JetPack -- Room使用简介

简介

Room是对 Android中SqlLite数据库的一个抽象，实现了流畅的访问SqlLite数据库

基本使用

创建Entity实体类

@Entity
public class Word {
    // 声明主键
    @PrimaryKey(autoGenerate = true)
    private int id;

    @ColumnInfo(name = "english_word")
    private String word;

    @ColumnInfo(name = "chinese_meaning")
    private String chineseMeaning;

    public Word(String word, String chineseMeaning) {
        this.word = word;
        this.chineseMeaning = chineseMeaning;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public void setWord(String word) {
        this.word = word;
    }

    public String getWord() {
        return word;
    }

    public void setChineseMeaning(String chineseMeaning) {
        this.chineseMeaning = chineseMeaning;
    }

    public String getChineseMeaning() {
        return chineseMeaning;
    }
}

创建Dao

/**
* Description: 访问数据库操作的接口，CRUD操作
*/
@Dao
public interface WordDao {
    // 系统会帮助我们生成代码
    @Insert
    void insertWord(Word... words);


    @Update
    int updateWord(Word... words);


    @Delete
    void deleteWords(Word... words);


    @Query("DELETE FROM WORD")
    void deleteAllWords();


    @Query("SELECT * FROM WORD ORDER BY ID DESC")
    List<Word> getAllWords();
}

创建DataBase

// 四个参数，第一个多个entities可以使用逗号隔开， 版本号添加新的字段或者其他更改数据库结构的操作需要更改版本号
@Database(entities = {Word.class}, version = 1, exportSchema = false)
public abstract class WordDataBase extends RoomDatabase{
    public abstract WordDao getWordDao();
}

在Activity中使用

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">


    <androidx.constraintlayout.widget.Guideline
        android:id="@+id/guideline"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:orientation="horizontal"
        app:layout_constraintGuide_percent="0.6" />


    <ScrollView
        android:layout_width="0dp"
        android:layout_height="0dp"
        app:layout_constraintBottom_toTopOf="@+id/guideline"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent">


        <TextView
            android:id="@+id/textView"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="TextView"
            android:textSize="24sp" />
    </ScrollView>


    <Button
        android:id="@+id/buttonInsert"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="8dp"
        android:layout_marginBottom="8dp"
        android:text="Insert"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toStartOf="@+id/buttonUpdate"
        app:layout_constraintHorizontal_bias="0.5"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="@+id/guideline"
        app:layout_constraintVertical_bias="0.26999998" />


    <Button
        android:id="@+id/buttonUpdate"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="update"
        app:layout_constraintBottom_toBottomOf="@+id/buttonInsert"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.5"
        app:layout_constraintStart_toEndOf="@+id/buttonInsert"
        app:layout_constraintTop_toTopOf="@+id/buttonInsert" />


    <Button
        android:id="@+id/buttonClear"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="8dp"
        android:layout_marginBottom="8dp"
        android:text="clear"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toStartOf="@+id/buttonDelete"
        app:layout_constraintHorizontal_bias="0.5"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/buttonInsert" />


    <Button
        android:id="@+id/buttonDelete"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="delete"
        app:layout_constraintBottom_toBottomOf="@+id/buttonClear"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.5"
        app:layout_constraintStart_toEndOf="@+id/buttonClear"
        app:layout_constraintTop_toTopOf="@+id/buttonClear" />
</androidx.constraintlayout.widget.ConstraintLayout>

class WordActivity : AppCompatActivity() {
    private lateinit var mWordDataBase: WordDataBase
    private lateinit var mWordDao: WordDao
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_word)
        mWordDataBase = Room.databaseBuilder(this, WordDataBase::class.java, "word data base")
                .allowMainThreadQueries()
                .build()
        mWordDao = mWordDataBase.wordDao


        updateView()


        buttonInsert.setOnClickListener({
            var newWord1 = Word("Hello", "你好")
            var newWord2 = Word("World", "世界")
            mWordDao.insertWord(newWord1, newWord2)
            updateView()
        })


        buttonClear.setOnClickListener({
            mWordDao.deleteAllWords()
        })


        buttonUpdate.setOnClickListener({
            var newWord3 = Word("Hi", "你好！")
            newWord3.id = 46
            mWordDao.updateWord(newWord3)
            updateView()
        })


        buttonDelete.setOnClickListener({
            var newWord4 = Word("Hi", "你好！")
            newWord4.id = 46
            mWordDao.deleteWords(newWord4)
            updateView()
        })
    }


    private fun updateView() {
        var list = mWordDao.getAllWords()
        var text : String = ""
        for(word in list) {
            text += word.id.toString() + ":"+ word.word + "=" +word.chineseMeaning
        }
        textView.text = text
    }
}

结合ViewModel来使用

实体类我们不做修改
Dao将返回全部数据膝盖为LiveData

@Query("SELECT * FROM WORD ORDER BY ID DESC")
LiveData<List<Word>> getAllWords();

数据库的创建我们使用单例模式

// 四个参数，第一个多个entities可以使用逗号隔开， 版本号添加新的字段或者其他更改数据库结构的操作需要更改版本号
@Database(entities = {Word.class}, version = 1, exportSchema = false)
public abstract class WordDataBase extends RoomDatabase {
    private static WordDataBase INSTANCE;


    static WordDataBase getDatabase(Context context) {
        if (INSTANCE == null) {
            synchronized (WordDataBase.class) {
                if (INSTANCE == null) {
                    INSTANCE = Room.databaseBuilder(context.getApplicationContext(), WordDataBase.class, "word database")
                            .build();
                }
            }
        }
        return INSTANCE;
    }


    public abstract WordDao getWordDao();
}

然后将Activity中的对数据的CRUD放到repository中

class WordRepository(context: Context) {
    val mAllWordLive: LiveData<List<Word?>?>?
    private val mWordDao: WordDao
    init {
        val wordDataBase = WordDataBase.getDatabase(context.applicationContext)
        mWordDao = wordDataBase!!.wordDao!!
        mAllWordLive = mWordDao.allWords
    }

    fun insertWords(vararg words: Word) {
        InsertAsyncTask(mWordDao).execute(*words)
    }

    fun updateWords(vararg words: Word) {
        UpdateAsyncTask(mWordDao).execute(*words)
    }

    fun deleteWords(vararg words: Word) {
        DeleteAsyncTask(mWordDao).execute(*words)
    }

    fun deleteAllWords() {
        DeleteAllAsyncTask(mWordDao).execute()
    }

    internal class InsertAsyncTask(private val mWordDao: WordDao) : AsyncTask<Word?, Void?, Void?>() {
        override fun doInBackground(vararg params: Word?): Void? {
            mWordDao.insertWord(*params)
            return null
        }
    }

    internal class DeleteAsyncTask(private val mWordDao: WordDao) : AsyncTask<Word?, Void?, Void?>() {
        override fun doInBackground(vararg params: Word?): Void? {
            mWordDao.deleteWords(*params)
            return null
        }
    }

    internal class DeleteAllAsyncTask(private val mWordDao: WordDao) : AsyncTask<Void?, Void?, Void?>() {
        override fun doInBackground(vararg params: Void?): Void? {
            mWordDao.deleteAllWords()
            return null
        }


    }

    internal class UpdateAsyncTask(private val mWordDao: WordDao) : AsyncTask<Word?, Void?, Void?>() {
        override fun doInBackground(vararg params: Word?): Void? {
            mWordDao.updateWord(*params)
            return null
        }
    }
}

ViewModel中保留数据操作的接口方法

class WordViewModel(application: Application) : AndroidViewModel(application) {
    private var mWordRepository: WordRepository
    var mAllWordLive: LiveData<List<Word?>?>?

    init {
        mWordRepository = WordRepository(application.applicationContext)
        mAllWordLive = mWordRepository.mAllWordLive
    }

    fun insertWords(vararg words: Word) {
        mWordRepository.insertWords(*words)
    }

    fun updateWords(vararg words: Word) {
        mWordRepository.updateWords(*words)
    }

    fun deleteWords(vararg words: Word) {
        mWordRepository.deleteWords(*words)
    }

    fun deleteAllWords() {
        mWordRepository.deleteAllWords()
    }
}

Activity


class WordActivity : AppCompatActivity() {
    private lateinit var mWordViewModel: WordViewModel
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_word)
        mWordViewModel = ViewModelProviders.of(this).get(WordViewModel::class.java)
        mWordViewModel.mAllWordLive!!.observe(this, Observer { data ->
            data.let {
                var text: String = ""
                for (word in it!!) {
                    text += word!!.id.toString() + ":" + word.word + "=" + word.chineseMeaning
                }
                textView.text = text
            }
        })

        buttonInsert.setOnClickListener {
            var newWord1 = Word("Hello", "你好")
            var newWord2 = Word("World", "世界")
            mWordViewModel.insertWords(newWord1, newWord2)
        }

        buttonClear.setOnClickListener {
            mWordViewModel.deleteAllWords()
        }

        buttonUpdate.setOnClickListener {
            var newWord3 = Word("Hi", "你好！")
            newWord3.id = 46
            mWordViewModel.updateWords(newWord3)
        }

        buttonDelete.setOnClickListener {
            var newWord4 = Word("Hi", "你好！")
            newWord4.id = 46
            mWordViewModel.deleteWords(newWord4)
        }
    }
}

DLUT_WJX

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JetPack -- Room使用简介

简介

基本使用

结合ViewModel来使用

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