I need to implement INotifyPropertyChanged into my class (my goal is, to update a ListView every time an Item from 'JobDataGroup.Items' gets deleted), but in every tutorial, OnPropertyChanged gets called from the setter. Since I have no setter, how do I procede?
My Class:
public class JobDataGroup : repVReportsDataCommon, INotifyPropertyChanged
{
public ObservableCollection<ServiceJobItem> Items
{
get { return new ObservableCollection<ServiceJobItem>(repVReportsDataSource.GetJobItems().Where(_predicate)); }
}
#region PropertyChanged
public event PropertyChangedEventHandler PropertyChanged;
protected void OnPropertyChanged(string info)
{
PropertyChangedEventHandler handler = PropertyChanged;
if(handler != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(info));
}
}
#endregion
}
It doesn't matter from where you call your OnPropertyChanged method, call it when the property needs to be reevaluated.
Since you are recreating your collection every time the getter is accessed, there is no point in using an ObservableCollection.
You might as well just use a List instead and raise OnPropertyChanged manually:
public List<ServiceJobItem> Items { get; private set; }
void UpdateItems() {
Items = new List<ServiceJobItem>(repVReportsDataSource.GetJobItems().Where(_predicate));
OnPropertyChanged("Items");
}
Related
I'm trying to add properties to my Model playing with my first MVVM app.
Now I want to add a place to save specific data in a clean way, so I used a struct.
But I am having issues to notify property changed, it does not have access to the method (An object reference is required for the non-static field)
Can someone explain to me why this happens and inform me on a strategy that fit my needs?
Thanks!
public ObservableCollection<UserControl> TimerBars
{
get { return _TimerBars; }
set
{
_TimerBars = value;
OnPropertyChanged("TimerBars");
}
}
public struct FBarWidth
{
private int _Stopped;
public int Stopped
{
get { return _Stopped; }
set
{
_Stopped = value;
OnPropertyChanged("Name"); //ERROR: An object reference is required for the non-static field
}
}
private int _Running;
//And more variables
}
private void OnPropertyChanged(string propertyName)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null)
{
handler(this, new PropertyChangedEventArgs(propertyName));
}
}
public event PropertyChangedEventHandler PropertyChanged;
OnPropertyChanged needs to be defined in the scope that you wish to update properties on.
For that to work you'll have to implement the interface INotifyPropertyChanged.
And finally you have to provide the correct argument to the OnPropertyChanged method. In this example "Stopped"
public struct FBarWidth : INotifyPropertyChanged
{
private int _Stopped;
public int Stopped
{
get { return _Stopped; }
set
{
_Stopped = value;
OnPropertyChanged("Stopped");
}
}
private int _Running;
//And more variables
private void OnPropertyChanged(string propertyName)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null)
{
handler(this, new PropertyChangedEventArgs(propertyName));
}
}
public event PropertyChangedEventHandler PropertyChanged;
}
Edit: In your comment you mentioned that you've got a class sorounding the code you provided in your example.
That means you've nested a struct inside a class.
Just because you've nested your struct, doesn't mean it inherits properties and methods from the outer class. You still need to implement INotifyPropertyChanged inside your struct and define the OnPropertyChanged method inside it.
I have implemented WPF data binding with INotifyPropertyChanged.
public class ExportNode : INotifyPropertyChanged
{
public uint Handle { get; set; }
public String Text { get; set; }
private bool _ischecked;
public bool IsChecked
{
get
{
return _ischecked;
}
set
{
_ischecked = value;
OnPropertyChanged("IsChecked");
}
}
public event PropertyChangedEventHandler PropertyChanged;
// Create the OnPropertyChanged method to raise the event
protected void OnPropertyChanged(string name)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null)
{
handler(this, new PropertyChangedEventArgs(name));
}
}
}
And than subscribing to event form my code, so whenever I change property in UI, it fires callback.
But now I'm trying to figure out the best way to change property from code, and than not fire callback, just update UI.
void newNode_PropertyChanged(object sender, PropertyChangedEventArgs e)
{
if (e.PropertyName == "IsChecked")
{
}
}
For now I just thought about implementing some "blocker" member property in ExportNode
protected void OnPropertyChanged(string name)
{
if (Blocked)
return;
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null)
{
handler(this, new PropertyChangedEventArgs(name));
}
}
or delete event form instance before change.
newNode.PropertyChanged -= newNode_PropertyChanged;
newNode.IsChecked = true;
newNode.PropertyChanged += newNode_PropertyChanged;
But is there any better way? I just don't understand some basics? :-)
Thank you very much
Roman
You've got this a little backwards.
INotifyPropertyChanged, and thus the PropertyChanged event, is what makes the UI update, in fact, its what makes the whole binding system work.
So to update the UI, you have to raise that event. Now, from the code side, you almost never subscribe to that event, because you could just invoke a method from the setter. Something like:
set
{
_ischecked = value;
OnPropertyChanged("IsChecked");
if (!Blocked)
MyOtherMethod();
}
Note that if you are dealing with threads, that Blocked condition is a major synchronization hazard.
If you really need to register for PropertyChanged from code, then your best bet is to just unregister with -=. That way the UI still gets its event, but you don't.
I'm using ObservableCollection<MyItemViewModel> myItemVMList as the ItemsSouce. I am able to bind Command perfectly but the INotifyPropertyChanged isn't working. Here's my code:
public class MyItemViewModel: INotifyPropertyChanged {
public event PropertyChangedEventHandler PropertyChanged;
protected void OnPropertyChanged(string name) {
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null) {
handler(this, new PropertyChangedEventArgs(name));
}
}
public MyItem MyItem { set; get; }
private RelayCommand _ChangeMyItemPropertyValue;
public ICommand ChangeMyItemPropertyValueCommand {
get {
if (_ChangeMyItemPropertyValue == null) _ChangeMyItemPropertyValue = new RelayCommand(o => ChangeMyItemPropertyValue());
return _ChangeMyItemPropertyValue;
}
}
private ChangeMyItemPropertyValue() {
MyItem.SomeProperty = someDifferentValue;
// NEITHER OF THESE CALLS WORK
OnPropertyChanged("MyItem.SomeProperty");
OnPropertyChagned("SomeProperty");
}
}
Needless to say, the binding is set as Content="{Binding MyItem.SomeProperty}" inside the DataTemplate, and it shows the correct value. Problem is it isn't updated when I run the function.
SideNote: If I implement the INotifyPropertyChanged inside MyItem it works, but I want it on the ViewModel.
If I implement the INotifyPropertyChanged inside MyItem it works, but I want it on the ViewModel
Yes, because that's how it's designed. How it's supposed to know it should listen to your ViewModel's property changed event? It doesn't bind to it, it binds to the model, so it listens to the changes on the model.
You have two choices basically:
Implement INotifyPropertyChanged on MyItem
Bind to the ViewModel
Content="{Binding SomeProperty}"
And add a wrapper property:
public string SomeProperty
{
get { return MyItem.SomeProperty; }
set
{
MyItem.SomeProperty = value;
OnPropertyChanged("SomeProperty");
}
}
You should prefer binding to the ViewModel if you want to follow MVVM practices.
Side note: If you add [CallerMemberName] to OnPropertyChanged like this:
protected void OnPropertyChanged([CallerMemberName] string name = null) {
var handler = PropertyChanged;
if (handler != null)
handler(this, new PropertyChangedEventArgs(name));
}
You'll be able to skip the property name altogether:
public string SomeProperty
{
get { return MyItem.SomeProperty; }
set
{
MyItem.SomeProperty = value;
OnPropertyChanged(); // <-- no need for property name anymore
}
}
So I have a class with 40 or so properties that are updated from communication with a micro controller. This class implements INotifyPropertyChanged.
Loose Example:
private int _Example;
public int Example
{
get
{
return _Example;
}
set
{
_Example = value;
OnPropertyChange("Example");
}
}
And the OnPropertyChange function:
protected void OnPropertyChange(string p_Property)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(p_Property));
}
}
public event PropertyChangedEventHandler PropertyChanged;
Binding (many of these)
Second_Class_Control.DataBindings.Clear();
Second_Class_Control.DataBindings.Add("My_Property", FirstClass, "Example");
In the main form I've set up binds to display and react to these values. One of those happens to land on another property in a another class. I happened to place a breakpoint in the set function of this property, and noticed it was being called any time any property from the first class changed.
Is this the correct behavior? I don't notice any performance hits but I plan on having many instances of these classes running together and wasn't expecting this.
Thanks
Hmm.. I noticed that you have the your OnPropertyChange virtual. Why is this, are you making a override somewhere?
I usually creates it like this :
public class ViewModelBase : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
protected void OnPropertyChanged(string propertyName)
{
if (this.PropertyChanged != null)
{
this.PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
}
then for the usage :
public class MainWindowViewModel : ViewModelBase
{
private string name;
public string Name
{
get { return name; }
set { name = value; OnPropertyChanged("Name"); }
}
}
So i have something along the lines of
private ObservableCollection<ViewModel> _internal;
public ObservableCollection<ViewModel> BoundInternal{get;set}; //this is Binded in the Itemssource like ItemSource={Binding BoundInternal}
Now In my code i do something like
BoundInternal=_internal, However the problem is the BoundInternal isn't trigger any collectionChanged event. I have to use the Add method. So I am wondering if there is a solution to this.
Here is what I suspect your code ought to look like like (although its not quite a match for what you currently doing):-
public class YourClassHoldingThisStuff : INotifyProperyChanged
{
private ObservableCollection<ViewModel> _internal;
public ObservableCollection<ViewModel> BoundInternal
{
get { return _internal; }
set
{
_internal = value;
NotifyPropertyChanged("BoundInternal");
};
}
public event PropertyChangedEventHandler PropertyChanged;
private void NotifyPropertyChanged(string name)
{
if (PropertyChanged != null)
PropertyChanged(this, new ProperytChangedEventArgs(name));
}
}
In this case the _internal field becomes the source of the value of BoundInternal directly and you should only assign it via BoundInternal, (don't assign a value directly to _internal). When that occurs anything currently bound to it will be informed of the change.
If for some reason you really do need to maintain _internal as a separate reference from the backing field of BoundInternal then:-
public class YourClassHoldingThisStuff : INotifyProperyChanged
{
private ObservableCollection<ViewModel> _internal;
private ObservableCollection<ViewModel> _boundInternal;
public ObservableCollection<ViewModel> BoundInternal
{
get { return _boundInternal; }
set
{
_boundInternal = value;
NotifyPropertyChanged("BoundInternal");
};
}
public event PropertyChangedEventHandler PropertyChanged;
private void NotifyPropertyChanged(string name)
{
if (PropertyChanged != null)
PropertyChanged(this, new ProperytChangedEventArgs(name));
}
}
Now at some point in your code when you do BoundInternal = _internal, anything bound to it will be informed of the change.
Every ItemsControl has a, Items property which has a Refresh() method that you can call, which will update your list.
MyList.Items.Refresh()