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我想從這個輔助頁面導航回到我的MainPage。我試圖使用NavigationService.GoBack()
,但我得到了NullReferenceException
。無法導航回Template10
我沒有改變viewmodel中的任何東西。我打算做的是先保存用戶輸入的SQLite,然後再返回炫魅廣東
這裏是我的代碼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);
}
這裏是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();
}
附註:我試圖使用vm.GotoMainPage()
從Detail.xaml.cs
訪問GotoMainPage
,但它仍然返回異常
哪行代碼引發空引用異常?導航服務是否爲空? –
this.Frame.Navigage(typeof(Mainpage)); –
@GlenThomas我從'NavigationService.GoBack()' –