组合框所选项目问题

Question

Today I am stucked in very basic concept again. What is the mistake I am doing.

I have XAML like

<ComboBox ItemsSource="{Binding MyItems}" Height="40" Width="200" SelectedIndex="0"
              SelectedItem="{Binding MySelectedItem}">
        <ComboBox.ItemTemplate>
            <DataTemplate>
                <TextBlock Text="{Binding Name}"/>
            </DataTemplate>
        </ComboBox.ItemTemplate>
    </ComboBox>
    <TextBlock Text="{Binding MySelectedItem.Name}"/>
    <Button Content="Test" Grid.Row="1" Click="Button_Click_1"/>

My ModelView looks like

public class MainViewModel : DependencyObject,INotifyPropertyChanged
{
    private MyModel mySelectedItem;
    public MyModel MySelectedItem
    {
        get
        {
            return mySelectedItem;
        }
        set
        {
            if (value != mySelectedItem)
            {
                mySelectedItem = value;
                RaisePropertyChange("MySelectedItem");
            }
        }
    }
    public IList<MyModel> MyItems
    {
        get
        {
            return new List<MyModel>() {new MyModel(){Name="A"},
                                        new MyModel(){Name="B"},
                                        new MyModel(){Name="C"}};
        }
    }
    public event PropertyChangedEventHandler PropertyChanged;

    private void RaisePropertyChange(string name)
    {
        if(PropertyChanged !=  null)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(name));
        }
    }
}

One MyItems property and one SelectedItem property

and Click handler like

    private void Button_Click_1(object sender, RoutedEventArgs e)
    {
        Random r = new Random();
        int icnt = r.Next(0,3);
        model.MySelectedItem = model.MyItems[icnt]; 
    }

I found that TextBlock.Text is updating but Combobox selected item is not updating. I try to dig out the reason and found that if I execute code below

   MyModel prevItem = model.MyItems.Where((m) => m.Name.Equals("A")).FirstOrDefault();
        MyModel newItem = model.MyItems.Where((m) => m.Name.Equals("A")).FirstOrDefault();
        bool result = prevItem.Equals(newItem);

The value is always false. But why, why I am getting the new reference to same object from collection.

How can resolve this issue.

Thanks

Answer 1

you are getting a new reference because each time the binding mechanism will ask for MyItems you will create a new list. try creating it once and use observable collection

Answer 2

You need to modify your MyItems code. You are getting new list every time. Try this out.

private List<MyModel> _myItems;
public IList<MyModel> MyItems
{
    get
    {
        if (_myItems == null)
        {
            myItems = new List<MyModel>();
            myItems.Add(new MyModel() { Name = "A" });
            myItems.Add(new MyModel() { Name = "B" });
            myItems.Add(new MyModel() { Name = "C" });
        }
        return _myItems}
    }
}