Android Studio 之 ROM【2】， LiveData+ViewModel+AsyncTask+Repository

改造上一节 ROM【1】，

1.利用 LiveData<List<Word>> 与 observe 中的 onChanged 配合，删除掉之前的textView更新函数（updateTextView）

引入 LiveData 与 observe ，只要数据发生改变，就会自动更新内容。

Database 单例模式，因为Database实例化，会消耗大量资源，所以整个过程只实例化一个对象

package com.example.roombasic;

import android.content.Context;

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

//抽象类

//singleton //单例模式，只允许实例化一个对象， Database 实例化很耗资源
@Database(entities = {Word.class},version = 1,exportSchema = false)  //如果有多个实体，再加上逗号后加实体.Class,这里版本比较重要，每次更新都要改变
public abstract class WordDatabase extends RoomDatabase {

    private static WordDatabase INSTANCE;
    static WordDatabase getDatabase(Context context){
        if(INSTANCE == null) {
            //context.getApplicationContext()  获取当前Activity 的唯一的 Context
            INSTANCE = Room.databaseBuilder(context.getApplicationContext(), WordDatabase.class, "word_database")
                    //.allowMainThreadQueries() 强制允许主线程操作
                    .build();
        }
        return INSTANCE;
    }

    public abstract WordDao getWordDao();
}

　　

MainActity类中的代码：

LiveData<List<Word>>    allWordsLive;

allWordsLive = wordDao.getAllWordLive();

//利用 LiveData<> 与 observe的onChanged配合，数据自动刷新
allWordsLive.observe(this, new Observer<List<Word>>() {
    @Override
    public void onChanged(List<Word> words) {
        //当数据改变时会自动呼叫这个函数
        //String text="";
        StringBuilder text = new StringBuilder();
        textView.setText(text); //先将 textView 清空
        for(int i=0;i<words.size();i++){
            Word word = words.get(i);
            text.append(word.getId() + ":" + word.getWord() + "=" + word.getChineseMeaning() + "\n");

            textView.setText(text);
        }
    }
});

　　

WordDao类 中将数据返回类型改成 LiveData<List<Word>> 类型

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

　　

2.引入 AsyncTask，用子线程更新数据

wordDatabase = Room.databaseBuilder(this,WordDatabase.class,"word_database")
                //.allowMainThreadQueries() //allowMainThreadQueries() 强制允许在主线程运行
                .build();

注释掉 allowMainThreadQueries()

在 MainActivity 中 添加内部类

//内部类，AsyncTask 类型的类 如果以内部类形式出现，必须用 static，否则告警，说内存泄漏
    static class InsertAsyncTask extends AsyncTask<Word,Void,Void>{
        private WordDao wordDao;

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

        @Override
        protected Void doInBackground(Word... words) {
            //在工作线程在后台做什么操作
            wordDao.insertWords(words);
            return null;
        }

        /*@Override
        protected void onPostExecute(Void aVoid) {
            //任务完成时会呼叫，将结果带回给主线程
            super.onPostExecute(aVoid);
        }

        @Override
        protected void onProgressUpdate(Void... values) {
            //当进度发生更新时，会呼叫
            super.onProgressUpdate(values);
        }

        @Override
        protected void onPreExecute() {
            //在后台任务执行之前会呼叫
            super.onPreExecute();
        }*/
    }

    //内部类，AsyncTask 类型的类 如果以内部类形式出现，必须用 static，否则告警，说内存泄漏
    static class UpdateAsyncTask extends AsyncTask<Word,Void,Void>{
        private WordDao wordDao;

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

        @Override
        protected Void doInBackground(Word... words) {
            //在工作线程在后台做什么操作
            wordDao.updateWords(words);
            return null;
        }
    }

    //内部类，AsyncTask 类型的类 如果以内部类形式出现，必须用 static，否则告警，说内存泄漏
    static class DeleteAsyncTask extends AsyncTask<Word,Void,Void>{
        private WordDao wordDao;

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

        @Override
        protected Void doInBackground(Word... words) {
            //在工作线程在后台做什么操作
            wordDao.deleteWords(words);
            return null;
        }
    }

    //内部类，AsyncTask 类型的类 如果以内部类形式出现，必须用 static，否则告警，说内存泄漏
    static class DeleteAllAsyncTask extends AsyncTask<Void,Void,Void>{
        private WordDao wordDao;

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

        @Override
        protected Void doInBackground(Void... Voids) {
            //在工作线程在后台做什么操作
            wordDao.deleteAllWords();
            return null;
        }
    }

　　

原来的4个操作方法中，注释掉主线程操作，改成由子线程操作数据

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); //这里是主线程直接插入数据

                new InsertAsyncTask(wordDao).execute(word1,word2); //改成子线程对父线程插入数据
                //updateView();
            }
        });

        buttonUpdate.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Word word = new Word("English","英语");
                word.setId(46); //更新是用主键来更新的
                //wordDao.updateWords(word);    //主线程操作
                new UpdateAsyncTask(wordDao).execute(word); //子线程操作

                //updateView();
            }
        });

        //删除所有的记录
        buttonClear.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                //wordDao.deleteAllWords(); //主线程操作
                new DeleteAllAsyncTask(wordDao).execute();//由子线程来操作
                //updateView();
            }
        });

        buttonDelete.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Word word = new Word("English","英语");
                word.setId(46); //删除也是用主键来更新的
                //wordDao.deleteWords(word);   主线程操作
                new DeleteAsyncTask(wordDao).execute(word); //子线程操作
                //updateView();
            }
        });

　　

 3. 引入 AndroidViewModel ，简化 MainActivity 

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.getAllWordLive();
    }

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

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

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

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

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

    //内部类，AsyncTask 类型的类 如果以内部类形式出现，必须用 static，否则告警，说内存泄漏
    static class InsertAsyncTask extends AsyncTask<Word,Void,Void> {
        private WordDao wordDao;

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

        @Override
        protected Void doInBackground(Word... words) {
            //在工作线程在后台做什么操作
            wordDao.insertWords(words);
            return null;
        }

        /*@Override
        protected void onPostExecute(Void aVoid) {
            //任务完成时会呼叫，将结果带回给主线程
            super.onPostExecute(aVoid);
        }

        @Override
        protected void onProgressUpdate(Void... values) {
            //当进度发生更新时，会呼叫
            super.onProgressUpdate(values);
        }

        @Override
        protected void onPreExecute() {
            //在后台任务执行之前会呼叫
            super.onPreExecute();
        }*/
    }

    //内部类，AsyncTask 类型的类 如果以内部类形式出现，必须用 static，否则告警，说内存泄漏
    static class UpdateAsyncTask extends AsyncTask<Word,Void,Void>{
        private WordDao wordDao;

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

        @Override
        protected Void doInBackground(Word... words) {
            //在工作线程在后台做什么操作
            wordDao.updateWords(words);
            return null;
        }
    }

    //内部类，AsyncTask 类型的类 如果以内部类形式出现，必须用 static，否则告警，说内存泄漏
    static class DeleteAsyncTask extends AsyncTask<Word,Void,Void> {
        private WordDao wordDao;

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

        @Override
        protected Void doInBackground(Word... words) {
            //在工作线程在后台做什么操作
            wordDao.deleteWords(words);
            return null;
        }
    }

    //内部类，AsyncTask 类型的类 如果以内部类形式出现，必须用 static，否则告警，说内存泄漏
    static class DeleteAllAsyncTask extends AsyncTask<Void,Void,Void>{
        private WordDao wordDao;

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

        @Override
        protected Void doInBackground(Void... Voids) {
            //在工作线程在后台做什么操作
            wordDao.deleteAllWords();
            return null;
        }
    }
}

　　

MainActivity.java

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.LiveData;
import androidx.lifecycle.Observer;
import androidx.lifecycle.SavedStateViewModelFactory;
import androidx.lifecycle.ViewModelProvider;

import java.util.List;

public class MainActivity extends AppCompatActivity {

    //WordDatabase wordDatabase;
    //WordDao wordDao;
    Button buttonInsert,buttonUpdate,buttonClear,buttonDelete;
    TextView textView;
    LiveData<List<Word>> allWordsLive;

    WordViewModel wordViewModel;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        //wordDatabase = Room.databaseBuilder(this,WordDatabase.class,"word_database")
                //.allowMainThreadQueries() //allowMainThreadQueries() 强制允许在主线程运行
        //        .build();

        //wordDao = wordDatabase.getWordDao();

        //wordViewModel = ViewModelProviders
        wordViewModel = new ViewModelProvider(this,new SavedStateViewModelFactory(getApplication(),this)).get(WordViewModel.class);

        //allWordsLive = wordDao.getAllWordLive();

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

        //利用 LiveData<> 与 observe的onChanged配合，数据自动刷新
        //allWordsLive.observe(this, new Observer<List<Word>>() {
        wordViewModel.getAllWordsLive().observe(this, new Observer<List<Word>>() {
            @Override
            public void onChanged(List<Word> words) {
                //当数据改变时会自动呼叫这个函数
                //String text="";
                StringBuilder text = new StringBuilder();
                textView.setText(text); //先将 textView 清空
                for(int i=0;i<words.size();i++){
                    Word word = words.get(i);
                    text.append(word.getId() + ":" + word.getWord() + "=" + word.getChineseMeaning() + "\n");

                    textView.setText(text);
                }
            }
        });

        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);
                //wordDao.insertWords(word1,word2);  主线程操作
                //new InsertAsyncTask(wordDao).execute(word1,word2); //改成子线程对父线程插入数据
                //updateView();
            }
        });

        buttonUpdate.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Word word = new Word("English","英语");
                word.setId(68); //更新是用主键来更新的
                wordViewModel.updateWords(word);
                //wordDao.updateWords(word);
                //new UpdateAsyncTask(wordDao).execute(word);
                //updateView();
            }
        });

        //删除所有的记录
        buttonClear.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                //wordDao.deleteAllWords();
                //new DeleteAllAsyncTask(wordDao).execute();
                //updateView();
                wordViewModel.deleteAllWords();
            }
        });

        buttonDelete.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Word word = new Word("English","英语");
                word.setId(68); //删除也是用主键来更新的
                wordViewModel.deleteWords(word);
                //wordDao.deleteWords(word);
                //new DeleteAsyncTask(wordDao).execute(word);
                //updateView();
            }
        });

    }

    /*void updateView(){
        List<Word> list = wordDao.getAllWords();
        String text="";
        textView.setText(text); //先将 textView 清空
        for(int i=0;i<list.size();i++){
            Word word = list.get(i);
            text += word.getId() + ":" + word.getWord() + "=" + word.getChineseMeaning() + "\n";

            textView.setText(text);
        }
    }*/

}

　　

 4. 创建 仓库类，简化 ViewModel

package com.example.roombasic;

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

import androidx.lifecycle.LiveData;

import java.util.List;

public class WordRepository {
    //数据仓库

    private WordDao wordDao;

    private LiveData<List<Word>>    allWordsListLive;

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

    public LiveData<List<Word>> getAllWordsListLive() {
        return allWordsListLive;
    }

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

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

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

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

    //内部类，AsyncTask 类型的类 如果以内部类形式出现，必须用 static，否则告警，说内存泄漏
    static class InsertAsyncTask extends AsyncTask<Word,Void,Void> {
        private WordDao wordDao;

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

        @Override
        protected Void doInBackground(Word... words) {
            //在工作线程在后台做什么操作
            wordDao.insertWords(words);
            return null;
        }

        /*@Override
        protected void onPostExecute(Void aVoid) {
            //任务完成时会呼叫，将结果带回给主线程
            super.onPostExecute(aVoid);
        }

        @Override
        protected void onProgressUpdate(Void... values) {
            //当进度发生更新时，会呼叫
            super.onProgressUpdate(values);
        }

        @Override
        protected void onPreExecute() {
            //在后台任务执行之前会呼叫
            super.onPreExecute();
        }*/
    }

    //内部类，AsyncTask 类型的类 如果以内部类形式出现，必须用 static，否则告警，说内存泄漏
    static class UpdateAsyncTask extends AsyncTask<Word,Void,Void>{
        private WordDao wordDao;

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

        @Override
        protected Void doInBackground(Word... words) {
            //在工作线程在后台做什么操作
            wordDao.updateWords(words);
            return null;
        }
    }

    //内部类，AsyncTask 类型的类 如果以内部类形式出现，必须用 static，否则告警，说内存泄漏
    static class DeleteAsyncTask extends AsyncTask<Word,Void,Void> {
        private WordDao wordDao;

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

        @Override
        protected Void doInBackground(Word... words) {
            //在工作线程在后台做什么操作
            wordDao.deleteWords(words);
            return null;
        }
    }

    //内部类，AsyncTask 类型的类 如果以内部类形式出现，必须用 static，否则告警，说内存泄漏
    static class DeleteAllAsyncTask extends AsyncTask<Void,Void,Void>{
        private WordDao wordDao;

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

        @Override
        protected Void doInBackground(Void... Voids) {
            //在工作线程在后台做什么操作
            wordDao.deleteAllWords();
            return null;
        }
    }
}