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我正在尝试从此辅助页面导航回我的 MainPage。我尝试使用NavigationService.GoBack()，但我得到了NullReferenceException.

我没有从视图模型中改变任何东西。我打算先将用户输入保存到 SQLite，然后导航回 MainPage

这是我的代码DetailPage.xaml.cs

    private SQLiteService database = new SQLiteService();
    DetailPageViewModel vm = new DetailPageViewModel();

    public DetailPage()
    {
        InitializeComponent();
        NavigationCacheMode = NavigationCacheMode.Disabled;
    }

    private void yesButton_Click(object sender, Windows.UI.Xaml.RoutedEventArgs e)
    {            
        var _name = Name.Text;
        var _uptake = UptakeTime.SelectedIndex + 1; // database index Morning start at 1
        var _intake = int.Parse(Intake.Text);

        vm.ProcessData(_name, _intake, _uptake);
    }

这里是DetailPageViewModel.cs

    SQLiteService database = new SQLiteService();

    public DetailPageViewModel()
    {
        if (Windows.ApplicationModel.DesignMode.DesignModeEnabled)
        {
            Value = "Designtime value";
        }
    }

    private string _Value = "Default";
    public string Value { get { return _Value; } set { Set(ref _Value, value); } }

    public override async Task OnNavigatedToAsync(object parameter, NavigationMode mode, IDictionary<string, object> state)
    {
        Value = (state.ContainsKey(nameof(Value))) ? state[nameof(Value)]?.ToString() : parameter?.ToString();
        await Task.CompletedTask;
    }

    public override async Task OnNavigatedFromAsync(IDictionary<string, object> pageState, bool suspending)
    {
        if (suspending)
        {
            pageState[nameof(Value)] = Value;
        }
        await Task.CompletedTask;
    }

    public override async Task OnNavigatingFromAsync(NavigatingEventArgs args)
    {
        args.Cancel = false;
        await Task.CompletedTask;
    }

    public void GotoMainPage() =>
        NavigationService.GoBack();    

    public void ProcessData(string _name, int _type, int _uptake)
    {
        database.AddNewItem(_name, _uptake, _type);
        GotoMainPage();
    }

旁注：我尝试通过 using访问GotoMainPagefrom ，但它仍然返回异常Detail.xaml.csvm.GotoMainPage()

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1 回答 1

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  • 要在不同页面之间导航，请使用该Frame.Navigate方法。
  • 页面导航到名为 Mainpage 的 xaml 页面的示例是： this.Frame.Navigage(typeof(Mainpage));

有关更多信息，请查看文档：Frame.Navigate

正在使用的命名空间称为System.Windows.Controls.

于 2016-08-24T18:21:59.120 回答