android-architecture:TO-DO-MVVM-Lifecycles解析

GitHub:https://github.com/googlesamples/android-architecture/tree/todo-mvvm-live/

架构图

LAUNCHER

TasksActivity

<activity
            android:name="com.example.android.architecture.blueprints.todoapp.tasks.TasksActivity"
            android:theme="@style/AppTheme.OverlapSystemBar">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>

TasksActivity.java
TasksActivity extends AppCompatActivity

tasks_act.xml
DrawerLayout(
    LinearLayout(
        AppBarLayout(
            Toolbar
        )
        CoordinatorLayout(
            FrameLayout
            FloatingActionButton
        )
    )
    NavigationView
)

1. onCreate:
    1. 获取TasksViewModel.java
        public static TasksViewModel obtainViewModel(FragmentActivity activity) {
            // Use a Factory to inject dependencies into the ViewModel
            ViewModelFactory factory = ViewModelFactory.getInstance(activity.getApplication());
            TasksViewModel viewModel =
                    ViewModelProviders.of(activity, factory).get(TasksViewModel.class);
            return viewModel;
        }
    2. 添加LiveData感知
        // Subscribe to "open task" event  fragment -> 过来的数据
        mViewModel.getOpenTaskEvent().observe(this, new Observer<String>() {
            @Override
            public void onChanged(@Nullable String taskId) {
                if (taskId != null) {
                    openTaskDetails(taskId);
                }
            }
        });
        // Subscribe to "new task" event
        mViewModel.getNewTaskEvent().observe(this, new Observer<Void>() {
            @Override
            public void onChanged(@Nullable Void _) {
                addNewTask();
            }
        });
    3. 设置要显示的Fragment
        private void setupViewFragment() {
            //检测该contentFrame是否添加过
            TasksFragment tasksFragment =
                    (TasksFragment) getSupportFragmentManager().findFragmentById(R.id.contentFrame);
            if (tasksFragment == null) {
                // Create the fragment
                tasksFragment = TasksFragment.newInstance();
                ActivityUtils.replaceFragmentInActivity(
                        getSupportFragmentManager(), tasksFragment, R.id.contentFrame);
            }
        }
    4. 其他 ...

TasksFragment

1. tasks_frag.xml
    Android Studio 开启 
        dataBinding {
            enabled = true
        }
    会生成相应的Binding管理对象
    ->TasksFragBinding.java
<layout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto">
    <data>
        <!--变量-->
        <variable
            name="viewmodel"
            type="com.example.android.architecture.blueprints.todoapp.tasks.TasksViewModel" />
    </data>
    <com.example.android.architecture.blueprints.todoapp.ScrollChildSwipeRefreshLayout
        android:id="@+id/refresh_layout"
        ...
        android:onRefresh="@{viewmodel}"
        app:refreshing="@{viewmodel.dataLoading}">
        <RelativeLayout
            android:id="@+id/tasksContainer"
            ...>
            <LinearLayout
                android:id="@+id/tasksLL"
                ...
                android:visibility="@{viewmodel.empty ? View.GONE : View.VISIBLE}">
                <TextView
                    android:id="@+id/filteringLabel"
                    ...
                    android:text="@{viewmodel.currentFilteringLabel}"
                    />
                <ListView
                    android:id="@+id/tasks_list"
                    ...
                    app:items="@{viewmodel.items}" />
            </LinearLayout>
            <!-- 中间提示-->
            <LinearLayout
                android:id="@+id/noTasks"
                ...
                android:visibility="@{viewmodel.empty ? View.VISIBLE : View.GONE}">
                <ImageView
                    android:id="@+id/noTasksIcon"
                    ...
                    android:src="@{viewmodel.noTaskIconRes}" />
                <TextView
                    android:id="@+id/noTasksMain"
                    ...
                    android:text="@{viewmodel.noTasksLabel}" />
                <TextView
                    android:id="@+id/noTasksAdd"
                    ...
                    android:onClick="@{() -> viewmodel.addNewTask()}"
                    android:visibility="@{viewmodel.tasksAddViewVisible ? View.VISIBLE : View.GONE}" />
            </LinearLayout>
        </RelativeLayout>
    </com.example.android.architecture.blueprints.todoapp.ScrollChildSwipeRefreshLayout>
</layout>   

2. TasksFragment.java
    public class TasksFragment extends Fragment {}

    1. onCreateView:
        // 绑定 View 与 ViewModel
        @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        mTasksFragBinding = TasksFragBinding.inflate(inflater, container, false);
        mTasksViewModel = TasksActivity.obtainViewModel(getActivity());
        // 向View 设置 ViewModel
        mTasksFragBinding.setViewmodel(mTasksViewModel);
        ...
        //从 TasksFragBinding.inflate 中获取 layout
        return mTasksFragBinding.getRoot();
    }
    2. onActivityCreated:
        // 添加LiveData感知
        @Override
        public void onActivityCreated(@Nullable Bundle savedInstanceState) {
            super.onActivityCreated(savedInstanceState);
            setupSnackbar();
            setupFab();
            setupListAdapter();
            setupRefreshLayout();
        }

        private void setupSnackbar() {
            // 设置 Snackbar 的感知，当数据改变时会显示 snackbar
            mTasksViewModel.getSnackbarMessage().observe(this, new SnackbarMessage.SnackbarObserver() {
                @Override
                public void onNewMessage(@StringRes int snackbarMessageResourceId) {
                    SnackbarUtils.showSnackbar(getView(), getString(snackbarMessageResourceId));
                }
            });
        }

        private void setupFab() {
            FloatingActionButton fab =
                    (FloatingActionButton) getActivity().findViewById(R.id.fab_add_task);
            fab.setImageResource(R.drawable.ic_add);
            fab.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    // 触发事件
                    mTasksViewModel.addNewTask();
                    /*
                        public void addNewTask() {
                            mNewTaskEvent.call();
                        }
                    */
                }
            });
        }
        // 绑定 ListView
        private void setupListAdapter() {
            // 获取 android:id="@+id/tasks_list" 
            ListView listView = mTasksFragBinding.tasksList;
            mListAdapter = new TasksAdapter(
                    new ArrayList<Task>(0),
                    mTasksViewModel
            );
            listView.setAdapter(mListAdapter);
        }
        // 绑定 SwipeRefreshLayout
        private void setupRefreshLayout() {
            //android:id="@+id/tasks_list"
            ListView listView = mTasksFragBinding.tasksList;
            //android:id="@+id/refresh_layout"
            final ScrollChildSwipeRefreshLayout swipeRefreshLayout = mTasksFragBinding.refreshLayout;
            swipeRefreshLayout.setColorSchemeColors(
                    ContextCompat.getColor(getActivity(), R.color.colorPrimary),
                    ContextCompat.getColor(getActivity(), R.color.colorAccent),
                    ContextCompat.getColor(getActivity(), R.color.colorPrimaryDark)
            );
            // Set the scrolling view in the custom SwipeRefreshLayout.
            swipeRefreshLayout.setScrollUpChild(listView);
        }
    2. onResume:
        //加载数据
        @Override
        public void onResume() {
            super.onResume();
            mTasksViewModel.start();
        }