Question

我一直试图阻止在数据库为空时意外点击删除按钮。点击后它会崩溃。

数据库处理程序

public void deleteLastMessage(Class a) {
    SQLiteDatabase db = this.getWritableDatabase();
    db.delete(TABLE_NAME, KEY_MSG + " = ?",
            new String[] { String.valueOf(a.get_message()) });
    db.close();
}
public String getLastString() {

    String selectQuery = "SELECT  * FROM " + TABLE_NAME;
    SQLiteDatabase db = this.getReadableDatabase();
    Cursor cursor = db.rawQuery(selectQuery, null);
    cursor.moveToLast();
    LastString = cursor.getString(0);
    cursor.close();
    db.close();
    return LastString;
}

活动

public void deleteMessage(View v) {
    LastMessage = new SubliminalClass(db.getLastString());
    db.deleteLastMessage(LastMessage);

当有数据要删除时，它正常工作，没有数据时崩溃。我的数据是一列字符串。提到这个Application crashes while reading an empty table in android但无济于事。

我在下面尝试了这个，但是在没有数据时仍然崩溃了。

public boolean checkdb(){
    SQLiteDatabase db = this.getReadableDatabase();
    Cursor mCursor = db.rawQuery("SELECT * FROM " + TABLE_NAME, null);
    Boolean rowExists;
    String nullString="";
    if (nullString.equals(getLastString())) //todo change this
        // DO SOMETHING WITH CURSOR
        rowExists = false;

    else
    {
        // I AM EMPTY
        rowExists = true;
    }
    return rowExists;
}

任何人都可以帮我解决这个问题吗？

Answer 1

试试这个

检查表row count is greater than zero然后执行删除操作。

//添加您的活动

int rowCount = db.getRowCount();
    db.close();


if(rowCount>0)
{
db.deleteLastMessage(LastMessage);
}else{

}

//在DBhelperClass中添加

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



public void deleteLastMessage(Class a) {
 try{
    SQLiteDatabase db = this.getWritableDatabase();
    db.delete(TABLE_NAME, KEY_MSG + " = ?",
            new String[] { String.valueOf(a.get_message()) });
    db.close();
     } catch (Exception e){
            e.printStackTrace();
    }
}

Answer 2

您可以在删除代码周围添加try / catch。

checkdb函数也可以像这样

public boolean checkdb(){
    SQLiteDatabase db = this.getReadableDatabase();
    Log.d(TAG,"Got Readable DB")
    Cursor mCursor = db.rawQuery("SELECT * FROM " + TABLE_NAME, null);
    Boolean rowExists = false;
    String nullString="";
    if(mCursor != null){
        Log.d(TAG,"Cursor is not null")
        try{
            rowExists = mCursor.getCount() > 0;
            Log.d(TAG,"rowExists is " + rowExists);
            mCursor.close();
        } catch (Exception e){
            e.printStackTrace();
        }
    }
    return rowExists;
}

删除空数据库后如何防止应用程序崩溃

2 个答案: