ObservableCollection，OnPropertyChanged未触发

Question

I'm beginner and I tried to search everywhere for a similar problem, this question has been asked many times but I couldn't find any solution.

I implemented INotifyPropertyChanged like this (it is working correctly):

    public event PropertyChangedEventHandler PropertyChanged;
    public void OnPropertyChanged(string propertyName)
    {
        PropertyChangedEventHandler handler = PropertyChanged;
        if (handler != null)
        {
            MessageBox.Show("property changed");
            handler(this, new PropertyChangedEventArgs(propertyName));
        }
    }

My observablecollection look like this :

    ObservableCollection<bool>  Test = new ObservableCollection<bool>(new[] { false, false, false, false, false, false });

    private ObservableCollection<bool> _Collection;
    public ObservableCollection<bool> Collection
    {
        get { return _Collection = Test; }
        set { _Collection = value; OnPropertyChanged("Collection"); }
    }

This collection is bound to togglebutton's property contained in usercontrols :

VidFlipX="{Binding DataContext.Collection[1], ElementName=cmix, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"

Data changed correctly while using them but if I set the collection in an other way, OnPropertyChanged is not firing and so my togglebuttons are not updated.

Can't find out why...

Answer 1

With changing a item of your collection, you are not changing your collection. So you are not calling the setter of your collection. To update the item on your Ui, your items in your collection have to implement the INotifyPropertyChanged like described here .

A solution could be like this:

ObservableCollection<ClassA> Test { get; set; }

With your class:

class ClassA : INotifyPropertyChanged
{
    private bool _isEnabled;
    public bool IsEnabled
    {
        get { return _isEnabled; }
        set
        {
            if (value != _isEnabled)
            {
                _isEnabled = value;
                OnPropertyChanged("IsEnabled");
            }
        }
    }

    public event PropertyChangedEventHandler PropertyChanged;

    protected void OnPropertyChanged(string propertyName)
    {
        PropertyChangedEventHandler handler = PropertyChanged;
        if (handler != null)
            handler(this, new PropertyChangedEventArgs(propertyName));
    }
}

Answer 2

You must not call

return _Collection = Test;

in the getter of your Collection property, because this renders the setter (and hence the whole INotifyPropertyChanged implementation) useless. The value passed to the setter is never used anywhere.

When you need to initialize your property with a predefined collection, you could do it like this:

private ObservableCollection<bool> _Collection
    = new ObservableCollection<bool>(new[] { false, false, false, false, false, false });

public ObservableCollection<bool> Collection
{
    get { return _Collection; }
    set { _Collection = value; OnPropertyChanged("Collection"); }
}