I'm trying to find the best way to inject into an inheritance hierarchy.
The base class takes one "live" parameter ("name", not injectable) and a
bunch of injected dependencies, "dep1", "dep2", etc. The most obvious
solution is to use assisted injection:
public class Base {
private Dep1 dep1;
private String name;
protected Base(String name, Dep1 dep1) {
this.name = name;
this.dep1 = dep1;
}
}
public class A extends Base {
public interface IFactory {
A create(@Assisted("name") String name);
}
@Inject
private A(String name, Dep1 dep1) {
super(name, dep1);
}
}
Two things bother me with this approach:
1. It's a lot of boiler plate. Each new subclass needs to create its own
factory, its own constructor with all the dependencies, call super with all
these dependencies and add itself to the FactoryModuleBuilder.
2. If I add a new dependency in the base class, I need to modify all the
subclasses (add a parameter to their constructor and to their super() call).
I considered passing the injector as the sole dependency to the base class
and let the base class do its own look ups:
public class Base {
private Dep1 dep1;
private String name;
protected Base(String name, Injector inj) {
this.name = name;
this.dep1 = inj.getInstance(Dep1.class);
}
}
public class A extends Base {
public interface IFactory {
A create(@Assisted("name") String name);
}
@Inject
public A(String name, Injector inj) {
super(name, inj);
}
This addresses point 2: when a new dependency is added to the base class,
only the base class needs to be modified, but it's still awkward to do
these look ups manually (and injectMembers() doesn't work since we're in
the constructor).
This still doesn't address point 1: there's still a lot of boiler plate
involved for each subclass.
Is there a better way?
If not, can we discuss this as a potential new feature?
--
Cédric
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