Java 尝试重新打开已关闭的对象：SQLiteQuery

我知道这个问题已经被问过好几次了，但在我看来，其他答案都不适用于我的情况。我试图在按下按钮后删除数据库中的4项，但在尝试删除时，我得到了一个非法状态异常。我尝试用以下方式删除我的数据库，但似乎不起作用：

getActivity().deleteDatabase("TABLE_CATTLE");

我还尝试使用循环逐个删除条目，如下所示：

int cattle_i=0;
int numCattle = cattleDb.getCattleCount(); 
while(cattle_i<numCattle){
    Cattle cattle = cattleDb.getCattle(cattle_i);
    cattleDb.deleteCattle(cattle);
    cattle_i++;
}

下面是GetBown方法：

Cattle getCattle(int id){
    SQLiteDatabase db = this.getReadableDatabase();

    Cursor cursor = db.query(TABLE_CATTLE,  new String[] 
            {KEY_ID,  KEY_TAG_ID, KEY_ALIAS, KEY_TIME, KEY_DATA}, KEY_ID + "=?",
            new String[] {String.valueOf(id) }, null, null, null, null);
    if(cursor!=null)
        cursor.moveToFirst();
    Cattle cattle = new Cattle(Integer.parseInt(cursor.getString(0)),
            cursor.getString(1),
            cursor.getString(2),
            cursor.getString(3),
            cursor.getString(4));
    cursor.close();
    db.close();//test
    return cattle;
}  

    //Deleting single cow
public void deleteCattle(Cattle cattle){
    SQLiteDatabase db = this.getWritableDatabase();
    db.delete(TABLE_CATTLE, KEY_ID + " = ?",
            new String[] {String.valueOf(cattle.getID())});
    db.close();
}

删除方法：

Cattle getCattle(int id){
    SQLiteDatabase db = this.getReadableDatabase();

    Cursor cursor = db.query(TABLE_CATTLE,  new String[] 
            {KEY_ID,  KEY_TAG_ID, KEY_ALIAS, KEY_TIME, KEY_DATA}, KEY_ID + "=?",
            new String[] {String.valueOf(id) }, null, null, null, null);
    if(cursor!=null)
        cursor.moveToFirst();
    Cattle cattle = new Cattle(Integer.parseInt(cursor.getString(0)),
            cursor.getString(1),
            cursor.getString(2),
            cursor.getString(3),
            cursor.getString(4));
    cursor.close();
    db.close();//test
    return cattle;
}  

    //Deleting single cow
public void deleteCattle(Cattle cattle){
    SQLiteDatabase db = this.getWritableDatabase();
    db.delete(TABLE_CATTLE, KEY_ID + " = ?",
            new String[] {String.valueOf(cattle.getID())});
    db.close();
}

黄豆：

public class Cattle {

    // private variables
    int _id = 0;
    String _tag_id = null;
    String _alias = null;
    String _time_stamp = null;
    String _tag_data = null;
    String _user_email = null;

    // Empty Constructor
    public Cattle() {

    }

    // Constructor
    public Cattle(int id, String tag_id, String alias, String _time_stamp, String _tag_data) {
        this._id = id;
        this._tag_id = tag_id;
        this._alias = alias;
        this._time_stamp = _time_stamp;
        this._tag_data = _tag_data;
    }

    // Constructor
    public Cattle(String tag_id, String alias, String _time_stamp, String tag_data) {
        this._tag_id = tag_id;
        this._alias = alias;
        this._time_stamp = _time_stamp;
        this._tag_data = tag_data;
    }

    // getting ID
    public int getID() {
        return this._id;
    }

    // setting ID
    public void setID(int id) {
        this._id = id;
    }

    // getting tagID
    public String getTagID() {
        return this._tag_id;
    }

    // setting tagID
    public void setTagID(String tag_id) {
        this._tag_id = tag_id;
    }

    // getting alias
    public String getAlias() {
        return this._alias;
    }

    // setting alias
    public void setAlias(String alias) {
        this._alias = alias;
    }

    // getting time stamp
    public String getTimeStamp() {
        return this._time_stamp;
    }

    // setting time stamp
    public void setTimeStamp(String time_stamp) {
        this._time_stamp = time_stamp;
    }

    // getting tag data
    public String getTagData() {
        return this._tag_data;
    }

    // setting tag data
    public void setTagData(String tag_data) {
        this._tag_data = tag_data;
    }

}

编辑：我使用本教程构建我的SQLiteDatabase

---

关闭此行中的光标：

cursor.close();

然后试着用在那一个

return cursor.getCount();

这将不起作用，因为光标已关闭

您可以通过以下方式重写您的方法：

public int getCattleCount(){
    String countQuery = "SELECT  * FROM " + TABLE_CATTLE;
    SQLiteDatabase db = this.getReadableDatabase();
    Cursor cursor = db.rawQuery(countQuery, null);
    int count = cursor.getCount();
    cursor.close();
    db.close();
    return count;
}

您的

GetCown

应该是：

Cattle getCattle(int id){
    Cattle cattle = null;
    SQLiteDatabase db = this.getReadableDatabase();

    Cursor cursor = db.query(TABLE_CATTLE,  new String[] 
            {KEY_ID,  KEY_TAG_ID, KEY_ALIAS, KEY_TIME, KEY_DATA}, KEY_ID + "=?",
            new String[] {String.valueOf(id) }, null, null, null, null);
    if(cursor!=null) {
        if (cursor.moveToFirst()) {
            cattle = new Cattle(Integer.parseInt(cursor.getString(0)),
                cursor.getString(1),
                cursor.getString(2),
                cursor.getString(3),
                cursor.getString(4));
        }
        cursor.close();
    }
    db.close();//test
    return cattle;
} 

---

当我按照您的建议删除cursor.close（）行时，仍然会得到一个IllegalStateException，但是这次它会说“无法执行此操作，因为连接池已关闭”。这是同一行。它在执行以下行时无法返回整数：return cursor.getCount（）；隐马尔可夫模型。。现在我得到一个游标索引越界异常？在我看来，它似乎是在这条线上出现的：牛=cattleDb.gettown（牛i）；我在问题描述中添加了getBown方法。现在，我在deleteBown方法中得到一个空指针异常，在这里我调用了在我的BownBean类中定义的getID（）方法。我包括了我的JavaBean类和DeleteBown方法。