WPF列表框/查看数据绑定结果

当我尝试将可观察列表与listbox/view同步时,出现了这个问题 但它不会改变变量的

这是XAML

   <ListBox x:Name="PostListView" BorderThickness="0"
                  MinHeight="300" 
                  Background="{x:Null}"
                  BorderBrush="{x:Null}"
                  Foreground="{x:Null}"
                  VerticalContentAlignment="Top"
                  ScrollViewer.HorizontalScrollBarVisibility="Disabled"
                  ScrollViewer.VerticalScrollBarVisibility="Disabled"
                 DataContext="{Binding Source={StaticResource PostListData}}"
                  ItemsSource="{Binding Mode=OneWay}"
                  IsSynchronizedWithCurrentItem="True"
                  MinWidth="332" SelectedIndex="0" SelectionMode="Extended" AlternationCount="1">
            <ListBox.ItemTemplate>
                <DataTemplate>
                  <DockPanel x:Name="SinglePost" VerticalAlignment="Top" ScrollViewer.CanContentScroll="True" ClipToBounds="True" Width="333" Height="70" d:LayoutOverrides="VerticalAlignment" d:IsEffectDisabled="True">
            <DockPanel.DataContext>
                <local:PostList/>
            </DockPanel.DataContext>
            <StackPanel x:Name="AvatarNickHolder" Width="60">
                            <Label x:Name="Nick" HorizontalAlignment="Center" Margin="5,0" VerticalAlignment="Top" Height="15" Content="{Binding Path=pUsername, FallbackValue=pUsername}" FontFamily="Arial" FontSize="10.667" Padding="5,0"/>
                <Image x:Name="Avatar" HorizontalAlignment="Center" Margin="5,0,5,5" VerticalAlignment="Top" Width="50" Height="50" IsHitTestVisible="False" Source="1045443356IMG_0972.jpg" Stretch="UniformToFill"/>
            </StackPanel>
                        <TextBlock x:Name="userPostText" Margin="0,0,5,0" VerticalAlignment="Center" FontSize="10.667" Text="{Binding Path=pMsg, FallbackValue=pMsg}" TextWrapping="Wrap"/>
        </DockPanel>
    </DataTemplate>
            </ListBox.ItemTemplate>
    </ListBox>  

下面是ovservable list类

  public class PostList : ObservableCollection<PostData>
    {
        public PostList()
            : base()
        {
            Add(new PostData("this is test msg", "Cather", "1045443356IMG_0972.jpg"));
            Add(new PostData("this is test msg1", "t1", "1045443356IMG_0972.jpg"));
            Add(new PostData("this is test msg2", "t2", "1045443356IMG_0972.jpg"));
            Add(new PostData("this is test msg3", "t3", "1045443356IMG_0972.jpg"));
            Add(new PostData("this is test msg4", "t4", "1045443356IMG_0972.jpg"));
            Add(new PostData("this is test msg5", "t5", "1045443356IMG_0972.jpg"));
           // Add(new PostData("Isak", "Dinesen"));
          //  Add(new PostData("Victor", "Hugo"));
          //  Add(new PostData("Jules", "Verne"));
        }
    }

    public class PostData
    {
        private string Username;
        private string Msg;
        private string Avatar;
        private string LinkAttached;
        private string PicAttached;
        private string VideoAttached;

        public PostData(string msg ,string username, string avatar=null, string link=null,string pic=null ,string video=null)
        {
            this.Username = username;
            this.Msg = msg;
            this.Avatar = avatar;
            this.LinkAttached = link;
            this.PicAttached = pic;
            this.VideoAttached = video;
        }

        public string pMsg
        {
            get { return Msg; }
            set { Msg = value; }
        }

        public string pUsername
        {
            get { return Username; }
            set { Username = value; }
        }

        public string pAvatar
        {
            get { return Avatar; }
            set { Avatar = value; }
        }

        public string pLink
        {
            get { return LinkAttached; }
            set { LinkAttached = value; }
        }

        public string pPic
        {
            get { return PicAttached; }
            set { PicAttached = value; }
        }

        public string pVideo
        {
            get { return VideoAttached; }
            set { VideoAttached = value; }
        }
    }

有什么想法吗?