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();

1. 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();
    }

}