如何将 pubnub 服务器中的数据以 xamarin 形式添加到列表视图中

我的日志文件中出现错误

[0:] 绑定：在“Saileela：Testmessage”上找不到“Usermessage”属性，目标属性：“Xamarin.Forms.Label.Text”

private void MessageReceived(object sender, MessageEventArgs e)
{
    _chatWindowViewModel.Usermessage = e.Message;
    _chatWindowViewModel.MessagesList.Add(e.Message);
}

我的列表视图是：

<ListView x:Name="Listview" ItemsSource="{Binding MessagesList}">
     <ListView.ItemTemplate>
          <DataTemplate>
              <ViewCell>
                  <StackLayout Orientation="Vertical">
                      <Label Text="{Binding Usermessage}" FontSize="15"/>
                  </StackLayout>
              </ViewCell>
          </DataTemplate>
      </ListView.ItemTemplate>
</ListView>

我的视图模型是：

namespace MobileChat.ViewModels.Chat
{
    public class ChatWindowViewModel : INotifyPropertyChanged
    {
        private string _message;
        private ObservableCollection<string> _messageslist = new ObservableCollection<string>();
        public ChatWindowViewModel()
        {
        }

        public ObservableCollection<string> MessagesList
        {
            get { return _messageslist;}
            set{_messageslist = value;OnPropertyChanged();}
        }

        public string Usermessage
        {
            get { return _message; }
            set{_message = value;OnPropertyChanged();}
        }

        public event PropertyChangedEventHandler PropertyChanged;
        protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
        {
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
        }
    }
}