Android—Jetpack教程(Android Jetpack应用指南)
前言
在上一篇中，对Jetpack里面的Room进行了初步的使用，但每次操作数据后需要额外查询一次。在本篇中，将会对Room以及前面所学的进行一个整合。
话不多说，直接开始！
1、Room+ViewModel+LiveData
如图所示
这是官方推荐我们使用的架构，
ViewModel和Repository交互
Repository与对应的数据库、网络请求交互
在上一篇的基础上，对应Room数据库相关的暂且不动。
因为数据库和Repository相互关联，而Repository又与ViewModel相互关联，因此先来看看Repository究竟长啥样？
1.1 StudentRepository
class StudentRepository { var studentDao: StudentDao? = null constructor(context: Context) { val database = MyDatabase.getInstance(context) studentDao = database!!.getStudentDao() } fun insertStudent(vararg student: Student?) { studentDao!!.insertStudent(*student) } fun deleteStudent(vararg student: Student) { studentDao!!.deleteStudent(*student) } fun updateStudent(vararg student: Student) { studentDao!!.updateStudent(*student) } fun deleteAllStudents() { studentDao!!.deleteAllStudents() } fun getAllStudentsLive(): LiveData<List<Student>> { return studentDao!!.getAllStudentsLive() } fun queryAll(): List<Student>? { return studentDao!!.queryAll() } } 复制代码我们可以看到，之前关于Dao的所有操作都转移至Repository，也比较简单。
不过注意的是：getAllStudentsLive()方法返回的是LiveData<List<Student>>，LiveData集合！
接下来看看ViewModel?
1.2 StudentViewModel
class StudentViewModel(application: Application) : AndroidViewModel(application) { //初始化对应的Repository对象 private val repository by lazy { StudentRepository(application) } //定义对应得到LiveData集合 private var liveDataStudent: LiveData<List<Student>>? = null init { liveDataStudent = repository.getAllStudentsLive() Log.d("StudentViewModel", "init liveDataStudent ${liveDataStudent?.value?.size}") } private fun insertStudent(vararg student: Student) { viewModelScope.launch(Dispatchers.Default) { repository.insertStudent(*student) } } private fun deleteStudent(vararg student: Student) { viewModelScope.launch(Dispatchers.Default) { repository.deleteStudent(*student) } } private fun updateStudent(vararg student: Student) { viewModelScope.launch(Dispatchers.Default) { repository.updateStudent(*student) } } private fun deleteAllStudents() { viewModelScope.launch(Dispatchers.Default) { repository.deleteAllStudents() } } fun getAllStudentsLive(): LiveData<List<Student>>? { viewModelScope.launch(Dispatchers.Default) { liveDataStudent = repository.getAllStudentsLive() } return liveDataStudent } //以下为DataBinding布局调用的方法------------------- fun mInsert() { val s1 = Student("hqk", 26) val s2 = Student("Rose", 18) insertStudent(s1, s2) } fun mClear() { deleteAllStudents() } fun mDelete() { var s1 = Student(3) deleteStudent(s1) } fun mUpdate() { val s1 = Student(2, "Jason", 21) updateStudent(s1) } } 复制代码我们也能看到，这里的ViewModel与repository相互关联，而对应的布局通过DataBinding又与ViewModel相互绑定！
注意这里在ViewModel里面使用了viewModelScope，因此需要添加如下依赖
implementation "androidx.activity:activity-ktx:1.2.0" implementation "androidx.fragment:fragment-ktx:1.3.0" 复制代码
接下来看看如何使用：
1.3 mainActivity
class MainActivity : AppCompatActivity() { private var adapter: StudentRecyclerViewAdapter? = null private var listStudent: ArrayList<Student> = ArrayList() private var viewModel: StudentViewModel? = null override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) // setContentView(R.layout.activity_main) val binding = DataBindingUtil.setContentView<ActivityMainBinding>(this, R.layout.activity_main) viewModel = ViewModelProvider(this)[StudentViewModel::class.java] binding.studentViewModel = viewModel binding.lifecycleOwner = this // val recycleView = findViewById<RecyclerView>(R.id.recycleView) binding.recycleView.layoutManager = LinearLayoutManager(this) adapter = StudentRecyclerViewAdapter(listStudent) binding.recycleView.adapter = adapter //监听对应的LiveData,当数据库发生数据改变时，将会主动回调通知！ viewModel!!.getAllStudentsLive()!!.observe(this, androidx.lifecycle.Observer { Log.d("StudentViewModel", "main it ${it.size}") adapter!!.students = it adapter!!.notifyDataSetChanged() }) } } 复制代码这里很简单，就是通过ActivityMainBinding获取对应控件然后添加对应的逻辑，其次使用getAllStudentsLive方法获取到对应的LiveData，并通过observe监听LiveData集合。
Item对应的DataBinding为ItemBinding，相信经过第三篇DataBinding的讲解，读者应该轻易掌握了，这里就不贴对应代码了。
最后来看看运行效果吧
这里我们看到，每操作一次，数据自动加载，无需手动查询！
结束语
好了，本篇优化到这就结束了！在下一篇中，将会讲解Room对应的升级和预填充！
作者：hqk
链接：https://juejin.cn/post/7035171862560636958