刚开始学java 学android 下面学习笔记，发现什么问题欢迎给位指正
在android中当需要操作SQLite数据库的时候需要得到一个SQLiteOpenHelper对象，而SQLiteOpenHelper是一个抽象类（只能够继承之后被使用），用户需要继承这个类，并实现该类中的一些方法。
SQLiteOpenHelper继承：
package DatabaseHelper;
import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteDatabase.CursorFactory;
import android.database.sqlite.SQLiteOpenHelper;
public class DatabaseHelper extends SQLiteOpenHelper {
private final static int VERSION=1;
//创建sqlite必须使用SQLiteOpenHelper中的getWritableDatabase()，或getReadableDatabase()
//但是SQLiteOpenHelper，是abstract类，所以必须继承后使用，在继承SQLiteOpenHelper时必须复写
//继承自父类的构造函数
public DatabaseHelper(Context context, String name, CursorFactory factory,
int version) {
super(context, name, factory, version);
// TODO Auto-generated constructor stub
}
public DatabaseHelper(Context context, String name,int version) {
super(context, name, null, version);
// TODO Auto-generated constructor stub
}
public DatabaseHelper(Context context, String name) {
super(context, name, null, VERSION);
// TODO Auto-generated constructor stub
}
@Override
public void onCreate(SQLiteDatabase db) {
// TODO Auto-generated method stub
System.out.println("sqlite is created");
//定义键值对类型，与insert的键值对对应
db.execSQL("create table user(id int,name varchar(20))");
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
// TODO Auto-generated method stub
System.out.println("sqlite is updated");
}
}
layout xml:
<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"
android:orientation="vertical"
tools:context=".MainActivity" >
<Button
android:id="@+id/button1"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:onClick="sqlitecreate"
android:text="@string/createsqlite" />
<Button
android:id="@+id/button2"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:onClick="sqliteupdate"
android:text="@string/updatesqlite" />
<Button
android:id="@+id/button3"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:onClick="sqliteinsert"
android:text="@string/insertsqlite" />
<Button
android:id="@+id/button4"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:onClick="dataupdate"
android:text="@string/dataupdate" />
<Button
android:id="@+id/button5"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:onClick="sqlitequery"
android:text="@string/querysqlite" />
<Button
android:id="@+id/button6"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:onClick="deletesqlite"
android:text="@string/deletesqlite" />
<Button
android:id="@+id/button7"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:onClick="closesqlite"
android:text="@string/closesqlite" />
<Button
android:id="@+id/button8"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:onClick="exitprogram"
android:text="@string/exitprogram"/>
</LinearLayout>
sqlite操作：
package com.example.sqlite;
import java.sql.SQLDataException;
import DatabaseHelper.DatabaseHelper;
import android.os.Bundle;
import android.app.Activity;
import android.content.ContentValues;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.view.Menu;
import android.view.View;
import android.widget.Button;
public class MainActivity extends Activity {
/* 在button android:onclick="函数名" 但中调用 可以部再次声明， 同时避免自己编写clicklistenner
private Button createbutton;
private Button updatebutton;
private Button insertbutton;
private Button dataupdatabutton;
private Button querybutton;
private Button deletebutton;
private Button closebutton;
private Button exitbutton;
*/
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
/*
createbutton = (Button) findViewById(R.id.button1);
updatebutton= (Button) findViewById(R.id.button2);
insertbutton = (Button) findViewById(R.id.button3);
dataupdatabutton = (Button) findViewById(R.id.button4);
querybutton = (Button) findViewById(R.id.button5);
deletebutton = (Button) findViewById(R.id.button6);
closebutton = (Button) findViewById(R.id.button7);
exitbutton = (Button) findViewById(R.id.button8);
*/
}
// 创建sqlite
public void sqlitecreate(View view) {
// 创建sqlite必须使用SQLiteOpenHelper中的getWritableDatabase()，或getReadableDatabase()
// 但是SQLiteOpenHelper，是abstract类，所以必须继承后使用，在继承SQLiteOpenHelper时必须复写
// 继承自父类的构造函数
// Create/or open a database WritableDatabase
DatabaseHelper dbhelper = new DatabaseHelper(MainActivity.this,
"sqlite_test3.db");
SQLiteDatabase db = dbhelper.getWritableDatabase();
System.out.println("sqlite is created");
}
// 更新sqlite版本
public void sqliteupdate(View view) {
DatabaseHelper dbhelper = new DatabaseHelper(MainActivity.this,
"sqlite_test3.db", 2);
SQLiteDatabase db = dbhelper.getWritableDatabase();
System.out.println("sqlite is updated");
}
// 向sqlite插入内容
public void sqliteinsert(View view) {
ContentValues values = new ContentValues();
// 键值对类型，与继承sqlteOpenHelper时sql与句定义的键值对格式一致
// db.execSQL("create table user(id int,name varchar(20))");
values.put("id", 1);
values.put("name", "张三");
//values.put("id", 2);
//values.put("name", "李四");
//values.put("id", 3);
//values.put("name", "王五");
DatabaseHelper dbhelper = new DatabaseHelper(MainActivity.this,
"sqlite_test3.db", 2);
SQLiteDatabase db = dbhelper.getWritableDatabase();
db.insert("user", null, values);
System.out.println("sqlite is inserted");
}
// 更新内容
public void dataupdate(View view) {
DatabaseHelper dbhelper = new DatabaseHelper(MainActivity.this,"sqlite_test3.db", 2);
SQLiteDatabase db = dbhelper.getWritableDatabase();
ContentValues values = new ContentValues();
values.put("name", "王五");
db.update("user", values, "id=?", new String[]{"1"});
System.out.println("data is updated");
}
// 查询sqlite
public void sqlitequery(View view) {
DatabaseHelper dbhelper = new DatabaseHelper(MainActivity.this,
"sqlite_test3.db", 2);
SQLiteDatabase db = dbhelper.getWritableDatabase();
Cursor cursor = db.query("user", new String[]{"id","name"}, "id=?", new String[]{"1"}, null, null, null);
//cursor.moveToFirst();//刚创建 指向头部
System.out.print(cursor.moveToNext());
while (cursor.moveToNext()) {
String name = cursor.getString(cursor.getColumnIndex("name"));
System.out.println("query--->" + name);
}
System.out.println("sqlite is queryed");
}
// delete sqlite
public void deletesqlite(View view) {
this.deleteDatabase("sqlite_test3.db");
System.out.println("sqlite is deleted");
}
// exit program
public void exitprogram(View view) {
System.exit(0);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
}
问题：
1.多次value.put()之后 value.insert()无法一次向.db输入多个键值对：这是因为value只保存了一个键值对，insert的只是对后的一对。
2.query读取数据没有反应，是因为创建.db文件忘记了加.db后缀。
总结：
1. sqliteOpenHelper为abstract类，应该继承之后再去创建实例对象（本例当中的DatabaseHelper）;
2. 对于已经存在的数据库，getWritableDatabase getReadableDatabase函数在.db文件已经存在的情况下为打开文件
3. 保存的database位于虚拟机的data/data/文件包名 当中，可点击右上角符号 pull a file from the device 导出到电脑，然后用sqlitespy等软件查看。
4.删除数据库时直接this.deleteDatabase("sqlite_test3.db");