[英]Cannot navigate back in Template10
我正在嘗試從此輔助頁面導航回我的MainPage。 我嘗試使用NavigationService.GoBack()
但得到了NullReferenceException
。
我沒有從視圖模型中進行任何更改。 我打算做的是先將用戶輸入保存到SQLite,然后導航回MainPage
這是我來自DetailPage.xaml.cs
代碼
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:我嘗試使用vm.GotoMainPage()
從Detail.xaml.cs
訪問GotoMainPage
,但它仍返回異常
Frame.Navigate
方法。 this.Frame.Navigage(typeof(Mainpage));
有關更多信息,請參見文檔: Frame.Navigate
使用的命名空間稱為System.Windows.Controls
。
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