Goodle Clean设计架构

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！