更改ComboBox项源并使用CollectionChanged更新通知

Question

I have a ComboBox cbo1 .

I'm trying to change the item source using the ViewModel with CollectionChanged but the ComboBox items stay blank and won't update.

I've tried several examples and solutions here, but don't know how to implement them right.

---

XAML

<ComboBox x:Name="cbo1" 
          ItemsSource="{Binding cbo1_Items, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"
          SelectedItem="{Binding cbo1_SelectedItem, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"
          HorizontalAlignment="Left" 
          Margin="0,0,0,0"
          VerticalAlignment="Top"
          Width="105" 
          Height="22" />

---

ViewModelBase Class

Bind ComboBox Items

public class ViewModelBase : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;

    protected void Notify(string propName)
    {
        if (this.PropertyChanged != null)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(propName));
        }
    }

    public ViewModelBase()
    {
        _cbo1_Items = new ObservableCollection<string>();
        _cbo1_Items.CollectionChanged += cbo1_Items_CollectionChanged;
    }

    // Notify Collection Changed
    //
    public void cbo1_Items_CollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
    {
        Notify("cbo1_Items");
    }


    // Item Source
    //
    public static ObservableCollection<string> _cbo1_Items = new ObservableCollection<string>();
    public static ObservableCollection<string> cbo1_Items
    {
        get { return _cbo1_Items; }
        set { _cbo1_Items = value; }
    }

    // Selected Item
    //
    public static string cbo1_SelectedItem { get; set; }

}

---

Example Class

In this class I want to change the ComboBox Item Source.

// Change ViewModel Item Source
//
ViewModelBase._cbo1_Items = new ObservableCollection<string>()
{
    "Item 1",
    "Item 2",
    "Item 3"
};

// ...

// Change Item Source Again
//
ViewModelBase._cbo1_Items = new ObservableCollection<string>()
{
    "Item 4",
    "Item 5",
    "Item 6"
};

Answer 1

Implement - RaisePropertyChanged("ComboBoxItemsource");/NotifyPropertyChanged("ComboBoxItemsource") in your property declaration. Ex: -

In View

<ComboBox Width="40" Height="40" ItemsSource="{Binding ComboBoxItemsource, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" />

In View Model-

private ObservableCollection<string> comboBoxItemsource;
 public ObservableCollection<string> ComboBoxItemsource
        {
            get { return comboBoxItemsource; }
            set
            {
                if (comboBoxItemsource != value)
                {
                    comboBoxItemsource = value; 
                    RaisePropertyChanged("ComboBoxItemsource");
                }
            }
        }

    In Class Constructor-

public ClassViewModel()
        {
            ComboBoxItemsource = new ObservableCollection<string>();
            ComboBoxItemsource.Add("Item1");
            ComboBoxItemsource.Add("Item2");
           ....
       }

    //Event on which you want to change the collection

    public void OnClickEvent()
    {
                ComboBoxItemsource = new ObservableCollection<string>();
                ComboBoxItemsource.Add("Item5");
                ComboBoxItemsource.Add("Item6");
    }

Class should Inherit and Implement INotifyPropertyChanged. Hope this Helps..