1、在util包下看到了幾個文件，是文件不是class，打開一看

/*
 * Copyright (C) 2017 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.util

/**
 * Various extension functions for AppCompatActivity.
 */

import android.app.Activity
import android.arch.lifecycle.ViewModel
import android.arch.lifecycle.ViewModelProviders
import android.support.annotation.IdRes
import android.support.v4.app.Fragment
import android.support.v4.app.FragmentManager
import android.support.v4.app.FragmentTransaction
import android.support.v7.app.ActionBar
import android.support.v7.app.AppCompatActivity
import com.example.android.architecture.blueprints.todoapp.ViewModelFactory


const val ADD_EDIT_RESULT_OK = Activity.RESULT_FIRST_USER + 1
const val DELETE_RESULT_OK = Activity.RESULT_FIRST_USER + 2
const val EDIT_RESULT_OK = Activity.RESULT_FIRST_USER + 3

/**
 * The `fragment` is added to the container view with id `frameId`. The operation is
 * performed by the `fragmentManager`.
 */
fun AppCompatActivity.replaceFragmentInActivity(fragment: Fragment, frameId: Int) {
    supportFragmentManager.transact {
        replace(frameId, fragment)
    }
}

/**
 * The `fragment` is added to the container view with tag. The operation is
 * performed by the `fragmentManager`.
 */
fun AppCompatActivity.addFragmentToActivity(fragment: Fragment, tag: String) {
    supportFragmentManager.transact {
        add(fragment, tag)
    }
}

fun AppCompatActivity.setupActionBar(@IdRes toolbarId: Int, action: ActionBar.() -> Unit) {
    setSupportActionBar(findViewById(toolbarId))
    supportActionBar?.run {
        action()
    }
}

fun <T : ViewModel> AppCompatActivity.obtainViewModel(viewModelClass: Class<T>) =
        ViewModelProviders.of(this, ViewModelFactory.getInstance(application)).get(viewModelClass)

/**
 * Runs a FragmentTransaction, then calls commit().
 */
private inline fun FragmentManager.transact(action: FragmentTransaction.() -> Unit) {
    beginTransaction().apply {
        action()
    }.commit()
}

里面存放著一些擴展函數(shù)，供activity直接方便的調用。還有最后的inline內聯(lián)函數(shù)等都是kotlin的特點。這個文件可以看成是java的一個工具類了。
如果是對view進行操作的工具類 ，那就建立ViewExt.kt，里面是

/**
 * Transforms static java function Snackbar.make() to an extension function on View.
 */
fun View.showSnackbar(snackbarText: String, timeLength: Int) {
    Snackbar.make(this, snackbarText, timeLength).show()
}

/**
 * Triggers a snackbar message when the value contained by snackbarTaskMessageLiveEvent is modified.
 */
fun View.setupSnackbar(lifecycleOwner: LifecycleOwner,
        snackbarMessageLiveEvent: SingleLiveEvent<Int>, timeLength: Int) {
    snackbarMessageLiveEvent.observe(lifecycleOwner, Observer {
//        這個it是singleLiveEvent.value，存放的是snackbar要展示的文本的resId
//        如果it不是null，才做showSnackbar的操作
        it?.let { showSnackbar(context.getString(it), timeLength) }
    })
}

/**
 * Reloads the data when the pull-to-refresh is triggered.
 *
 * Creates the `android:onRefresh` for a [SwipeRefreshLayout].
 */
@BindingAdapter("android:onRefresh")
fun ScrollChildSwipeRefreshLayout.setSwipeRefreshLayoutOnRefreshListener(
        viewModel: TasksViewModel) {
    setOnRefreshListener { viewModel.loadTasks(true) }
}

除了擴展函數(shù)，還包含了DataBinding的一些自定義的BindingAdapter比如上面的那個SwipeRefreshLayout的刷新監(jiān)聽。

2、 viewmodle在生成完之后，可以直接通過.apply{}對vm存放的一些LiveData的監(jiān)聽放在里面。

3、fragment的onCreateView里設置setHasOptionsMenu(true)之后，可以對onOptionsItemSelected onCreateOptionsMenu進行重寫來操作toolbar.

4、SwipeRefreshLayout的第一個child如果不是list的話會不能觸發(fā)refresh的監(jiān)聽，可以繼承他來設置監(jiān)聽具體哪個childView

class ScrollChildSwipeRefreshLayout @JvmOverloads constructor(
        context: Context,
        attrs: AttributeSet? = null
) : SwipeRefreshLayout(context, attrs) {

    var scrollUpChild: View? = null

    override fun canChildScrollUp() =
            scrollUpChild?.canScrollVertically(-1) ?: super.canChildScrollUp()
}

直接綁定上刷新監(jiān)聽需要先弄兩個靜態(tài)方法，標上@BindingAdapter

object TestBindingAdapter {
    @BindingAdapter("android:items")
    @JvmStatic
    fun setItems(rv: RecyclerView, items: List<String>) {
        with(rv.adapter as BaseQuickAdapter<String,BaseBindingViewHolder>){
            notifyDataSetChanged()
        }
    }

    @BindingAdapter("android:onRefresh")
    @JvmStatic fun SwipeRefreshLayout.setOnRefreshListener(
            viewModel: Vm) {
        setOnRefreshListener { viewModel.refresh() }
    }
}

然后在xml里

<android.support.v4.widget.SwipeRefreshLayout
        android:id="@+id/srl"
        android:onRefresh="@{vm}" //就直接可以這么用了
        app:refreshing="@{vm.dataLoading}"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toBottomOf="@id/appbar" >
        <android.support.v7.widget.RecyclerView
            android:items="@{vm.datas}"
            android:id="@+id/rv"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"/>
    </android.support.v4.widget.SwipeRefreshLayout>

如果要自動更新刷新狀態(tài)app:refreshing="@{vm.dataLoading}"，那么vm.dataLoading是個ObservableBoolean(),且在attrs.xml中加上下面的

<resources>
    <declare-styleable name="SwipeRefreshLayout">
        <attr name="refreshing" format="boolean" />
    </declare-styleable>
</resources>

5、在fragment中對activity里的fab（floatActionButton）進行操作，就直接通過

activity.findViewById<FloatingActionButton>(R.id.fab_add_task).run {
            setImageResource(R.drawable.ic_add)
            setOnClickListener {
                viewDataBinding.viewmodel?.addNewTask()
            }
        }

去設置圖標和點擊事件，不要寫在activity里再傳進frag。

6、Toolbar用得少?；径际亲远x，頭一次看見除了popupWindow還有個東西叫popupMenu。。用來在ActionBar上顯示一個窗口

7、對于listview和databinding的使用：
首先申明一個單例TaskListBindings

/**
 * Contains [BindingAdapter]s for the [Task] list.
 */
object TasksListBindings {

    @BindingAdapter("app:items")
    @JvmStatic fun setItems(listView: ListView, items: List<Task>) {
        with(listView.adapter as TasksAdapter) {
            replaceData(items)
        }
    }
}

在xml里配置上

  <ListView
                android:id="@+id/tasks_list"
                app:items="@{viewmodel.items}"
                android:layout_width="match_parent"
                android:layout_height="wrap_content" />

注意這個items是一個ObservableArrayList
val items: ObservableList<Task> = ObservableArrayList()
當他發(fā)生變化的時候，會去上面的bindingadapter里調用tasksAdapter.replaceData(items)方法進行刷新

8、因為binding與xml是綁定的，所以可以直接FragmentXXXBinding.inflate(),不用寫R.layout.xxx了。

9、事件的流轉通過調用vm的方法，改變vm.liveData，從而通知到注冊了liveData的地方進行處理事件。比如頁面的跳轉，彈個snackbar，彈個dialog，彈個popupWindow，都從liveData通知到Activity，讓activity去做。

10、intent包含的key 以及requestCode，往哪里去，就把這些常量寫在哪里。

11、設置actionbar左上角返回

//這個方法在第一個代碼段中定義的，往上翻↑
setupActionBar(R.id.toolbar) {
            setDisplayHomeAsUpEnabled(true) //顯示返回圖標
            setDisplayShowHomeEnabled(true) //顯示左上圖標
        }

 override fun onSupportNavigateUp(): Boolean {
        onBackPressed()
        return true
    }

12、接受單個事件或數(shù)據(jù)變動

class SingleLiveEvent<T> : MutableLiveData<T>() {

    private val pending = AtomicBoolean(false)

    @MainThread
    override fun observe(owner: LifecycleOwner, observer: Observer<T>) {
//        判斷是否曾經(jīng)注冊過監(jiān)聽了
        if (hasActiveObservers()) {
            Log.w(TAG, "Multiple observers registered but only one will be notified of changes.")
        }

        // Observe the internal MutableLiveData
        super.observe(owner, Observer<T> { t ->
            if (pending.compareAndSet(true, false)) {
                observer.onChanged(t)
            }
        })
    }

    @MainThread
    override fun setValue(t: T?) {
        pending.set(true)
        super.setValue(t)
    }

    /**
     * Used for cases where T is Void, to make calls cleaner.
     */
    @MainThread
    fun call() {
        value = null
    }

    companion object {
        private const val TAG = "SingleLiveEvent"
    }
}

在vm中建立一個對象 val newTaskEvent= SingleLiveEvent<Void>()
在某個Activity或Fragment中注冊監(jiān)聽。

viewModel = obtainViewModel().apply {
            // Subscribe to "new task" event
            newTaskEvent.observe(this@TasksActivity, Observer<Void> {
                this@TasksActivity.addNewTask()
            })
        }

image.png

可以看到分包是根據(jù)PBF（package by feature）的，而不是PBL （package by layer），根據(jù)業(yè)務特征來分類。而其中有一個data包是這樣的

image.png

分為了本地數(shù)據(jù)和遠程數(shù)據(jù)。
在TasksDataSource中定義了操作數(shù)據(jù)的接口。在LocalDataSource和RemoteDataSource中具體實現(xiàn)。比如本地就用room去數(shù)據(jù)庫拿，remote就去操作retrofit去網(wǎng)絡獲取。
TaskRepository數(shù)據(jù)倉庫 也是繼承自TasksDataSource，且同時持有本地和遠程的DataSource，綜合獲取、處理并對外提供數(shù)據(jù)。
可以看到層次非常清晰。我想起了一張圖，等我去google官網(wǎng)找下。。
找到了，是這個

image.png