2024年3月11日第十一篇

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代码量	200
博客	1
花费时间	2
知识点	安卓本地数据库的增删改查及登录的实现

 

 

 

 

 

今天主要学习了安卓本地数据库SQLite的Room增删改查操作以及登录页面的实现，学习了一些安卓java开发的中级控件。

下面是我整理的一些代码

# 1.创建entity然后创建实体类

```
package com.example.anew.entity;

import androidx.room.Entity;
import androidx.room.PrimaryKey;

@Entity
public class Book {
    @PrimaryKey(autoGenerate = true)
    private int id;

    private String name; // 书籍名称
    private String author; // 作者
    private String press; // 出版社
    private String price; // 价格

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getAuthor() {
        return author;
    }

    public void setAuthor(String author) {
        this.author = author;
    }

    public String getPress() {
        return press;
    }

    public void setPress(String press) {
        this.press = press;
    }

    public String getPrice() {
        return price;
    }

    public void setPrice(String price) {
        this.price = price;
    }

    @Override
    public String toString() {
        return "BookInfo{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", author='" + author + '\'' +
                ", press='" + press + '\'' +
                ", price=" + price +
                '}';
    }
}

```

# 2.然后创建database包，创建对应的database类

```
package com.example.anew.database;

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

import com.example.anew.Dao.BookDao;
import com.example.anew.entity.Book;

@Database(entities = {Book.class}, version = 1, exportSchema = true)
public abstract class BookDatabase extends RoomDatabase {
    // 获取该数据库中某张表的持久化对象
    public abstract BookDao bookDao();

}
```

# 3.创建Dao类，创建对应的Dao包

```
package com.example.anew.Dao;

import androidx.room.Dao;
import androidx.room.Delete;
import androidx.room.Insert;
import androidx.room.Query;
import androidx.room.Update;

import com.example.anew.entity.Book;

import java.util.List;
@Dao
public interface BookDao {
    @Insert
    void insert(Book book);

    @Delete
    void delete(Book book);

    // 删除所有书籍信息
    @Query("DELETE FROM Book")
    void deleteAll();

    @Update()
    int update(Book book);

    // 加载所有书籍信息
    @Query("SELECT * FROM Book")
    List<Book> queryAll();

    // 根据名字加载书籍
    @Query("SELECT * FROM Book WHERE name = :name ORDER BY id DESC limit 1")
    Book queryByName(String name);
}

```

# 4.最后创建对应的activity

```
package com.example.anew;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.EditText;

import com.example.anew.entity.Book;
import com.example.anew.util.Toastutil;
import com.example.anew.Dao.BookDao;

import java.util.List;

public class RoomWriteActivity extends AppCompatActivity implements View.OnClickListener {

    private EditText et_name;
    private EditText et_author;
    private EditText et_press;
    private EditText et_price;
    private BookDao bookDao;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_room);

        et_name = findViewById(R.id.et_name);
        et_author = findViewById(R.id.et_author);
        et_press = findViewById(R.id.et_press);
        et_price = findViewById(R.id.et_price);
        findViewById(R.id.btn_save).setOnClickListener(this);
        findViewById(R.id.btn_query).setOnClickListener(this);
        findViewById(R.id.btn_update).setOnClickListener(this);
        findViewById(R.id.btn_delete).setOnClickListener(this);

        bookDao = MyApplication.getInstance().getBookDB().bookDao();
    }

    @Override
    public void onClick(View v) {
       String name = et_name.getText().toString();
         String author = et_author.getText().toString();
            String press = et_press.getText().toString();
            String price = et_price.getText().toString();
            if(v.getId() == R.id.btn_save){
                Book b1 = new Book();
                b1.setName(name);
                b1.setAuthor(author);
                b1.setPress(press);
                b1.setPrice(price);
                bookDao.insert(b1);
                Toastutil.showMsg(this, "保存成功");
    }
            if(v.getId() == R.id.btn_query){
                    List<Book> list = bookDao.queryAll();
                    for (Book b : list) {
                        Log.d("ning", b.toString());
                    }
                }
            if(v.getId() == R.id.btn_update){
                Book b2=bookDao.queryByName(name);
                Book b1=new Book();
                b1.setId(b2.getId());
                b1.setName(name);
                b1.setAuthor(author);
                b1.setPress(press);
                b1.setPrice(price);
                bookDao.update(b1);
                Toastutil.showMsg(this, "更新成功");
            }
            if(v.getId() == R.id.btn_delete){
                Book b1 = bookDao.queryByName(name);
                bookDao.delete(b1);
                Toastutil.showMsg(this, "删除成功");
            }
}}

```

# 在与之对应的xml文件下写如下代码：

```
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:padding="5dp">

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="40dp"
        android:orientation="horizontal">

        <TextView
            android:id="@+id/tv_name"
            android:layout_width="wrap_content"
            android:layout_height="match_parent"
            android:gravity="center"
            android:text="　书名："
            android:textColor="@color/black"
            android:textSize="17sp" />

        <EditText
            android:id="@+id/et_name"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_marginTop="3dp"
            android:layout_marginBottom="3dp"
            android:layout_weight="1"
            android:background="@drawable/editext_selector"
            android:hint="请输入书籍名称"
            android:inputType="text"
            android:textColor="@color/black"
            android:textSize="17sp" />
    </LinearLayout>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="40dp"
        android:orientation="horizontal">

        <TextView
            android:id="@+id/tv_author"
            android:layout_width="wrap_content"
            android:layout_height="match_parent"
            android:gravity="center"
            android:text="　作者："
            android:textColor="@color/black"
            android:textSize="17sp" />

        <EditText
            android:id="@+id/et_author"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_marginTop="3dp"
            android:layout_marginBottom="3dp"
            android:layout_weight="1"
            android:background="@drawable/editext_selector"
            android:hint="请输入作者姓名"
            android:textColor="@color/black"
            android:textSize="17sp" />
    </LinearLayout>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="40dp"
        android:orientation="horizontal">

        <TextView
            android:id="@+id/tv_press"
            android:layout_width="wrap_content"
            android:layout_height="match_parent"
            android:gravity="center"
            android:text="出版社："
            android:textColor="@color/black"
            android:textSize="17sp" />

        <EditText
            android:id="@+id/et_press"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_marginTop="3dp"
            android:layout_marginBottom="3dp"
            android:layout_weight="1"
            android:background="@drawable/editext_selector"
            android:hint="请输入出版社名称"
            android:textColor="@color/black"
            android:textSize="17sp" />
    </LinearLayout>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="40dp"
        android:orientation="horizontal">

        <TextView
            android:id="@+id/tv_price"
            android:layout_width="wrap_content"
            android:layout_height="match_parent"
            android:gravity="center"
            android:text="　价格："
            android:textColor="@color/black"
            android:textSize="17sp" />

        <EditText
            android:id="@+id/et_price"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_marginTop="3dp"
            android:layout_marginBottom="3dp"
            android:layout_weight="1"
            android:background="@drawable/editext_selector"
            android:hint="请输入书籍价格"
            android:inputType="numberDecimal"
            android:textColor="@color/black"
            android:textSize="17sp" />
    </LinearLayout>

    <Button
        android:id="@+id/btn_save"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="添加"
        android:textColor="@color/black"
        android:textSize="17sp" />

    <Button
        android:id="@+id/btn_delete"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="删除"
        android:textColor="@color/black"
        android:textSize="17sp" />

    <Button
        android:id="@+id/btn_update"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="修改"
        android:textColor="@color/black"
        android:textSize="17sp" />

    <Button
        android:id="@+id/btn_query"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="查询"
        android:textColor="@color/black"
        android:textSize="17sp" />

</LinearLayout>
```

# 还有与之对应的myapplication

```
package com.example.anew;

import android.app.Application;
import android.util.Log;

import androidx.room.Room;

import com.example.anew.database.BookDatabase;

import java.util.HashMap;

public class MyApplication extends Application {

    private static MyApplication mApp;
    // 声明一个公共的信息映射对象，可当作全局变量使用
    public HashMap<String, String> infoMap = new HashMap<>();

    // 声明一个书籍数据库对象
    private BookDatabase bookDatabase;

    // 购物车中的商品总数量
    public int goodsCount;

    public static MyApplication getInstance() {
        return mApp;
    }


    //在App启动时调用
    @Override
    public void onCreate() {
        super.onCreate();
        mApp = this;
        Log.d("ning", "MyApplication onCreate");

        // 构建书籍数据库的实例
        bookDatabase = Room.databaseBuilder(mApp, BookDatabase.class, "book")
                // 允许迁移数据库（发生数据库变更时，Room默认删除原数据库再创建新数据库。如此一来原来的记录会丢失，故而要改为迁移方式以便保存原有记录）
                .addMigrations()
                // 允许在主线程中操作数据库（Room默认不能在主线程中操作数据库）
                .allowMainThreadQueries()
                .build();
    }

    @Override
    public void onTerminate() {
        super.onTerminate();
        Log.d("ning", "onTerminate");
    }


    // 获取书籍数据库的实例
    public BookDatabase getBookDB() {
        return bookDatabase;
    }
}
```