Package dagger

Annotation Interface MapKey

@Documented
@Target(ANNOTATION_TYPE)
@Retention(RUNTIME)
public @interface MapKey

Identifies annotation types that are used to associate keys with values returned by provider methods in order to compose a map.

Every provider method annotated with @Provides and @IntoMap must also have an annotation that identifies the key for that map entry. That annotation's type must be annotated with @MapKey.

Typically, the key annotation has a single member, whose value is used as the map key.

For example, to add an entry to a Map<SomeEnum, Integer> with key SomeEnum.FOO, you could use an annotation called @SomeEnumKey:

 @MapKey
 @interface SomeEnumKey {
   SomeEnum value();
 }

 @Module
 class SomeModule {
   @Provides
   @IntoMap
   @SomeEnumKey(SomeEnum.FOO)
   Integer provideFooValue() {
     return 2;
   }
 }

 class SomeInjectedType {
   @Inject
   SomeInjectedType(Map<SomeEnum, Integer> map) {
     assert map.get(SomeEnum.FOO) == 2;
   }
 }
 

If unwrapValue is true, the annotation's single member can be any type except an array.

See dagger.multibindings for standard unwrapped map key annotations for keys that are boxed primitives, strings, or classes.

Annotations as keys

If unwrapValue() is false, then the annotation itself is used as the map key. For example, to add an entry to a Map<MyMapKey, Integer> map:

 @MapKey(unwrapValue = false)
 @interface MyMapKey {
   String someString();
   MyEnum someEnum();
 }

 @Module
 class SomeModule {
   @Provides
   @IntoMap
   @MyMapKey(someString = "foo", someEnum = BAR)
   Integer provideFooBarValue() {
     return 2;
   }
 }

 class SomeInjectedType {
   @Inject
   SomeInjectedType(Map<MyMapKey, Integer> map) {
     assert map.get(new MyMapKeyImpl("foo", MyEnum.BAR)) == 2;
   }
 }
 

(Note that there must be a class MyMapKeyImpl that implements MyMapKey in order to call Map.get(Object) on the provided map.)

See Also:

• Map multibinding

Optional Element Summary

Optional Elements

Modifier and Type	Optional Element	Description
boolean	unwrapValue	True to use the value of the single member of the annotated annotation as the map key; false to use the annotation instance as the map key.

Element Details

unwrapValue

boolean unwrapValue

True to use the value of the single member of the annotated annotation as the map key; false to use the annotation instance as the map key.

If true, the single member must not be an array.

Default:

true