged event of the Charges collection.
// somewhere, maybe the constructor of your view model
this.Charges.CollectionChanged += ChargesChanged;
private void ChargesChanged(object sender, NotifyCollectionChangedEventArgs e)
{
this.NotifyOfPropertyChanged(() => IsMeasure11);
}
You need to make your "add item" action to fire up the INotifyChanged Interface's PropertyChanged event as described here: http://msdn.microsoft.com/en-us/library/system.componentmodel.inotifypropertychanged.aspx
If not then WPF will never know when the value changes as the binding isnt sourced at the ObservableCollection but to another property that accesses it instead.
Hope it helps.
Related
Is it possible to bind to a value in Properties.Settings.Default in a way that will keep my UI current with the value stored there?
I have a class:
public class FavoritePlayer
{
public string Name
{
get
{
return wpfSample021.Properties.Settings.Default.FavoritePlayer.ToString();
}
set
{
wpfSample021.Properties.Settings.Default.FavoritePlayer = value;
}
}
}
In my XAML, I have a resource:
<local:FavoritePlayer x:Key="fvPlayer"/>
and a binding:
<Label DataContext="{DynamicResource fvPlayer}" Content="{Binding Path=Name}"/>
What I would like is for the data-binding to update any time the property is changed. Is there a way to do this?
Conveniently for you, ApplicationSettingsBase implements INotifyPropertyChanged so you just need to subscribe to PropertyChanged on Properties.Settings.Default and raise your own PropertyChanged in response.
You need your properties to implement INotifyPropertyChanged in order for bindings to recognise when the property value changes.
I want to change a value (textBlock) according to an event. Then, I want to refresh my window, but I couldn't. I used invalidateVisual as well as solutions of other posts, but nothing worked.
Thank you in advance
Several solutions (the first and second one does not make use of databinding).
txtMyControl.text = "New value";
If not on the main thread, you could use the dispatcher to update the value.
Application.Current.Dispatcher.BeginInvoke(() => txtMyControl.text == "New Value")
However, the most WPF friendly way to do it is to use the databinding.
Any change made to the value in code will be instantly reflected in the UI.
XAML
<TextBox x:Name="txtExample" Text="{Binding MyTextProperty,Mode=TwoWay}" Height="24" Width="120"/>
In your code, you have to declare a variable that will be persistent.
private ExampleModel _ExampleModel = new ExmampleModel();
When you load your code, you associate that variable to your textbox data context.
txtExample.DataContext = _ExampleModel
Then, you have the class that will contains all the editable properties on screen (textboxes, radio boxes, etc...)
public class ExampleModel : INotifyPropertyChanged
{
private string _MyTextProperty = "test";
public string MyTextProperty {
get { return _MyTextProperty; }
set {
if (string.Compare(_MyTextProperty, value) != 0) {
_MyTextProperty = value;
RaisePropertyChanged("MyTextProperty");
}
}
}
public void RaisePropertyChanged(string PropertyName)
{
if (PropertyChanged != null) {
PropertyChanged(this, new PropertyChangedEventArgs(PropertyName));
}
}
public event PropertyChangedEventHandler INotifyPropertyChanged.PropertyChanged;
public delegate void PropertyChangedEventHandler(object sender, PropertyChangedEventArgs e);
}
Whenever you handle your event, you just have to change the value of the property containing the information and the UI will refresh accordingly. Also, since we use a two-way binding, the value from your textbox will always be the same than the one contained by MyTextProperty property in ExampleModel class, which make value retrieval very easy.
ex:
_ExampleModel.MyTextProperty = "New value";
If you were already using databinding, make sure the class used implements INotifyPropertyChanged and that the propertyChanged event is called when the property value change or otherwise it won't update the UI.
The best approach to what you're trying to do would be to use Data Binding.
You need to have a string object that will always hold the value of your textblock. Next you need to bind that object to your textblock and then use the event provided by the INotifyPropertyChanged interface and each time the value changes its representation (the textblock) will change to, no need to refresh the window.
More information here
If your event updates the textblock and the textblock you are using is bound to a string property and that property issues a NotifyPropertyChanged() in it's set method, that will cause the display to refresh as you desire.
There are other ways, but this is the easiest given my understanding of your question.
(this is similar to the other answer, but I tried to word so it is easier to understand/implement.)
I can't understand what's happening here. I have two public properties in my ViewModel:
public ObservableCollection<vw_ClientesFull> MyClients { get; set; }
private IEnumerable<vw_ClientesFull> _clients;
public IEnumerable<vw_ClientesFull> Clients
{
get
{
return _clients;
}
set
{
_clients= value;
OnPropertyChanged("Clients");
}
}
Then I have a method to refresh both of them:
private void RefreshClientes()
{
this.serviceClient.Clientes_ListarCompleted += (s, e) =>
{
Clients = e.Result;
MyClients = new ObservableCollection<vw_ClientesFull>(Clients);
};
this.serviceClient.Clientes_ListarAsync(_sRazonSocial, VendedorSel, TransporteSel, _nID, bInactivos);
}
Them i bind my dataGrid to show the information. If I do:
ItemsSource="{Binding Path=Clients}"
If works perfect, but if i do:
ItemsSource="{Binding Path=MyClients}"
Nothing is show! Why? Doesn't ObservableCollection fire onPropertyChange Automaticaly?
Thanks for the help!!!
UPDATE
So if i need to fire the OnPropertyChange manualy, why this work without it?
public ObservableCollection<Vendedores> Vendedores { get; set; }
private void CargarVendedores()
{
Vendedores = new ObservableCollection<Vendedores>(this.serviceClient.GetVendedores());
this.VendedorSel = this.Vendedores.FirstOrDefault();
}
If i bind a combobox like this:
ItemsSource="{Binding Path=Vendedores}"
Work without the OnPropertyChange! Why!
This problem is due to a misconception. ObservableCollection does not raise PropertyChanged, (which happens when the entire property is reassigned) when you replace it, but rather CollectionChanged (which is raised when items are added or removed). You still need to raise PropertyChanged if you plan to reassign the whole object.
Yes, ObservableCollection implements INotifyPropretyChanged. However, it isn't going to help you here :)
ObservableCollection is special because it implements INotifyCollectionChanged. In other words, it raises an event when items are added to or removed from the underlying collection. It also implements INotifyPropertyChanged, so anything bound to a property of the collection will get updated.
You are changing the variable itself though (setting to a new instance no less). This requires that the "instance" of the ObservableCollection property raise the event. In other words, you need:
private ObservableCollection<vw_ClientesFull> myClients;
public ObservableCollection<vw_ClientesFull> MyClients
{
get { return myClients; }
set
{
myClients = value;
OnPropertyChanged("MyClients");
}
In your update, the binding hasn't fired yet (you set in the constructor) so it gets the correct list. Subsequent changes to the list wouldn't work, however.
You must raise the PropertyChanged event when you set the value of MyClients, same as you've already done for Clients.
Here's the deal: I have to take a SelectedItem from a Listbox, that I got from this question and add it to a ListBox in another UserControl. The ViewModels and models are all setup, I just need to know how to refer to the ListBox that is getting the items.
This would be under ViewModel A -- the ViewModel that controls the user control with the ListBox that receives the items.
//This is located in ViewModelA
private void buttonClick_Command()
{
//ListBoxA.Items.Add(ViewModelB -> SelectedListItem);
}
I don't understand how to get ListBoxA.
Would it be an ObservableCollection of strings?
For further clarification: ListBoxA, controlled by ViewModelA will be receiving values from ListBoxB in ViewModelB. I have included a property for ViewModelB in ViewModelA
You need to have a property in ViewModelA that can be any type that implements IEnumerable. I will use a list:
public const string MyListPropertyName = "MyList";
private List<string> _myList;
/// <summary>
/// Sets and gets the MyList property.
/// Changes to that property's value raise the PropertyChanged event.
/// </summary>
public List<string> MyList
{
get
{
return _myList;
}
set
{
if (_myList == value)
{
return;
}
RaisePropertyChanging(MyListPropertyName);
_myList = value;
RaisePropertyChanged(MyListPropertyName);
}
}
Then in your Listbox, you need to set the ItemsSource to this list
<ListBox ItemsSource="{Binding MyList}">
.......
</ListBox>
Now in your constructer, fill MyList with the data you want to display, and on the Add Command, you want to put
MyList.Add(ViewModelB.myString);
ViewModelB.myString assuming from your previous question that in ViewModelB you have a property myString bound to the SelectedItem of ListBoxB, and you have a reference to the instance of ViewModelB in ViewModelA.
This should do it, let me know
Update:
You should be using an ObservableCollection in VMA since the collection will be added to.
I have an application which shows some ListBox's. These ListBox's are bound to data. One of the lists is a list of Doors, while the other list is a list of Users.
The list of Doors are coming from a DataManager class which communicates with the database. The list of Users is coming from an other class which does some calculations.
I've bound the two ListBox's to their appropiate ObservableList getter setter.
For the door:
public ObservableList<Door> Doors
{
get { return DataManager.Doors; }
}
and for the user:
public ObservableList<User> Users
{
get { return classLogic._users; }
}
Here comes the problem. When I add or remove a Door, the list on the UI gets updated. When I add or remove a User, the list doesn't get updated. I have to reload the view (restart the application) to update it. What am I missing? Why isn't it working?
an observable collection raises PropertyChanged for properties of each item
like if you had a IsDoorClosed Property it would update
removing an element raises a CollectionChanged event on Doors but the UI is not updated since
a PropertyChanged event was not Raised on the Bound Property Doors .
you need to Raise A PropertyChanged event on Doors on each CollectionChanged of Doors .
something along the lines of : this is psado code , it was written here for as an example
for your benefit , so check for any syntax errors .
Doors.CollectionChanged += OnDoorsCollectionChanged;
private static void OnDoorsCollectionChanged(object sender , CollectionChangedEventArgs e)
{
PropertyChanged(sender,new PropertyChangedEventArgs("Doors"));
}
I've found out myself that there are three steps to complete. I don't believe a PropertyChanged event is needed to update the ListBox. This may be since .NET 4.0 because I've read in versions below, the databinding isn't really correct yet.
The first step is that the list has to be a private static ObservableList<...>. The second is that the getter of this list has to be the appropiate type as well. This means in my case, the following code needs to be in ClassLogic:
private static readonly ObservableList<User> _users= new ObservableList<User>();
public static ObservableList<User> Users
{
get { return _users; }
}
And the third thing is, when calling this function (getter) in the DataContext class to bind the data to the ListBox, the classname has to be used instead of an instance of that class!
So, in this case it would be:
/// <summary>
/// Gets the Users that are managed by the ClassLogic class
/// </summary>
public ObservableList<User> Users
{
get { return ClassLogic.Users; }
//wrong would be:
//get { return classLogic.Users }
}
These 3 steps bound my data and made sure the ListBox updated when the contents of the list was updated as well.