学习视频来源:
- https://www.bilibili.com/video/BV1sJ41127EMlongway777
- 模型图来源也全截取来自该Up的视频
一.Boat
- 通过建立Repository进行解耦
1. Entity，行，实体，定义了表格结构
2. 添加Room依赖
- 先添加kapt的插件依赖
- 按需导入
3. 代码一：通过Dao，Entity和Database建立简单数据库，进行增删改查
1. 建立word类
- java式
- kotlin
- kotlin加入get和set方法
@Entity//Room表示创建实体类
class Word(word: String, chineseMeaning: String) {
@PrimaryKey(autoGenerate = true)
private var id = 0
@ColumnInfo(name = "english_word")
private var word: String
@ColumnInfo(name = "chinese_meaning")
private var chineseMeaning: String
fun getId(): Int {
return id
}
fun setId(id: Int) {
this.id = id
}
fun getWord(): String {
return word
}
fun setWord(word: String) {
this.word = word
}
fun getChineseMeaning(): String {
return chineseMeaning
}
fun setChineseMeaning(chineseMeaning: String) {
this.chineseMeaning = chineseMeaning
}
init {
this.word = word
this.chineseMeaning = chineseMeaning
}
}
2. 建立wordDao类
-
java写法，接收多个参数，insert java写法可返回当前id
-
kotlin写法
-
补充dao层接口
interface WordDao {
@Insert
fun insertWords(vararg words: Word?)
@Update//返回修改的记录条数
fun updateWords(vararg words: Word?) //通过id进行替换内容
@Delete
fun deleteWords(vararg words: Word?)
@Query("DELETE FROM WORD")//删除所有内容
fun deleteAllWords();
@Query("SELECT * FROM WORD ORDER BY ID DESC")//降序查询
fun getAllWords():List<Word>
}
-
建立Database
-
java式写法
-
注意kotlin式
3. MainActivity
- 声明database（数据库名称）与dao对象
- 试图绑定一个text和4个button与监听事件即可
class MainActivity : AppCompatActivity() {
private var worddatabase:WordDatabase?=null
lateinit var worddao: WordDao
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
worddatabase= Room.databaseBuilder( this,WordDatabase::class.java,"word_database")
.allowMainThreadQueries().build()//强制主线程运行 但不太好
worddao= worddatabase?.getWordDao()!!
button_insert.setOnClickListener {
var word:Word = Word("Hello","你好")
var word1:Word = Word("ByeBye","再见")
worddao.insertWords(word1,word)
updateView();
}
button_delete.setOnClickListener {
var word:Word = Word("Word","世界")
word.setId(40)
worddao.deleteWords(word)
updateView()
}
button_clear.setOnClickListener{
worddao.deleteAllWords()
updateView()
}
button_update.setOnClickListener {
var word:Word = Word("Word","世界")
word.setId(40)
worddao.updateWords(word)
updateView()
}
}
fun updateView(){
var list:List<Word> =worddao.getAllWords()
var text=""
for (i in (0 until list.size)){
var word:Word =list.get(i)
text+=""+word.getId()+":"+word.getWord()+"="+word.getChineseMeaning();
}
text2.text=text
}
}
4. 查看存储位置与导出表
4. 代码二:JetPack融入(LiveData)，线程控制(AsyncTask)，SingleTon与仓库类，结合ViewModel精简
1. LiveData
- 将查询的返回值改为LiveData，PS：返回的
livedata比较特殊,会 自动放入副线程，所以之后不用封装单独线程方法
- 增删改查原本都要调用updateView方法进行更新界面，现在通过观察者模式，
观察总数据，若总数据产生变动,则会自动调用更新方法
- lifedata观察者模式，将原本代码中所以的updateview删除，
lifedata在处理多处会调用UI相同操作的地方很好用。完成插入删除后界面自动刷新
allwordslive=worddao.getAllWordsLive()
updateView();
allwordslive.observe(this,object: Observer<List<Word>>{
override fun onChanged(t: List<Word>?) {
var text=""
if (t != null) {
for (i in (0 until t.size)){
var word:Word =t.get(i)
text+=""+word.getId()+":"+word.getWord()+"="+word.getChineseMeaning()+"\n";
}
}
text2.text=text
}
})
2. 单例模式Singleton与抽象类的静态方法。
- 建立INSTANCE单例
- @Synchronized关键字
- 抽象类的静态方法用open关键字修饰
@Database(entities = [Word::class],version = 1,exportSchema = false)
abstract class WordDatabase: RoomDatabase() {
//若有多个entities则返回多个Dao
companion object{
private var INSTANCE: WordDatabase? = null
@Synchronized//如果有多个客户端 且同时instance时保证不会有碰撞 只有一个instance生成
open fun getDatabase(context: Context): WordDatabase? {
//静态类的静态方法写open
if (INSTANCE==null){
INSTANCE=Room.databaseBuilder(context.applicationContext,WordDatabase::class.java,"word_database")
.build()
}
return INSTANCE
}
}
abstract fun getWordDao(): WordDao
}
2.5. 建立工作线程/后期优化进入单独文件
- 使用AsyncTask，写Player的时候优化查询前用过
- 新建插入线程，后两个参数分别是报告进度和报告结果，使用构造函数传递一个结果
internal class InsertAsyncTask(private val worddao: WordDao) : AsyncTask<Word?, Unit, Unit>(){
//在后台工作
override fun doInBackground(vararg params: Word?) {
publishProgress()//该方法用于一段时间报告工作进度
worddao.insertWords(*params)
}
//将结果带回给主线程
override fun onPostExecute(result: Unit?) {
super.onPostExecute(result)
}
//进度发送更新时
override fun onProgressUpdate(vararg values: Unit?) {
super.onProgressUpdate(*values)
}
//后台工作开始之前反馈
override fun onPreExecute() {
super.onPreExecute()
}
}
- 保留doinbackground，建立增删改查
internal class InsertAsyncTask(private val worddao: WordDao) : AsyncTask<Word?, Unit, Unit>(){
//在后台工作
override fun doInBackground(vararg params: Word?) {
publishProgress()//该方法用于一段时间报告工作进度
worddao.insertWords(*params)
}
}
internal class UpdateAsyncTask(private val worddao: WordDao) : AsyncTask<Word?, Unit, Unit>(){
//在后台工作
override fun doInBackground(vararg params: Word?) {
publishProgress()//该方法用于一段时间报告工作进度
worddao.updateWords(*params)
}
}
internal class DeleteAsyncTask(private val worddao: WordDao) : AsyncTask<Word?, Unit, Unit>(){
//在后台工作
override fun doInBackground(vararg params: Word?) {
publishProgress()//该方法用于一段时间报告工作进度
worddao.deleteWords(*params)
}
}
internal class DeleteAllAsyncTask(private val worddao: WordDao) : AsyncTask<Unit, Unit, Unit>(){
//在后台工作
override fun doInBackground(vararg params: Unit?) {
publishProgress()//该方法用于一段时间报告工作进度
worddao.deleteAllWords()
}
}
- 取代原数据库语句调用操作，以insert为例，替换后把.allowMainThreadQueries()去掉即可。
3. 抽取MVVM
- 建立WordViewModel，使用主构造器与init初始化（因为getDatabase()进行单例创建时需要context），进行数据库创建与dao层相关的生成。
- 建立LiveData类存储List用于MainAC观察者的监听，并写对应方法
- 将MAC封装的Async方法移植过来，抽取方法，MAC新建ViewModel对象时直接可以调用。
1）
class WordViewModel(application: Application) : AndroidViewModel(application){
private lateinit var allwordslive :LiveData<List<Word>>
lateinit var worddatabase: WordDatabase
private lateinit var worddao:WordDao
init{
worddatabase= WordDatabase.getDatabase(application)!!
worddao= worddatabase?.getWordDao()
allwordslive=worddao.getAllWordsLive()
}
public fun getAllWordsLive():LiveData<List<Word>>{
return allwordslive
}
//写方法调用这些
fun insertWords(vararg params: Word?){
InsertAsyncTask(worddao).execute(*params)
}
fun updateWords(vararg params: Word?){
UpdateAsyncTask(worddao).execute(*params)
}
fun deleteWords(vararg params: Word?){
DeleteAsyncTask(worddao).execute(*params)
}
fun deleteAllWords(vararg params: Word?){
DeleteAllAsyncTask(worddao).execute()
}
internal class InsertAsyncTask(private val worddao: WordDao) : AsyncTask<Word?, Unit, Unit>(){
//在后台工作
override fun doInBackground(vararg params: Word?) {
publishProgress()//该方法用于一段时间报告工作进度
worddao.insertWords(*params)
}
}
internal class UpdateAsyncTask(private val worddao: WordDao) : AsyncTask<Word?, Unit, Unit>(){
//在后台工作
override fun doInBackground(vararg params: Word?) {
publishProgress()//该方法用于一段时间报告工作进度
worddao.updateWords(*params)
}
}
internal class DeleteAsyncTask(private val worddao: WordDao) : AsyncTask<Word?, Unit, Unit>(){
//在后台工作
override fun doInBackground(vararg params: Word?) {
publishProgress()//该方法用于一段时间报告工作进度
worddao.deleteWords(*params)
}
}
internal class DeleteAllAsyncTask(private val worddao: WordDao) : AsyncTask<Unit, Unit, Unit>(){
//在后台工作
override fun doInBackground(vararg params: Unit?) {
publishProgress()//该方法用于一段时间报告工作进度
worddao.deleteAllWords()
}
}
}
2）MAC修改
class MainActivity : AppCompatActivity() {
/* private var worddatabase:WordDatabase?=null*/
/* lateinit var worddao: WordDao*/
/* lateinit var allwordslive:LiveData<List<Word>>*/
//创建Viewmodel实例
lateinit var wordviewmodel: WordViewModel
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
wordviewmodel=ViewModelProvider(this).get(WordViewModel::class.java)
/* worddatabase= Room.databaseBuilder( this,WordDatabase::class.java,"word_database")
.build()//强制主线程运行 但不太好*/
/* worddao= worddatabase?.getWordDao()!!*/
/* allwordslive=worddao.getAllWordsLive()*/
wordviewmodel.getAllWordsLive().observe(this,object: Observer<List<Word>>{
override fun onChanged(t: List<Word>?) {
var text=""
if (t != null) {
for (i in (0 until t.size)){
var word:Word =t.get(i)
text+=""+word.getId()+":"+word.getWord()+"="+word.getChineseMeaning()+"\n";
}
}
text2.text=text
}
})
button_insert.setOnClickListener {
var word:Word = Word("Hello","你好")
var word1:Word = Word("ByeBye","再见")
//worddao.insertWords(word1,word)
wordviewmodel.insertWords(word1,word)//副线程的插入
}
button_delete.setOnClickListener {
var word:Word = Word("Word","世界")
word.setId(40)
//worddao.deleteWords(word)
wordviewmodel.deleteWords(word)
}
button_clear.setOnClickListener{
wordviewmodel.deleteAllWords()//副线程的插入
}
button_update.setOnClickListener {
var word:Word = Word("Word","世界")
word.setId(40)
//worddao.updateWords(word)
wordviewmodel.updateWords(word)//副线程的插入
}
}
}
点击运行一切正常
4.数据的获取不是ViewModel的职责，优化ViewModel，创建仓库类作为数据的中介。
- 建立WordRepository(作为model)
//用于本地/云端数据库获取数据
class WordRepository(context: Context) {
private var allwordslive : LiveData<List<Word>>
private var worddao:WordDao
var worddatabase: WordDatabase = WordDatabase.getDatabase(context.applicationContext)!!
init {
worddao= worddatabase.getWordDao()
allwordslive=worddao.getAllWordsLive()
}
//写接口调用这些
fun insertWords(vararg params: Word?){
InsertAsyncTask(worddao).execute(*params)
}
fun updateWords(vararg params: Word?){
UpdateAsyncTask(worddao).execute(*params)
}
fun deleteWords(vararg params: Word?){
DeleteAsyncTask(worddao).execute(*params)
}
fun deleteAllWords(){
DeleteAllAsyncTask(worddao).execute()
}
fun getAllWordsLive():LiveData<List<Word>>{
return allwordslive
}
internal class InsertAsyncTask(private val worddao: WordDao) : AsyncTask<Word?, Unit, Unit>(){
//在后台工作
override fun doInBackground(vararg params: Word?) {
publishProgress()//该方法用于一段时间报告工作进度
worddao.insertWords(*params)
}
}
internal class UpdateAsyncTask(private val worddao: WordDao) : AsyncTask<Word?, Unit, Unit>(){
//在后台工作
override fun doInBackground(vararg params: Word?) {
publishProgress()//该方法用于一段时间报告工作进度
worddao.updateWords(*params)
}
}
internal class DeleteAsyncTask(private val worddao: WordDao) : AsyncTask<Word?, Unit, Unit>(){
//在后台工作
override fun doInBackground(vararg params: Word?) {
publishProgress()//该方法用于一段时间报告工作进度
worddao.deleteWords(*params)
}
}
internal class DeleteAllAsyncTask(private val worddao: WordDao) : AsyncTask<Unit, Unit, Unit>(){
//在后台工作
override fun doInBackground(vararg params: Unit?) {
publishProgress()//该方法用于一段时间报告工作进度
worddao.deleteAllWords()
}
}
}
- 修改ViewModel
class WordViewModel(application: Application) : AndroidViewModel(application){
private var wordrepository:WordRepository = WordRepository(application)
fun getAllWordsLive():LiveData<List<Word>>{
return wordrepository.getAllWordsLive()
}
//写接口调用这些
fun insertWords(vararg params: Word?){
wordrepository.insertWords(*params)
}
fun updateWords(vararg params: Word?){
wordrepository.updateWords(*params)
}
fun deleteWords(vararg params: Word?){
wordrepository.deleteWords(*params)
}
fun deleteAllWords(){
wordrepository.deleteAllWords()
}
}
- MainActivity不变
class MainActivity : AppCompatActivity() {
//创建Viewmodel实例
lateinit var wordviewmodel: WordViewModel
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
wordviewmodel=ViewModelProvider(this).get(WordViewModel::class.java)
wordviewmodel.getAllWordsLive().observe(this,object: Observer<List<Word>>{
override fun onChanged(t: List<Word>?) {
var text=""
if (t != null) {
for (i in (0 until t.size)){
var word:Word =t.get(i)
text+=""+word.getId()+":"+word.getWord()+"="+word.getChineseMeaning()+"\n";
}
}
text2.text=text
}
})
button_insert.setOnClickListener {
var word:Word = Word("Hello","你好")
var word1:Word = Word("ByeBye","再见")
//worddao.insertWords(word1,word)
wordviewmodel.insertWords(word1,word)//副线程的插入
}
button_delete.setOnClickListener {
var word:Word = Word("Word","世界")
word.setId(40)
//worddao.deleteWords(word)
wordviewmodel.deleteWords(word)
}
button_clear.setOnClickListener{
wordviewmodel.deleteAllWords()//副线程的插入
}
button_update.setOnClickListener {
var word:Word = Word("Word","世界")
word.setId(40)
//worddao.updateWords(word)
wordviewmodel.updateWords(word)//副线程的插入
}
}
}
精简后MainActivity仅持有ViewModel对象和UI监听，更新，其余所以操作交给ViewModel' ；ViewModel持有Repository对象，及调用其方法；所有数据存储实体及数据库操作都在Repository类中。