Dagger throw a NoSuchMethodException when creating

问题:

I am using Dagger as dependency injection framwork. It's working well so far but I am having an issue while using Dagger for Android unit testing and can't figure out why (Probably because of an incorrect use of Dagger).

I am having the following exception

java.lang.IllegalArgumentException: Failed to construct com.couchsurfing.mobile.android.CSApplication$ProdModule
at dagger.internal.plugins.reflect.ReflectiveModuleAdapter.newModule(ReflectiveModuleAdapter.java:94)
at dagger.internal.RuntimeAggregatingPlugin.getModuleAdapter(RuntimeAggregatingPlugin.java:99)
at dagger.internal.RuntimeAggregatingPlugin.collectIncludedModulesRecursively(RuntimeAggregatingPlugin.java:85)
at dagger.internal.RuntimeAggregatingPlugin.getAllModuleAdapters(RuntimeAggregatingPlugin.java:71)
at dagger.ObjectGraph.makeGraph(ObjectGraph.java:115)
at dagger.ObjectGraph.create(ObjectGraph.java:103)
at com.couchsurfing.mobile.android.core.MessageManagerTest.setUp(MessageManagerTest.java:34)
at android.test.AndroidTestRunner.runTest(AndroidTestRunner.java:190)
at android.test.AndroidTestRunner.runTest(AndroidTestRunner.java:175)
at android.test.InstrumentationTestRunner.onStart(InstrumentationTestRunner.java:555)
at android.app.Instrumentation$InstrumentationThread.run(Instrumentation.java:1661)
Caused by: java.lang.NoSuchMethodException: <init> []
at java.lang.Class.getConstructorOrMethod(Class.java:460)
at java.lang.Class.getDeclaredConstructor(Class.java:588)
at dagger.internal.plugins.reflect.ReflectiveModuleAdapter.newModule(ReflectiveModuleAdapter.java:88)
... 15 more

The code generating the exception is the following:

public class MessageManagerTest extends InstrumentationTestCase {

    @Inject
    MessageManager mMessageManager;

    @Inject
    MessageOperations.Factory mMOFactory;

    @Inject
    Context mAppContext;

    @Override
    public void setUp() {
        ObjectGraph.create(new TestModule()).inject(this);
    }

    @Module(
        includes = CSApplication.ProdModule.class,
        entryPoints = MessageManagerTest.class,
        overrides = true)
    static class TestModule {
        @Provides
        MessageOperations.Factory provideMessageOperationsFactory() {
            return Mockito.mock(MessageOperations.Factory.class);
        }

        @Provides
        Context provideAppContext() {
            return Mockito.mock(Context.class);
        }
    }

    public void testCreateMessage() throws RemoteException, OperationApplicationException {

      ...
    }
}

Note that the module CSApplication$ProdModule is used in the production version of the app and works well.

回答1:

You need to give ProdModule a no-args non-private constructor. And the class needs to be static. Without this Dagger can't construct your module.

回答2:

You need to either add a no-args accessible (in this case, public) constructor or you need to pass in an instance of the module. If you don't pass in an instance, then Dagger has to construct the module itself, which it cannot do if there is no accessible no-args constructor.