I currently have an app that has many activities and needs to have a way of maintaining state between these activities.
I use the Application class to do this, declaring my global variables and using getters and setters to interact with my activities.
I was hoping to place a few custom methods in there, so that when I want to do a common task like, for instance, display an error message, I can declare the method in my application class and call it from any activity that uses it
EscarApplication application = (EscarApplication) this.getApplication();
EscarApplication being the name of my application class above.
I have tried to include this method in my application class:
public void showError(String title, String message) {
Log.i("Application level",message);
this.alertDialog.setTitle(title);
alertDialog.setMessage(message);
alertDialog.setButton("OK", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog,int which) {
return;
}
});
alertDialog.show();
}
In the hope that I can call this method from activity without having to redeclare it, but when I call it using something like below I get an null pointer exception:
Visit.this.application.showError("Update error", "An error has occurred while trying to communicate with the server");
Visit being the name of my current activity above.
Should this work, or can I only use getters and setters to change global vars in an Application Class.
Stack Trace:
java.lang.RuntimeException: Unable to start activity ComponentInfo{escar.beedge/escar.beedge.HomeScreen}: android.view.WindowManager$BadTokenException: Unable to add window -- token null is not for an application
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2401)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2417)
at android.app.ActivityThread.access$2100(ActivityThread.java:116)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1794)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:123)
at android.app.ActivityThread.main(ActivityThread.java:4203)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:521)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:791)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:549)
at dalvik.system.NativeStart.main(Native Method)
ERROR/AndroidRuntime(375): Caused by: android.view.WindowManager$BadTokenException: Unable to add window -- token null is not for an application
at android.view.ViewRoot.setView(ViewRoot.java:460)
at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:177)
at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:91)
at android.app.Dialog.show(Dialog.java:238)
at escar.beedge.EscarApplication.showError(EscarApplication.java:98)
at escar.beedge.HomeScreen.onCreate(HomeScreen.java:30)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1123)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2364)
The dialog is declared as such in the application class:
AlertDialog alertDialog;
Created in that same class:
alertDialog = new AlertDialog.Builder(this).create();
and the method to call it in that class is as follows:
public void showError(String title, String message) {
alertDialog.setTitle(title);
alertDialog.setMessage(message);
alertDialog.setButton("OK", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog,int which) {
return;
}
});
alertDialog.show();
}
And finally, it is called from an activity like so:
EscarApplication application;
application = (EscarApplication) this.getApplication();
application.showError("test", "display this message");
If you need to maintain state between activities, then use a service. Anything else is a hack
Someone correct me if Im wrong, but an Application class wont be able to execute view related objects as they need to be bound to a view which needs to be bound to an activity.
In that sense, you could use your Application class to implement a static method that customises the dialog
public static void setDialog(String title, String message,AlertDialog alertDialog){
alertDialog.setTitle(title);
alertDialog.setMessage(message);
alertDialog.setButton("OK", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog,int which) {
return;
}
});
}
but you would have to create the dialog and call the show method on the activities themselves (actually maybe even the button to be set in the dialog would need to be created on the activity)
Another option could be to implement a class that extends the AlertDialog class and whose button is pre-set to the behavior you want.
You could use the Singleton pattern.
I'm looking to achieve something similar to you.
I haven't found an official answer, but it looks like you shouldn't be using the application context for Toast and Dialogs. Instead, try using the context of an Activity like so :
// From inside your activity
Dialog dialog = new Dialog(this);
instead of this:
// From inside your Application instance
Dialog dialog = new Dialog(getApplicationContext());
Read this :
Android: ProgressDialog.show() crashes with getApplicationContext
Related
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)
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.
I have my MainActivity and inside that I have a number of fragments. I also have another activity that works as my launcher and does everything to do with the Google Drive section of my app. On start up this activity launches, connects to Drive and then launches the MainActivity. I have a button in one of my fragments that, when pushed, needs to call a method in the DriveActivity. I can't create a new instance of DriveActivity because then googleApiClient will be null. Is this possible and how would I go about doing it? I've already tried using getActivity and casting but I'm assuming that isn't working because DriveActivity isn't the fragments parent.
button.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
//TODO for test only remove
directory = new Directory(SDCARD + LOCAL_STORAGE);
byte[] zippedFile = directory.getZippedFile(SDCARD + STORAGE_LOCATION + directory.getZipFileName());
//Here I need to somehow call DriveActivity.uploadFileToDrive(zippedFile);
//((DriveActivity)getActivity()).uploadFileToDrive(zippedFile);
}
});
Right, so I'm having a bit of difficulty with the heirarchy but I think what you want to do is define a method in the fragment that the activity will be required to override to use.
This will allow you to press the button, and then fire a method whos actual implementation is inside the parent.
public interface Callbacks {
/**
* Callback for when an item has been selected.
*/
public void onItemSelected(String id);
}
example implementation:
private static Callbacks sDummyCallbacks = new Callbacks() {
#Override
public void onItemSelected(String id) {
//Button fired logic
}
};
so in the child you'd do just call:
this.onItemSelected("ID of Class");
EDITED
In retrospect what I believe you need is an activity whos sole purpose is to upload files, not fire off other activities.
Heres an example of a 'create file' activity:Google Demo for creating a file on drive
Heres an example of the 'base upload' activity' Base Service creator
I've looked at 'Messenger and references' discussion, but I'm writing a new topic, because my issue is not technical, and I don't want to offtop there.
I've encountered a doubt - Have I to code cleanup()/RequestCleanup() method implementation to unregister previously registered Messenger in my viewmodel class? I'm afraid of memory leaks in the future.
I think I've found the documentation not to be enough bright for me.
Description of Messenger.Register is: '... Registering a recipient does not create a hard reference to it, so if this recipient is deleted, no memory leak is caused.'
1) Is this mean that I don't have to take care of it and implement-develop following solutions?
On the other hand, we can find in the code of GalaSoft.MvvmLight.ViewModelBase abstract class the short info about the Cleanup() method:
//
// Summary:
// Unregisters this instance from the Messenger class.
// To cleanup additional resources, override this method, clean up and then
// call base.Cleanup().
public virtual void Cleanup();
so 2) Is only invoking a Cleanup enough to unregister class-instance out of the Messenger?
3) Or maybe I have to invoke Messenger.Default.Unregister(this); in the body of a Cleanup method?
4) In the Unregister(Object) doc we read 'Unregisters a messager recipient completely' - what does the 'completely' mean?
I'm very sorry if my post seems to have out of the context quotes, I wanted to point out what I'm more interested in.
EDIT 1:
Hello Joel, thanks for reply. I've got several questions:
1) I have used your code. There's defined override void Cleanup() in CustomerMasterViewModel. Where to call it? Should I declare destructor in this case or maybe the ViewModelBase has an automatic mechanism for invoking the Cleanup()?
2) I have in my project another base class from a different toolkit, so my VMs cannot derive from both at the same time. How to organise your code to get the same effect by implementing only ICleanup interface?
public class CustomerMasterViewModel : SomeBaseClass, ICleanup
{
public CustomerMasterViewModel()
{
Messenger.Default.Register<Message>(this, this.MessageReceived);
}
#region messages
private void MessageReceived(Message obj)
{
//do something
}
#endregion
#region helper methods
public override void Cleanup()
{
//base.Cleanup();//there's no implementaction in an interface
ViewModelLocator.Cleanup();
}
#endregion
}
You have to invoke the Cleanup() method in GalaSoft.MvvmLight.ViewModelBase on each of you view models you wan't to dispose don't need any longer.
Example:
Let say your application has a tab control with different tabs. Each of your tabs displays a UserControl which has a dedicated ViewModel. The user has the ability to close a tabs which causes the underlining ViewModel to become obsolete.
Want you want to do now is to clean up the ViewModel calling the Cleanup() method in GalaSoft.MvvmLight.ViewModelBase. This will unregister ALL registered messages. The GarbageCollector will take care of you viewmodel if there are no other references.
Assuming you use the ViewModelLocator which also comes with the MVVM Light Framework you're not done yet because at least the ViewModelLocator itself has a reference to your viewmodel! Therefore the Garbage Collector can't finalize your viewmodel.
But it also has another side effect. When the user reopens the tab (Lets say the user is able to do so) the UserControl is loaded again and the ViewModelLocator will give you the same ViewModel instance. The only difference is that there are not registered messages because you cleaned them by calling the CleanUp() method.
What you need is a new instance of your ViewModel. To achieve this you have to clean up your ViewModelLocator as well!
You have to unregister them (Unregister<CustomerMasterViewModel>()) one by one or simply call Reset() which will unregister all viewmodels.
Then there should be no other reference to you viewmodel and the GarbageCollector can finally take care about it.
Here is an example to do so:
ViewModelLocator:
public class ViewModelLocator
{
public ViewModelLocator()
{
ServiceLocator.SetLocatorProvider(() => SimpleIoc.Default);
SimpleIoc.Default.Register<CustomerMasterViewModel>();
}
public CustomerMasterViewModel CustomerMasterViewModel
{
get
{
return ServiceLocator.Current.GetInstance<CustomerMasterViewModel>();
}
}
public static void Cleanup()
{
SimpleIoc.Default.Reset();
//Don't forget to register them if the user attempts to open the new.
//The viewmodel initialization is lazy by default so this comes at no costs.
SimpleIoc.Default.Register<CustomerMasterViewModel>();
}
}
ViewModel
public class CustomerMasterViewModel : ViewModelBase
{
public CustomerMasterViewModel()
{
Messenger.Default.Register<Message>(this, this.MessageReceived);
}
#region messages
private void MessageReceived(Message obj)
{
//do something
}
#endregion
#region helper methods
public override void Cleanup()
{
base.Cleanup();
ViewModelLocator.Cleanup();
}
#endregion
}
In Short:
1) As far as i understood clean up is necessary after you're done.
2) Yes, calling the Cleanup() method in GalaSoft.MvvmLight.ViewModelBase will unregister all messages for this viewmodel.
3) No, see above.
4) Completely means it will unregister ALL registered messages.