I have a problem with this sample from Mvvmcross5 documentation :
public class MyViewModel : MvxViewModel
{
private readonly IMvxNavigationService _navigationService;
public MyViewModel(IMvxNavigationService navigation)
{
_navigationService = navigationService;
}
public async Task SomeMethod()
{
var result = await _navigationService.Navigate<NextViewModel, MyObject, MyReturnObject>(new MyObject());
//Do something with the result MyReturnObject that you get back
}
}
public class NextViewModel : MvxViewModel<MyObject, MyReturnObject>
{
public async Task Initialize(MyObject parameter)
{
//Do something with parameter
}
public async Task SomeMethod()
{
await Close(new MyReturnObject());
}
}
It seems to work with a simple Xamarin app with Mvvmcross project. Now, i need to use it with Xamarin.Forms : the close method is called but after showing the previous page, nothing happen :/
In output : "Requesting presentation change" maybe a clue ?
Related
I have a controller with many action method. The requirement for me is to check a value of a field from database and if the field value is "true" all the action methods can execute otherwise these action methods should not execute.
The method is in service layer
public class CustomAttributeFilter : ActionFilterAttribute
{
public override void OnActionExecuting(ActionExecutingContext filterContext)
{
var myFlag = await _adminDB.GetFlagSettingsAsync();
// how do i call async method from OnActionExecuting filter
if (!myFlag)
{
//Create your result
filterContext.Result = new EmptyResult();
}
else
{
base.OnActionExecuting(filterContext);
}
}
}
Interface implementaion
public interface IAdminDB
{
Task<MySettings> GetMySettingsAsync();
}
public class AdminDB : IAdminDB
{
public async Task<MySettings> GetMySettingsAsync()
{
var dbName = _appSettings.AdminDbName;
var blobName = _appSettings.AdminBlobName;
return await _dbStorage.GetBlobAsync<MySettings>(blobName, dbName);
}
}
public class MySettings
{
public bool MyFlag { get; set; }
}
I get an error message "no suitable method found to override". How do i clear this error and how to inject service properly . Above is what i have tried, the call to async getting failed here.
I don't see where the _adminDB dependency comes from in your code, but I'm guessing that is causing the problem.
If you want to use async filters you have to implement the IAsyncActionFilter interface.
You can retrieve services from the executing context's DI container and use async methods the following way:
public class CustomAttributeFilter : ActionFilterAttribute
{
public override async Task OnActionExecutionAsync(
ActionExecutingContext context, ActionExecutionDelegate next)
{
var adminDb = filterContext.HttpContext.RequestServices.GetService<AdminDb>();
var myFlag = await adminDb.GetFlagSettingsAsync();
//..
await next();
}
}
Depending on your your needs, you can place your custom logic after the next() call as well.
See the documentation for more information.
When i try to run the project, i am getting this kind of error: "System.NullReferenceException: Object reference not set to an instance of an object"
pointing in this code:
sqliteconnection = DependencyService.Get().GetConnection();
This is my Class for DB actions:
namespace DevoApp.DevoAppFinal.Helpers
{
public class DatabaseHelper
{
static SQLiteConnection sqliteconnection;
public const string DbFileName = "Devotion.db";
public DatabaseHelper()
{
sqliteconnection = DependencyService.Get<ISQLite>().GetConnection();
sqliteconnection.CreateTable<Devotion>();
}
// Get All Contact data
public List<Devotion> GetAllDevotionsData()
{
return (from data in sqliteconnection.Table<Devotion>() select data).ToList();
}
//Get Specific Contact data
public Devotion GetDevotionData(int id)
{
return sqliteconnection.Table<Devotion>().FirstOrDefault(t => t.devotionalId == id);
}
// Delete all Contacts Data
public void DeleteAllDevotions()
{
sqliteconnection.DeleteAll<Devotion>();
}
// Delete Specific Contact
public void DeleteDevotion(int id)
{
sqliteconnection.Delete<Devotion>(id);
}
// Insert new Contact to DB
public void InsertDevotion(Devotion contact)
{
sqliteconnection.Insert(contact);
}
// Update Contact Data
public void UpdateDevotion(Devotion contact)
{
sqliteconnection.Update(contact);
}
}
}
When using the DependencyService, you have to implement the interface in each targeted platform project.
In this case, you should have the ISQLite interface implemented on the platforms you're targeting, i.e. iOS and Android.
To make Xamarin find it at runtime, you will have to register the implementation with the Dependency attribute above the namespace. Observe the following example based on a few assumptions of your project.
In your shared library you have declared the interface:
public interface ISQLite
{
// Members here
}
Nothing fancy going on there. Then for each platform, you want to run the app on, do something like this:
[assembly: Xamarin.Forms.Dependency (typeof (SQLiteImplementation_iOS))]
namespace DevoApp.DevoAppFinal.iOS
{
public class SQLiteImplementation_iOS : ISQLite
{
// ... Your code
}
}
From the error, it looks like you forgot to add the attribute
i updating my app from asp core 1.0 to 2.0. In 1.0 i have a soulution for my longlive import-task, initialated as singleton. The singleton used the DBContext. But in core 2.0 this soulution dosn't work. Can you help me?
My soulution in aps core 1.0 was
services.AddDbContext<ApplicationDbContext>(options => options.UseSqlServer(Configuration.GetConnectionString("LocalConnection")));
services.AddSingleton<IHttpContextAccessor, HttpContextAccessor>();
services.AddTransient<IDataStore, DataStore>();
services.AddSingleton<IImportRepository, ImportRepository>();
with
public class ImportRepository : IImportRepository
{
Importer Importer;
private readonly ApplicationDbContext DBContext;
private readonly IDataStore store;
private ImportSet runningSet = null;
public ImportRepository(ApplicationDbContext context, IDataStore store)
{
this.DBContext = context;
this.store = store;
Importer = new Importer(DBContext, store);
}
With this soulutions i get errormessages (in german, but i try to translate). "you cannot use scoped services in singleton"
Last attempt i used this solution
services.AddSingleton<ImportService>(
provider => new ImportService((ApplicationDbContext)provider.GetService(typeof(ApplicationDbContext)))
);
But here i get the errormessage "Cannot resolve scoped service 'Portal.Data.ApplicationDbContext' from root provider."
How can i get access to my database in my Import-Service?
You may resolve dependencies manually using IServiceProvider instance.
public class ImportRepository : IImportRepository
{
private readonly IServiceProvider _provider;
public ImportRepository(IServiceProvider provider)
{
_provider = provider;
...
}
public void DoSomething()
{
var dBContext = (ApplicationDbContext) provider.GetService(typeof(ApplicationDbContext));
...
}
}
By the way, there is an extension method GetService<T>(); defined in Microsoft.Extensions.DependencyInjection namespace:
// using Microsoft.Extensions.DependencyInjection;
var dBContext = provider.GetService<ApplicationDbContext>();
Since your singleton lives longer and is shared, the only option I see is that you take it as a parameter to the functions.
public class ImportRepository : IImportRepository
{
public void DoSomething(ApplicationDbContext context, IDataStore store)
{
}
}
The other option is to make ImportRepository scoped as well.
Ok. I have a soulution, that works, but not perfektly.
Like Juunas example i build a long life funktion
public async Task RunImportAsync(string fileName, DataService data)
{
await Task.Run(() =>
{
if (!System.IO.File.Exists(internalPath + fileName))
{
throw new Exception($"Datei {fileName} nicht gefunden.");
}
[long Operations...]
data.DBContext.Add(new ImportHistory(set));
data.DBContext.SaveChanges();
});
}
the call is simple
[HttpPost]
[Route("runImport")]
public async Task<IActionResult> RunImport([FromBody]dynamic body)
{
string id = "";
try
{
id = body.filename;
_logger.LogInformation($"Import from {id}");
await ImportService.RunImportAsync(id, DB);
return StatusCode(StatusCodes.Success_2xx.OK);
}
catch (Exception e)
{
return SendError(e);
}
}
But postmen get no Response with this solution. Is there a idea, how i can fix it?
When I navigate from page A to page B, I need to remove page A.
How can I do this with Prism's navigation service in Xamarin Forms?
There are a few scenarios that people run into on this one.
As a common example say you have a LoginPage, and once the user successfully logs in you want to Navigate to the MainPage. Your code might look something like the following:
public class App : PrismApplication
{
protected override async void OnInitialized()
{
await NavigationService.NavigateAsync("LoginPage");
}
protected override void RegisterTypes()
{
Container.RegisterTypeForNavigation<LoginPage>();
Container.RegisterTypeForNavigation<MainPage>();
}
}
public class LoginPageViewModel : BindableBase
{
public DelegateCommand LoginCommand { get; }
private async void OnLoginCommandExecuted()
{
// Do some validation
// Notice the Absolute URI which will reset the navigation stack
// to start with MainPage
await _navigationService.NavigateAsync("/MainPage");
}
}
Now if what you're looking for is some flow where your navigation stack looks like MainPage/ViewA and what you want is MainPage/ViewB and you don't want to reinitialize MainPage, then this is something that we are currently evaluating and wanting to improve this so you could do something like _navigationService.NavigateAsync("../ViewB"). In the mean time what I might suggest is something like this:
public class ViewAViewModel : BindableBase
{
public DelegateCommand ViewBCommand { get; }
private async void OnViewBCommandExecuted()
{
var parameters = new NavigationParameters
{
{ "navigateTo", "ViewB" }
};
await _navigationService.GoBackAsync(parameters);
}
}
public class MainPageViewModel : BindableBase, INavigatedAware
{
public async void OnNavigatingTo(NavigationParameters parameters)
{
if(parameters. GetNavigationMode() == NavigationMode.Back &&
parameters.TryGetValue("navigateTo", out string navigateTo))
{
await _navigationService.NavigateAsync(navigateTo);
return;
}
}
}
Given: "NavigationPage/ViewA/ViewB/ViewC/ViewD"
Navigate from ViewD with:
NavigationService.NavigateAsync("../../../ViewE");
Results in: "NavigationPage/ViewA/ViewE"
Referred from here
Need Prism >= 7.0
Another approach would be to have your page implement INavigationAware and in the OnNavigatedFrom, call Navigatin.RemovePage(this).
I do it that way, it's simpler.
navigationService.NavigateAsync("../PageB");
I am using Prims 7.0.0.396.
I am beginning using MVVMLight with Xamarin.Forms and need some help to get the IOC set up to create my first ContentPage in App.GetMainPage.
My ViewModels have constructors like so -
public class NewsType1ViewModel : ViewModelBase
{
private readonly IContentService contentService;
private readonly INavigation navigation;
public List<ContentModel> ContentModels { get; set; }
public NewsType1ViewModel (INavigation navigation, IContentService contentService)
{
this.contentService = contentService;
this.navigation = navigation;
}
My ContentPages have constructors like so -
public partial class NewsType1CP : ContentPage
{
private NewsType1ViewModel vm;
public NewsType1CP (NewsType1ViewModel vm)
{
InitializeComponent ();
I am using a ViewModelLocator class as follows -
public class ViewModelLocator
{
public ViewModelLocator ()
{
ServiceLocator.SetLocatorProvider (() => SimpleIoc.Default);
// Services
if (App.StubMode) {
SimpleIoc.Default.Register<IContentService, ContentServiceStub> ();
} else {
SimpleIoc.Default.Register<IContentService, ContentService> ();
}
// How do I wire up INavigation?
// I could not just register default NavigationPage() as it has 2
// possible constructors so tried [PreferredConstructor] on my derived class
SimpleIoc.Default.Register<INavigation, AppNavigationPage> ();
// View Models
SimpleIoc.Default.Register<NewsType1ViewModel> ();
SimpleIoc.Default.Register<NewsDetailsViewModel> ();
}
public NewsType1ViewModel NewsType1ViewModel {
get {
return ServiceLocator.Current.GetInstance<NewsType1ViewModel> ();
}
}
public NewsDetailsViewModel NewsDetailsViewModel {
get {
return ServiceLocator.Current.GetInstance<NewsDetailsViewModel> ();
}
}
public static void Cleanup ()
{
// TODO Clear the ViewModels
}
}
public class AppNavigationPage : NavigationPage
{
[PreferredConstructor]
public AppNavigationPage ()
{
}
}
My App.cs is "in progress" as follows -
public static class App
{
public static AppNavigationPage Nav;
public static ViewModelLocator Locator = new ViewModelLocator ();
public static bool StubMode = true;
public static Page GetMainPage ()
{
try {
// Want to return a Nav with NewsType1CP as the starting Page
NewsType1CP newsType1CP = new NewsType1CP(ServiceLocator.Current.GetInstance<NewsType1ViewModel> ());
Nav.PushAsync (newsType1CP);
return Nav;
} catch (Exception ex) {
//
Exception baseexception = ex.GetBaseException ();
Debug.WriteLine (baseexception.Message);
}
return null;
}
}
My latest exception is -
Cannot cast from source type to destination type.
Am I barking up the wrong tree trying to supply an INavigation to each of my ViewModels like so?
Update: After a couple of answers showing other ways of controlling the Navigation in Xamarin Forms, I think it would help if someone could clarify why attempting constructor injection for Navigation is not such a good thing.
I think my example is a bit confusing with AppNavigationPage as a static, ideally I would like this to be in the IOC also, so I could just call return ServiceLocator.Current.GetInstance< AppNavigationPage >(), but I had a go with various factory methods and am in the middle of debugging this, so the code is obviously half baked ...
If you want a ready to use solution, instead of MVVM Light, you could try to use Xamarin Forms Labs ViewModel base, it injects a Navigation propety in your ViewModel:
that way you cold do something like this:
public Command NavigateToViewModel
{
get
{
return navigateToViewModel ?? (navigateToViewModel = new Command(
async () => await Navigation.PushAsync<NewPageViewModel>(),
() => true));
}
}
I'm not using MvvmLight, but I can tell you that yes, you're barking up the wrong tree in trying to supply an INavigation to each ViewModel.
The easiest way to achieve what you're trying to do is to use a public static on your App.
public static INavigation Navigation
{
get;
set;
}
public static Page GetMainPage()
{
var firstPage = new NavigationPage(new MyRootPage())
{
Navigation = firstPage.Navigation;
return firstPage;
}
}
Now this falls apart when you're using a MasterDetail page because you need your Navigation to wrap your DetailPage, not your MasterDetailPage. Therefore, don't set Navigation in the GetMainPage method, but instead from within the MD Page.
var master = new MainMenuPage();
var detail = new NavigationPage(new FirstPage());
if (App.Navigation == null)
{
App.Navigation = detail.Navigation;
}
Master = master;
Detail = detail;
Oh ok, when looking better at your code i maybe spotted the problem:
SimpleIoc.Default.Register<INavigation, AppNavigationPage> ();
Shoult it be:
SimpleIoc.Default.Register<INavigation, AppNavigationPage.Navigation> ();