Qt Creator ComboBox crashes everytime and doesn't display a drop down menu

Faris Elbaz

Everytime i try to connect to my SQL server to populate a Combobox the box and any other drop down widget no longer "drops down". This is the code im using

void mainwin::populateTableComboBox() {
    SqlFunc sqlFunc;
    QSqlDatabase db = sqlFunc.getDatabase();

    if (db.isOpen()) {
        QSqlQuery query(db);
        query.exec("SELECT name FROM sys.tables WHERE type = 'U'");

        combobox->clear();
        while (query.next()) {
            combobox->addItem(query.value(0).toString());
        }
    } else {
        qDebug() << "Failed to open the SQL Server connection.";
    }
}

The second i run this code and this code only it breaks Combobox for the whole project and i need to create a new one, i've done this 6 times until now.

Axel Spoerl

@Faris-Elbaz
If we are talking a QComboBox, this code can’t break it.
What exactly happens, how and when?

JonB

@Faris-Elbaz
Start by replacing combobox->addItem(query.value(0).toString()); by qDebug() << query.value(0).toString(); and see how your program goes. Also check the return result from the exec(). And try combobox->addItem("Hello"); instead of yours.

Faris Elbaz

@Axel-Spoerl basically when i run this exact line of code, the combo box stops displaying a drop down menu entirely. I've made multiple new projects to narrow it down and it only happens whenever populateTableComboBox (the code i wrote above) runs. And even when i comment it out or remove it from the code entirely, no matter how many new ui files i make the combobox does not work correctly

JonB

@Faris-Elbaz
You want to start by isolating whether the issue lies in reading from the database or adding items to a combobox. If you try carefully each of my suggestions in reply above you should discover where the problem manifests.

Faris Elbaz

@JonB Hi, so i tried replacing the line with

qDebug() << query.value(0).toString(); <

The issue is not that my code doesn't run or that it doesn't open/build the application, the problem is that when i do build the application the drop down menu itself doesn't work.
@Axel-Spoerl
i only have a limited amount of times i can post per 5 minutes so here is some additional information, QODBC does not work for me. Im on macbook running my SQL server through docker to azure data studio, when i try to connect to the server using QODBC it doesn't work and i have to use a normal ODBC connection string to connect to it like this

bool SqlFunc::connOpen() {
    // Allocate the environment handle
    SQLAllocHandle(SQL_HANDLE_ENV, SQL_NULL_HANDLE, &henv);
    SQLSetEnvAttr(henv, SQL_ATTR_ODBC_VERSION, (SQLPOINTER)SQL_OV_ODBC3, 0);

    // Allocate the connection handle
    SQLAllocHandle(SQL_HANDLE_DBC, henv, &hdbc);

    // Connection string
    // Replace the connection string with your actual connection details
    SQLCHAR* connectionString = (SQLCHAR*)"DRIVER={ODBC Driver 18 for SQL Server};SERVER=localhost;SqlFunc=HospitalDS;UID=sa;PWD=reallyStrongPwd123;Encrypt=no";

    // Connect to the SQL Server
    SQLRETURN ret = SQLDriverConnect(hdbc, NULL, connectionString, SQL_NTS, NULL, 0, NULL, SQL_DRIVER_COMPLETE);

    return ret == SQL_SUCCESS || ret == SQL_SUCCESS_WITH_INFO;
}

void SqlFunc::connClose() {
    if (hdbc!= nullptr) {
        SQLDisconnect(hdbc);
        SQLFreeHandle(SQL_HANDLE_DBC, hdbc);
    }
    if (henv!= nullptr) {
        SQLFreeHandle(SQL_HANDLE_ENV, henv);
    }
}

From all the debugging and analysis i've been doing over the past 2-3 days I believe it has something to do with that and that also somehow the query is executing at the same time as the designer causing errors. This is just my theory.

jsulm

@Faris-Elbaz said in Qt Creator ComboBox crashes everytime and doesn't display a drop down menu:

The issue is not that my code doesn't run or that it doesn't open/build the application

This is not what @JonB was suggesting. He suggested to do some debugging to see where the issue is. Why don't you follow his suggestions?