标签:java stringbu model ctas 自动 sync 世界 pen hello
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。
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(); } });
Android Studio 之 ROM【2】, LiveData+ViewModel+AsyncTask+Repository
标签:java stringbu model ctas 自动 sync 世界 pen hello
原文地址:https://www.cnblogs.com/gfwei/p/11808966.html