sqlite是android 轻量级数据库

主要是两个类实现创建数据库和数据的增删改查

这个类是MainActivity 是创建数据库对象，通过这个对象dbHelper调用getWritableDatabase()方法就可以去创建数据库了

接下来就是对数据库的增删改查操作。getWritableDatabase()这个方法很重要 数据库的创建升级增删改查都需要这个方法。ContentValues（）这个方法是用来添加数据的。

package com.example.sqlitetest;
 
import com.example.sqlitetest.R;
 
import android.app.Activity;
import android.content.ContentValues;
import android.database.Cursor;
import android.database.sqlite.sqliteDatabase;
import android.os.Bundle;
import android.util.Log;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
 
public class MainActivity extends Activity {
 
	private MyDatabaseHelper dbHelper;
	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		//生成数据库对象
		dbHelper = new MyDatabaseHelper(this,"BookStore.db",null,4);
		
		Button createDatabase = (Button) findViewById(R.id.create_database);
		createDatabase.setOnClickListener(new OnClickListener() {
			
			@Override
			public void onClick(View v) {
				// 创建数据库,这个方法会调用MyDatabaseHelper中的onCreate()方法和onUpgrade()方法
				dbHelper.getWritableDatabase();
			}
		});
		
		//添加数据
		Button Add_date = (Button) findViewById(R.id.Add_date);
		Add_date.setOnClickListener(new OnClickListener() {
			
			@Override
			public void onClick(View v) {
				//getWritableDatabase()方法会返回一个sqliteDatabase对象，这个
				//对象可以对数据库进行增删改查的操作
				sqliteDatabase db = dbHelper.getWritableDatabase();	
				//通过这个方法添加数据
				ContentValues values = new ContentValues();
				//开始组装第一条数据
				values.put("name","sunning");
				values.put("author","Dan Brown");
				values.put("pages","500");
				values.put("price","16.6");
				//插入第一条数据
				db.insert("Book",values);
				
				values.clear();
				
				//开始组装第二条数据
				values.put("name","leoveo");
				values.put("author","Frown Brown");
				values.put("pages","13.6");
				//插入第一条数据
				db.insert("Book",values);
				
			}
		});
		
		//更新数据
		
		Button Update_data = (Button) findViewById(R.id.Update_data);
		Update_data.setOnClickListener(new OnClickListener() {
			
			@Override
			public void onClick(View v) {
				sqliteDatabase db = dbHelper.getWritableDatabase();	
				ContentValues values = new ContentValues();
				values.put("price",66.6);
				db.update("Book",values,"name = ?",new String[]{"sunning"});
				
			}
		});
		
		//删除数据
		Button Delete_data = (Button) findViewById(R.id.Delete_data);
		Delete_data.setOnClickListener(new OnClickListener() {
			
			@Override
			public void onClick(View v) {
				sqliteDatabase db = dbHelper.getWritableDatabase();	
				db.delete("Book","pages>= ?",new String []{"500"});
				
			}
		});
		
		//查询数据
		Button Query_data = (Button) findViewById(R.id.Query_data);
		Query_data.setOnClickListener(new 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 );
				//cursor.moveToFirst() 表示是否指针移动到第一行的位置
				if(cursor.moveToFirst()){
					
					do{
						
						//遍历Cursor对象，取出数据并打印,注意写的时候不要写错字符，要不然报错
						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","name=="+name);
						Log.d("MainActivity","author=="+author);
						Log.d("MainActivity","pages=="+pages);
						Log.d("MainActivity","prices=="+price);
						
					}while(cursor.moveToNext());
				}
				
				cursor.close();
				
			}
		});
		
	
	}
 
 
	
	
}

下面这个类给我的感觉像一个工具类。就是继承sqliteOpenHelper 这个类 ，覆写onCreate()方法和onUpGrade()方法，对表进行创建和升级操作。还有就是创建表的字段语句

import android.content.Context;
import android.database.sqlite.sqliteDatabase;
import android.database.sqlite.sqliteDatabase.CursorFactory;
import android.database.sqlite.sqliteOpenHelper;
import android.widget.Toast;
 
public class MyDatabaseHelper extends sqliteOpenHelper {
	//创建表  书
	public static final String CREATE_BOOK = "create table Book ("+"id integer primary key autoincrement,"
	+"author text,"+"price real,"+"pages integer,"+"name text)";
	
	//创建表  书的分类
	
	public static final String CREATE_CATEGORY = "create table Category("
			+"id integer primary key autoincrement,"
			+"category_name text,"
			+"categoty_code integer)"
			;
	
	private Context mContext;
 
	public MyDatabaseHelper(Context context,String name,CursorFactory factory,int version) {
		super(context,name,factory,version);
			
		mContext =  context;
	
	}
 
	@Override
	public void onCreate(sqliteDatabase db) {
		db.execsql(CREATE_BOOK);
		db.execsql(CREATE_CATEGORY);
		Toast.makeText(mContext,"Create succeeded",Toast.LENGTH_SHORT).show();
			
		
		
	}
	//表的升级 
	@Override
	public void onUpgrade(sqliteDatabase db,int oldVersion,int newVersion) {
 
		db.execsql("drop table if exists Book");
		db.execsql("drop table if exists Category");
		//在升级的方法里面重新创建表
		onCreate(db);
	}
 
	
	
}

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.example.sqlitetest.MainActivity"
    android:orientation="vertical"
     >
 
    <Button
        android:id="@+id/create_database"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="@string/Create_database" />
    <Button
        android:id="@+id/Add_date"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="@string/Add_date" />
    <Button
        android:id="@+id/Update_data"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="@string/Update_data" />
    <Button
        android:id="@+id/Delete_data"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="@string/Delete_data" />
    <Button
        android:id="@+id/Query_data"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="@string/Query_data" />
    
    
 
</LinearLayout>