初步了解JetPack中的Room(2)

其他 2020-04-15 16:30:17 阅读次数: 0

初步了解JetPack中的Room（2）


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初步了解JetPack中的Room（2）

在了解了Entity、Dao、Database后，继续引入AsyncTask、Repository、ViewModel、LiveData。
使用AsyncTask对Room的数据库操作转移至该线程中（不能放在主线程）
将数据库内容存入ViewModel中并引入LiveData
将数据库的各类操作放入抽象类Repository中

使用上次的项目

做修改：

  1. List数据改为LiveData<List<>>:
    @Query("SELECT * FROM WORD ORDER BY ID DESC")
    //List<Word> getAllWords();
    LiveData<List<Word>>getAllWordsLive(); //更改返回值为LiveData类型

MainActivity.java中(添加变量，链接Dao接口函数，设置观察者以完成数据变动时自动更新)：

package com.example.roombasic;

import androidx.appcompat.app.AppCompatActivity;
import androidx.lifecycle.LiveData;
import androidx.lifecycle.Observer;
import androidx.room.Room;
import androidx.room.RoomDatabase;

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

import java.util.List;

public class MainActivity extends AppCompatActivity {
    WordDatabase wordDatabase;
    WordDao wordDao;
    TextView textView;
    Button buttonInsert,buttonUpdate,buttonDelete,buttonClear;
    //编辑变量保存LiveData
    LiveData<List<Word>> allWordsLive;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        //获取database对象需要一个函数databaseBuilder并创建
        wordDatabase = Room.databaseBuilder(this,WordDatabase.class,"word_database")
                .allowMainThreadQueries() //强制允许主线程执行，该方法不好，
                .build();
        wordDao = wordDatabase.getWordDao();

        allWordsLive = wordDao.getAllWordsLive();
        textView = findViewById(R.id.textView);

        //LiveData观察变动呼叫onchange函数，完成界面自动刷新
        allWordsLive.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);

        //插入
        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");
                wordDao.insertWords(word1,word2);
                //updateView();
            }
        });

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

        //删除
        buttonDelete.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Word word = new Word("",""); //删除只与id有关，内容无所谓
                word.setId(1);  //根据ID修改对应的表单名
                wordDao.deleteWords(word);
            }
        });

        //修改
        buttonUpdate.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Word word = new Word("Android","安卓");
                word.setId(1);  //根据ID修改对应的表单名
                wordDao.updateWords(word);
            }
        });
    }
}
  1. Database变更为Singleton模式（单实例，database实例化比较耗费资源）
        import android.content.Context;
        import androidx.room.Database;
        import androidx.room.Room;
        import androidx.room.RoomDatabase;

@Database(entities = {Word.class},version = 1,exportSchema = false)  //三个参数分别为数据库中的表、数据库版本号和导出模式
public abstract class WordDatabase extends RoomDatabase {
    //变更为Singleton模式
    private static WordDatabase INSTANCE;
    static synchronized WordDatabase getDatabase(Context context) {  //synchronized避免碰撞冲突
        if (INSTANCE == null) {
            INSTANCE = Room.databaseBuilder(context.getApplicationContext(),WordDatabase.class,"word_database")
                    .allowMainThreadQueries()
                    .build();
        }
        return INSTANCE;
    }
    public abstract WordDao getWordDao(); //只需写一个函数原型即可
}
  1. 借助AsyncTask将数据库脱离主线程并放入正确的工作线程中：
    AsyncTsak为抽象类，每个操作都要生成单独的子类
    在MainActivity.java中添加代码
//内部类存在形式声明为static避免内存泄漏
    static class InsertAsyncTask extends AsyncTask<Word,Void,Void> {
        private WordDao wordDao;

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

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

        /*

        //任务完成时将结果带回线程
        @Override
        protected void onPostExecute(Void aVoid) {
            super.onPostExecute(aVoid);
        }

        //进度更新发生呼叫
        @Override
        protected void onProgressUpdate(Void... values) {
            super.onProgressUpdate(values);
        }

        //后台任务执行前做某类操作
        @Override
        protected void onPreExecute() {
            super.onPreExecute();
        }

        */

    }

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

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

        //重写函数
        @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;
        }

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

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

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

        //重写函数
        @Override
        protected Void doInBackground(Void... voids) {
            wordDao.deleteAllWords();
            return null;
        }
    }
  1. 变动数据库操作按钮点击的响应事件,并删除主线程强制执行功能：
wordDao.insertWords(word1,word2);

变更为

new InsertAsyncTask(wordDao).execute(word1,word2);

MainActivity.java

import androidx.appcompat.app.AppCompatActivity;
import androidx.lifecycle.LiveData;
import androidx.lifecycle.Observer;
import androidx.room.Room;
import androidx.room.RoomDatabase;
import android.os.AsyncTask;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import java.util.List;

public class MainActivity extends AppCompatActivity {
    WordDatabase wordDatabase;
    WordDao wordDao;
    TextView textView;
    Button buttonInsert,buttonUpdate,buttonDelete,buttonClear;
    //编辑变量保存LiveData
    LiveData<List<Word>> allWordsLive;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        //获取database对象需要一个函数databaseBuilder并创建
        wordDatabase = Room.databaseBuilder(this,WordDatabase.class,"word_database")
                .build();
        wordDao = wordDatabase.getWordDao();

        allWordsLive = wordDao.getAllWordsLive();

        textView = findViewById(R.id.textView);

        //LiveData观察变动呼叫onchange函数，完成界面自动刷新
        allWordsLive.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);

        //插入
        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");
                new InsertAsyncTask(wordDao).execute(word1,word2);  //创建线程操作并将创建的变量执行到父线程中操作，下同
            }
        });

        //清空
        buttonClear.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                new ClearAsyncTask(wordDao).execute();
            }
        });

        //删除
        buttonDelete.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Word word = new Word("",""); //删除只与id有关，内容无所谓
                word.setId(1);  //根据ID修改对应的表单名
                new DeleteAsyncTask(wordDao).execute(word);
            }
        });

        //修改
        buttonUpdate.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Word word = new Word("Android","安卓");
                word.setId(1);  //根据ID修改对应的表单名
                new UpdateAsyncTask(wordDao).execute(word);
            }
        });

    }

    //内部类存在形式声明为static避免内存泄漏
    static class InsertAsyncTask extends AsyncTask<Word,Void,Void> {
        private WordDao wordDao;

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

        //重写函数
        @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;
        }

        //重写函数
        @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;
        }

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

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

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

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

将数据相关的代码存入ViewModel中（使用AndroidViewModel）

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 clearWords(Word...words) {
        new ClearAsyncTask(wordDao).execute();
    }

    //内部类存在形式声明为static避免内存泄漏
    static class InsertAsyncTask extends AsyncTask<Word,Void,Void> {
        private WordDao wordDao;

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

        //重写函数
        @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;
        }

        //重写函数
        @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;
        }

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

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

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

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

MainActivity.java精简后的代码：

import androidx.appcompat.app.AppCompatActivity;
import androidx.lifecycle.LiveData;
import androidx.lifecycle.Observer;
import androidx.lifecycle.ViewModelProvider;
import androidx.room.Room;
import androidx.room.RoomDatabase;
import android.os.AsyncTask;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import java.util.List;

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

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        wordViewModel = new ViewModelProvider(this).get(WordViewModel.class);
        textView = findViewById(R.id.textView);
        //LiveData观察变动呼叫onchange函数，完成界面自动刷新
        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);

        //插入
        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);
            }
        });

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

        //删除
        buttonDelete.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Word word = new Word("",""); //删除只与id有关，内容无所谓
                word.setId(1);  //根据ID修改对应的表单名
                wordViewModel.deleteWords(word);
            }
        });

        //修改
        buttonUpdate.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Word word = new Word("Android","安卓");
                word.setId(1);  //根据ID修改对应的表单名
                wordViewModel.deleteWords(word);
            }
        });
    }
}

运行无问题

建立仓库类Repository将ViewModel中的数据直接操作的信息提取出来

WordRepository.java

package com.example.roombasic;

import android.content.Context;
import android.os.AsyncTask;

import androidx.lifecycle.LiveData;

import java.util.List;

public class WordRepository {
    private LiveData<List<Word>> allWordsLive;  //ViewModel中就不用保留变量了
    private WordDao wordDao;

    public WordRepository(Context context) {
        WordDatabase wordDatabase = WordDatabase.getDatabase(context.getApplicationContext());
        wordDao = wordDatabase.getWordDao();
        allWordsLive = wordDao.getAllWordsLive();
    }

    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 clearWords(Word... words) {
        new ClearAsyncTask(wordDao).execute();
    }

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

    //内部类存在形式声明为static避免内存泄漏
    static class InsertAsyncTask extends AsyncTask<Word,Void,Void> {
        private WordDao wordDao;

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

        //重写函数
        @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;
        }

        //重写函数
        @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;
        }

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

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

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

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

}

MainActivity.java中修改代码：

import android.app.Application;
import androidx.annotation.NonNull;
import androidx.lifecycle.AndroidViewModel;
import androidx.lifecycle.LiveData;
import java.util.List;

public class WordViewModel extends AndroidViewModel {
    private WordRepository wordRepository;
    public WordViewModel(@NonNull Application application) {
        super(application);
        wordRepository = new WordRepository(application);
    }

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

    void insertWords(Word... words) {
        wordRepository.insertWords(words);
    }

    void updateWords(Word... words) {
        wordRepository.updateWords(words);
    }

    void deleteWords(Word... words) {
        wordRepository.deleteWords(words);
    }

    void clearWords() {
        wordRepository.clearWords();
    }
}

运行无问题

小结

将上次的数据库做完善

  1. 引入LiveData
  2. 引入AsyncTask进行后台执行
  3. database类修改为singleton模式保证只有一个实例
  4. 引入ViewModel使controller中数据代码得到精简，并将数据代码的获取部分封装到Repository中
Lin_Stack
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