UWP MVVM 轻型网格视图所选项触发器具有旧值

Question

我有一个网格视图，其中 selectedItem 绑定到我的视图模型：

<GridView  x:Name="Patients"
               Grid.Row="1"
               ItemsSource="{x:Bind ViewModel.Patients}"
               SelectedItem="{x:Bind ViewModel.SelectedPatient, Mode=Twoway, UpdateSourceTrigger=PropertyChanged}">
        <GridView.ItemsPanel>
            <ItemsPanelTemplate>
                <ItemsStackPanel Margin="14,0,0,0" Orientation="Vertical" />
            </ItemsPanelTemplate>
        </GridView.ItemsPanel>
        <GridView.ItemTemplate>
            <DataTemplate x:DataType="datamodel:Patient">
                <TextBlock Text="{x:Bind Name}"
                                   FontWeight="Medium"
                                   TextWrapping="NoWrap"
                                   HorizontalAlignment="Left">
                </TextBlock>
            </DataTemplate>
        </GridView.ItemTemplate>
</GridView>

这一切似乎都工作了 1 次，但是当我离开并返回并按下一个项目时，该项目被空对象覆盖。我的财产上的setter被调用了4次，我试图找到堆栈跟踪的问题，但它一直说外部代码。

这是我的观点模型：

    public RelayCommand GoToEditPatientCommand { get; set; }
    public RelayCommand GoToInfoPatientCommand { get; set; }
    //PROPERTIES
    public static NavigationServiceEx NavigationService => ViewModelLocator.Current.NavigationService;
    private ObservableCollection<Patient> _patients;
    public ObservableCollection<Patient> Patients {
        get { return _patients = (_patients ?? new ObservableCollection<Patient>()); }
        set { _patients = value; RaisePropertyChanged("Patients"); }
    }
    private Patient _selectedPatient;
    public Patient SelectedPatient {
        get { return _selectedPatient = (_selectedPatient ?? new Patient()); }
        set
        {
            if (_selectedPatient != value)
            {
                _selectedPatient = value;
                RaisePropertyChanged("SelectedPatient");
            }
        }
    }
    //CONSTRUCTOR
    public PatientsViewModel()
    {
        GoToAddPatientCommand = new RelayCommand(() => NavigationService.Navigate("PatientApp.UWP.ViewModels.AddPatientViewModel"));
        GoToEditPatientCommand = new RelayCommand(() =>
        {
            if (SelectedPatient.Name != null)
            {
                NavigationService.Navigate("PatientApp.UWP.ViewModels.EditPatientViewModel", SelectedPatient);
                SelectedPatient = new Patient();
            }
        });
        GoToInfoPatientCommand = new RelayCommand(() =>
        {
            if (SelectedPatient.Name != null)
            {
                NavigationService.Navigate("PatientApp.UWP.ViewModels.InfoPatientViewModel", SelectedPatient);
                SelectedPatient = new Patient();
            }
        });
    }

Answer 1

这一切似乎都工作了 1 次，但是当我离开并返回并按下一个项目时，该项目被空对象覆盖。

请检查GoToEditPatientCommand方法，导航到新页面后，SelectedPatient设置了新实例。这将使SelectedPatient空虚。请尝试删除SelectedPatient = new Patient();。

GoToEditPatientCommand = new RelayCommand(() =>
{
    if (SelectedPatient.Name != null)
    {
       NavigationService.Navigate("PatientApp.UWP.ViewModels.EditPatientViewModel", SelectedPatient);
      // SelectedPatient = new Patient();
    }
});