我有一个带有两个 HamburgerMenuButtons 的应用程序：TYMLY 和 NEWTYMLY。TYMLY 是主页。我正在使用 Template10 MVVM。在启动时它根据需要导航到 TYMLY 页面，我点击 NEWTYMLY 页面并继续执行一些任务以创建一个要添加到 TYMLY 主页中的 Griview 的对象。在 PageHeader 部分中，我有一个按钮，用于保存此对象并继续导航到 TYMLY 主页并将对象添加到 Gridview。每当我按下此按钮时，我都会在以下行收到 System.NullException：
public void SaveNewTymly() =>
NavigationService.Navigate(typeof(Views.MainPage), New_Tymly);
我还注意到，如果我按下模板附带的其他按钮（如设置、隐私和关于我们），也会发生 System.NullException；
public void GotoSettings() =>
NavigationService.Navigate(typeof(Views.SettingsPage), 0);
public void GotoPrivacy() =>
NavigationService.Navigate(typeof(SettingsPage), 1);
public void GotoAbout() =>
NavigationService.Navigate(typeof(Views.SettingsPage), 2);
我想知道在这种情况下如何处理导航。谢谢你。 MainPage NewPage 创建对象以添加到主页中的gridview
新TymlyModel.cs
using System.Collections.Generic;
using System.Diagnostics;
using System.Threading.Tasks;
using Template10.Mvvm;
using Template10.Services.NavigationService;
using Tymly_Revamped.Models;
using Tymly_Revamped.Views;
using Windows.UI.Xaml.Navigation;
namespace Tymly_Revamped.ViewModels
{
class NewTymlyViewModel : ViewModelBase
{
private Tymly newTymly;
public Tymly New_Tymly { get { return newTymly; } set { Set(ref newTymly, value); } }
bool trafficFlow;
public NewTymlyViewModel()
{
newTymly = new Tymly();
}
public override async Task OnNavigatedToAsync(object parameter, NavigationMode mode, IDictionary<string, object> suspensionState)
{
New_Tymly = (suspensionState.ContainsKey(nameof(New_Tymly))) ? suspensionState[nameof(New_Tymly)] as Tymly : parameter as Tymly;
await Task.CompletedTask;
}
public override async Task OnNavigatedFromAsync(IDictionary<string, object> suspensionState, bool suspending)
{
if (suspending)
{
suspensionState[nameof(New_Tymly)] = New_Tymly;
}
await Task.CompletedTask;
}
public bool TrafficFlow
{
get { return trafficFlow; Debug.WriteLine(trafficFlow); }
set { trafficFlow = !trafficFlow; }
}
public override async Task OnNavigatingFromAsync(NavigatingEventArgs args)
{
args.Cancel = false;
await Task.CompletedTask;
}
public void SaveNewTymly() =>
NavigationService.Navigate(typeof(Views.MainPage), New_Tymly);
public void GotoSettings() =>
NavigationService.Navigate(typeof(Views.SettingsPage), 0);
public void GotoPrivacy() =>
NavigationService.Navigate(typeof(SettingsPage), 1);
public void GotoAbout() =>
NavigationService.Navigate(typeof(Views.SettingsPage), 2);
}
}
using NodaTime.TimeZones;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using Windows.Devices.Geolocation;
using Windows.UI.Xaml;
using Windows.UI.Xaml.Controls;
using Windows.UI.Xaml.Controls.Maps;
using Tymly_Revamped.Models;
using Tymly_Revamped.ViewModels;
using Tymly_Revamped.Views;
using Windows.UI.Xaml.Media;
using Windows.UI.Xaml.Markup;
using System.Collections.ObjectModel;
using Windows.ApplicationModel.Contacts;
using System.IO;
using System.Diagnostics;
using Windows.Storage.Streams;
using Windows.UI.Xaml.Media.Imaging;
namespace Tymly_Revamped.Views
{
public sealed partial class NewTymly : Page
{
private uint desiredAccuracy_meters = 0;
private CancellationTokenSource cancelTokenSrc = null;
private IEnumerable<string> zonalIds;
IReadOnlyList<GetContactDetails> condetails;
public IReadOnlyList<GetContactDetails> ConDetails { get { return condetails; } set { condetails = value; } }
ObservableCollection<GetContactDetails> contacts;
public ObservableCollection<GetContactDetails> Contacts { get { return contacts; } set { contacts = value; } }
public NewTymly()
{
this.InitializeComponent();
NavigationCacheMode = Windows.UI.Xaml.Navigation.NavigationCacheMode.Enabled;
DataContext = new NewTymlyViewModel();
searchLocation.Loaded += Map_Loaded;
searchLocation.MapTapped += Map_Tapped;
searchLocation.MapDoubleTapped += Map_DoubledTapped;
searchLocation.Style = MapStyle.Road;
}
private void Map_DoubledTapped(MapControl sender, MapInputEventArgs args)
{
throw new NotImplementedException();
}
private void Map_Tapped(MapControl sender, MapInputEventArgs args)
{
var tappedPositon = args.Location.Position;
if (sender.ZoomLevel < 20)
{
sender.ZoomLevel += 2;
}
else if (sender.ZoomLevel >= 20)
{
sender.ZoomLevel = 12;
}
}
private async void Map_Loaded(object sender, RoutedEventArgs e)
{
try
{
var requestLocationAccess = await Geolocator.RequestAccessAsync();
switch (requestLocationAccess)
{
case GeolocationAccessStatus.Allowed:
cancelTokenSrc = new CancellationTokenSource();
CancellationToken token = cancelTokenSrc.Token;
Geolocator geolocator = new Geolocator { DesiredAccuracyInMeters = desiredAccuracy_meters };
Geoposition pos = await geolocator.GetGeopositionAsync().AsTask(token);
searchLocation.Center =
new Geopoint(new BasicGeoposition()
{
Latitude = pos.Coordinate.Point.Position.Latitude,
Longitude = pos.Coordinate.Point.Position.Longitude
});
searchLocation.ZoomLevel = 1;
break;
}
}
catch (TaskCanceledException)
{
throw new TaskCanceledException();
}
finally
{
cancelTokenSrc = null;
}
}
private async void ShowOnMap(double lati, double longi)
{
try
{
var accessLocation = await Geolocator.RequestAccessAsync();
switch (accessLocation)
{
case GeolocationAccessStatus.Allowed:
cancelTokenSrc = new CancellationTokenSource();
CancellationToken token = cancelTokenSrc.Token;
Geolocator geolocator = new Geolocator { DesiredAccuracyInMeters = desiredAccuracy_meters };
Geoposition pos = await geolocator.GetGeopositionAsync().AsTask(token);
searchLocation.Center =
new Geopoint(new BasicGeoposition()
{
Latitude = lati,
Longitude = longi,
});
searchLocation.ZoomLevel = 5;
break;
}
}
catch (TaskCanceledException)
{
}
finally
{
cancelTokenSrc = null;
}
}
private void styleCombobox_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
switch (mapStyle.SelectedIndex)
{
case 0:
searchLocation.Style = MapStyle.None;
break;
case 1:
searchLocation.Style = MapStyle.Road;
break;
case 2:
searchLocation.Style = MapStyle.Aerial;
break;
case 3:
searchLocation.Style = MapStyle.AerialWithRoads;
break;
case 4:
searchLocation.Style = MapStyle.Terrain;
break;
}
}
public void InputLocation_TextChanged(AutoSuggestBox sender, AutoSuggestBoxTextChangedEventArgs args)
{
if (args.Reason == AutoSuggestionBoxTextChangeReason.UserInput)
{
zonalIds = TzdbDateTimeZoneSource.Default.ZoneLocations.
Where(loc => loc.CountryName.IndexOf(sender.Text, StringComparison.CurrentCultureIgnoreCase) > -1).
Select(loc => loc.ZoneId);
sender.ItemsSource = zonalIds.ToList();
}
}
public void InputLocation_QuerySubmitted(AutoSuggestBox sender, AutoSuggestBoxQuerySubmittedEventArgs args)
{
MapGlyphs mapGlyph = new MapGlyphs();
if (args.ChosenSuggestion != null)
{
var selectedZonalId = args.ChosenSuggestion as string;
string state = selectedZonalId.Remove(0, selectedZonalId.IndexOf("/") + 1).Replace("_", " ");
var country = TzdbDateTimeZoneSource.Default.ZoneLocations.
Where(zoneloc => zoneloc.ZoneId == selectedZonalId).Select(zoneloc => zoneloc.CountryName).
ElementAtOrDefault(0);
var timeZone = TzdbDateTimeZoneSource.Default.ZoneLocations.
Where(tym => tym.ZoneId == selectedZonalId).Select(tymZone => TzdbDateTimeZoneSource.Default.WindowsMapping.
MapZones.FirstOrDefault(tym => tym.TzdbIds.Contains(selectedZonalId))).
Where(tym => tym != null).Select(tym => tym.WindowsId).Distinct();
var lattitude = TzdbDateTimeZoneSource.Default.ZoneLocations.
Where(lat => lat.ZoneId == selectedZonalId).Select(tym => tym.Latitude);
var longitude = TzdbDateTimeZoneSource.Default.ZoneLocations.
Where(lon => lon.ZoneId == selectedZonalId).Select(tym => tym.Longitude);
if (timeZone.Count() != 0)
{
var dateTime = TimeZoneInfo.ConvertTime(
DateTime.Now, TimeZoneInfo.FindSystemTimeZoneById(timeZone.ElementAt(0)));
if (mapGlyph.PlaceIcon.ContainsKey(state))
{
locationText.Text = state;
ViewModel.New_Tymly.Location = state;
ViewModel.New_Tymly.MapIcon = mapGlyph.MapLocationIcon(state);
}
else
{
locationText.Text = country;
ViewModel.New_Tymly.Location = country;
ViewModel.New_Tymly.MapIcon = mapGlyph.MapLocationIcon(country);
}
dateText.Text = dateTime.ToString("D");
timeText.Text = dateTime.ToString("T");
ViewModel.New_Tymly.Datetime = dateTime;
IconPath.Data = PathMarkupToGeometry(ViewModel.New_Tymly.MapIcon);
}
else
{
}
ShowOnMap(lattitude.ElementAt(0), longitude.ElementAt(0));
}
}
public void InputLocation_SuggestionChosen(AutoSuggestBox sender, AutoSuggestBoxSuggestionChosenEventArgs args)
{
MapGlyphs mapGlyph = new MapGlyphs();
var place = args.SelectedItem as string;
string state = place.Remove(0, place.IndexOf("/") + 1).Replace("_", " ");
var country = TzdbDateTimeZoneSource.Default.ZoneLocations.
Where(zoneloc => zoneloc.ZoneId == place).Select(zoneloc => zoneloc.CountryName).
ElementAtOrDefault(0);
var timeZone = TzdbDateTimeZoneSource.Default.ZoneLocations.
Where(x => x.ZoneId == place).Select(tz => TzdbDateTimeZoneSource.Default.WindowsMapping.
MapZones.FirstOrDefault(x => x.TzdbIds.Contains(place))).
Where(x => x != null).Select(x => x.WindowsId).Distinct();
var latitude = TzdbDateTimeZoneSource.Default.ZoneLocations.
Where(x => x.ZoneId == place).Select(tz => tz.Latitude);
var longitude = TzdbDateTimeZoneSource.Default.ZoneLocations.
Where(x => x.ZoneId == place).Select(tz => tz.Longitude);
if (timeZone.Count() != 0)
{
var dateTime = TimeZoneInfo.ConvertTime(
DateTime.Now, TimeZoneInfo.FindSystemTimeZoneById(timeZone.ElementAt(0)));
if (mapGlyph.PlaceIcon.ContainsKey(state))
{
locationText.Text = state;
ViewModel.New_Tymly.Location = state;
ViewModel.New_Tymly.MapIcon = mapGlyph.MapLocationIcon(state);
}
else
{
locationText.Text = country;
ViewModel.New_Tymly.Location = country;
ViewModel.New_Tymly.MapIcon = mapGlyph.MapLocationIcon(country);
}
dateText.Text = dateTime.ToString("D");
timeText.Text = dateTime.ToString("T");
ViewModel.New_Tymly.Datetime = dateTime;
IconPath.Data = PathMarkupToGeometry(ViewModel.New_Tymly.MapIcon);
}
else
{
}
ShowOnMap(latitude.ElementAt(0), longitude.ElementAt(0));
}
Geometry PathMarkupToGeometry(string pathMarkup)
{
string xaml =
"<Path " +
"xmlns='http://schemas.microsoft.com/winfx/2006/xaml/presentation'>" +
"<Path.Data>" + pathMarkup + "</Path.Data></Path>";
var path = XamlReader.Load(xaml) as Windows.UI.Xaml.Shapes.Path;
// Detach the PathGeometry from the Path
Geometry geometry = path.Data;
path.Data = null;
return geometry;
}
private async void AddContacts(object sender, RoutedEventArgs e)
{
var contactPicker = new ContactPicker();
contactPicker.DesiredFieldsWithContactFieldType.Add(ContactFieldType.Email);
contactPicker.DesiredFieldsWithContactFieldType.Add(ContactFieldType.PhoneNumber);
var selectedContacts = await contactPicker.PickContactsAsync();
ContactStore contactStore = await ContactManager.RequestStoreAsync(ContactStoreAccessType.AllContactsReadOnly);
if (selectedContacts != null && selectedContacts.Count > 0)
{
foreach (var item in selectedContacts)
{
Contact realContact = await contactStore.GetContactAsync(item.Id);
ViewModel.New_Tymly.ContactList.Add(new ContactItemAdapter(realContact));
var t = new ContactItemAdapter(realContact).Thumbnail;
Debug.WriteLine(t);
}
}
}
private void DeleteContact(object sender, RoutedEventArgs e)
{
ContactItemAdapter item = (ContactItemAdapter)(sender as Button).DataContext;
Debug.WriteLine(item.Name);
if (addContacts.Items.Contains(item))
{
ViewModel.New_Tymly.ContactList.Remove(item);
}
}
}
}