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

時間 2019-11-17

標籤 android studio rom livedata+viewmodel+asynctask+repository livedata viewmodel asynctask repository 欄目 Android 简体版

原文原文鏈接

改造上一節 ROM【1】，java

1.利用 LiveData<List<Word>> 與 observe 中的 onChanged 配合，刪除掉以前的textView更新函數（updateTextView）android

引入 LiveData 與 observe ，只要數據發生改變，就會自動更新內容。app

Database 單例模式，由於Database實例化，會消耗大量資源，因此整個過程只實例化一個對象ide

package com.example.roombasic;

import android.content.Context;

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

//抽象類

//singleton //單例模式，只容許實例化一個對象， Database 實例化很耗資源
@Database(entities = {Word.class},version = 1,exportSchema = false)  //若是有多個實體，再加上逗號後加實體.Class,這裏版本比較重要，每次更新都要改變
public abstract class WordDatabase extends RoomDatabase {

    private static WordDatabase INSTANCE;
    static WordDatabase getDatabase(Context context){
        if(INSTANCE == null) {
            //context.getApplicationContext()  獲取當前Activity 的惟一的 Context
            INSTANCE = Room.databaseBuilder(context.getApplicationContext(), WordDatabase.class, "word_database")
                    //.allowMainThreadQueries() 強制容許主線程操做
                    .build();
        }
        return INSTANCE;
    }


    public abstract WordDao getWordDao();
}

MainActity類中的代碼：函數

LiveData<List<Word>>    allWordsLive;


allWordsLive = wordDao.getAllWordLive();

//利用 LiveData<> 與 observe的onChanged配合，數據自動刷新
allWordsLive.observe(this, new Observer<List<Word>>() {
    @Override
    public void onChanged(List<Word> words) {
        //當數據改變時會自動呼叫這個函數
        //String text="";
        StringBuilder text = new StringBuilder();
        textView.setText(text); //先將 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類中將數據返回類型改爲 LiveData<List<Word>> 類型ui

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

2.引入 AsyncTask，用子線程更新數據 this

wordDatabase = Room.databaseBuilder(this,WordDatabase.class,"word_database")
                //.allowMainThreadQueries() //allowMainThreadQueries() 強制容許在主線程運行
                .build();

註釋掉 allowMainThreadQueries()spa

在 MainActivity 中添加內部類線程

//內部類，AsyncTask 類型的類 若是之內部類形式出現，必須用 static，不然告警，說內存泄漏
    static class InsertAsyncTask extends AsyncTask<Word,Void,Void>{
        private WordDao wordDao;

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

        @Override
        protected Void doInBackground(Word... words) {
            //在工做線程在後臺作什麼操做
            wordDao.insertWords(words);
            return null;
        }


        /*@Override
        protected void onPostExecute(Void aVoid) {
            //任務完成時會呼叫，將結果帶回給主線程
            super.onPostExecute(aVoid);
        }

        @Override
        protected void onProgressUpdate(Void... values) {
            //當進度發生更新時，會呼叫
            super.onProgressUpdate(values);
        }

        @Override
        protected void onPreExecute() {
            //在後臺任務執行以前會呼叫
            super.onPreExecute();
        }*/
    }


    //內部類，AsyncTask 類型的類 若是之內部類形式出現，必須用 static，不然告警，說內存泄漏
    static class UpdateAsyncTask extends AsyncTask<Word,Void,Void>{
        private WordDao wordDao;

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

        @Override
        protected Void doInBackground(Word... words) {
            //在工做線程在後臺作什麼操做
            wordDao.updateWords(words);
            return null;
        }
    }


    //內部類，AsyncTask 類型的類 若是之內部類形式出現，必須用 static，不然告警，說內存泄漏
    static class DeleteAsyncTask extends AsyncTask<Word,Void,Void>{
        private WordDao wordDao;

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

        @Override
        protected Void doInBackground(Word... words) {
            //在工做線程在後臺作什麼操做
            wordDao.deleteWords(words);
            return null;
        }
    }


    //內部類，AsyncTask 類型的類 若是之內部類形式出現，必須用 static，不然告警，說內存泄漏
    static class DeleteAllAsyncTask extends AsyncTask<Void,Void,Void>{
        private WordDao wordDao;

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

        @Override
        protected Void doInBackground(Void... Voids) {
            //在工做線程在後臺作什麼操做
            wordDao.deleteAllWords();
            return null;
        }
    }

原來的4個操做方法中，註釋掉主線程操做，改爲由子線程操做數據server

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); //這裏是主線程直接插入數據

                new InsertAsyncTask(wordDao).execute(word1,word2); //改爲子線程對父線程插入數據
                //updateView();
            }
        });

        buttonUpdate.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Word word = new Word("English","英語");
                word.setId(46); //更新是用主鍵來更新的
                //wordDao.updateWords(word);    //主線程操做
                new UpdateAsyncTask(wordDao).execute(word); //子線程操做

                //updateView();
            }
        });

        //刪除全部的記錄
        buttonClear.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                //wordDao.deleteAllWords(); //主線程操做
                new DeleteAllAsyncTask(wordDao).execute();//由子線程來操做
                //updateView();
            }
        });

        buttonDelete.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Word word = new Word("English","英語");
                word.setId(46); //刪除也是用主鍵來更新的
                //wordDao.deleteWords(word);   主線程操做
                new DeleteAsyncTask(wordDao).execute(word); //子線程操做
                //updateView();
            }
        });

3. 引入 AndroidViewModel ，簡化 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();
    }



    //內部類，AsyncTask 類型的類 若是之內部類形式出現，必須用 static，不然告警，說內存泄漏
    static class InsertAsyncTask extends AsyncTask<Word,Void,Void> {
        private WordDao wordDao;

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

        @Override
        protected Void doInBackground(Word... words) {
            //在工做線程在後臺作什麼操做
            wordDao.insertWords(words);
            return null;
        }


        /*@Override
        protected void onPostExecute(Void aVoid) {
            //任務完成時會呼叫，將結果帶回給主線程
            super.onPostExecute(aVoid);
        }

        @Override
        protected void onProgressUpdate(Void... values) {
            //當進度發生更新時，會呼叫
            super.onProgressUpdate(values);
        }

        @Override
        protected void onPreExecute() {
            //在後臺任務執行以前會呼叫
            super.onPreExecute();
        }*/
    }


    //內部類，AsyncTask 類型的類 若是之內部類形式出現，必須用 static，不然告警，說內存泄漏
    static class UpdateAsyncTask extends AsyncTask<Word,Void,Void>{
        private WordDao wordDao;

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

        @Override
        protected Void doInBackground(Word... words) {
            //在工做線程在後臺作什麼操做
            wordDao.updateWords(words);
            return null;
        }
    }


    //內部類，AsyncTask 類型的類 若是之內部類形式出現，必須用 static，不然告警，說內存泄漏
    static class DeleteAsyncTask extends AsyncTask<Word,Void,Void> {
        private WordDao wordDao;

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

        @Override
        protected Void doInBackground(Word... words) {
            //在工做線程在後臺作什麼操做
            wordDao.deleteWords(words);
            return null;
        }
    }


    //內部類，AsyncTask 類型的類 若是之內部類形式出現，必須用 static，不然告警，說內存泄漏
    static class DeleteAllAsyncTask extends AsyncTask<Void,Void,Void>{
        private WordDao wordDao;

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

        @Override
        protected Void doInBackground(Void... Voids) {
            //在工做線程在後臺作什麼操做
            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() 強制容許在主線程運行
        //        .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<> 與 observe的onChanged配合，數據自動刷新
        //allWordsLive.observe(this, new Observer<List<Word>>() {
        wordViewModel.getAllWordsLive().observe(this, new Observer<List<Word>>() {
            @Override
            public void onChanged(List<Word> words) {
                //當數據改變時會自動呼叫這個函數
                //String text="";
                StringBuilder text = new StringBuilder();
                textView.setText(text); //先將 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);  主線程操做
                //new InsertAsyncTask(wordDao).execute(word1,word2); //改爲子線程對父線程插入數據
                //updateView();
            }
        });

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

        //刪除全部的記錄
        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","英語");
                word.setId(68); //刪除也是用主鍵來更新的
                wordViewModel.deleteWords(word);
                //wordDao.deleteWords(word);
                //new DeleteAsyncTask(wordDao).execute(word);
                //updateView();
            }
        });

    }

    /*void updateView(){
        List<Word> list = wordDao.getAllWords();
        String text="";
        textView.setText(text); //先將 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. 建立倉庫類，簡化 ViewModel

package com.example.roombasic;

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

import androidx.lifecycle.LiveData;

import java.util.List;

public class WordRepository {
    //數據倉庫

    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();
    }


    //內部類，AsyncTask 類型的類 若是之內部類形式出現，必須用 static，不然告警，說內存泄漏
    static class InsertAsyncTask extends AsyncTask<Word,Void,Void> {
        private WordDao wordDao;

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

        @Override
        protected Void doInBackground(Word... words) {
            //在工做線程在後臺作什麼操做
            wordDao.insertWords(words);
            return null;
        }


        /*@Override
        protected void onPostExecute(Void aVoid) {
            //任務完成時會呼叫，將結果帶回給主線程
            super.onPostExecute(aVoid);
        }

        @Override
        protected void onProgressUpdate(Void... values) {
            //當進度發生更新時，會呼叫
            super.onProgressUpdate(values);
        }

        @Override
        protected void onPreExecute() {
            //在後臺任務執行以前會呼叫
            super.onPreExecute();
        }*/
    }


    //內部類，AsyncTask 類型的類 若是之內部類形式出現，必須用 static，不然告警，說內存泄漏
    static class UpdateAsyncTask extends AsyncTask<Word,Void,Void>{
        private WordDao wordDao;

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

        @Override
        protected Void doInBackground(Word... words) {
            //在工做線程在後臺作什麼操做
            wordDao.updateWords(words);
            return null;
        }
    }


    //內部類，AsyncTask 類型的類 若是之內部類形式出現，必須用 static，不然告警，說內存泄漏
    static class DeleteAsyncTask extends AsyncTask<Word,Void,Void> {
        private WordDao wordDao;

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

        @Override
        protected Void doInBackground(Word... words) {
            //在工做線程在後臺作什麼操做
            wordDao.deleteWords(words);
            return null;
        }
    }


    //內部類，AsyncTask 類型的類 若是之內部類形式出現，必須用 static，不然告警，說內存泄漏
    static class DeleteAllAsyncTask extends AsyncTask<Void,Void,Void>{
        private WordDao wordDao;

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

        @Override
        protected Void doInBackground(Void... Voids) {
            //在工做線程在後臺作什麼操做
            wordDao.deleteAllWords();
            return null;
        }
    }
}

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