MembersInjectors.java

/*
 * Copyright (C) 2014 The Dagger Authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package dagger.internal;

import dagger.MembersInjector;

import javax.inject.Inject;

import static dagger.internal.Preconditions.checkNotNull;

/**
 * Basic {@link MembersInjector} implementations used by the framework.
 *
 * @author Gregory Kick
 * @since 2.0
 */
public final class MembersInjectors {
    /**
     * Injects members into {@code instance} using {@code membersInjector}.  This method is a
     * convenience for cases in which you would want to chain members injection, but can't because
     * {@link MembersInjector#injectMembers} returns {@code void}.
     */
    public static <T> T injectMembers(MembersInjector<T> membersInjector, T instance) {
        membersInjector.injectMembers(instance);
        return instance;
    }

    /**
     * Returns a {@link MembersInjector} implementation that injects no members
     * <p>
     * <p>Note that there is no verification that the type being injected does not have {@link Inject}
     * members, so care should be taken to ensure appropriate use.
     */
    @SuppressWarnings("unchecked")
    public static <T> MembersInjector<T> noOp() {
        return (MembersInjector<T>) NoOpMembersInjector.INSTANCE;
    }

    private static enum NoOpMembersInjector implements MembersInjector<Object> {
        INSTANCE;

        @Override
        public void injectMembers(Object instance) {
            checkNotNull(instance);
        }
    }

    /**
     * Returns a {@link MembersInjector} that delegates to the {@link MembersInjector} of its
     * supertype.  This is useful for cases where a type is known not to have its own {@link Inject}
     * members, but must still inject members on its supertype(s).
     * <p>
     * <p>Note that there is no verification that the type being injected does not have {@link Inject}
     * members, so care should be taken to ensure appropriate use.
     */
    @SuppressWarnings("unchecked")
    public static <T> MembersInjector<T> delegatingTo(MembersInjector<? super T> delegate) {
        return (MembersInjector<T>) checkNotNull(delegate);
    }

    private MembersInjectors() {
    }
}