新建一个MyDatabaseHelper类：
package com.example.admin.databasetest;
import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.widget.Toast;
public class MyDatabaseHelper extends SQLiteOpenHelper {
//建表的SQL语句
public static final String CREATE_BOOK = "create table Book ("
+ "id integer primary key autoincrement, "
+ "author text, "
+ "price real, "
+ "pages integer, "
+ "name text)";
public static final String CREATE_CATEGORY = "create table Category ("
+ "id integer primary key autoincrement, "
+ "category_name text, "
+ "category_code integer)";
//
private Context mContext;
//构造方法
public MyDatabaseHelper(Context context, String name,
SQLiteDatabase.CursorFactory factory, int version) {
super(context, name, factory, version);
mContext = context;
}
/**
* 该函数在数据库创建时执行
* 尚未创建数据库是，调用以下方法就会创建数据库：dbHelper.getWritableDatabase();
* 在onCreate中执行建表操作
* 也就是创建数据库的同时，建表
* @param db
*/
@Override
public void onCreate(SQLiteDatabase db) {
db.execSQL(CREATE_BOOK); //
db.execSQL(CREATE_CATEGORY);
Toast.makeText(mContext, "Create succeeded", Toast.LENGTH_SHORT).show();
}
/**
* 该函数在版本号比已存在的数据库更大时调用
* 可以在里面重新建表
* @param db
* @param oldVersion
* @param newVersion
*/
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
db.execSQL("drop table if exists Book");
db.execSQL("drop table if exists Category");
onCreate(db);
}
}
调用该Helper，建表
private MyDatabaseHelper dbHelper;
//注意参数二：表名，参数四：版本
dbHelper = new MyDatabaseHelper(this, "BookStore.db", null, 1);
dbHelper.getWritableDatabase(); //检测有没有该名字的数据库，若没有则创建，同时调用dbHelper 的 onCreate 方法；若有就不会再创建了
完整版：
package com.example.admin.databasetest;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
public class MainActivity extends AppCompatActivity {
private MyDatabaseHelper dbHelper;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
//注意参数二：表名，参数四：版本
dbHelper = new MyDatabaseHelper(this, "BookStore.db", null, 1);
Button createDatabase = (Button) findViewById(R.id.create_database);
createDatabase.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
dbHelper.getWritableDatabase(); //检测有没有该名字的数据库，若没有则创建，同时调用dbHelper 的 onCreate 方法；若有就不会再创建了
}
});
}
}
增删改查
image.png
完整的main：
package com.example.admin.databasetest;
import android.content.ContentValues;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
public class MainActivity extends AppCompatActivity {
private MyDatabaseHelper dbHelper;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
//注意参数二：表名，参数四：版本
dbHelper = new MyDatabaseHelper(this, "BookStore.db", null, 1);
//按钮：创建数据库
Button createDatabase = (Button) findViewById(R.id.create_database);
createDatabase.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
dbHelper.getWritableDatabase(); //检测有没有该名字的数据库，若没有则创建，同时调用dbHelper 的 onCreate 方法；若有就不会再创建了
}
});
//按钮：添加数据
Button addData = (Button) findViewById(R.id.add_data);
addData.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
SQLiteDatabase db = dbHelper.getWritableDatabase(); //获得该数据库实例
ContentValues values = new ContentValues();
// 开始组装第一条数据
values.put("name", "The Da Vinci Code");
values.put("author", "Dan Brown");
values.put("pages", 454);
values.put("price", 16.96);
db.insert("Book", null, values); // 插入第一条数据
values.clear();
// 开始组装第二条数据
values.put("name", "The Lost Symbol");
values.put("author", "Dan Brown");
values.put("pages", 510);
values.put("price", 19.95);
db.insert("Book", null, values); // 插入第二条数据
//------------方法二直接用sql---------------
// db.execSQL("insert into Book (name, author, pages, price) values(?, ?, ?, ?)",
// new String[] { "The Da Vinci Code", "Dan Brown", "454", "16.96" });
// db.execSQL("insert into Book (name, author, pages, price) values(?, ?, ?, ?)",
// new String[] { "The Lost Symbol", "Dan Brown", "510", "19.95" });
//--------------------------------------------
}
});
Button queryButton = (Button) findViewById(R.id.query_data);
queryButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
SQLiteDatabase db = dbHelper.getWritableDatabase();
// 查询Book表中所有的数据
// Cursor cursor = db.query("Book", null, null, null, null, null, null);
Cursor cursor = db.rawQuery("select * from Book",null);
if (cursor.moveToFirst()) {
do {
// 遍历Cursor对象，取出数据并打印
String name = cursor.getString(cursor.getColumnIndex
("name"));
String author = cursor.getString(cursor.getColumnIndex
("author"));
int pages = cursor.getInt(cursor.getColumnIndex("pages"));
double price = cursor.getDouble(cursor.getColumnIndex
("price"));
Log.d("MainActivity", "book name is " + name);
Log.d("MainActivity", "book author is " + author);
Log.d("MainActivity", "book pages is " + pages);
Log.d("MainActivity", "book price is " + price);
} while (cursor.moveToNext());
}
cursor.close();
}
});
}
}
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