Android数据库操作

1、数据库的建立

package my.pack;import android.app.ListActivity;import android.os.Bundle;import android.view.View;import android.widget.AdapterView;import android.widget.ArrayAdapter;import android.widget.ListView;import android.widget.TextView;import android.widget.Toast;import android.widget.AdapterView.OnItemClickListener;import android.app.Activity;import android.os.Bundle;import android.widget.*;import java.util.*;import android.content.Context;import android.database.*;import android.database.sqlite.*;import android.database.sqlite.SQLiteDatabase.CursorFactory;public class MyDatabaseHelper extends SQLiteOpenHelper{private static final String DB_NAME = "Notepad_1.db";    private static final int DB_VERSION = 1;    private static final String TABLE_NAME = "Table_1";    MyDatabaseHelper(Context context) {  super(context, DB_NAME, null, DB_VERSION);  }  @Override  public void onCreate(SQLiteDatabase db) {  String Sql = "CREATE TABLE Table_1 ('Time' varchar(200) not null,'Title' varchar (200) not null,'Content' text ,primary key(Title));";db.execSQL(Sql);}  @Override  public void onUpgrade(SQLiteDatabase db, int oldVersion,   int newVersion) {  }}

2、数据库操作帮组类（选择、插入、删除、）

package my.pack;import java.util.ArrayList;import java.util.HashMap;import java.util.List;import android.content.Context;import android.database.Cursor;import android.database.SQLException;import android.database.sqlite.SQLiteDatabase;public class MySqlHelper {public MyDatabaseHelper mOpenHelper;     public SQLiteDatabase db;     //构造函数    MySqlHelper(Context context)    {    mOpenHelper = new MyDatabaseHelper(context);     }    //选择    public int SelectItem(String mytitle)    {    db = mOpenHelper.getReadableDatabase();     //String col[] = {"Time","Title","Content"};    //String Sql = "where 'Title' = " + mytitle;    //Cursor cur = db.query("Table_1",col,Sql,null,null,null,null);        Cursor cur = db.rawQuery("SELECT * FROM Table_1 WHERE Title=?", new String[] { mytitle});      int num = cur.getCount();    cur.close();    db.close();    return num;    }    //插入    public void InsertItem(String mytime,String mytitle,String mycontent){    db = mOpenHelper.getWritableDatabase();     String Sql= "insert into Table_1 values('" + mytime +"', '" + mytitle +"', '" + mycontent+"' )";    try    {    db.execSQL(Sql);    //setTitle("Yes");    }    catch(SQLException e)    {    //setTitle(Sql);    }    db.close();}    //显示    public ArrayList<HashMap<String, Object>> ShowItem()    {    ArrayList<HashMap<String, Object>> listItem = new ArrayList<HashMap<String, Object>>();      db = mOpenHelper.getReadableDatabase();     String col[] = {"Time","Title","Content"};    Cursor cur = db.query("Table_1",col,null,null,null,null,"Time desc"); //按时间降序    int num = cur.getCount();    //setTitle(Integer.toString(num) + " 条记录");    cur.moveToFirst();    for(int i=0;i<num;i++)    {    HashMap<String, Object> map = new HashMap<String, Object>();      map.put("ItemTitle", cur.getString(1));              map.put("ItemText", cur.getString(0));              listItem.add(map);      cur.moveToNext();    }    cur.close();    db.close();    return listItem;    }    //删除Item    public void DeleteItem(String mytitle)    {    try    {    db = mOpenHelper.getWritableDatabase();     db.delete("Table_1","Title = '"+mytitle + "'",null);    //setTitle("删除Title为" + mytitle +"的记录");    db.close();    }    catch(SQLException e)    {}    }    //删除表项    public void DeleteTable(String mytable)    {    try    {    db = mOpenHelper.getWritableDatabase();     String Sql = "drop table " +mytable;    db.execSQL(Sql);    db.close();    //setTitle("已删除" + mytable +"表项");    }    catch(SQLException e)    {}    }}

3、删除数据库

**删除数据库final File file = this.getDatabasePath(DB_NAME);file.delete();

Ps、第一次调用getWritableDatabase()或getReadableDatabase()方法后，SQLiteOpenHelper会缓存当前的SQLiteDatabase实例，SQLiteDatabase实例正常情况下会维持数据库的打开状态，所以在你不再需要SQLiteDatabase实例时，请及时调用close()方法释放资源。一旦SQLiteDatabase实例被缓存，多次调用getWritableDatabase()或getReadableDatabase()方法得到的都是同一实例。

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