Goodle Clean设计架构
23 * @param <P> the response type
24 */
25 public abstract class UseCase<Q extends UseCase.RequestValues, P extends UseCase.ResponseValue> {
26
27 private Q mRequestValues;
28
29 private UseCaseCallback<P> mUseCaseCallback;
30
31 public void setRequestValues(Q requestValues) {
32 mRequestValues = requestValues;
33 }
34
35 public Q getRequestValues() {
36 return mRequestValues;
37 }
38
39 public UseCaseCallback<P> getUseCaseCallback() {
40 return mUseCaseCallback;
41 }
42
43 public void setUseCaseCallback(UseCaseCallback<P> useCaseCallback) {
44 mUseCaseCallback = useCaseCallback;
45 }
46
47 void run() {
48 executeUseCase(mRequestValues);
49 }
50
51 protected abstract void executeUseCase(Q requestValues);
52
53 /**
54 * Data passed to a request.
55 */
56 public interface RequestValues {
57 }
58
59 /**
60 * Data received from a request.
61 */
62 public interface ResponseValue {
63 }
64
65 public interface UseCaseCallback<R> {
66 void onSuccess(R response);
67 void onError();
68 }
69 }
实体基类UseCase的设计用了泛型和接口，仅仅设计了两个字段mRequestValues和mUseCaseCallback。其中，mRequestValues代表数据请求参数，用泛型进行了封装，它其实也是一个类的对象；mUseCaseCallback代表请求结果，同样的，它也是一个类的对象，只不过这个类是用接口的形式进行抽象和封装的。同时，UseCase中定义抽象方法executeUseCase()作为实体操作的入口。
接下来，我们随便看一个UseCase的实现类，就拿ActivateTask来说，ActivateTask继承了UseCase，其实现代码如下：
1 /*
2 * Copyright 2016, The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17 package com.example.android.architecture.blueprints.todoapp.tasks.domain.usecase;
18
19 import android.support.annotation.NonNull;
20
21 import com.example.android.architecture.blueprints.todoapp.UseCase;
22 import com.example.android.architecture.blueprints.todoapp.data.source.TasksRepository;
23
24 import static com.google.common.base.Preconditions.checkNotNull;
25
26 /**
27 * Marks a task as active (not completed yet).
28 */
29 public class ActivateTask extends UseCase<ActivateTask.RequestValues, ActivateTask.ResponseValue> {
30
31 private final TasksRepository mTasksRepository;
32
33 public ActivateTask(@NonNull TasksRepository tasksRepository) {
34 mTasksRepository = checkNotNull(tasksRepository, "tasksRepository cannot be null!");
35 }
36
37 @Override
38 protected void executeUseCase(final RequestValues values) {
39 String activeTask = values.getActivateTask();
40 mTasksRepository.activateTask(activeTask);
41 getUseCaseCallback().onSuccess(new ResponseValue());
42 }
43
44 public static final class RequestValues implements UseCase.RequestValues {
45
46 private final String mActivateTask;
47
48 public RequestValues(@NonNull String activateTask) {
49 mActivateTask = checkNotNull(activateTask, "activateTask cannot be null!");
50 }
51
52 public String getActivateTask() {
53 return mActivateTask;
54 }
55 }
56
57 public static final class ResponseValue implements UseCase.ResponseValue { }
58 }
可以看到，在ActivateTask 中，实现了父类UseCase的两个接口RequestValues 和ResponseValue ，这两个类将分别作为最终的实体请求对象类和返回结果对象类，同时，UseCase中的抽象方法executeUseCase()也被实现。因为实现的代码里面加入了泛型和接口，所以看起来会比较复杂，但是说到底无非就是继承和实现的关系，仅此而已。通过这种面向接口的设计方式，可以让我们的代码看起来结构更清晰、更统一。
接下来，我们可以看一下这个项目中的任务执行类UseCaseThreadPoolScheduler，同样，UseCaseThreadPoolScheduler的设计采用了面向接口的方式，它实现了seCaseScheduler接口，UseCaseScheduler和UseCaseThreadPoolScheduler的实现分别如下：
1 /*
2 * Copyright 2016, The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17 package com.example.android.architecture.blueprints.todoapp;
18
19 /**
20 * Interface for schedulers, see {@link UseCaseThreadPoolScheduler}.
21 */
22 public interface UseCaseScheduler {
23
24 void execute(Runnable runnable);
25
26 <V extends UseCase.ResponseValue> void notifyResponse(final V response,
27 final UseCase.UseCaseCallback<V> useCaseCallback);
28
29 <V extends UseCase.ResponseValue> void onError(
30 final UseCase.UseCaseCallback<V> useCaseCallback);
31 }
1 /*
2 * Copyright 2016, The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17 package com.example.android.architecture.blueprints.todoapp;
18
19 import android.os.Handler;
20
21 import java.util.concurrent.ArrayBlockingQueue;
22 import java.util.concurrent.Executors;
23 import java.util.concurrent.ThreadPoolExecutor;
24 import java.util.concurrent.TimeUnit;
25
26 /**
27 * Executes asynchronous tasks using a {@link ThreadPoolExecutor}.
28 * <p>
29 * See also {@link Executors} for a list of factory methods to create common
30 * {@link java.util.concurrent.ExecutorService}s for different scenarios.
31 */
32 public class UseCaseThreadPoolScheduler implements UseCaseScheduler {
33
34 private final Handler mHandler = new Handler();
35
36 public static final int POOL_SIZE = 2;
37
38 public static final int MAX_POOL_SIZE = 4;
39
40 public static final int TIMEOUT = 30;
41
42 ThreadPoolExecutor mThreadPoolExecutor;
43
44 public UseCaseThreadPoolScheduler() {
45 mThreadPoolExecutor = new ThreadPoolExecutor(POOL_SIZE, MAX_POOL_SIZE, TIMEOUT,
46 TimeUnit.SECONDS, new ArrayBlockingQueue<Runnable>(POOL_SIZE));
47 }
48
49 @Override
50 public void execute(Runnable runnable) {
51 mThreadPoolExecutor.execute(runnable);
52 }
53
54 @Override
55 public <V extends UseCase.ResponseValue> void notifyResponse(final V response,
56 final UseCase.UseCaseCallback<V> useCaseCallback) {
57 mHandler.post(new Runnable() {
58 @Override
59 public void run() {
60 useCaseCallback.onSuccess(response);
61 }
62 });
63 }
64
65 @Override
66 public <V extends UseCase.ResponseValue> void onError(
67 final UseCase.UseCaseCallback<V> useCaseCallback) {
68 mHandler.post(new Runnable() {
69 @Override
70 public void run() {
71 useCaseCallback.onError();
72 }
73 });
74 }
75
76 }
可以看出，UseCaseThreadPoolScheduler实现了UseCaseScheduler中的三个抽象方法。
接下来，我们再看看UseCaseHandler这个类，在UseCaseHandler中，通过子类实例化父类的形式，用UseCaseThreadPoolScheduler实例化了UseCaseScheduler对象。UseCaseHandler的代码如下：
/*
* Copyright 2016, The Android Open Source Project
*
* 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 com.example.android.architecture.blueprints.todoapp; import com.example.android.architecture.blueprints.todoapp.util.EspressoIdlingResource; /**
* Runs {@link UseCase}s using a {@link UseCaseScheduler}.
*/
public class UseCaseHandler { private static UseCaseHandler INSTANCE; private final UseCaseScheduler mUseCaseScheduler; public UseCaseHandler(UseCaseScheduler useCaseScheduler) {
mUseCaseScheduler = useCaseScheduler;
} public <T extends UseCase.RequestValues, R extends UseCase.ResponseValue> void execute(
final UseCase<T, R> useCase, T values, UseCase.UseCaseCallback<R> callback) {
useCase.setRequestValues(values);
useCase.setUseCaseCallback(new UiCallbackWrapper(callback, this)); // The network request might be handled in a different thread so make sure
// Espresso knows
// that the app is busy until the response is handled.
EspressoIdlingResource.increment(); // App is busy until further notice mUseCaseScheduler.execute(new Runnable() {
@Override
public void run() { useCase.run();
// This callback may be called twice, once for the cache and once for loading
// the data from the server API, so we check before decrementing, otherwise
// it throws "Counter has been corrupted!" exception.
if (!EspressoIdlingResource.getIdlingResource().isIdleNow()) {
EspressoIdlingResource.decrement(); // Set app as idle.
}
}
});
} public <V extends UseCase.ResponseValue> void notifyResponse(final V response,
final UseCase.UseCaseCallback<V> useCaseCallback) {
mUseCaseScheduler.notifyResponse(response, useCaseCallback);
} private <V extends UseCase.ResponseValue> void notifyError(
final UseCase.UseCaseCallback<V> useCaseCallback) {
mUseCaseScheduler.onError(useCaseCallback);
} private static final class UiCallbackWrapper<V extends UseCase.ResponseValue> implements
UseCase.UseCaseCallback<V> {
private final UseCase.UseCaseCallback<V> mCallback;
private final UseCaseHandler mUseCaseHandler; public UiCallbackWrapper(UseCase.UseCaseCallback<V> callback,
UseCaseHandler useCaseHandler) {
mCallback = callback;
mUseCaseHandler = useCaseHandler;
} @Override
public void onSuccess(V response) {
mUseCaseHandler.notifyResponse(response, mCallback);
} @Override
public void onError() {
mUseCaseHandler.notifyError(mCallback);
}
} public static UseCaseHandler getInstance() {
if (INSTANCE == null) {
INSTANCE = new UseCaseHandler(new UseCaseThreadPoolScheduler());
}
return INSTANCE;
}
}
从上面的代码中，我们可以看到，声明的变量mUseCaseScheduler是UseCaseScheduler的对象，但是在构建UseCaseHandler对象的时候，传入的参数却是UseCaseThreadPoolScheduler对象，即用UseCaseThreadPoolScheduler实例化了UseCaseScheduler对象。然后，对mUseCaseScheduler的所有操作都转化成了对UseCaseThreadPoolScheduler对象的操作。
然后，我们仔细看UseCaseHandler的实现的代码，我们会发现其实对实体进行操作的入口就是execute()方法！因为这个方法里面调用了UseCase的run()，而UseCase的run()最终调用了UseCase的executeUseCase()。通过刚刚的分析，我们应该知道，我们实际上操作的实体应该是UseCase的实现类，而不是UseCase类本身，那么这中间是通过什么方式将对UseCase的操作转移到UseCase的实现类上面的呢？我们会发现UseCaseHandler的execute()传入了UseCase对象作为参数，好的，那么我们就看看execute()是在哪里被调用的吧！
经过追踪，我们看到在TasksPresenter类中调用了此方法，调用处的代码如下：
1 @Override
2 public void activateTask(@NonNull Task activeTask) {
3 checkNotNull(activeTask, "activeTask cannot be null!");
4 mUseCaseHandler.execute(mActivateTask, new ActivateTask.RequestValues(activeTask.getId()),
5 new UseCase.UseCaseCallback<ActivateTask.ResponseValue>() {
6 @Override
7 public void onSuccess(ActivateTask.ResponseValue response) {
8 mTasksView.showTaskMarkedActive();
9 loadTasks(false, false);
10 }
11
12 @Override
13 public void onError() {
14 mTasksView.showLoadingTasksError();
15 }
16 });
17 }
可以看到，我们传入的参数实际上是UseCase的实现类ActivateTask的对象，到这里，我们就明白啦！原来也是子类实例化父类的方式。
上面我只是简单粗略地讲述了一下项目中部分模块的代码，仅仅是举个例子，更多的东西需要大家自己用面向对象的思想去理解。我说这些的目的就是想告诉大家，充分运面向对象的思想就可以设计出很多看似复杂的架构和项目，但是不管再怎么复杂的代码也肯定是有迹可循的，我们只要抓住了这些设计思想的本质，多看几遍代码，一定会豁然开朗！