1.要想使用Room首先需要在build.grade中添加依賴
dependencies { def room_version = "2.2.2" implementation "androidx.room:room-runtime:$room_version" annotationProcessor "androidx.room:room-compiler:$room_version" // For Kotlin use kapt instead of annotationProcessor // optional - Kotlin Extensions and Coroutines support for Room implementation "androidx.room:room-ktx:$room_version" // optional - RxJava support for Room implementation "androidx.room:room-rxjava2:$room_version" // optional - Guava support for Room, including Optional and ListenableFuture implementation "androidx.room:room-guava:$room_version" // Test helpers testImplementation "androidx.room:room-testing:$room_version" }
2.數據庫可視化工具可以選擇DB Browser for SQLite，具體請點擊下方鏈接進行下載
具體案例(對Word實體進行增刪改)
使用ViewModel，LiveData，Room等工具。
界面設計
- 上方是一個ScrollView（數據多的時候可滑動),ScrollView內有一個TextView
- 下方是四個按鍵，分別代表插入、刪除、清空、修改
activity_main.xml代碼如下：
<?xml version="1.0" encoding="utf-8"?> <androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:app="http://schemas.android.com/apk/res-auto" xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent" android:layout_height="match_parent" tools:context=".MainActivity"> <androidx.constraintlayout.widget.Guideline android:id="@+id/guideline" android:layout_width="wrap_content" android:layout_height="wrap_content" android:orientation="horizontal" app:layout_constraintGuide_percent="0.6" /> <ScrollView android:layout_width="0dp" android:layout_height="0dp" app:layout_constraintBottom_toTopOf="@+id/guideline" app:layout_constraintEnd_toEndOf="parent" app:layout_constraintStart_toStartOf="parent" app:layout_constraintTop_toTopOf="parent"> <TextView android:id="@+id/textView" android:layout_width="match_parent" android:layout_height="wrap_content" android:text="TextView" android:textSize="24sp" /> </ScrollView> <Button android:id="@+id/buttonInsert" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="insert" app:layout_constraintBottom_toBottomOf="parent" app:layout_constraintEnd_toStartOf="@+id/buttonUpdate" app:layout_constraintHorizontal_bias="0.5" app:layout_constraintStart_toStartOf="parent" app:layout_constraintTop_toTopOf="@+id/guideline" app:layout_constraintVertical_bias="0.25" /> <Button android:id="@+id/buttonUpdate" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="update" app:layout_constraintBottom_toBottomOf="@+id/buttonInsert" app:layout_constraintEnd_toEndOf="parent" app:layout_constraintHorizontal_bias="0.5" app:layout_constraintStart_toEndOf="@+id/buttonInsert" app:layout_constraintTop_toTopOf="@+id/buttonInsert" /> <Button android:id="@+id/buttonClear" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="clear" app:layout_constraintBottom_toBottomOf="@+id/buttonDelete" app:layout_constraintEnd_toStartOf="@+id/buttonDelete" app:layout_constraintHorizontal_bias="0.5" app:layout_constraintStart_toStartOf="parent" app:layout_constraintTop_toTopOf="@+id/buttonDelete" /> <Button android:id="@+id/buttonDelete" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="delete" app:layout_constraintBottom_toBottomOf="parent" app:layout_constraintEnd_toEndOf="parent" app:layout_constraintHorizontal_bias="0.5" app:layout_constraintStart_toEndOf="@+id/buttonClear" app:layout_constraintTop_toBottomOf="@+id/buttonUpdate" /> </androidx.constraintlayout.widget.ConstraintLayout>
因為是學習新的知識，所以不是太注重書寫，所以一些地方不是很規范。
創建實體(Entity)
package com.example.roombasic; import androidx.room.ColumnInfo; import androidx.room.Entity; import androidx.room.PrimaryKey; @Entity public class Word { @PrimaryKey(autoGenerate = true) private int id; @ColumnInfo(name = "english_word") private String word; @ColumnInfo(name = "chinese_meaning") private String chineseMeaning; public Word(String word, String chineseMeaning) { this.word = word; this.chineseMeaning = chineseMeaning; } public int getId() { return id; } public void setId(int id) { this.id = id; } public String getWord() { return word; } public void setWord(String word) { this.word = word; } public String getChineseMeaning() { return chineseMeaning; } public void setChineseMeaning(String chineseMeaning) { this.chineseMeaning = chineseMeaning; } }
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必須在類前使用注解 @Entity 來聲明。
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表結構中必須有一個主鍵，主鍵的聲明為 @PrimaryKey ，而主鍵遞增則在其后添加 (autoGenerate = true)。
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列名的注解使用 @ColumnInfo ，可以定義表結構中的列名，如 (name = "english_word") 。
創建Dao
package com.example.roombasic; import androidx.lifecycle.LiveData; import androidx.room.Dao; import androidx.room.Delete; import androidx.room.Insert; import androidx.room.Query; import androidx.room.Update; import java.util.List; @Dao public interface WordDao { @Insert void insertWords(Word... words); @Update void updateWords(Word... words); @Delete void deleteWords(Word... words); @Query("DElETE FROM WORD") void deleteAllWords(); @Query("SELECT * FROM WORD ORDER BY ID DESC ") LiveData<List<Word>> getAllWordsLive(); }
- 需要使用注解來聲明 @Dao 。
- 每種接口需要使用注解來聲明，如@Insert、@Update、@Delete。
- @Query("select * from word order by id desc") 是查詢語句。
- 接口不需要自己來實現，room已經幫我們寫出了具體的代碼。
- Word... words 表明可以傳進多個參數。類名... 對象名s 代表可以傳遞多個參數。
創建database
package com.example.roombasic; import android.content.Context; import androidx.room.Database; import androidx.room.Room; import androidx.room.RoomDatabase; @Database(entities = {Word.class}, version = 1, exportSchema = false) public abstract class WordDataBase extends RoomDatabase { private static WordDataBase INSTANCE; static synchronized WordDataBase getDatabase(Context context) { if (INSTANCE == null) { INSTANCE = Room.databaseBuilder(context.getApplicationContext(), WordDataBase.class, "word_database").build(); } return INSTANCE; } public abstract WordDao getWordDao(); }
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使用注解來聲明 @Database(entities = {Word.class},version = 1,exportSchema = false)
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entities = {Word.class}的{}中來填寫entity，可添加多個。
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version 是當前數據庫版本。
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synchronized為java中的鎖機制，多線程防止出錯。
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Room.databaseBuilder(context.getApplicationContext(),WordDatabase.class,"word_database").build
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第一個參數是activity，第二個參數為database的映射，第三個參數為數據庫名稱。
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創建ViewModel綁定數據
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.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 deleteAllWords(Word... words) { new DeleteAllAsyncTask(wordDao).execute(); } static class InsertAsyncTask extends AsyncTask<Word, Void, Void> { private WordDao wordDao; public InsertAsyncTask(WordDao wordDao) { this.wordDao = wordDao; } @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; } @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; } @Override protected Void doInBackground(Word... words) { wordDao.deleteWords(words); return null; } } static class DeleteAllAsyncTask extends AsyncTask<Void, Void, Void> { private WordDao wordDao; public DeleteAllAsyncTask(WordDao wordDao) { this.wordDao = wordDao; } @Override protected Void doInBackground(Void... voids) { wordDao.deleteAllWords(); return null; } } }
在MainActivity.java中添加按鍵監聽
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.Observer; import androidx.lifecycle.ViewModelProviders; import java.util.List; public class MainActivity extends AppCompatActivity { TextView textView; Button buttonInsert, buttonDelete, buttonUpdate, buttonClear; WordViewModel wordViewModel; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); wordViewModel = ViewModelProviders.of(this).get(WordViewModel.class); textView = findViewById(R.id.textView); 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); 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); } }); buttonClear.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { wordViewModel.deleteAllWords(); } }); buttonUpdate.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { Word word = new Word("Hi", "你好啊！"); word.setId(9); wordViewModel.updateWords(word); } }); buttonDelete.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { Word word = new Word("Hi", "你好啊！"); word.setId(7); wordViewModel.deleteWords(word); } }); } }
該實例中修改與刪除使用主鍵進行的，以后會進行修改與完善 。
暫時只學習了一點皮毛，后續會增加一些新的內容。