Dagger 2 - Null Pointer in Field Injection
I am using dagger 2 for dependency injection and got stuck with field injection. Below is the complete scenario with code sample:
Let's say we have a class A which depends on a library B
class A {
@Inject
B b;
}
Module for B:
@Module
public class BModule {
@Provides
@Singleton
public B provideB() {
return new C.methodA();
// C - static class; C.methodA returns B
}
}
But when I try to use b in class A then I get null pointer exception but if I do the same using constructor injection then it works perfectly.
I can assure that component and other dependencies are fine as the constructor part works correctly.
A is a dependency of some other class (let's call X) and A is being initialized using constructor injection (tested). Also, X is being injected as void inject(X x);
I have 2 questions:
- Is there anything I am missing out for field injection due to which it is not being injected?
- I am able to successfully compile the code and get runtime exception, but dagger2 is compile-time DI then why is it unable to catch this while compiling?
P.S.: I have just shared a part of the code as there are multiple dependencies, so just trying to explain the scenario. Let me know if the question/scenario is still unclear or needs more info.
Thanks.
java dependency-injection dagger-2 dagger dagger-android
asked Nov 14 '18 at 18:11
divyumdivyum
780818
add a comment |
I am using dagger 2 for dependency injection and got stuck with field injection. Below is the complete scenario with code sample:
Let's say we have a class A which depends on a library B
class A {
@Inject
B b;
}
Module for B:
@Module
public class BModule {
@Provides
@Singleton
public B provideB() {
return new C.methodA();
// C - static class; C.methodA returns B
}
}
But when I try to use b in class A then I get null pointer exception but if I do the same using constructor injection then it works perfectly.
I can assure that component and other dependencies are fine as the constructor part works correctly.
A is a dependency of some other class (let's call X) and A is being initialized using constructor injection (tested). Also, X is being injected as void inject(X x);
I have 2 questions:
- Is there anything I am missing out for field injection due to which it is not being injected?
- I am able to successfully compile the code and get runtime exception, but dagger2 is compile-time DI then why is it unable to catch this while compiling?
P.S.: I have just shared a part of the code as there are multiple dependencies, so just trying to explain the scenario. Let me know if the question/scenario is still unclear or needs more info.
Thanks.
java dependency-injection dagger-2 dagger dagger-android
asked Nov 14 '18 at 18:11
divyumdivyum
780818
add a comment |
I am using dagger 2 for dependency injection and got stuck with field injection. Below is the complete scenario with code sample:
Let's say we have a class A which depends on a library B
class A {
@Inject
B b;
}
Module for B:
@Module
public class BModule {
@Provides
@Singleton
public B provideB() {
return new C.methodA();
// C - static class; C.methodA returns B
}
}
But when I try to use b in class A then I get null pointer exception but if I do the same using constructor injection then it works perfectly.
I can assure that component and other dependencies are fine as the constructor part works correctly.
A is a dependency of some other class (let's call X) and A is being initialized using constructor injection (tested). Also, X is being injected as void inject(X x);
I have 2 questions:
- Is there anything I am missing out for field injection due to which it is not being injected?
- I am able to successfully compile the code and get runtime exception, but dagger2 is compile-time DI then why is it unable to catch this while compiling?
P.S.: I have just shared a part of the code as there are multiple dependencies, so just trying to explain the scenario. Let me know if the question/scenario is still unclear or needs more info.
Thanks.
java dependency-injection dagger-2 dagger dagger-android
asked Nov 14 '18 at 18:11
divyumdivyum
780818
I am using dagger 2 for dependency injection and got stuck with field injection. Below is the complete scenario with code sample:
Let's say we have a class A which depends on a library B
class A {
@Inject
B b;
}
Module for B:
@Module
public class BModule {
@Provides
@Singleton
public B provideB() {
return new C.methodA();
// C - static class; C.methodA returns B
}
}
But when I try to use b in class A then I get null pointer exception but if I do the same using constructor injection then it works perfectly.
I can assure that component and other dependencies are fine as the constructor part works correctly.
A is a dependency of some other class (let's call X) and A is being initialized using constructor injection (tested). Also, X is being injected as void inject(X x);
I have 2 questions:
- Is there anything I am missing out for field injection due to which it is not being injected?
- I am able to successfully compile the code and get runtime exception, but dagger2 is compile-time DI then why is it unable to catch this while compiling?
P.S.: I have just shared a part of the code as there are multiple dependencies, so just trying to explain the scenario. Let me know if the question/scenario is still unclear or needs more info.
Thanks.
java dependency-injection dagger-2 dagger dagger-android
java dependency-injection dagger-2 dagger dagger-android
asked Nov 14 '18 at 18:11
divyumdivyum
780818
asked Nov 14 '18 at 18:11
divyumdivyum
780818
edited Nov 14 '18 at 19:47
divyum
asked Nov 14 '18 at 18:11
divyumdivyum
780818
asked Nov 14 '18 at 18:11
divyumdivyum
780818
asked Nov 14 '18 at 18:11
divyumdivyum
780818
780818
add a comment |
add a comment |
1 Answer
1
active
oldest
votes
Field injection in dagger is a bit more complicated than constructor injection. When you use constructor injection like this
class A {
@Inject
public A(B b) {}
}
and you have provider for class B
@Module
class DaggerModule {
@Provides
B provideB() {}
}
now dagger will know how to create instance of A and pass it required constructor parameter. So everything is fine, compile successfully and works perfect.
But if we speak about field injection
class A {
@Inject
B b;
}
and have somewhere provider for B, dagger can't know how to create A instance and when inject b property (in case of manually creating instance of A by hand). To make it work you need write special method in component
@Component(DaggetModule.class)
interface DaggerComponent {
void inject(A a);
}
and somewhere in code
A a = new A();
DaggerComponent component = //TODO getDaggerComponent()
component.inject(a);
After that b property will be initialized and available for later usage. Hope, it's clear now how to make field injection work.
answered Nov 14 '18 at 19:18
ConstOrVarConstOrVar
1,094149
Thanks @ConstOrVar, I forgot to mention here that A is a dependency of some other class (let's call X) and A is being initialized correctly. Also, X is being initialized as you have suggested i.e. void inject(X x); I will update in the question as well.
– divyum
Nov 14 '18 at 19:44
add a comment |
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1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
Field injection in dagger is a bit more complicated than constructor injection. When you use constructor injection like this
class A {
@Inject
public A(B b) {}
}
and you have provider for class B
@Module
class DaggerModule {
@Provides
B provideB() {}
}
now dagger will know how to create instance of A and pass it required constructor parameter. So everything is fine, compile successfully and works perfect.
But if we speak about field injection
class A {
@Inject
B b;
}
and have somewhere provider for B, dagger can't know how to create A instance and when inject b property (in case of manually creating instance of A by hand). To make it work you need write special method in component
@Component(DaggetModule.class)
interface DaggerComponent {
void inject(A a);
}
and somewhere in code
A a = new A();
DaggerComponent component = //TODO getDaggerComponent()
component.inject(a);
After that b property will be initialized and available for later usage. Hope, it's clear now how to make field injection work.
answered Nov 14 '18 at 19:18
ConstOrVarConstOrVar
1,094149
Thanks @ConstOrVar, I forgot to mention here that A is a dependency of some other class (let's call X) and A is being initialized correctly. Also, X is being initialized as you have suggested i.e. void inject(X x); I will update in the question as well.
– divyum
Nov 14 '18 at 19:44
add a comment |
Field injection in dagger is a bit more complicated than constructor injection. When you use constructor injection like this
class A {
@Inject
public A(B b) {}
}
and you have provider for class B
@Module
class DaggerModule {
@Provides
B provideB() {}
}
now dagger will know how to create instance of A and pass it required constructor parameter. So everything is fine, compile successfully and works perfect.
But if we speak about field injection
class A {
@Inject
B b;
}
and have somewhere provider for B, dagger can't know how to create A instance and when inject b property (in case of manually creating instance of A by hand). To make it work you need write special method in component
@Component(DaggetModule.class)
interface DaggerComponent {
void inject(A a);
}
and somewhere in code
A a = new A();
DaggerComponent component = //TODO getDaggerComponent()
component.inject(a);
After that b property will be initialized and available for later usage. Hope, it's clear now how to make field injection work.
answered Nov 14 '18 at 19:18
ConstOrVarConstOrVar
1,094149
Thanks @ConstOrVar, I forgot to mention here that A is a dependency of some other class (let's call X) and A is being initialized correctly. Also, X is being initialized as you have suggested i.e. void inject(X x); I will update in the question as well.
– divyum
Nov 14 '18 at 19:44
add a comment |
Field injection in dagger is a bit more complicated than constructor injection. When you use constructor injection like this
class A {
@Inject
public A(B b) {}
}
and you have provider for class B
@Module
class DaggerModule {
@Provides
B provideB() {}
}
now dagger will know how to create instance of A and pass it required constructor parameter. So everything is fine, compile successfully and works perfect.
But if we speak about field injection
class A {
@Inject
B b;
}
and have somewhere provider for B, dagger can't know how to create A instance and when inject b property (in case of manually creating instance of A by hand). To make it work you need write special method in component
@Component(DaggetModule.class)
interface DaggerComponent {
void inject(A a);
}
and somewhere in code
A a = new A();
DaggerComponent component = //TODO getDaggerComponent()
component.inject(a);
After that b property will be initialized and available for later usage. Hope, it's clear now how to make field injection work.
answered Nov 14 '18 at 19:18
ConstOrVarConstOrVar
1,094149
Field injection in dagger is a bit more complicated than constructor injection. When you use constructor injection like this
class A {
@Inject
public A(B b) {}
}
and you have provider for class B
@Module
class DaggerModule {
@Provides
B provideB() {}
}
now dagger will know how to create instance of A and pass it required constructor parameter. So everything is fine, compile successfully and works perfect.
But if we speak about field injection
class A {
@Inject
B b;
}
and have somewhere provider for B, dagger can't know how to create A instance and when inject b property (in case of manually creating instance of A by hand). To make it work you need write special method in component
@Component(DaggetModule.class)
interface DaggerComponent {
void inject(A a);
}
and somewhere in code
A a = new A();
DaggerComponent component = //TODO getDaggerComponent()
component.inject(a);
After that b property will be initialized and available for later usage. Hope, it's clear now how to make field injection work.
answered Nov 14 '18 at 19:18
ConstOrVarConstOrVar
1,094149
answered Nov 14 '18 at 19:18
ConstOrVarConstOrVar
1,094149
answered Nov 14 '18 at 19:18
ConstOrVarConstOrVar
1,094149
answered Nov 14 '18 at 19:18
ConstOrVarConstOrVar
1,094149
1,094149
Thanks @ConstOrVar, I forgot to mention here that A is a dependency of some other class (let's call X) and A is being initialized correctly. Also, X is being initialized as you have suggested i.e. void inject(X x); I will update in the question as well.
– divyum
Nov 14 '18 at 19:44
add a comment |
Thanks @ConstOrVar, I forgot to mention here that A is a dependency of some other class (let's call X) and A is being initialized correctly. Also, X is being initialized as you have suggested i.e. void inject(X x); I will update in the question as well.
– divyum
Nov 14 '18 at 19:44
Thanks @ConstOrVar, I forgot to mention here that A is a dependency of some other class (let's call X) and A is being initialized correctly. Also, X is being initialized as you have suggested i.e. void inject(X x); I will update in the question as well.
– divyum
Nov 14 '18 at 19:44
Thanks @ConstOrVar, I forgot to mention here that A is a dependency of some other class (let's call X) and A is being initialized correctly. Also, X is being initialized as you have suggested i.e. void inject(X x); I will update in the question as well.
– divyum
Nov 14 '18 at 19:44
add a comment |
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