Xamarin选项卡式页面MVVM在页面之间传递数据

public class MessageViewModel : INotifyPropertyChanged
{
    private string message;

    public string Message
    {
        get { return message; }
        set
        {
            if (message != value)
            {
                message = value;
                OnPropertyChanged(nameof(Message));
                MessagingCenter.Send(this, "MessageUpdated", message);
            }
        }
    }

    public event PropertyChangedEventHandler PropertyChanged;

    protected virtual void OnPropertyChanged(string propertyName)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }
}

public partial class SendMessagePage : ContentPage
{
    private MessageViewModel viewModel;

    public SendMessagePage()
    {
        InitializeComponent();

        viewModel = new MessageViewModel();
        BindingContext = viewModel;
    }

    private void SendMessageButton_Clicked(object sender, EventArgs e)
    {
        viewModel.Message = MessageEntry.Text;
    }
}

public partial class ReceiveMessagePage : ContentPage
{
    private MessageViewModel viewModel;

    public ReceiveMessagePage()
    {
        InitializeComponent();

        viewModel = new MessageViewModel();
        BindingContext = viewModel;

        MessagingCenter.Subscribe<MessageViewModel, string>(this, "MessageUpdated", (sender, message) =>
        {
            viewModel.Message = message;
        });
    }
}