最近接触了room，可以完成数据库的工作，使用的感觉有点像spring boot，一起来看看吧
效果和结构
效果如下，很简单，只是为了显示room的作用
作为一个demo，文件结构很简单
导入包
首先进入room导入依赖包，也就是下面的代码贴到build.gradle中的dependencies中，这里我删除kotlin相关
def room_version = "2.2.1"
implementation "androidx.room:room-runtime:$room_version"
annotationProcessor "androidx.room:room-compiler:$room_version"
// For Kotlin use kapt instead of annotationProcessor
// 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"
实体类
然后构建word实体类，实体类我们可以用gsonFormat插件快速完成，具体可以自己搜索
这里构建单词实体时，通过PrimaryKey等注解的形式确定主键，属性列等
package com.example.roombaisic;
import androidx.room.ColumnInfo;
import androidx.room.Entity;
import androidx.room.PrimaryKey;
@Entity
public class Word {
/** * id : 0 * word : * chineseMeaning : */
@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;
}
}
然后创建WordDao，对word的增删改查操作都来自于此，这是个接口，由于注解可以帮我们执行sql语句，所以不需要实例化，非常方便
Word…words表示可以传任意参数
Dao层
package com.example.roombaisic;
import androidx.room.Dao;
import androidx.room.Delete;
import androidx.room.*;
import java.util.List;
//对数据库的操作
@Dao
public interface WordDao {
@Insert
void insertWords(Word... words);
@Update
void updateWords(Word... words);
@Delete
void deleteWords(Word... words);
@Delete
void deleteAllWords(List<Word>words);
@Query("SELECT * FROM WORD ORDER BY ID DESC")
List<Word> getAllWord();
}
数据库
最后时wordDatabase，很简单，注意时抽象类，因为同样不需要实例化，有多少个实体就有多少给Dao，都可以统一在wordDatabase中声明
package com.example.roombaisic;
import androidx.room.Database;
import androidx.room.RoomDatabase;
@Database(entities = {Word.class},version = 1,exportSchema = false)
public abstract class WordDatabase extends RoomDatabase {
public abstract WordDao getWordDao();
}
android实现
完成了以上工作，就到了android时间了，就剩下一个activity的java和xml文件
activity_main.xml
<?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">
<ScrollView
android:layout_width="411dp"
android:layout_height="367dp"
android:layout_marginBottom="404dp"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.0">
<TextView
android:id="@+id/text"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Hello World!"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent" />
</ScrollView>
<Button
android:id="@+id/btn_insert"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginBottom="248dp"
android:text="insert"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.256"
app:layout_constraintStart_toStartOf="parent" />
<Button
android:id="@+id/btn_delete"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginBottom="248dp"
android:text="delete"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.48"
app:layout_constraintStart_toEndOf="@+id/btn_insert" />
<Button
android:id="@+id/btn_update"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginBottom="148dp"
android:text="update"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.49"
app:layout_constraintStart_toEndOf="@+id/btn_clear"
app:layout_constraintTop_toBottomOf="@+id/btn_delete"
app:layout_constraintVertical_bias="1.0" />
<Button
android:id="@+id/btn_clear"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginStart="80dp"
android:layout_marginTop="32dp"
android:text="clear"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/btn_insert"
app:layout_constraintVertical_bias="0.119" />
</androidx.constraintlayout.widget.ConstraintLayout>
MainActivity
package com.example.roombaisic;
import androidx.appcompat.app.AppCompatActivity;
import androidx.room.Room;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import java.util.ArrayList;
public class MainActivity extends AppCompatActivity implements View.OnClickListener {
private static final String TAG = "MainActivity";
TextView textView;
Button btnInsert;
Button btnDelete;
Button btnUpdate;
Button btnClear;
WordDao wordDao;
WordDatabase wordDatabase;
ArrayList<Word>list;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
//通过room构建数据库
wordDatabase = Room.databaseBuilder(this, WordDatabase.class, "wordDatabase")
.allowMainThreadQueries()
.build();
//拿到wordDao
wordDao = wordDatabase.getWordDao();
init();
initView();
}
private void initView() {
btnInsert.setOnClickListener(this);
btnDelete.setOnClickListener(this);
btnUpdate.setOnClickListener(this);
btnClear.setOnClickListener(this);
}
private void init() {
btnInsert = (Button) findViewById(R.id.btn_insert);
btnDelete = (Button) findViewById(R.id.btn_delete);
btnUpdate = (Button) findViewById(R.id.btn_update);
btnClear = (Button) findViewById(R.id.btn_clear);
textView=(TextView)findViewById(R.id.text);
}
@Override
public void onClick(View v) {
switch (v.getId()) {
case R.id.btn_insert:
insertView();
break;
case R.id.btn_delete:
deleteView();
break;
case R.id.btn_update:
updateView();
break;
case R.id.btn_clear:
clearView();
break;
}
}
private void clearView() {
if (list !=null){
wordDao.deleteAllWords(list);
}
updateView();
}
private void deleteView() {
}
private void insertView() {
Word word1 = new Word( "hello", "你好");
Word word2 = new Word( "world", "世界");
wordDao.insertWords(word1, word2);
updateView();
Log.d(TAG, "insertView: 更新完毕");
}
//无论做什么操作后，都要更新一次text列表
private void updateView() {
list=(ArrayList<Word>) wordDao.getAllWord();
StringBuilder text=new StringBuilder();
for (int i = 0; i <list.size() ; i++) {
Word word=list.get(i);
text.append(word.getId()).append(" ").append(word.getWord()).append(" ").append(word.getChineseMeaning()).append("\n");
}
textView.setText(text.toString());
Log.d(TAG, "insertView: 写入text完毕");
}
}
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