I have developed and released one application in market long ago. Now some some users pointed crashes when holding application for long time. Now I identified the reason for the crash, that is I am using a class with static variable and methods to store data (getters and setters). Now I want to replace the static way with any other ways.From my study I got the following suggestions:
shared preferences: I have to store more than 40 variable (strings, int and json arrays and objects), So I think using shared preferences is not a good idea.
SQLite: more than 40 fields are there and I don't need to keep more than one value at a time.I am getting values for fields from different activities. I mean name from one activity , age from another activity, etc So using SQLite also not a good Idea I think.
Application classes: Now I am thinking about using application classes to store these data. Will it loss the data like static variable after hold the app for long time?
Now I replace the static variable with application class . Please let me know that application data also became null after long time?
It may useful to somebody.
Even though I didn't get a solution for my problem, I got the reason for why shouldn't we use application objects to hold the data. Please check the below link
Don't use application object to store data
Normally if you have to keep something in case your Activity gets destroyed you save all these things in onSaveInstanceState and restore them in onCreate or in onRestoreInstanceState
public class MyActivity extends Activity {
int myVariable;
final String ARG_MY_VAR="myvar";
public void onCreate(Bundle savedState) {
if(savedState != null {
myVariable = savedState.getInt(ARG_MY_VAR);
} else {
myVariable = someDefaultValue;
}
public void onSaveInstanceState(Bundle outState) {
outState.putInt(ARG_MY_VAR, myVariable);
super.onSaveInstanceState(outState);
}
}
Here if Android OS destroys your Activity onSaveInstanceState will be called and your important variable will be saved. Then when the user returns to your app again Android OS restores the activity and your variable will be correctly initialized
This does not happen when you call finish() yourself though, it happens only when Android destroys your activity for some reasons (which is quite likely to happen anytime while your app is in background).
First you should overwrite the onSaveInstanceState and onRestoreInstanceState methods in you activity:
#Override
protected void onSaveInstanceState (Bundle outState){
outState.putString("myVariable", myVariable);
// Store all you data inside the bundle
}
#Override
protected void onRestoreInstanceState (Bundle savedInstanceState){
if(savedInstanceState != null){
myVariable = savedInstanceState.getString("myVariable");
// Restore all the variables
}
}
May be try use static variable inside Application space?
public class YourApplication extends Application
{
private static ApplicationBubblick singleton;
public String str;
public static YourApplication getInstance()
{
return singleton;
}
}
And use variable via:
YourApplication.getInstance().str = ...; // set variable
... = YourApplication.getInstance().str; // get variable
This variable will be live until your app will start and stop all services or activities of your app. This is not work when your app crash.
Related
I have an aggregate root like this:
Aggregate root:
#NoArgsConstructor
#Aggregate(repository = "positionAggregateRepository")
#AggregateRoot
#XSlf4j
#Data
public class HopAggregate {
#AggregateIdentifier
private String hopId;
private FilteredPosition position;
private LocalDate positionDate;
#AggregateMember
private Security security;
#CommandHandler
public HopAggregate(NewHopCommand cmd) {
log.info("creating new position , {}", cmd.getDateId());
apply(new HopEvent(cmd.getHopId(), cmd.getDateId(), cmd.getFilteredPosition(), cmd.getSecurity(), false));
}
#CommandHandler
public void handle(UpdateHopCommand cmd) {
log.info("creating hop update event {}", cmd);
apply(new HopEvent(this.hopId, this.positionDate, cmd.getFilteredPosition(), this.security, true));
}
#CommandHandler
public void handle(SecurityUpdate cmd) {
log.info("updating security {}", cmd);
apply(new SecurityUpdateEvent(this.hopId, cmd.getFilteredSecurity()));
}
#EventSourcingHandler
public void on(HopEvent evt) {
if (evt.getIsUpdate()) {
log.info("updating position {}", evt);
this.position = evt.getFilteredPosition();
} else {
log.info("adding new position to date {}", evt);
this.hopId = evt.getHopId();
this.positionDate = evt.getDate();
this.position = evt.getFilteredPosition();
this.security= evt.getSecurity();
}
}
#EventSourcingHandler
public void on(SecurityUpdateEvent evt) {
log.info("hop id {}, security update {}", this.hopId, evt.getFilteredSecurity().getSecurityId());
}
}
Child entity:
#XSlf4j
#Data
#RequiredArgsConstructor
#NoArgsConstructor
public class IpaSecurity implements Serializable {
#EntityId
#NonNull
private String id;
#NonNull
private FilteredSecurity security;
}
My issue is that when i am pushing and update like this:
#EventHandler
public void handleSecurityEvent(SecurityUpdate securityUpdate) {
log.info("got security event {}", securityUpdate);
commandGateway.send(securityUpdate);
}
and my command being:
#Data
#RequiredArgsConstructor
#NoArgsConstructor
#ToString
public class SecurityUpdate {
#NonNull
#TargetAggregateIdentifier
private String id;
#NonNull
private FilteredSecurity filteredSecurity;
}
I am getting aggregate root not found exception:
Command 'com.hb.apps.ipa.events.SecurityUpdate' resulted in org.axonframework.modelling.command.AggregateNotFoundException(The aggregate was not found in the event store)
I am not sure how to handle this scenario. My requirement is that each aggregate should check whether it contains the security and then update it if the command was issued. What am i missing? let me know if you need any more info on the code.
Thanks for your help.
A Command is always targeted towards a single entity.
This entity can be an Aggregate, an entity contained in an Aggregate (what Axon Framework calls an Aggregate Member) or a simple singleton component.
Important to note though, is that there will only be one entity handling the command.
This is what requires you to set the #TargetAggregateIdentifier in your Command for Axon to be able to route it to a single Aggregate instance if the Command Handler in question is part of it.
The AggregateNotFoundException you're getting signals that the #TargetAggregateIdentifier annotated field in your SecurityUpdate command does no correspond to any existing Aggregate.
I'd thus suspect that the id field in the SecurityUpdate does not correspond to any #AggregateIdentifier annotated field in your HopAggregate aggregates.
A part from the above, I have a couple of other suggestions when looking at your snippets which I'd like to share with you:
#Aggregate is meta-annotated with #AggregateRoot. You're thus not required to specify both on an Aggregate class
For logging messages being handled, you can utilize LoggingInterceptor. You can configure this on any component capable of handling messages, thus providing a universal way of logging. This will omit the necessity to add log lines in your message handling functions
You're publishing a HopEvent on both the create and update commands. Doing so makes your HopEvent very generic. Ideally, your events clarify business operations occurring in your system. My rule of thumb typically is such: "If I tell my business manager/customer about the event class, he/she should know exactly what it does". I'd thus suggest to rename the event to something more specific
Just as with the HopEvent, the UpdateHopCommand is quite generic. Your commands should express the intent to perform an operation in your application. Users will typically not desire an update, they desire an address change for example. Your commands classes ideally reflect this
The suggested naming convention for commands is to start with verb in the present tense. Thus, it should no be SecurityUpdate, but UpdateSecurity. A command is a request expressing intent, the messages ideally reflect this
Hope this helps you out #juggernaut!
I'm trying to implement a web application using ASP.NET MVC and the Microsoft Unity DI framework. The application needs to support multiple user sessions at the same time, each of them with their own connection to a separate database (but all users using the same DbContext; the database schemas are identical, it's just the data that is different).
Upon a user's log-in, I register the necessary type mappings to the application's Unity container, using a session-based lifetime manager that I found in another question here.
My container is initialized like this:
// Global.asax.cs
public static UnityContainer CurrentUnityContainer { get; set; }
protected void Application_Start()
{
// ...other code...
CurrentUnityContainer = UnityConfig.Initialize();
// misc services - nothing data access related, apart from the fact that they all depend on IRepository<ClientContext>
UnityConfig.RegisterComponents(CurrentUnityContainer);
}
// UnityConfig.cs
public static UnityContainer Initialize()
{
UnityContainer container = new UnityContainer();
DependencyResolver.SetResolver(new UnityDependencyResolver(container));
GlobalConfiguration.Configuration.DependencyResolver = new Unity.WebApi.UnityDependencyResolver(container);
return container;
}
This is the code that's called upon logging in:
// UserController.cs
UnityConfig.RegisterUserDataAccess(MvcApplication.CurrentUnityContainer, UserData.Get(model.AzureUID).CurrentDatabase);
// UnityConfig.cs
public static void RegisterUserDataAccess(IUnityContainer container, string databaseName)
{
container.AddExtension(new DataAccessDependencies(databaseName));
}
// DataAccessDependencies.cs
public class DataAccessDependencies : UnityContainerExtension
{
private readonly string _databaseName;
public DataAccessDependencies(string databaseName)
{
_databaseName = databaseName;
}
protected override void Initialize()
{
IConfigurationBuilder configurationBuilder = Container.Resolve<IConfigurationBuilder>();
Container.RegisterType<ClientContext>(new SessionLifetimeManager(), new InjectionConstructor(configurationBuilder.GetConnectionString(_databaseName)));
Container.RegisterType<IRepository<ClientContext>, RepositoryService<ClientContext>>(new SessionLifetimeManager());
}
}
// SessionLifetimeManager.cs
public class SessionLifetimeManager : LifetimeManager
{
private readonly string _key = Guid.NewGuid().ToString();
public override void RemoveValue(ILifetimeContainer container = null)
{
HttpContext.Current.Session.Remove(_key);
}
public override void SetValue(object newValue, ILifetimeContainer container = null)
{
HttpContext.Current.Session[_key] = newValue;
}
public override object GetValue(ILifetimeContainer container = null)
{
return HttpContext.Current.Session[_key];
}
protected override LifetimeManager OnCreateLifetimeManager()
{
return new SessionLifetimeManager();
}
}
This works fine as long as only one user is logged in at a time. The data is fetched properly, the dashboards work as expected, and everything's just peachy keen.
Then, as soon as a second user logs in, disaster strikes.
The last user to have prompted a call to RegisterUserDataAccess seems to always have "priority"; their data is displayed on the dashboard, and nothing else. Whether this is initiated by a log-in, or through a database access selection in my web application that calls the same method to re-route the user's connection to another database they have permission to access, the last one to draw always imposes their data on all other users of the web application. If I understand correctly, this is a problem the SessionLifetimeManager was supposed to solve - unfortunately, I really can't seem to get it to work.
I sincerely doubt that a simple and common use-case like this - multiple users logged into an MVC application who each are supposed to access their own, separate data - is beyond the abilities of Unity, so obviously, I must be doing something very wrong here. Having spent most of my day searching through depths of the internet I wasn't even sure truly existed, I must, unfortunately, now realize that I am at a total and utter loss here.
Has anyone dealt with this issue before? Has anyone dealt with this use-case before, and if yes, can anyone tell me how to change my approach to make this a little less headache-inducing? I am utterly desperate at this point and am considering rewriting my entire data access methodology just to make it work - not the healthiest mindset for clean and maintainable code.
Many thanks.
the issue seems to originate from your registration call, when registering the same type multiple times with unity, the last registration call wins, in this case, that will be data access object for whoever user logs-in last. Unity will take that as the default registration, and will create instances that have the connection to that user's database.
The SessionLifetimeManager is there to make sure you get only one instance of the objects you resolve under one session.
One option to solve this is to use named registration syntax to register the data-access types under a key that maps to the logged-in user (could be the database name), and on the resolve side, retrieve this user key, and use it resolve the corresponding data access implementation for the user
Thank you, Mohammed. Your answer has put me on the right track - I ended up finally solving this using a RepositoryFactory which is instantiated in an InjectionFactory during registration and returns a repository that always wraps around a ClientContext pointing to the currently logged on user's currently selected database.
// DataAccessDependencies.cs
protected override void Initialize()
{
IConfigurationBuilder configurationBuilder = Container.Resolve<IConfigurationBuilder>();
Container.RegisterType<IRepository<ClientContext>>(new InjectionFactory(c => {
ClientRepositoryFactory repositoryFactory = new ClientRepositoryFactory(configurationBuilder);
return repositoryFactory.GetRepository();
}));
}
// ClientRepositoryFactory.cs
public class ClientRepositoryFactory : IRepositoryFactory<RepositoryService<ClientContext>>
{
private readonly IConfigurationBuilder _configurationBuilder;
public ClientRepositoryFactory(IConfigurationBuilder configurationBuilder)
{
_configurationBuilder = configurationBuilder;
}
public RepositoryService<ClientContext> GetRepository()
{
var connectionString = _configurationBuilder.GetConnectionString(UserData.Current.CurrentPermission);
ClientContext ctx = new ClientContext(connectionString);
RepositoryService<ClientContext> repository = new RepositoryService<ClientContext>(ctx);
return repository;
}
}
// UserData.cs (multiton-singleton-hybrid)
public static UserData Current
{
get
{
var currentAADUID = (string)(HttpContext.Current.Session["currentAADUID"]);
return Get(currentAADUID);
}
}
public static UserData Get(string AADUID)
{
UserData instance;
lock(_instances)
{
if(!_instances.TryGetValue(AADUID, out instance))
{
throw new UserDataNotInitializedException();
}
}
return instance;
}
public static UserData Current
{
get
{
var currentAADUID = (string)(HttpContext.Current.Session["currentAADUID"]);
return Get(currentAADUID);
}
}
public static UserData Get(string AADUID)
{
UserData instance;
lock(_instances)
{
if(!_instances.TryGetValue(AADUID, out instance))
{
throw new UserDataNotInitializedException();
}
}
return instance;
}
How can I dispose and re-instantiate a singleton with Prism/DryIoC in Xamarin Forms?
I'm working with Azure Mobile Apps for offline data. Occasionally, I need to delete the local sqlite database and re-initialize it. Unfortunately the MobileServiceClient occasionally holds the db connection open and there's no method exposed to close it. The suggested solution (https://github.com/Azure/azure-mobile-apps-net-client/issues/379) is to dispose of MobileServiceClient. Only problem is that is registered with DryIoC as a singleton.
I'm not overly familiar with DryIoC, or Prism and Forms for that matter... But for the life of me, I can't see a way to do this.
I did cook up a pretty elaborate scheme that almost worked.
In my ViewModel method, when I needed the db freed up, I fired off an event -
_eventAggregator.GetEvent<RegisterDatabaseEvent>().Publish(false);
Then in App.xaml.cs, I wired up a listener and a handler like so -
_eventAggregator.GetEvent<RegisterDatabaseEvent>().Subscribe(OnRegisterDatabaseEventPublished);
private void OnRegisterDatabaseEventPublished()
{
Container.GetContainer().Unregister<IAppMobileClient>();
Container.GetContainer().Unregister<IMobileServiceClient>();
Container.GetContainer().Register<IMobileServiceClient, AppMobileClient>(new SingletonReuse());
Container.GetContainer().Register<IAppMobileClient, AppMobileClient>(new SingletonReuse());
_eventAggregator.GetEvent<RegisterDatabaseCompletedEvent>().Publish(register);
}
Lastly, back in the ViewModel constructor, I had a final listener that handled the event coming back from App.xaml and finished processing.
_eventAggregator.GetEvent<RegisterDatabaseCompletedEvent>().Subscribe(OnRegisterDatabaseCompletedEventPublished);
So the amazing thing is that this worked. The database was able to be deleted and all was good. But then I navigated to a different page and BOOM. DryIoC said it couldn't wire up the ViewModel for that page. I assume the unregister/register jacked up DryIoC for all injection... So how can I accomplish what needs to be done?
FINAL SOLUTION
Thanks so much to dadhi for taking the time to help. You are certainly a class act and I'm now considering using DryIoC elsewhere.
For anyone who stumbles on this, I'm posting the final solution below. I'll be as verbose as I can to avoid any confusion.
First, in my App.xaml.cs, I added a method for registering my database.
public void RegisterDatabase(IContainer container)
{
container.RegisterMany<AppMobileClient>(Reuse.Singleton,
setup: Setup.With(asResolutionCall: true),
ifAlreadyRegistered: IfAlreadyRegistered.Replace,
serviceTypeCondition: type =>
type == typeof(IMobileServiceClient) || type == typeof(IAppMobileClient));
}
I simply add a call to that method in RegisterTypes in place of registering the types in there directly.
protected override void RegisterTypes(IContainerRegistry containerRegistry)
{
containerRegistry.GetContainer().Rules.WithoutEagerCachingSingletonForFasterAccess();
...
RegisterDatabase(containerRegistry.GetContainer());
...
}
Note also the added rule for eager caching, per dadhi.
Later on when I need to release the database in the ViewModel... I kick things off by resetting my local db variable and sending an event to App.xaml.cs
_client = null;
_eventAggregator.GetEvent<RegisterDatabaseEvent>().Publish(true);
In App.xaml.cs, I have subscribed to that event and tied it to the following method.
private void OnRegisterDatabaseEventPublished()
{
RegisterDatabase(Container.GetContainer());
_eventAggregator.GetEvent<RegisterDatabaseCompletedEvent>().Publish(register);
}
Here I just call RegisterMany again, exactly the same as I do when the app starts up. No need to unregister anything. With the setup and ifAlreadyRegistered arguments (thanks, dadhi!), DryIoC allows the object to be replaced. Then I raise an event back to the VM letting it know the database has been released.
Finally, back in the ViewModel, I'm listening for the completed event. The handler for that event updates the local copy of the object like so.
_client = ((PrismApplication)App.Current).Container.Resolve<IAppMobileClient>();
And then I can work with the new object, as needed. This is key. Without setting _client to null above and resolving it again here, I actually ended up with 2 copies of the object and calls to methods were being hit 2x.
Hope that helps someone else looking to release their Azure Mobile Apps database!
I am not sure how exactly XF handles these things.
But in DryIoc in order for service to be fully deleted or replaced it need to be registered with setup: Setup.With(asResolutionCall: true). Read here for more details: https://bitbucket.org/dadhi/dryioc/wiki/UnregisterAndResolutionCache#markdown-header-unregister-and-resolution-cache
Update
Here are two options and considerations that work in pure DryIoc and may not work XF. But it probably may help with solution.
public class Foo
{
public IBar Bar { get; private set; }
public Foo(IBar bar) { Bar = bar; }
}
public interface IBar {}
public class Bar : IBar {}
public class Bar2 : IBar { }
[Test]
public void Replace_singleton_dependency_with_asResolutionCall()
{
var c = new Container(rules => rules.WithoutEagerCachingSingletonForFasterAccess());
c.Register<Foo>();
//c.Register<Foo>(Reuse.Singleton); // !!! If the consumer of replaced dependency is singleton, it won't work
// cause the consumer singleton should be replaced too
c.Register<IBar, Bar>(Reuse.Singleton,
setup: Setup.With(asResolutionCall: true)); // required
var foo = c.Resolve<Foo>();
Assert.IsInstanceOf<Bar>(foo.Bar);
c.Register<IBar, Bar2>(Reuse.Singleton,
setup: Setup.With(asResolutionCall: true), // required
ifAlreadyRegistered: IfAlreadyRegistered.Replace); // required
var foo2 = c.Resolve<Foo>();
Assert.IsInstanceOf<Bar2>(foo2.Bar);
}
[Test]
public void Replace_singleton_dependency_with_UseInstance()
{
var c = new Container();
c.Register<Foo>();
//c.Register<Foo>(Reuse.Singleton); // !!! If the consumer of replaced dependency is singleton, it won't work
// cause the consumer singleton should be replaced too
c.UseInstance<IBar>(new Bar());
var foo = c.Resolve<Foo>();
Assert.IsInstanceOf<Bar>(foo.Bar);
c.UseInstance<IBar>(new Bar2());
var foo2 = c.Resolve<Foo>();
Assert.IsInstanceOf<Bar2>(foo2.Bar);
}
The new obsolete warning in Xamarin.Forms 2.5 really puzzled me.
What context should I be using in Dependency Services, for example, to call GetSystemService()?
Should I store in a static field the context of activity the xamarin forms were initialized against?
Should I override the android Application class and use its Context?
Should I call GetSystemService at activity create and save it somewhere?
I was having the same issue with several Dependency Services
The simplest solution
In a lot of cases for Single Activity Applications
Xamarin.Forms.Forms.Context
Can be replaced with
Android.App.Application.Context
The Background in more detail
Android.App.Application.Context returns the global Application Context of the current process tied to the lifecycle of the Application, as apposed to an Activity context.
A typical example of using the Application context is for starting an Activity e.g.
Android.App.Application.Context.StartActivity(myIntent);
The general rule of thumb is to use the current Activity Context, unless you need
to save a reference to a context from an object that lives beyond your
Activity. In which case use the Application context
Why did Forms.Context go obsolete?
Xmarin.Forms 2.5 introduced a new "Forms embedding" feature, which can embed Forms pages into Xamarin.iOS / Xamarin.Android apps. However, since Xamarin.Android apps can use multiple Activities, seemingly there was a danger of Xamarin.Android users calling Forms.Context and in turn getting a reference to the MainActivity, which has the potential cause problems.
The work around
Inside a Renderer you now get a reference to the view’s context which is passed into the constructor.
With any other class you are faced with the issue of how to get the Activity Context. In a single Activity application (in most cases) the Application.Context will work just fine.
However to get the current Activity Context in a Multiple Activity Application you will need to hold a reference to it. The easiest and most reliable way to do this is via a class that implements the Application.IActivityLifecycleCallbacks Interface.
The main idea is to keep a reference of the Context when an Activity
is created, started, or resumed.
[Application]
public partial class MainApplication : Application, Application.IActivityLifecycleCallbacks
{
internal static Context ActivityContext { get; private set; }
public MainApplication(IntPtr handle, JniHandleOwnership transfer) : base(handle, transfer) { }
public override void OnCreate()
{
base.OnCreate();
RegisterActivityLifecycleCallbacks(this);
}
public override void OnTerminate()
{
base.OnTerminate();
UnregisterActivityLifecycleCallbacks(this);
}
public void OnActivityCreated(Activity activity, Bundle savedInstanceState)
{
ActivityContext = activity;
}
public void OnActivityResumed(Activity activity)
{
ActivityContext = activity;
}
public void OnActivityStarted(Activity activity)
{
ActivityContext = activity;
}
public void OnActivityDestroyed(Activity activity) { }
public void OnActivityPaused(Activity activity) { }
public void OnActivitySaveInstanceState(Activity activity, Bundle outState) { }
public void OnActivityStopped(Activity activity) { }
}
With the above approach, single Activity Applications and multiple Activity Applications can now always have access to the Current/Local Activity Context. e.g instead of relying on the global context
Android.App.Application.Context
// or previously
Xamarin.Forms.Forms.Context
Can now be replaced with
MainApplication.ActivityContext
Example call in a Dependency Service
if (MainApplication.ActivityContext!= null)
{
versionNumber = MainApplication.ActivityContext
.PackageManager
.GetPackageInfo(MainApplication.ActivityContext.PackageName, 0)
.VersionName;
}
Additional Resources
Android.App.Application.IActivityLifecycleCallbacks
registerActivityLifecycleCallbacks
In the latest scaffold of a new Xamarin Forms solution the CrossActivityPlugin (https://github.com/jamesmontemagno/CurrentActivityPlugin) is referenced in the Android project. So you can use
CrossCurrentActivity.Current.Activity.StartActivity(myIntent)
How to pass global variable to a referenced assembly?
I am modifying an asp.net app. It is required to log all Employee (the current user of the website) actions like saving a new customer or update invoice data. The UI layer is calling a referenced assembly BLL.dll.
I want to pass current Emplyee to the referenced assembly. The passed Employee should be shared accross all static methods in that dll. It should be thread safe because the Employee can be changed accross requests.
I can't expose static field in the BLL because the Employee is stored in session state.
I need something not static, Global, accessible by both assemblies (UI layer and BLL.dll), and thread safe.
I am thinking about using some variable stored in current thread object. but I don't know what exactly I should do??
Any workarrounds ??
Thanks
Basically you need something in your BLL that can get the reference. You can use a strategy pattern with an interface.
// IN BLL.dll
public interface IEmployeeContextImplementation
{
Employee Current { get; }
}
public static EmployeeContext
{
private static readonly object ImplementationLock = new object();
private static IEmployeeContextImplementation Implementation;
public static void SetImplementation(IEmployeeContextImplementation impl)
{
lock(ImplementationLock)
{
Implementation = impl;
}
}
public static Employee Current { get { return Implementation.Current; }
}
Then in your web app, implement IEmployeeContextImplementation with the session state and call SetImplementation only once in application start.
However, Session state is only good enough for within the context of a request. If you need it to go on a different thread, you will have to explicitly pass it to a different thread.