Room----Android数据库(SQLite)

1.要想使用Room首先需要在build.grade中添加依赖

dependencies {
      def room_version = "2.2.2"

      implementation "androidx.room:room-runtime:$room_version"
      annotationProcessor "androidx.room:room-compiler:$room_version" // For Kotlin use kapt instead of annotationProcessor

      // optional - Kotlin Extensions and Coroutines support for Room
      implementation "androidx.room:room-ktx:$room_version"

      // optional - RxJava support for Room
      implementation "androidx.room:room-rxjava2:$room_version"

      // optional - Guava support for Room, including Optional and ListenableFuture
      implementation "androidx.room:room-guava:$room_version"

      // Test helpers
      testImplementation "androidx.room:room-testing:$room_version"
    }

2.数据库可视化工具可以选择DB Browser for SQLite，具体请点击下方链接进行下载

http://www.sqlitebrowser.org/

具体案例(对Word实体进行增删改)

使用ViewModel，LiveData，Room等工具。

1.界面设计

• 上方是一个ScrollView（数据多的时候可滑动),ScrollView内有一个TextView
• 下方是四个按键，分别代表，插入、删除、清空、修改

activity_main.xml代码如下：

<?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: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="0.25" />

    <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:text="clear"
        app:layout_constraintBottom_toBottomOf="@+id/buttonDelete"
        app:layout_constraintEnd_toStartOf="@+id/buttonDelete"
        app:layout_constraintHorizontal_bias="0.5"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="@+id/buttonDelete" />

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

以为是学习新的知识，所以不是太注重规定，导致 一些地方写的不是很规范。

2.创建实体(Entity)

package com.example.roombasic;

import androidx.room.ColumnInfo;
import androidx.room.Entity;
import androidx.room.PrimaryKey;

@Entity
public class Word {
    @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 String getWord() {
        return word;
    }

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

    public String getChineseMeaning() {
        return chineseMeaning;
    }

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

3.创建Dao

package com.example.roombasic;

import androidx.lifecycle.LiveData;
import androidx.room.Dao;
import androidx.room.Delete;
import androidx.room.Insert;
import androidx.room.Query;
import androidx.room.Update;

import java.util.List;

@Dao
public interface WordDao {
    @Insert
    void insertWords(Word... words);

    @Update
    void updateWords(Word... words);

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

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

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

4.创建database

package com.example.roombasic;

import android.content.Context;

import androidx.room.Database;
import androidx.room.Room;
import androidx.room.RoomDatabase;

@Database(entities = {Word.class}, version = 1, exportSchema = false)
public abstract class WordDataBase extends RoomDatabase {
    private static WordDataBase INSTANCE;

    static synchronized WordDataBase getDatabase(Context context) {
        if (INSTANCE == null) {
            INSTANCE = Room.databaseBuilder(context.getApplicationContext(), WordDataBase.class, "word_database").build();
        }
        return INSTANCE;
    }
    public abstract WordDao getWordDao();
}

5.创建ViewModel绑定数据

package com.example.roombasic;

import android.app.Application;
import android.os.AsyncTask;

import androidx.annotation.NonNull;
import androidx.lifecycle.AndroidViewModel;
import androidx.lifecycle.LiveData;

import java.util.List;

public class WordViewModel extends AndroidViewModel {
    private WordDao wordDao;
    private LiveData<List<Word>> allWordsLive;

    public WordViewModel(@NonNull Application application) {
        super(application);
        WordDataBase wordDataBase = WordDataBase.getDatabase(application);
        wordDao = wordDataBase.getWordDao();
        allWordsLive = wordDao.getAllWordsLive();
    }

    public LiveData<List<Word>> getAllWordsLive() {
        return allWordsLive;
    }

    void insertWords(Word... words) {
        new InsertAsyncTask(wordDao).execute(words);
    }

    void updateWords(Word... words) {
        new UpdateAsyncTask(wordDao).execute(words);
    }

    void deleteWords(Word... words) {
        new DeleteAsyncTask(wordDao).execute(words);
    }

    void deleteAllWords(Word... words) {
        new DeleteAllAsyncTask(wordDao).execute();
    }

    static class InsertAsyncTask extends AsyncTask<Word, Void, Void> {
        private WordDao wordDao;

        public InsertAsyncTask(WordDao wordDao) {
            this.wordDao = wordDao;
        }

        @Override
        protected Void doInBackground(Word... words) {
            wordDao.insertWords(words);
            return null;
        }
    }

    static class UpdateAsyncTask extends AsyncTask<Word, Void, Void> {
        private WordDao wordDao;

        public UpdateAsyncTask(WordDao wordDao) {
            this.wordDao = wordDao;
        }

        @Override
        protected Void doInBackground(Word... words) {
            wordDao.updateWords(words);
            return null;
        }
    }

    static class DeleteAsyncTask extends AsyncTask<Word, Void, Void> {
        private WordDao wordDao;

        public DeleteAsyncTask(WordDao wordDao) {
            this.wordDao = wordDao;
        }

        @Override
        protected Void doInBackground(Word... words) {
            wordDao.deleteWords(words);
            return null;
        }
    }

    static class DeleteAllAsyncTask extends AsyncTask<Void, Void, Void> {
        private WordDao wordDao;

        public DeleteAllAsyncTask(WordDao wordDao) {
            this.wordDao = wordDao;
        }

        @Override
        protected Void doInBackground(Void... voids) {
            wordDao.deleteAllWords();
            return null;
        }
    }
}

6.在MainActivity.java中添加按键监听

package com.example.roombasic;

import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

import androidx.appcompat.app.AppCompatActivity;
import androidx.lifecycle.Observer;
import androidx.lifecycle.ViewModelProviders;

import java.util.List;

public class MainActivity extends AppCompatActivity {
    TextView textView;
    Button buttonInsert, buttonDelete, buttonUpdate, buttonClear;
    WordViewModel wordViewModel;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        wordViewModel = ViewModelProviders.of(this).get(WordViewModel.class);
        textView = findViewById(R.id.textView);
        wordViewModel.getAllWordsLive().observe(this, new Observer<List<Word>>() {
            @Override
            public void onChanged(List<Word> words) {
                StringBuilder text = new StringBuilder();
                for (int i = 0; i < words.size(); i++) {
                    Word word = words.get(i);
                    text.append(word.getId()).append(":").append(word.getWord()).append("=").append(word.getChineseMeaning()).append("\n");
                }
                textView.setText(text.toString());
            }
        });

        buttonInsert = findViewById(R.id.buttonInsert);
        buttonClear = findViewById(R.id.buttonClear);
        buttonDelete = findViewById(R.id.buttonDelete);
        buttonUpdate = findViewById(R.id.buttonUpdate);

        buttonInsert.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Word word1 = new Word("Hello", "你好！");
                Word word2 = new Word("World", "世界！");
                wordViewModel.insertWords(word1,word2);
            }
        });

        buttonClear.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                wordViewModel.deleteAllWords();
            }
        });

        buttonUpdate.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Word word = new Word("Hi", "你好啊！");
                word.setId(9);
                wordViewModel.updateWords(word);
            }
        });

        buttonDelete.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Word word = new Word("Hi", "你好啊！");
                word.setId(7);
                wordViewModel.deleteWords(word);
            }
        });
    }
}

该实例中修改与删除使用主键进行的，以后会进行修改与完善 。

暂时只学习了一点皮毛，后续会增加一些新的内容。