We Keep Coding

XAML custom collection binding async collection update

I have a custom class inheriting from ObservableCollection and INotifyPropertyChanged (i.e. the custom class also has properties) that serves as a Collection<T> where T also inherits from INotifyPropertyChanged:
public class CustomCollection<T> : ObservableCollection<T>, INotifyPropertyChanged where T: INotifyPropertyChanged {
private string _name;
public string Name {
get {
return _name;
}
set {
if (_name != value) {
_name = value;
NotifyPropertyChanged("Name");
}
}
}
private int _total;
public int Total {
get {
return _total;
}
set {
if (_total != value) {
_total = value;
NotifyPropertyChanged("Total");
}
}
}
public event PropertyChangedEventHandler PropertyChanged;
private void NotifyPropertyChanged(String propertyName) {
PropertyChangedEventHandler handler = PropertyChanged;
if (null != handler) {
handler(this, new PropertyChangedEventArgs(propertyName));
}
}
And T item class:
public class DataItem : INotifyPropertyChanged {
private string _fname;
public string Fname {
get {
return _fname;
}
set {
if (value != _fname) {
_fname = value;
NotifyPropertyChanged("Fname");
}
}
}
private int_value;
public int Value {
get {
return _value;
}
set {
if (value != _value) {
_value = value;
NotifyPropertyChanged("Value");
}
}
}
public event PropertyChangedEventHandler PropertyChanged;
private void NotifyPropertyChanged(String propertyName) {
PropertyChangedEventHandler handler = PropertyChanged;
if (null != handler) {
handler(this, new PropertyChangedEventArgs(propertyName));
}
}
}
And the ViewModel:
public class ViewModel : ViewModelBase {
private readonly IService _dataService;
private bool _isLoading;
public bool IsLoading {
get {
return _isLoading;
}
private set {
_isLoading = value;
RaisePropertyChanged("IsLoading");
}
}
private CustomCollection<DataItem> _items;
public CustomCollection<DataItem> Items
{
get
{
return _items;
}
set
{
_items= value;
RaisePropertyChanged("Items");
}
}
public ViewModel(IService dataService) {
_dataService = dataService;
}
public void Refresh() {
if (!this.IsLoading) {
this.IsLoading = true;
_dataService.RefreshData(
this, (error) => {
if (error != null) {
return;
}
if (!IsInDesignMode)
this.IsLoading = false;
}
);
}
}
public void GetData() {
if (Games == null) {
Games = new CustomCollection<DataItem>();
} else {
Games.Clear();
}
if (!this.IsLoading) {
this.IsLoading = true;
_dataService.GetData(
this, (error) => {
if (error != null) {
return;
}
if (!IsInDesignMode)
this.IsLoading = false;
}
);
}
}
And I have bound the CustomCollection<T> to a control in my View (xaml). Everything works fine initially, upon navigating to the page, the ViewModel calls for a DataService to retrieve the data and populate the CustomCollection<T>. However, when refreshing the data, the View is not updated until all the data has been iterated over and refreshed/updated!
Here is the code for the refresh/updated (keep in mind, I'm retrieving the data via a web service, and for the purposes of testing have just manually updated the Value property in DataItem at each passover of the CustomCollection<T>):
public async RefreshData(ViewModel model, Action<Exception> callback) {
if (model.Items == null) return;
// ... retrieve data from web service here (omitted) ...
foreach (DataItem item in retrievedItems) { // loop for each item in retrieved items
DataItem newItem = new DataItem() { Fname = item.Fname, Value = item.Value };
if (model.Items.contains(newItem)) { // override for .Equals in CustomCollection<T> allows for comparison by just Fname property
model.Items[model.Items.IndexOf(newItem)].Value += 10; // manual update
} else {
model.Items.Add(newItem);
}
System.Threading.Thread.Sleep(1000); // 1 second pause to "see" each item updated sequentially...
}
callback(null);
}
So in summary, how can I make it so updating Value of my DataItem will instantly reflect in the View, given my current setup of CustomCollection<DateItem>? Something to do with async perhaps? I mean, when Sleep(1000) gets called, the UI does not hang, maybe this has something to do with it?
Any ideas on how to fix this? As you might have guessed, this issue is also present when first retrieving the data (but is barely noticeable as data is retrieved/processed during the navigation to the View).
Note: I'm using the MVVMLight Toolkit.
Thanks.

INotifyPropertyChanged with singelton class

i'm trying to implement INotifyPropertyChanged within singelton class.
Here is my code:
public class plc : INotifyPropertyChanged
{
private static plc instance;
public plc()
{
}
public static plc Instance
{
get
{
if (instance == null)
{
instance = new plc();
}
return instance;
}
set
{
instance = value;
}
}
private static string _plcIp{get; set;}
public string plcIp
{
get
{
return _plcIp;
OnPropertyChanged();
}
set
{
_plcIp = value;
}
}
public event PropertyChangedEventHandler PropertyChanged;
private void OnPropertyChanged([CallerMemberName]string propertyName = null)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
I'm getting error unreachable code deleted and of course NotifyPropertyChange isn't working

It's because you are calling OnPropertyChanged(); after you return _plcIp;.
It should be called after you set the value. i.e.:
public string plcIp
{
get
{
return _plcIp;
}
set
{
if (value != _plcIp)
{
_plcIp = value;
OnPropertyChanged();
}
}
}
You should also check that the value is actually changing in the setter before raising the event.

There are several issues in your code:
if you are implementing singleton, then constructor of class should be private
use fields instead of private properties
properties should not be static (you are using singleton)
verify if property value really changed before raising OnPropertyChanged event
raise event before returning property value
use PascalNames for class name and properties names
raise event from setter instead of getter
Code:
public class Plc : INotifyPropertyChanged {
private static Plc _instance;
private Plc() { } // constructor should be private
public static Plc Instance
{
get
{
if (_instance == null)
_instance = new Plc();
return _instance;
} // you don't need setter
}
private string _plcIp; // instance field instead of static property
public string PlcIp
{
get { return _plcIp; }
set
{
if (_plcIp == value)
return; // check if value changed
_plcIp = value; // change value
OnPropertyChanged(); // raise event
}
}
// ...
}

This contains the error :
public string plcIp
{
get
{
return _plcIp;
OnPropertyChanged(); //This row..
}
set { _plcIp = value; }
}
It's in the Set method you want the update in the UI, not when you get the value.
Something like this :
public string plcIp
{
get { return _plcIp; }
set { _plcIp = value; OnPropertyChanged(); }
}

INotifyPropertyChanged 'Double' binding

I'm trying to bind some XAML code to a property in my ViewModel.
<Grid Visibility="{Binding HasMovies, Converter={StaticResources VisibilityConverter}}">
...
</Grid>
My ViewModel is setup like this:
private bool _hasMovies;
public bool HasMovies
{
get { return _hasMovies; }
set { _hasMovies = value; RaisePropertyChanged("HasMovies"); }
}
In the constructor of the ViewModel, I set the HasMovies link:
MovieListViewModel()
{
HasMovies = CP.Connection.HasMovies;
}
in CP:
public bool HasMovies
{
get { return MovieList != null && MovieList.Count > 0; }
}
private ObservableCollection<Movie> _movies;
public ObservableCollection<Movie> MovieList
{
get { return _movies; }
set
{
_movies = value;
RaisePropertyChanged("MovieList");
RaisePropertyChanged("HasMovies");
_movies.CollectionChanged += MovieListChanged;
}
}
private void MovieListChanged(object sender, NotifyCollectionChangedEventArgs e)
{
RaisePropertyChanged("HasMovies");
}
What am I doing wrong? How should I change this binding so that it reflects the current state of CP.Connection.HasMovies?

Either directly expose the object in the ViewModel and bind directly through that (so that the value is not just copied once which is what happens now) or subscribe to the PropertyChanged event and set HasMovies to the new value every time it changes in your source object.
e.g.
CP.Connection.PropertyChanged += (s,e) =>
{
if (e.PropertyName = "HasMovies") this.HasMovies = CP.Connection.HasMovies;
};

First of all, the setter for a collection type, such as your MovieList property, is not called when you change the content of the collection (ie. Add/Remove items).
This means all your setter code for the MovieList property is pointless.
Secondly, it's very silly code. A much better solution, is to use NotifyPropertyWeaver. Then your code would look like this, in the viewmodel:
[DependsOn("MovieList")]
public bool HasMovies
{
get { return MovieList != null && MovieList.Count > 0; }
}
public ObservableCollection<Movie> MovieList
{
get;
private set;
}
Alternatively you would have to add a listener for the CollectionChanged event when you initialize the MovieList property the first time (no reason to have a backing property, really really no reason!), and then call RaisePropertyChanged("HasMovies") in the event handler.
Example:
public class CP : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
public CP()
{
MovieList = new ObservableCollection<Movie>();
MovieList.CollectionChanged += MovieListChanged;
}
public bool HasMovies
{
get { return MovieList != null && MovieList.Count > 0; }
}
public ObservableCollection<Movie> MovieList
{
get;
private set;
}
private void MovieListChanged(object sender, NotifyCollectionChangedEventArgs e)
{
RaisePropertyChanged("HasMovies");
}
private void RaisePropertyChanged(string propertyName)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
}

How to intercept NotifyPropertyChange event

I just recently discovered an INotifyPropertyChange interface. I managed to implement this interface in my clss and everything works fine. However I was wondering if it is possible to intercept this event in code and fire a function
Let's say that I have a function
DoStuff()
and I wan't to fire this function everytime property1, property2 or property3 changes.
Of course I could put this function in set block in my class but this is not a good idea(I think).

If you mean to internal method that'll handle this event you can do it by registering to the event in the class constructor. For example:
public class AnswerViewModel : IAnswerViewModel
{
public event PropertyChangedEventHandler PropertyChanged;
private string content;
public AnswerViewModel()
{
PropertyChanged += (sender, args) => DoStuff();
}
public string Content
{
get { return content; }
set
{
content = value;
PropertyChanged(this, new PropertyChangedEventArgs("Content"));
}
}
public void DoStuff()
{
// this method will be called whenever PropertyChanged event raised
}
}
If the intercepting method belongs to other class:
public class PropertiesInterceptor
{
private readonly AnswerViewModel viewModel;
private readonly List<string> propertiesToIntercept =
new List<string> { "property1", "property2", "property3" };
public PropertiesInterceptor(AnswerViewModel viewModel)
{
this.viewModel = viewModel;
viewModel.PropertyChanged += OnPropertyChanged;
}
private void OnPropertyChanged(object sender, PropertyChangedEventArgs args)
{
if (propertiesToIntercept.Contains(args.PropertyName))
{
DoStuff();
}
}
private void DoStuff()
{
// Do something with viewModel
}
}

Intercept the PropertyChanged Event:
http://msdn.microsoft.com/en-us/library/system.componentmodel.inotifypropertychanged.propertychanged.aspx

You could fire the method from a RaisePropertyChanged() method:
public int Property1
{
get { return this.property1; }
set
{
if (this.property1 != value)
{
this.property1 = value;
RaisePropertyChanged("Property1");
}
}
}
private void RaisePropertyChanged(string propertyName)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
DoStuff(); // Call DoStuff here.
}

Stealing Elisha's answer to answer your question in Merlyn's answer
public class AnswerViewModel : IAnswerViewModel
{
public event PropertyChangedEventHandler PropertyChanged;
private string property1;
private string property2;
private string propertyX;
public AnswerViewModel()
{
PropertyChanged += (sender, args) =>
{
if(args.PropertyName == "Property1" || args.PropertyName == "Property2")
DoStuff();
}
}
public string Property1
{
get { return content; }
set
{
property1 = value;
PropertyChanged(this, new PropertyChangedEventArgs("Property1"));
}
}
public string Property2
{
get { return content; }
set
{
property2 = value;
PropertyChanged(this, new PropertyChangedEventArgs("Property2"));
}
}
public string PropertyX
{
get { return content; }
set
{
propertyX = value;
PropertyChanged(this, new PropertyChangedEventArgs("PropertyX"));
}
}
public void DoStuff()
{
// this method will be called whenever PropertyChanged event raised from Property1 or Property2
}
}
If the class DoStuff is in is a member you can do
private otherClass
public AnswerViewModel()
{
PropertyChanged += (sender, args) =>
{
if(args.PropertyName == "Property1" || args.PropertyName == "Property2")
otherClass.DoStuff();
}
}
Otherwise you can just have otherClass register a event on its own in your main code.

Did you need it to replace the existing NotifyPropertyChanged event handlers, or just get called when NotifyPropertyChanged is called?
If you mean the second, you can simply register an event handler
edit
You can add an event handler that gets called on NotifyPropertyChanged, checks if the property parameter is equal to Property1, Property2, or Property3, and only then forwards it to the actual function you want to call.

.NET Databinding ignores property change

I have written a control in C# that derives from System.Windows.Forms.Control. I have added a property Selected to which I want to databind to a business entity using a BindingSource.
I’ve implemented the PropertyNameChanged pattern by adding a SelectedChanged event that I fire when the Selected property is changed.
This is my code:
public partial class RateControl : Control
{
[Category("Property Changed")]
public event EventHandler SelectedChanged;
public int Selected
{
get
{ return m_selected; }
set
{
if (m_selected != value)
{
m_selected = value;
OnSelectedChanged();
Invalidate();
}
}
}
protected virtual void OnSelectedChanged()
{
if (this.SelectedChanged != null)
this.SelectedChanged(this, new EventArgs());
}
}
When I bind to the Selected property, I see the event being subscibed to. The event is also fired when the property changes.
However the business entity is not updated. I don’t even see the getter of the Selected property being accessed.
What am I missing?

Have you got the binding's update mode set to DataSourceUpdateMode.OnPropertyChanged? Either via binding.DataSourceUpdateMode = DataSourceUpdateMode.OnPropertyChanged;, or using one of the DataBindings.Add(...) overloads.
The following works for me to push values to the business object...
using System;
using System.Diagnostics;
using System.Windows.Forms;
class MyForm : Form
{
public MyForm()
{
MyBusinessObject obj = new MyBusinessObject();
Button btn = new Button();
btn.Click += delegate { Foo++; };
DataBindings.Add("Foo", obj, "Bar", false, DataSourceUpdateMode.OnPropertyChanged);
DataBindings.Add("Text", obj, "Bar");
Controls.Add(btn);
}
private int foo;
public event EventHandler FooChanged;
public int Foo
{
get { return foo; }
set
{
if (foo != value)
{
foo = value;
Debug.WriteLine("Foo changed to " + foo);
if (FooChanged != null) FooChanged(this, EventArgs.Empty);
}
}
}
}
class MyBusinessObject
{
private int bar;
public event EventHandler BarChanged;
public int Bar
{
get { return bar; }
set
{
if (bar != value)
{
bar = value;
Debug.WriteLine("Bar changed to " + bar);
if (BarChanged != null) BarChanged(this, EventArgs.Empty);
}
}
}
}
static class Program
{
[STAThread]
static void Main()
{
Application.Run(new MyForm());
}
}