13 SQLiteOpenHelper SQLiteDatabase详解

创建数据库:

1. 创建一个类继承SQLiteOpenHelper
2. 创建继承对象 new SQLiteOpenHelper()
3. 用创建的对象获取可写或者可读的SQLiteDatabase
4. 用得到的SQLiteDatabase执行sql语句
* 手动写sql语句
* 调用内置的sql语句API

步骤1详解:

*一个继承的SQLiteOpenHelper类

```java
package com.fmy.sql.db;

import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteDatabase.CursorFactory;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;

public class MyOpenHelper extends SQLiteOpenHelper {

static final String DPNAME = "info.db";
static final int VERSION = 1;

public MyOpenHelper(Context context, String name, CursorFactory factory, int version) {
super(context, name, factory, version);
}

public MyOpenHelper(Context context) {
super(context, DPNAME, null, VERSION);
}

@Override
public void onCreate(SQLiteDatabase db) {
Log.e("fmy", "被创建了");
}

@Override
public void onOpen(SQLiteDatabase db) {
// TODO Auto-generated method stub
super.onOpen(db);
Log.e("fmy", "数据库被打开了");
}

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

}

}

```

步骤2详解:

*创建继承对象 new SQLiteOpenHelper()

MyOpenHelper myOpenHelper = new MyOpenHelper(this);

步骤3详解:

*用创建的对象获取可写或者可读的SQLiteDatabase

SQLiteDatabase db = myOpenHelper.getReadableDatabase();

用得到的SQLiteDatabase执行sql语句

手动写sql语句执行

package com.fmy.sql;
import com.fmy.sql.db.MyOpenHelper;

import android.app.Activity;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.os.Bundle;
import android.util.Log;
import android.view.View;

public class MainActivity extends Activity {

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

}

public void create(View v) {
MyOpenHelper myOpenHelper = new MyOpenHelper(this);
SQLiteDatabase db = myOpenHelper.getReadableDatabase();
Log.e("fmy", "创建表");
db.execSQL("create table if not exists person(_id INTEGER  primary key autoincrement,name varchar,age int)");
db.close();
myOpenHelper.close();
}

public void insert(View v) {
MyOpenHelper myOpenHelper = new MyOpenHelper(this);
SQLiteDatabase db = myOpenHelper.getReadableDatabase();
Log.e("fmy", "创建表");
String sql = "insert into person (name,age) values()";
for (int i = 0; i < 50; i++) {
db.execSQL("insert into person (name,age) values(" + "'张三" + i + "'" + "," + i + ")");
Log.e("fmy", "创建表");
}
db.close();
myOpenHelper.close();
}

public void update(View v) {
MyOpenHelper myOpenHelper = new MyOpenHelper(this);
SQLiteDatabase db = myOpenHelper.getReadableDatabase();
Log.e("fmy", "跟新表");
String sql = "UPDATE  person SET name = '李四' WHERE _id=1";
db.execSQL(sql);
db.close();
myOpenHelper.close();
}

public void delete(View v) {
MyOpenHelper myOpenHelper = new MyOpenHelper(this);
SQLiteDatabase db = myOpenHelper.getReadableDatabase();
Log.e("fmy", "创建表");
String sql = "DELETE FROM person WHERE _id=2";
db.execSQL(sql);
db.close();
myOpenHelper.close();
}

public void select(View v) {
Log.e("fmy", "查询");
MyOpenHelper myOpenHelper = new MyOpenHelper(this);
SQLiteDatabase db = myOpenHelper.getReadableDatabase();
String sql = "select *from person";
Cursor cursor = db.rawQuery(sql,null);
while (cursor.moveToNext()){
String name = cursor.getString(cursor.getColumnIndex("name"));
Log.e("fmy", "查询"+name);
}
db.close();
myOpenHelper.close();
}

}

```
* API 增删改查

```java
package com.fmy.dbapi;

import com.fmy.dbapi.db.MyOpenHelper;

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.View;

public class MainActivity extends Activity {

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

}

public void create(View v) {
MyOpenHelper myOpenHelper = new MyOpenHelper(this);
SQLiteDatabase db = myOpenHelper.getReadableDatabase();
Log.e("fmy", "创建表");
db.execSQL("create table if not exists person(_id INTEGER  primary key autoincrement,name varchar,age int)");
db.close();
myOpenHelper.close();
}

public void insert(View v) {
MyOpenHelper myOpenHelper = new MyOpenHelper(this);
SQLiteDatabase db = myOpenHelper.getReadableDatabase();
Log.e("fmy", "插入表");
String sql = "insert into person (name,age) values()";

ContentValues value = new ContentValues();

for (int i = 0; i < 50; i++) {
value.put("name", "张三" + i);
long insert = db.insert("person", null, value);
Log.e("fmy", "插入表" + insert);
}
db.close();
myOpenHelper.close();
}

public void update(View v) {
MyOpenHelper myOpenHelper = new MyOpenHelper(this);
SQLiteDatabase db = myOpenHelper.getReadableDatabase();
ContentValues values = new ContentValues();
values.put("name", "李四");
int update = db.update("person", values, "_id=?", new String[] { "1" });
Log.e("fmy", "跟新表" + update);
db.close();
myOpenHelper.close();
}

public void delete(View v) {
MyOpenHelper myOpenHelper = new MyOpenHelper(this);
SQLiteDatabase db = myOpenHelper.getReadableDatabase();
Log.e("fmy", "创建表");
db.delete("person", "_id=?", new String[] { "2" });
db.close();
myOpenHelper.close();
}

public void select(View v) {
Log.e("fmy", "查询");
MyOpenHelper myOpenHelper = new MyOpenHelper(this);
SQLiteDatabase db = myOpenHelper.getReadableDatabase();

Cursor cursor = db.query("person", null, null, null, null, null, null, "1,2");
while (cursor.moveToNext()) {
String name = cursor.getString(cursor.getColumnIndex("name"));
Log.e("fmy", "查询" + name);
}
db.close();
myOpenHelper.close();
}

}