ViewModel中的集合不会通知我的View

Question

我将View的数据上下文设置为ViewModel，如下所示

PersonVM pvm = null;

public MainPage()
    {
        this.InitializeComponent();

        pvm = new PersonVM();
        this.DataContext = pvm;
    }

然后点击按钮我想在我的收藏中添加更多项目

private void Btn_PointerPressed(object sender, Windows.UI.Xaml.Input.TappedRoutedEventArgs e)
    {
        pvm.DataSource.Add(new PersonVMWrapper(new PersonModel() { Name = "asdasd", Age = 23 }));
    }

这是我的ViewModel，我显然做错了什么，但无法搞清楚..

namespace App3vv.ViewModel
{
public class PersonVMWrapper : INotifyPropertyChanged
{
    PersonModel _pm = null;

    public PersonVMWrapper(PersonModel pm)
    {
        _pm = pm;
    }

    public string Name
    {
        get
        {
            return "mr." + _pm.Name;
        }

        set { RaisePropertyChanged("Name"); }
    }

    public string Age
    {
        get
        {
            return _pm.Age.ToString() + " years";
        }

        set { RaisePropertyChanged("Age"); }
    }

    public event PropertyChangedEventHandler PropertyChanged;

    private void RaisePropertyChanged(string propertyName)
    {
        PropertyChangedEventHandler handler = this.PropertyChanged;
        if (handler != null)
        {
            handler(this, new PropertyChangedEventArgs(propertyName));
        }
    }
}

public class PersonVM : INotifyPropertyChanged
{
    private ObservableCollection<PersonVMWrapper> personDataSource;

    public PersonVM()
    {
        this.DataSource.Add(new PersonVMWrapper(new PersonModel() { Name = "John", Age = 32 }));
        this.DataSource.Add(new PersonVMWrapper(new PersonModel() { Name = "Kate", Age = 27 }));
        this.DataSource.Add(new PersonVMWrapper(new PersonModel() { Name = "Sam", Age = 30 }));

        DataSource.CollectionChanged += DataSource_CollectionChanged;
    }
    void DataSource_CollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
    {
        this.RaisePropertyChanged("DataSource");
    }

    public ObservableCollection<PersonVMWrapper> DataSource
    {
        get
        {
            if (this.personDataSource == null)
            {
                this.personDataSource = new ObservableCollection<PersonVMWrapper>();
            }
            return this.personDataSource;
        }
        set
        {
        }
    }

    public event PropertyChangedEventHandler PropertyChanged;

    private void RaisePropertyChanged(string propertyName)
    {
        PropertyChangedEventHandler handler = this.PropertyChanged;
        if (handler != null)
        {
            handler(this, new PropertyChangedEventArgs(propertyName));
        }
    }
}
}

编辑：我实现了CollectionChange，但我的View仍然没有添加新项目..