Android 官方示例:android-architecture 学习笔记(二)之todo-mvp

项目地址:https://github.com/googlesamples/android-architecture/tree/todo-mvp/
在第一篇说过,todo-mvp只是android-architecture项目的一个分支

项目结构

todo-mvp主要使用了mvp架构来实现,如图
匆忙拥挤repeat
图中的Repository就是数据源,即M,包括Local数据和Remote数据;Fragment为V;Activity中依赖了P,V(Fragment)与P相互依赖,P依赖了M(Repository),即P分离了M与V;当然有时我们不需要Fragment,那么可以直接使用Activity来作为V

项目的主要包结构及Base接口

(不含测试package):
Android 官方示例:android-architecture 学习笔记(二)之todo-mvp_第1张图片
除BaseView、BasePresenter两个接口,其他package都以业务功能来划分的:
addedittask —— 添加任务
data —— 数据源
statistics —— 任务统计
taskdetail —— 任务详情
tasks —— 任务列表
util —— 工具类

BaseView、BasePresenter两个接口:

public interface BaseView {
    void setPresenter(T presenter);
}
public interface BasePresenter {
    void start();
}

数据源Model

先来看下data模块,即M
Android 官方示例:android-architecture 学习笔记(二)之todo-mvp_第2张图片

Task —— 它就是一个java bean
TasksDataSource —— Task数据操作的接口
TasksRepository —— 实现了TasksDataSource,依赖了TasksLocalDataSource、TasksRemoteDataSource,实现根据不同情形,获取Local或Remote的相关数据
TasksRemoteDataSource —— 远程数据,一般可能走网络,当然这里没有,只是模拟
TasksPersistenceContract —— 约定了数据库表字段
TasksDbHelper —— 数据库操作
TasksLocalDataSource —— 本地数据源

注:项目中默认只操作了Local数据,若也想操作Remote,只需要将TasksRepository中的属性mCacheIsDirty=true,即可

tasks模块分析

接下来挑一个业务模块分析一下(其它模块大同小异),比如tasks
Android 官方示例:android-architecture 学习笔记(二)之todo-mvp_第3张图片
ScrollChildSwipeRefreshLayout —— 这是一个自定义Layout,不用理会
TasksActivity —— Activity
TasksContract —— 契约接口(每个功能模块都有一个),约定了两个子接口View和Presenter,及各自的公共方法;分别实现BaseView、BasePresenter两个接口
TasksFilterType —— enum类,任务过滤类型
TasksFragment —— Fragment,实现TasksContract.View
TasksPresenter —— Presenter,实现TasksContract.Presenter

再来分析一个具体的业务功能,比如展示tasks列表
在TasksContract#Presenter中,有一个方法:

void loadTasks(boolean forceUpdate);

相应的TasksContract#View中,有一个方法:

void showTasks(List<Task> tasks);

看下TasksPresenter的相关的一些代码:

public class TasksPresenter implements TasksContract.Presenter {

    private final TasksRepository mTasksRepository;

    private final TasksContract.View mTasksView;

    private TasksFilterType mCurrentFiltering = TasksFilterType.ALL_TASKS;

    private boolean mFirstLoad = true;

    public TasksPresenter(@NonNull TasksRepository tasksRepository, @NonNull TasksContract.View tasksView) {
        mTasksRepository = checkNotNull(tasksRepository, "tasksRepository cannot be null");
        mTasksView = checkNotNull(tasksView, "tasksView cannot be null!");

        mTasksView.setPresenter(this);
    }

    @Override
    public void start() {
        loadTasks(false);
    }

    @Override
    public void loadTasks(boolean forceUpdate) {
        // Simplification for sample: a network reload will be forced on first load.
        loadTasks(forceUpdate || mFirstLoad, true);
        mFirstLoad = false;
    }

    private void loadTasks(boolean forceUpdate, final boolean showLoadingUI) {
        if (showLoadingUI) {
            mTasksView.setLoadingIndicator(true);
        }
        if (forceUpdate) {
            mTasksRepository.refreshTasks();
        }

        // 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

        mTasksRepository.getTasks(new TasksDataSource.LoadTasksCallback() {
            @Override
            public void onTasksLoaded(List tasks) {
                List tasksToShow = new ArrayList();

                // 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.
                }

                // We filter the tasks based on the requestType
                for (Task task : tasks) {
                    switch (mCurrentFiltering) {
                        case ALL_TASKS:
                            tasksToShow.add(task);
                            break;
                        case ACTIVE_TASKS:
                            if (task.isActive()) {
                                tasksToShow.add(task);
                            }
                            break;
                        case COMPLETED_TASKS:
                            if (task.isCompleted()) {
                                tasksToShow.add(task);
                            }
                            break;
                        default:
                            tasksToShow.add(task);
                            break;
                    }
                }
                // The view may not be able to handle UI updates anymore
                if (!mTasksView.isActive()) {
                    return;
                }
                if (showLoadingUI) {
                    mTasksView.setLoadingIndicator(false);
                }

                processTasks(tasksToShow);
            }

            @Override
            public void onDataNotAvailable() {
                // The view may not be able to handle UI updates anymore
                if (!mTasksView.isActive()) {
                    return;
                }
                mTasksView.showLoadingTasksError();
            }
        });
    }

    private void processTasks(List tasks) {
        if (tasks.isEmpty()) {
            // Show a message indicating there are no tasks for that filter type.
            processEmptyTasks();
        } else {
            // Show the list of tasks
            mTasksView.showTasks(tasks);
            // Set the filter label's text.
            showFilterLabel();
        }
    }
}

从上,看出TasksPresenter依赖了TasksRepository、TasksContract.View,即P依赖了M和V;当loadTasks(boolean forceUpdate, final boolean showLoadingUI)被调用后,先从M中获取数据,再调用processTasks(List tasks),其内部调用mTasksView.showTasks(tasks)将数据显示在V上;最后还要说的一点是在TasksPresenter的构造方法中,mTasksView.setPresenter(this) 将P传递给了V

再来看下V如何通过P,来获取数据并显示
TasksFragment,即V的主要代码:

public class TasksFragment extends Fragment implements TasksContract.View {

    private TasksContract.Presenter mPresenter;

    public TasksFragment() {
        // Requires empty public constructor
    }

    public static TasksFragment newInstance() {
        return new TasksFragment();
    }

    @Override
    public void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        mListAdapter = new TasksAdapter(new ArrayList(0), mItemListener);
    }

    @Override
    public void onResume() {
        super.onResume();
        mPresenter.start();
    }

    @Override
    public void setPresenter(@NonNull TasksContract.Presenter presenter) {
        mPresenter = checkNotNull(presenter);
    }

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {

        swipeRefreshLayout.setOnRefreshListener(new SwipeRefreshLayout.OnRefreshListener() {
            @Override
            public void onRefresh() {
                mPresenter.loadTasks(false);
            }
        });

        return root;
    }

    @Override
    public void showTasks(List tasks) {
        mListAdapter.replaceData(tasks);
        mTasksView.setVisibility(View.VISIBLE);
        mNoTasksView.setVisibility(View.GONE);
    }
}

看TasksFragment的onResume()中,调用了mPresenter.start(),而mPresenter.start()中,就调用了TasksPresenter#loadTasks(false);TasksFragment的onCreateView()中还注册了一个监听回调,即下拉刷新时,也会调用TasksPresenter#loadTasks(false);

P和V的初始化在Activity中完成
TasksActivity的主要代码:

public class TasksActivity extends AppCompatActivity {

    private TasksPresenter mTasksPresenter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.tasks_act);

        TasksFragment tasksFragment =
                (TasksFragment) getSupportFragmentManager().findFragmentById(R.id.contentFrame);
        if (tasksFragment == null) {
            // Create the fragment
            tasksFragment = TasksFragment.newInstance();
            ActivityUtils.addFragmentToActivity(
                    getSupportFragmentManager(), tasksFragment, R.id.contentFrame);
        }

        // Create the presenter
        mTasksPresenter = new TasksPresenter(
                Injection.provideTasksRepository(getApplicationContext()), tasksFragment);

        // Load previously saved state, if available.
        if (savedInstanceState != null) {
            TasksFilterType currentFiltering =
                    (TasksFilterType) savedInstanceState.getSerializable(CURRENT_FILTERING_KEY);
            mTasksPresenter.setFiltering(currentFiltering);
        }
    }
}

至此,一条完整的MVP架构实现的业务链就分析完成了

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