第AndroidJetpack組件支持庫DataBinding與ViewModel與LiveData及Room詳解目錄一、官方推薦的Jetpack架構二、添加依賴三、創(chuàng)建Repository四、創(chuàng)建ViewModel五、activity中使用AndroidJetpack之ViewModel、LiveData

AndroidJetpack之LifeCycle

一、官方推薦的Jetpack架構

ViewModel是介于View（視圖）和Model（數(shù)據(jù)模型）之間的中間層，能夠使視圖和數(shù)據(jù)分離，又能提供視圖和數(shù)據(jù)之間的通信。

LiveData是一個能夠在ViewModel中數(shù)據(jù)發(fā)生變化時通知頁面刷新UI線程的組件庫。

Room是在SQLLite上提供了一層封裝。（Android采用SQLLite作為數(shù)據(jù)庫存儲）

二、添加依賴

implementationandroidx.activity:activity-ktx:1.2.0

implementationandroidx.fragment:fragment-ktx:1.3.0

下面的案例，只是簡潔的代碼片段，大致介紹一下，讓大家了解這個架構。具體詳細代碼及深度原理，請大家自行查閱其他深度講解文章。

三、創(chuàng)建Repository

StudentRepository

classStudentRepository{

varstudentDao:StudentDao=null

constructor(context:Context){

valdatabase=MyDatabase.getInstance(context)

studentDao=database!!.getStudentDao()

//LiveData集合

fungetAllStudentsLive():LiveDataListStudent{

returnstudentDao!!.getAllStudentsLive()

fundeleteAllStudents(){

studentDao!!.deleteAllStudents()

funqueryAll():ListStudent{

returnstudentDao!!.queryAll()

funinsertStudent(varargstudent:Student){

studentDao!!.insertStudent(*student)

fundeleteStudent(varargstudent:Student){

studentDao!!.deleteStudent(*student)

funupdateStudent(varargstudent:Student){

studentDao!!.updateStudent(*student)

}

StudentDao

@Dao

interfaceStudentDao{

@Insert

funinsertStudent(varargstudents:Student)

@Delete

fundeleteStudent(varargstudents:Student)

@Update

funupdateStudent(varargstudents:Student)

@Query("SELECT*FROMstudent")

fungetAllStudent():ListStudent

@Query("SELECT*FROMstudentWHEREid=:id")

fungetStudentById(id:Int):ListStudent

}

Repository類中是關于Dao的操作，getAllStudentsLive()方法返回的是一個LiveData集合。

四、創(chuàng)建ViewModel

StudentViewModel

classStudentViewModel(application:Application):AndroidViewModel(application){

//初始化Repository對象

privatevalrepositorybylazy{StudentRepository(application)}

//定義LiveData集合

privatevarliveDataStudent:LiveDataListStudent=null

init{

liveDataStudent=repository.getAllStudentsLive()

fungetAllStudentsLive():LiveDataListStudent{

viewModelScope.launch(Dispatchers.Default){

liveDataStudent=repository.getAllStudentsLive()

returnliveDataStudent

privatefuninsertStudent(varargstudent:Student){

viewModelScope.launch(Dispatchers.Default){

repository.insertStudent(*student)

privatefundeleteStudent(varargstudent:Student){

viewModelScope.launch(Dispatchers.Default){

repository.deleteStudent(*student)

privatefunupdateStudent(varargstudent:Student){

viewModelScope.launch(Dispatchers.Default){

repository.updateStudent(*student)

privatefundeleteAllStudents(){

viewModelScope.launch(Dispatchers.Default){

repository.deleteAllStudents()

//以下為DataBinding布局調(diào)用的方法-------------------

funmInsert(){

vals1=Student("zhangsan",26)

vals2=Student("lisi",18)

insertStudent(s1,s2)

funmClear(){

deleteAllStudents()

funmDelete(){

vars1=Student(3)

deleteStudent(s1)

funmUpdate(){

vals1=Student(2,"wanger",21)

updateStudent(s1)

}

初始化數(shù)據(jù)庫Repository，創(chuàng)建一個livedata集合的屬性，并提供對其操作的方法。

五、activity中使用

mainActivity

classMainActivity:AppCompatActivity(){

privatevaradapter:StudentRecyclerViewAdapter=null

privatevarlistStudent:ArrayListStudent=ArrayList()

privatevarviewModel:StudentViewModel=null

overridefunonCreate(savedInstanceState:Bundle){

super.onCreate(savedInstanceState)

//databinding

valbinding=DataBindingUtil.

setContentViewActivityMainBinding(this,R.layout.activity_main)

//viewmodel

viewModel=ViewModelProvider(this)[StudentViewModel::class.java]

binding.studentViewModel=viewModel

binding.lifecycleOwner=this

binding.recycleView.layoutManager=LinearLayoutManager(this)

adapter=StudentRecyclerViewAdapter(listStudent)

binding.recycleView.adapter=adapter

//livedata、room

viewModel!!.getAllStudentsLive()!!.

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