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How provide variants with Daggers in a multi-module project? [duplicate]

I have a BIG Android app that needs to run different code for depending on the OS version, the manufacturer, and many other things. This app however needs to be a single APK. It needs to be smart enough at runtime to determine which code to use. Until now we have been using Guice but performance issues are causing us to consider migrating to Dagger. However, I've been unable to determine if we can achieve the same use case.
The main goal is for us have some code that runs at startup to provide a list of compatible Modules. Then pass that this list to Dagger to wire everything up.
Here is some pseudocode of the current implementation in Guice we want to migrate
import com.google.inject.AbstractModule;
#Feature("Wifi")
public class WifiDefaultModule extends AbstractModule {
#Override
protected void configure() {
bind(WifiManager.class).to(WifiDefaultManager.class);
bind(WifiProcessor.class).to(WifiDefaultProcessor.class);
}
}
#Feature("Wifi")
#CompatibleWithMinOS(OS > 4.4)
class Wifi44Module extends WifiDefaultModule {
#Override
protected void configure() {
bind(WifiManager.class).to(Wifi44Manager.class);
bindProcessor();
}
#Override
protected void bindProcessor() {
(WifiProcessor.class).to(Wifi44Processor.class);
}
}
#Feature("Wifi")
#CompatibleWithMinOS(OS > 4.4)
#CompatibleWithManufacturer("samsung")
class WifiSamsung44Module extends Wifi44Module {
#Override
protected void bindProcessor() {
bind(WifiProcessor.class).to(SamsungWifiProcessor.class);
}
#Feature("NFC")
public class NfcDefaultModule extends AbstractModule {
#Override
protected void configure() {
bind(NfcManager.class).to(NfcDefaultManager.class);
}
}
#Feature("NFC")
#CompatibleWithMinOS(OS > 6.0)
class Nfc60Module extends NfcDefaultModule {
#Override
protected void configure() {
bind(NfcManager.class).to(Nfc60Manager.class);
}
}
public interface WifiManager {
//bunch of methods to implement
}
public interface WifiProcessor {
//bunch of methods to implement
}
public interface NfcManager {
//bunch of methods to implement
}
public class SuperModule extends AbstractModule {
private final List<Module> chosenModules = new ArrayList<Module>();
public void addModules(List<Module> features) {
chosenModules.addAll(features);
}
#Override
protected void configure() {
for (Module feature: chosenModules) {
feature.configure(binder())
}
}
}
so at startup the app does this:
SuperModule superModule = new SuperModule();
superModule.addModules(crazyBusinessLogic());
Injector injector = Guice.createInjector(Stage.PRODUCTION, superModule);
where crazyBusinessLogic() reads the annotations of all the modules and determines a single one to use for each feature based on device properties. For example:
a Samsung device with OS = 5.0 will have crazyBusinessLogic() return the list { new WifiSamsung44Module(), new NfcDefaultModule() }
a Samsung device with OS = 7.0 will have crazyBusinessLogic() return the list { new WifiSamsung44Module(), new Nfc60Module() }
a Nexus device with OS = 7.0 will have crazyBusinessLogic() return the list { new Wifi44Module(), new Nfc60Module() }
and so on....
Is there any way to do the same with Dagger? Dagger seems to require you to pass the list of modules in the Component annotation.
I read a blog that seems to work on a small demo, but it seems clunky and the extra if statement and extra interfaces for components might cause my code to balloon.
https://blog.davidmedenjak.com/android/2017/04/28/dagger-providing-different-implementations.html
Is there any way to just use a list of modules returned from a function like we are doing in Guice? If not, what would be the closest way that would minimize rewriting the annotations and the crazyBusinessLogic() method?

Dagger generates code at compile-time, so you are not going to have as much module flexibility as you did in Guice; instead of Guice being able to reflectively discover #Provides methods and run a reflective configure() method, Dagger is going to need to know how to create every implementation it may need at runtime, and it's going to need to know that at compile time. Consequently, there's no way to pass an arbitrary array of Modules and have Dagger correctly wire your graph; it defeats the compile-time checking and performance that Dagger was written to provide.
That said, you seem to be okay with a single APK containing all possible implementations, so the only matter is selecting between them at runtime. This is very possible in Dagger, and will probably fall into one of four solutions: David's component-dependencies-based solution, Module subclasses, stateful module instances, or #BindsInstance-based redirection.
Component dependencies
As in David's blog you linked, you can define an interface with a set of bindings that you need to pass in, and then supply those bindings through an implementation of that interface passed into the builder. Though the structure of the interface makes this well-designed to pass Dagger #Component implementations into other Dagger #Component implementations, the interface may be implemented by anything.
However, I'm not sure this solution suits you well: This structure is also best for inheriting freestanding implementations, rather than in your case where your various WifiManager implementations all have dependencies that your graph needs to satisfy. You might be drawn to this type of solution if you need to support a "plugin" architecture, or if your Dagger graph is so huge that a single graph shouldn't contain all of the classes in your app, but unless you have those constraints you may find this solution verbose and restrictive.
Module subclasses
Dagger allows for non-final modules, and allows for the passing of instances into modules, so you can simulate the approach you have by passing subclasses of your modules into the Builder of your Component. Because the ability to substitute/override implementations is frequently associated with testing, this is described on the Dagger 2 Testing page under the heading "Option 1: Override bindings by subclassing modules (don’t do this!)"—it clearly describes the caveats of this approach, notably that the virtual method call will be slower than a static #Provides method, and that any overridden #Provides methods will necessarily need to take all parameters that any implementation uses.
// Your base Module
#Module public class WifiModule {
#Provides WifiManager provideWifiManager(Dep1 dep1, Dep2 dep2) {
/* abstract would be better, but abstract methods usually power
* #Binds, #BindsOptionalOf, and other declarative methods, so
* Dagger doesn't allow abstract #Provides methods. */
throw new UnsupportedOperationException();
}
}
// Your Samsung Wifi module
#Module public class SamsungWifiModule {
#Override WifiManager provideWifiManager(Dep1 dep1, Dep2 dep2) {
return new SamsungWifiManager(dep1); // Dep2 unused
}
}
// Your Huawei Wifi module
#Module public class HuaweiWifiModule {
#Override WifiManager provideWifiManager(Dep1 dep1, Dep2 dep2) {
return new HuaweiWifiManager(dep1, dep2);
}
}
// To create your Component
YourAppComponent component = YourAppComponent.builder()
.baseWifiModule(new SamsungWifiModule()) // or name it anything
// via #Component.Builder
.build();
This works, as you can supply a single Module instance and treat it as an abstract factory pattern, but by calling new unnecessarily, you're not using Dagger to its full potential. Furthermore, the need to maintain a full list of all possible dependencies may make this more trouble than it's worth, especially given that you want all dependencies to ship in the same APK. (This might be a lighter-weight alternative if you need certain kinds of plugin architecture, or you want to avoid shipping an implementation entirely based on compile-time flags or conditions.)
Module instances
The ability to supply a possibly-virtual Module was really meant more for passing module instances with constructor arguments, which you could then use for choosing between implementations.
// Your NFC module
#Module public class NfcModule {
private final boolean useNfc60;
public NfcModule(boolean useNfc60) { this.useNfc60 = useNfc60; }
#Override NfcManager provideNfcManager() {
if (useNfc60) {
return new Nfc60Manager();
}
return new NfcDefaultManager();
}
}
// To create your Component
YourAppComponent component = YourAppComponent.builder()
.nfcModule(new NfcModule(true)) // again, customize with #Component.Builder
.build();
Again, this doesn't use Dagger to its fullest potential; you can do that by manually delegating to the right Provider you want.
// Your NFC module
#Module public class NfcModule {
private final boolean useNfc60;
public NfcModule(boolean useNfc60) { this.useNfc60 = useNfc60; }
#Override NfcManager provideNfcManager(
Provider<Nfc60Manager> nfc60Provider,
Provider<NfcDefaultManager> nfcDefaultProvider) {
if (useNfc60) {
return nfc60Provider.get();
}
return nfcDefaultProvider.get();
}
}
Better! Now you don't create any instances unless you need them, and Nfc60Manager and NfcDefaultManager can take arbitrary parameters that Dagger supplies. This leads to the fourth solution:
Inject the configuration
// Your NFC module
#Module public abstract class NfcModule {
#Provides static NfcManager provideNfcManager(
YourConfiguration yourConfiguration,
Provider<Nfc60Manager> nfc60Provider,
Provider<NfcDefaultManager> nfcDefaultProvider) {
if (yourConfiguration.useNfc60()) {
return nfc60Provider.get();
}
return nfcDefaultProvider.get();
}
}
// To create your Component
YourAppComponent component = YourAppComponent.builder()
// Use #Component.Builder and #BindsInstance to make this easy
.yourConfiguration(getConfigFromBusinessLogic())
.build();
This way you can encapsulate your business logic in your own configuration object, let Dagger provide your required methods, and go back to abstract modules with static #Provides for the best performance. Furthermore, you don't need to use Dagger #Module instances for your API, which hides implementation details and makes it easier to move away from Dagger later if your needs change. For your case, I recommend this solution; it'll take some restructuring, but I think you'll wind up with a clearer structure.
Side note about Guice Module#configure(Binder)
It's not idiomatic to call feature.configure(binder()); please use install(feature); instead. This allows Guice to better describe where errors occur in your code, discover #Provides methods in your Modules, and to de-duplicate your module instances in case a module is installed more than once.

Is there any way to just use a list of modules returned from a
function like we are doing in Guice? If not, what would be the closest
way that would minimize rewriting the annotations and the
crazyBusinessLogic() method?
Not sure this is the answer you're looking for, but just in case you do have other options and for other community members I will describe completely different approach.
I would say that the way you used Guice until now is an abuse of DI framework, and you will be much better off leveraging this opportunity to remove this abuse instead of implementing it in Dagger.
Let me explain.
The main goal of dependency injection architectural pattern is to have construction logic segregated from functional logic.
What you basically want to achieve is standard polymorphism - provide different implementations based on a set of parameters.
If you use Modules and Components for that purpose, you will end up structuring your DI code according to business rules governing the need for these polymorphic implementations.
Not only will this approach requires much more boilerplate, but it also prevents emergence of cohesive Modules that have meaningful structure and provide insights into application's design and architecture.
In addition, I doubt you will be able to unit test these business rules "encoded" inside dependency injection logic.
There are two approaches which are much better IMHO.
First approach is still not very clean, but, at least, it doesn't compromise the large scale structure of dependency injection code:
#Provides
WifiManager wifiManager(DeviceInfoProvider deviceInfoProvider) {
if (deviceInfoProvider.isPostKitKat() ) {
if (deviceInfoProvider.isSamsung()) {
return new WifiMinagerSamsungPostKitKat();
} else {
return new WifiMinagerPostKitKat();
}
} else {
return new WifiMinagerPreKitKat();
}
}
The logic that chooses between implementation still resides in DI code, but, at least, it did not make it into the large scale structure of that part.
But the best solution in this case is to make a proper object oriented design, instead of abusing DI framework.
I'm pretty sure that the source code of all these classes is very similar. They might even inherit from one another while overriding just one single method.
In this case, the right approach is not duplication/inheritance, but composition using Strategy design pattern.
You would extract the "strategy" part into a standalone hierarchy of classes, and define a factory class that constructs them based on system's parameters. Then, you could do it like this:
#Provides
WiFiStrategyFactory wiFiStrategyFactory(DeviceInfoProvider deviceInfoProvider) {
return new WiFiStrategyFactory(deviceInfoProvider);
}
#Provides
WifiManager wifiManager(WiFiStrategyFactory wiFiStrategyFactory) {
return new WifiMinager(WiFiStrategyFactory.newWiFiStrategy());
}
Now construction logic is simple and clear. The differentiation between strategies encapsulated inside WiFiStrategyFactory and can be unit tested.
The best part of this proper approach is that when a new strategy will need to be implemented (because we all know that Android fragmentation is unpredictable), you won't need to implement new Modules and Components, or make any changes to DI structure. This new requirement will be handled by just providing yet another implementation of the strategy and adding the instantiation logic to the factory.
All that while being kept safe with unit tests.

How can I override a method of an anonymous generic class?

I am working on GWT project with JDK7. It has two entryPoints (two clients) that are located in separate packages of the project. Clients share some code that is located in /common package, which is universal and accessible to both by having the following line in their respective xml-build files:
<source path='ui/common' />
Both clients have their own specific implementations of the Callback class which serves their running environments and performs various actions in case of failure or success. I have the following abstract class that implements AsyncCallback interface and then gets extended by its respective client.
public abstract class AbstractCallback<T> implements AsyncCallback<T> {
public void handleSuccess( T result ) {}
...
}
Here are the client's classes:
public class Client1Callback<T> extends AbstractCallback<T> {...}
and
public class Client2Callback<T> extends AbstractCallback<T> {...}
In the common package, that also contains these callback classes, I am working on implementing the service layer that serves both clients. Clients use the same back-end services, just handle the results differently. Based on the type of the client I want to build a corresponding instance of AbstractCallback child without duplicating anonymous class creation for each call. I am going to have many declarations that will look like the following:
AsyncCallback<MyVO> nextCallback = isClient1 ?
new Client1Callback<MyVO>("ABC") {
public void handleSuccess(MyVO result) {
doThatSameAction(result);
}
}
:
new Client2Callback<MyVO>("DEF") {
public void handleSuccess(MyVO result) {
doThatSameAction(result);
}
};
That will result in a very verbose code.
The intent (in pseudo-code) is to have the below instead:
AsyncCallback<MyVO> nextCallback = new CallbackTypeResolver.ACallback<MyVO>(clientType, "ABC"){
public void handleSuccess(MyVO result) {
doThatSameAction(result);
}
};
I was playing with the factory pattern to get the right child instance, but quickly realized that I am not able to override handleSuccess() method after the instance is created.
I think the solution may come from one of the two sources:
Different GWT way of dealing with custom Callback implementations, lets call it alternative existent solution.
Java generics/types juggling magic
I can miss something obvious, and would appreciate any advice.
I've read some articles here and on Oracle about types erasure for generics, so I understand that my question may have no direct answer.

Refactor out the handleSuccess behavior into its own class.
The handleSuccess behavior is a separate concern from what else is going on in the AsyncCallback classes; therefore, separate it out into a more useful form. See Why should I prefer composition over inheritance?
Essentially, by doing this refactoring, you are transforming an overridden method into injected behavior that you have more control over. Specifically, you would have instead:
public interface SuccessHandler<T> {
public void handleSuccess(T result);
}
Your callback would look something like this:
public abstract class AbstractCallback<T> implements AsyncCallback<T> {
private final SuccessHandler<T> handler; // Inject this in the constructor
// etc.
// not abstract anymore
public void handleSuccess( T result ) {
handler.handleSuccess(result);
}
}
Then your pseudocode callback creation statement would be something like:
AsyncCallback<MyVO> nextCallback = new CallbackTypeResolver.ACallback<MyVO>(
clientType,
"ABC",
new SuccessHandler<MyVO>() {
public void handleSuccess(MyVO result) {
doThatSameMethod(result);
}
});
The implementations of SuccessHandler don't have to be anonymous, they can be top level classes or even inner classes based on your needs. There's a lot more power you can do once you're using this injection based framework, including creating these handlers with automatically injected dependencies using Gin and Guice Providers. (Gin is a project that integrates Guice, a dependency injection framework, with GWT).

Using Guice with a custom class?

I'm working with a Guice enabled framework.
When using classes that were created by the framework (or subclasses that override existing bindings), I can instantiate framework provided variables very easily. Whatever I need, it's just a matter of
#Inject
FrameworkProvidedType variable;
However, in my custom created classes, that doesn't work. All of the injected variables are null.
It's my understanding that in order to use injection, my class has to have a binding.
If I'm subclassing an existing framework class, I can override the binding in my module class. That's pretty straightforward.
But I have a new class and I don't know how to bind it to the underlying framework.
public Class myCustomClass {
private String iNeedthis;
private Context thisToo;
#Inject
FrameWorkThing magic;
public myCustomClass(String iNeedThis, Context thisToo){
this.iNeedThis = iNeedThis;
this.thisToo = thisToo;
}
public void DoMagic(){
//null pointer error because magic was not injected
magic.doMagic(this.iNeedthis);
}
}
How do I Guice-enable this new class?
I tried this in my Runtime Module
public Class<myCustomClass> bindMyCustomClass(){
return MyCustomClass.class;
}
and failed miserably.

No thanks to #bmorris591 who dismissed and downvoted the question out of the gate, I found an answer.
#Inject-ing a field into a class means that the class instance needs to be created by Guice.
Step 1 is creating a factory for the class. This may not be necessary, but it worked for me.
public interface MyCustomClassFactory {
public MyCustomClass create(String iNeedThis, Context thisToo);
}
Step 2 is installing the factory into Guice
#Override
public void configure(Binder binder) {
super.configure(binder);
binder.install(new FactoryModuleBuilder().build(MyCustomClass.class));
}
In my particular case - the framework I'm working with provides a Module class that is an implementation of com.google.inject.Module.
Within that class is a "configure(Binder binder)" function that is called on startup.
Step 3 is actually annotating the constructor
#Inject
public myCustomClass(String iNeedThis, Context thisToo){
this.iNeedThis = iNeedThis;
this.thisToo = thisToo;
}
Useful and related web page that put me on the right track:
http://beust.com/weblog/2012/08/21/advanced-dependency-injection-with-guice/
This talks about assisted injection, but it gave enough information and a simple enough to understand example that taking the next step was pretty easy.

Guice: injection vs wiring

Lot's of times, classes need to be instantiated (constructed), and then "wired" (configured) before they can be used. For instance:
// Construction.
EventBus bus = new EventBus();
FizzEventHandler fizzHandler = new FizzHandler();
BuzzEventHandler buzzHandler = new BuzzHandler();
// Wiring.
bus.register(fizzHandler);
bus.register(buzzHandler);
In Guice, we accomplish the first part (construction; injection) with a Binder:
public class MyModule extends AbstractModule {
#Override
public void configure() {
bind(EventBus.class).to(SimpleEventBus.class);
bind(FizzEventHandler.class).to(DefaultFizzEventHandler.class);
bind(BuzzEventHandler.class).to(DefaultBuzzEventHandler.class);
}
}
But where does the wiring take place? When my Guice-based app starts up, we engage the DI "bootstrapping" process:
public class MyApp {
private EventBus bus;
private FizzEventHandler fizzHandler;
// ...etc.
public static void main(String[] args) {
MyApp app = new MyApp();
app.run();
}
public MyApp() {
// Bootstrap DI.
MyModule myModule = new MyModule();
Injector injector = Guice.createInjector(myModule);
bus = injector.inject(EventBus.class);
fizzHandler = injector.inject(FizzEventHandler.class);
// ...etc.
// Wire
bus.register(fizzHandler);
}
}
This works OK for the top-level (root) DI classes. But as we get further "down" the dependency tree, and get into all the other objects used by the application, putting the wiring logic in constructors like this is ugly and (I believe) is a discouraged practice.
So I ask: where doe battle-weary Guice veterans place their wiring/config code?

I work on a reasonably big system (~3000 classes) which uses Guice. I would say that our approach is to do everything with constructors. There aren't distinct "construction" and "wiring" activities as you describe, there's only construction.
In your example, the event handlers would be constructor parameters to the bus, which would register them in its constructor.
If you want to have fairly flexible injection of all the components of a given type (here, you would want to inject all event listeners into the bus), you could use multibindings. However, i don't think we actually use this in our codebase; we just write out manual lists of everything that needs injecting, which turns out not to be all that arduous in practice.

I generally use multiple modules, separated out by logical function. So one module might have authentication in it, another has data repositories, another the messaging system that I'm using, etc. This allows you to have different modules for mocking, caching Vs. non-caching, or just different implementations of the same service, and to switch out chunks of dependencies quickly and easily.
To make things even more flexible you could have a configuration file which declares the modules that should be used when the injector starts up.

When I have some logic to be done right after I instantiate my object I usually do it in methods annotated with #Provides. Your example might looks like this :
public class MyModule extends AbstractModule {
#Override
protected void configure() {
bind(FizzEventHandler.class).to(DefaultFizzEventHandler.class);
bind(BuzzEventHandler.class).to(DefaultBuzzEventHandler.class);
}
#Provides
public EventBus getEventBus(SimpleEventBuss simpleBus/* this here is going to be injected as it is a class not an interface and Guice is clever and it know how to do it ;) */
, FizzEventHandler fizz, BuzzEventHandler buzz) {
simpleBus.register(fizz);
simpleBus.register(buzz);
return simpleBus;
}
}

Guice scenario where multiple injector references appear unavoidable

I have a use case where it appears that referencing a Guice injector from multiple locations is the only solution—though this is generally discouraged.
My application is built on top of Talend, an open source ETL platform. Most of my actual application is in Java classes that are called by Talend components. These components include Java snippets that I write and that, in turn, instantiate/invoke my classes.
Now I intend to use Guice throughout my Java classes but there is absolutely no way for me to inject dependencies into the Talend components (so that they would be available to the Java snippets). Instead, I need to actually create these dependencies. I’d like to at least have Guice control the instantiation, which means that instead of using new, it appears that the only way I can instantiate my classes (the ones with #Inject constructors) is to call injector.getInstance. This, in turn, implies that I need to keep the injector around, presumably using an old-fashioned factory that creates it in the first place and makes it available as a singleton.
I just can’t see any other way to handle this but perhaps I’m missing something.

Consider static injection. This will still hide persistent references to your injector across your app, but it will save you from having to pepper your code with injector.getInstance(...) calls. In any case you can inject Injector if you really need to.
class TalendDependencyModule extends AbstractModule {
#Override public void configure() {
requestStaticInjection(ExtractorDependencies.class);
requestStaticInjection(ProcessorDependencies.class);
}
}
public class ExtractorDependencies {
#Inject private static Provider<ParserService> parserServiceProvider;
#Inject private static Provider<SomethingElse> somethingElseProvider;
private ExtractorDependencies() { }
static ParserService getParserService() {
return parserServiceProvider.get();
}
/* ... */
}

I don't know how many Talend objects you have but you might want to consider using providers. For instance suppose you have your own class that you want Guice to manage creation of:
public interface INotTalendControlled {}
public class NotTalendControlled implements INotTalendControlled {}
This will be added to a Talend object whose dependencies cannot be injected via Guice (although I assume there is some manual process for doing so either constructor or setter):
public class TalendControlled {
private INotTalendControlled notTalendControlled;
private TalendControlled(INotTalendControlled notTalendControlled) {
this.notTalendControlled = notTalendControlled;
}
public INotTalendControlled getValue() {
return notTalendControlled;
}
}
If you want Guice to manage these lifecycles and the lifecycle of Talend controlled objects you can use a provider like so:
public static class TestModule extends AbstractModule {
#Override
protected void configure() {
bind(INotTalendControlled.class).to(NotTalendControlled.class);
}
#Provides
public TalendControlled provideInjectsToTalendObject(INotTalendControlled notTalendControlled) {
return new TalendControlled(notTalendControlled);
}
}
The #Provides method will hide of the use of new for all objects as you can now directly inject TalendControlled objects (#Inject TalenControlled talendControlled) and an explicit injector is not needed to construct their dependencies.