Android Error處理：java.lang.IllegalStateException: databases  already closed

今天匯入一個基於Android 2.x版本SDK專案，執行的時候一直出錯，錯誤如下：

11-18 16:58:56.595:E/AndroidRuntime(22991): java.lang.RuntimeException: Unable to start [email protected] with Intent {act=xxx.xxx.xxx.APP_SERVICE (has extras) }: java.lang.IllegalStateException:database /data/data/xxx.xxx.xxx/databases/xxx.db (conn# 0) already closed

package org.yousee.utils;


import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.database.sqlite.SQLiteDatabase.CursorFactory;
/**
 * 儲存記錄的資料庫
 */
public class DBHelper extends SQLiteOpenHelper {
	private Cursor c = null;
	private static final String CREATE_TAB = "create table "
		+ "music(_id integer primary key autoincrement,music_id integer,clicks integer," + "latest text)";
	private static final String TAB_NAME = "list";
	private SQLiteDatabase db = null;
	public DBHelper(Context context, String name, CursorFactory factory,int version) {
		super(context, name, factory, version);
	}

	@Override
	public void onCreate(SQLiteDatabase db) {
		this.db = db;
		db.execSQL(CREATE_TAB);
	}
	
	public void insert(ContentValues values){
		SQLiteDatabase db = this.getWritableDatabase();
		db.insert(TAB_NAME, null, values);
		db.close();//應改為this.close()
	}

	public void update(ContentValues values,int id){
		SQLiteDatabase db = this.getWritableDatabase();
		db.update(TAB_NAME, values, "music_id="+id, null);
		db.close();//應改為this.close()

	}
	
	public void delete(int id){
		if (db == null){
			db = getWritableDatabase();
		}
		db.delete(TAB_NAME, "music_id=?", new String[]{String.valueOf(id)});
	}
	
	public Cursor query(int id){
		SQLiteDatabase db = getReadableDatabase();
		c = db.query(TAB_NAME, null, "music_id=?", new String[]{String.valueOf(id)}, null, null, null);
		db.close();//應改為this.close()

		return c;
	}
	
	public Cursor queryByClicks(){//按點選量查詢
		SQLiteDatabase db = getReadableDatabase();
		c = db.query(TAB_NAME, null, null, null, null, null, "clicks desc");
		return c;
	}
	
	public Cursor queryRecently(){//按時間降序查詢
		SQLiteDatabase db = getReadableDatabase();
		c = db.query(TAB_NAME, null, null, null, null, null, "latest desc");
		return c;
	}
	
	public void close(){
		if (db != null){
			db.close();//應改為this.close()

			db=null;
		}
		if (c!=null){
			c.close();
			c=null;
		}
	}
	
	@Override
	public void onUpgrade(SQLiteDatabase arg0, int arg1, int arg2) {

	}

}
 

出錯的具體原因為：

如果呼叫SQLiteDatabase.close()代替SQLiteOpenHelper.close()。那麼SQLiteOpenHelper就不知道通過helper獲取的DB是否是關閉的（getReadableDatabase或getWritableDatabase）。

總結：

1、SQLiteOpenHelper.close()是非同步的，而SQLiteDatabase.close()不是。

2、在使用安卓提供的SQLiteOpenHelper時，通過getReadableDatabase或

3、使用Android提供的資料庫介面進行資料庫操作的時候一定要遵循Andoid的規則。在多執行緒中要注意，所以養成好的面向物件的習慣，呼叫helper的close方法關閉資料庫。（誰提供的資料，就呼叫誰的方法來操作資料）

網上還看到有類似的問題：

http://androiddev.orkitra.com/?p=30756

http://stackoverflow.com/questions/6535908/android-sqlite-sqliteopenhelper-error-illegalstateexception-db-already-clo