Android(安卓)Room 增删改查 个人经验
16lz
2021-01-26
Write By xyx IN csdn @包罗万码 In Guangzhou
转载请注明出处:https://blog.csdn.net/a316375/article/details/83057528
Android Room官方Demo详解:
四个步骤带你秒懂Android数据库的Room使用方式:
附加优化了自己添加的真删改査使用代码
Room采用DAO模式,
新建一个O对象
@Entity(tableName = "word_table")public class Word { @PrimaryKey(autoGenerate = true) private int point; @NonNull @ColumnInfo(name = "word") private String mWord; public Word(@NonNull String word) { this.mWord = word; } @NonNull public void setPoint(int point) { this.point = point; } @NonNull public int getPoint() { return this.point; } @NonNull public String getWord() { return this.mWord; }}新建一个DAO对象
@Daopublic interface WordDao { @Query("UPDATE word_table SET word = :changword WHERE point = :Id") void updateWord(int Id,String changword); @Update void update(Word entity); @Query("SELECT * FROM word_table WHERE word LIKE :first AND " + "word LIKE :last LIMIT 1") Word findByName(String first, String last); // LiveData is a data holder class that can be observed within a given lifecycle. // Always holds/caches latest version of data. Notifies its active observers when the // data has changed. Since we are getting all the contents of the database, // we are notified whenever any of the database contents have changed. @Query("SELECT * from word_table ORDER BY word ASC") LiveData> getAlphabetizedWords(); // We do not need a conflict strategy, because the word is our primary key, and you cannot // add two items with the same primary key to the database. If the table has more than one // column, you can use @Insert(onConflict = OnConflictStrategy.REPLACE) to update a row. @Insert void insert(Word word); @Query("DELETE FROM word_table") void deleteAll(); //根据名字删除 @Query("DELETE FROM word_table where word=:word") void deleteFormName(String word); //根据名字+索引删除 @Query("DELETE FROM word_table where word=:word and point=:point") void deleteFormName(String word,int point);} 新建一个RoomDatabase对象
(以上记忆为三步骤Obj(数据库表的列设置)-->DAO(数据库增删改査语法)-->RoomDatabase(数据库操作类))
@Database(entities = {Word.class}, version = 2 )public abstract class WordRoomDatabase extends RoomDatabase { public abstract WordDao wordDao(); // marking the instance as volatile to ensure atomic access to the variable private static volatile WordRoomDatabase INSTANCE; static WordRoomDatabase getDatabase(final Context context) { if (INSTANCE == null) { synchronized (WordRoomDatabase.class) { if (INSTANCE == null) { INSTANCE = Room.databaseBuilder(context.getApplicationContext(), WordRoomDatabase.class, "word_database") // Wipes and rebuilds instead of migrating if no Migration object. // Migration is not part of this codelab. .fallbackToDestructiveMigration() .addCallback(sRoomDatabaseCallback) .build(); } } } return INSTANCE; } /** * Override the onOpen method to populate the database. * For this sample, we clear the database every time it is created or opened. * * If you want to populate the database only when the database is created for the 1st time, * override RoomDatabase.Callback()#onCreate */ private static RoomDatabase.Callback sRoomDatabaseCallback = new RoomDatabase.Callback() { @Override public void onOpen(@NonNull SupportSQLiteDatabase db) { super.onOpen(db); // If you want to keep the data through app restarts, // comment out the following line. new PopulateDbAsync(INSTANCE).execute(); } }; /** * Populate the database in the background. * If you want to start with more words, just add them. */ private static class PopulateDbAsync extends AsyncTask { private final WordDao mDao; PopulateDbAsync(WordRoomDatabase db) { mDao = db.wordDao(); } @Override protected Void doInBackground(final Void... params) { // Start the app with a clean database every time. // Not needed if you only populate on creation. //mDao.deleteAll(); Word word = new Word("Hello"); mDao.insert(word); word = new Word("World"); mDao.insert(word); return null; } }} 注意:Room不能运行在UI界面,所以数据采用仓储模式Repository
class WordRepository { private WordDao mWordDao; private LiveData> mAllWords; // Note that in order to unit test the WordRepository, you have to remove the Application // dependency. This adds complexity and much more code, and this sample is not about testing. // See the BasicSample in the android-architecture-components repository at // https://github.com/googlesamples WordRepository(Application application) { WordRoomDatabase db = WordRoomDatabase.getDatabase(application); mWordDao = db.wordDao(); mAllWords = mWordDao.getAlphabetizedWords(); } // Room executes all queries on a separate thread. // Observed LiveData will notify the observer when the data has changed. LiveData> getAllWords() { return mAllWords; } // You must call this on a non-UI thread or your app will crash. // Like this, Room ensures that you're not doing any long running operations on the main // thread, blocking the UI. void insert(Word word) { new insertAsyncTask(mWordDao).execute(word); } private static class insertAsyncTask extends AsyncTask { private WordDao mAsyncTaskDao; insertAsyncTask(WordDao dao) { mAsyncTaskDao = dao; } @Override protected Void doInBackground(final Word... params) { mAsyncTaskDao.insert(params[0]); mAsyncTaskDao.updateWord(1,"Changed"+params[0].getWord()); return null; } }} 如果是Activity要获取数据并且获取数据库实现更新,借助一个ViewModel
public class WordViewModel extends AndroidViewModel { private WordRepository mRepository; // Using LiveData and caching what getAlphabetizedWords returns has several benefits: // - We can put an observer on the data (instead of polling for changes) and only update the // the UI when the data actually changes. // - Repository is completely separated from the UI through the ViewModel. private LiveData> mAllWords; public WordViewModel(Application application) { super(application); mRepository = new WordRepository(application); mAllWords = mRepository.getAllWords(); } LiveData> getAllWords() { return mAllWords; } void insert(Word word) { mRepository.insert(word); }} 这是一个熟悉的Recycleview.Adatper,
public class WordListAdapter extends RecyclerView.Adapter { class WordViewHolder extends RecyclerView.ViewHolder { private final TextView wordItemView; private WordViewHolder(View itemView) { super(itemView); wordItemView = itemView.findViewById(R.id.textView); } } private final LayoutInflater mInflater; private List mWords = Collections.emptyList(); // Cached copy of words WordListAdapter(Context context) { mInflater = LayoutInflater.from(context); } @Override public WordViewHolder onCreateViewHolder(ViewGroup parent, int viewType) { View itemView = mInflater.inflate(R.layout.recyclerview_item, parent, false); return new WordViewHolder(itemView); } @Override public void onBindViewHolder(WordViewHolder holder, int position) { Word current = mWords.get(position); holder.wordItemView.setText(current.getWord()); } void setWords(List words) { mWords = words; notifyDataSetChanged(); } @Override public int getItemCount() { return mWords.size(); }} 下面两个Activity去实现
public class MainActivity extends AppCompatActivity { public static final int NEW_WORD_ACTIVITY_REQUEST_CODE = 1; private WordViewModel mWordViewModel; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); Toolbar toolbar = findViewById(R.id.toolbar); setSupportActionBar(toolbar); RecyclerView recyclerView = findViewById(R.id.recyclerview); final WordListAdapter adapter = new WordListAdapter(this); recyclerView.setAdapter(adapter); recyclerView.setLayoutManager(new LinearLayoutManager(this)); // Get a new or existing ViewModel from the ViewModelProvider. mWordViewModel = ViewModelProviders.of(this).get(WordViewModel.class); // Add an observer on the LiveData returned by getAlphabetizedWords. // The onChanged() method fires when the observed data changes and the activity is // in the foreground. mWordViewModel.getAllWords().observe(this, new Observer>() { @Override public void onChanged(@Nullable final List words) { // Update the cached copy of the words in the adapter. adapter.setWords(words); } }); FloatingActionButton fab = findViewById(R.id.fab); fab.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View view) { Intent intent = new Intent(MainActivity.this, NewWordActivity.class); startActivityForResult(intent, NEW_WORD_ACTIVITY_REQUEST_CODE); } }); } public void onActivityResult(int requestCode, int resultCode, Intent data) { super.onActivityResult(requestCode, resultCode, data); if (requestCode == NEW_WORD_ACTIVITY_REQUEST_CODE && resultCode == RESULT_OK) { Word word = new Word(data.getStringExtra(NewWordActivity.EXTRA_REPLY)); mWordViewModel.insert(word); } else { Toast.makeText( getApplicationContext(), R.string.empty_not_saved, Toast.LENGTH_LONG).show(); } }} 第二个Activity按钮实现:
public class NewWordActivity extends AppCompatActivity { public static final String EXTRA_REPLY = "com.example.android.wordlistsql.REPLY"; private EditText mEditWordView; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_new_word); mEditWordView = findViewById(R.id.edit_word); final Button button = findViewById(R.id.button_save); button.setOnClickListener(new View.OnClickListener() { public void onClick(View view) { Intent replyIntent = new Intent(); if (TextUtils.isEmpty(mEditWordView.getText())) { setResult(RESULT_CANCELED, replyIntent); } else { String word = mEditWordView.getText().toString(); replyIntent.putExtra(EXTRA_REPLY, word); setResult(RESULT_OK, replyIntent); } finish(); } }); }}附带编译遇到的坑:https://mp.csdn.net/postedit/83057354
另带配置导入设置
将以下代码添加到依赖项块末尾的build.gradle（Module：app）文件中。
// Room componentsimplementation "android.arch.persistence.room:runtime:$rootProject.roomVersion"annotationProcessor "android.arch.persistence.room:compiler:$rootProject.roomVersion"androidTestImplementation "android.arch.persistence.room:testing:$rootProject.roomVersion"// Lifecycle componentsimplementation "android.arch.lifecycle:extensions:$rootProject.archLifecycleVersion"annotationProcessor "android.arch.lifecycle:compiler:$rootProject.archLifecycleVersion"在您的工程Project 的 build.gradle 文件中，末尾添加以下代码，如下面的代码所示。
ext { roomVersion = '1.1.1' archLifecycleVersion = '1.1.1'}更多相关文章
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