Question

我是Android编程的新手。我有一个包含电子邮件和密码的SQLite数据库，我想在新用户创建新帐户时检查用户是否已经存在。谁能帮我？这是我检查用户是否存在的方法。

            usersAcc.setEmailUser(e);
            usersAcc.setPasswordUser(a);
            String query = "SELECT email FROM Emails WHERE email='"+ usersAcc.getEmailUser() +"';";
            Cursor cursor = helper.sqlite.rawQuery(query, null);
            cursor.moveToFirst();
            if(cursor.moveToNext()){
                helper.intput(usersAcc);
                Toast toast = Toast.makeText(RegistrationForm.this, "OK!", Toast.LENGTH_LONG);
                toast.setGravity(Gravity.BOTTOM, 0,0);
                toast.show();
            }else{
                Toast toast = Toast.makeText(RegistrationForm.this, "Fail!", Toast.LENGTH_LONG);
                toast.setGravity(Gravity.BOTTOM, 0,0);
                toast.show();
            }

Answer 1

您没有正确使用光标移动，因为在移动到第一个之后您将移动到不存在的下一个，请使用以下方法：

usersAcc.setEmailUser(e);
usersAcc.setPasswordUser(a);
String query = "SELECT email FROM Emails WHERE email='"+ usersAcc.getEmailUser() +"';";
Cursor cursor = helper.sqlite.rawQuery(query, null);

if(cursor.moveToFirst()){
    helper.intput(usersAcc);
    Toast toast = Toast.makeText(RegistrationForm.this, "OK!", Toast.LENGTH_LONG);
    toast.setGravity(Gravity.BOTTOM, 0,0);
    toast.show();
}else{
    Toast toast = Toast.makeText(RegistrationForm.this, "Fail!", Toast.LENGTH_LONG);
    toast.setGravity(Gravity.BOTTOM, 0,0);
    toast.show();
}

Answer 2

不要使用if(cursor.moveToNext()) --->如果光标已经超出结果集中的最后一个条目，则此方法将返回false。

您应该使用if(cursorOBJECT.moveToFirst())。

将光标移到第一行。如果光标为空。

Cursor cursor=helper.sqlite.rawQuery("SELECT * FROM user WHERE email ='"+ usersAcc.getEmailUser()+"'", null);
if(cursor.moveToFirst())
{
 helper.intput(usersAcc);
                Toast toast = Toast.makeText(RegistrationForm.this, "OK!", Toast.LENGTH_LONG);
                toast.setGravity(Gravity.BOTTOM, 0,0);
                toast.show();
}
else
{
 Toast toast = Toast.makeText(RegistrationForm.this, "Fail!", Toast.LENGTH_LONG);
                toast.setGravity(Gravity.BOTTOM, 0,0);
                toast.show();
}

仅供参考

"java.lang.IllegalStateException: Could not execute method of the activity"

表示已在非法或不适当的时间调用了方法。换句话说，Java环境或Java应用程序未处于所请求操作的适当状态。

如果用户已经存在，如何检查SQLite数据库？

2 个答案: