Problem with QProgressDialog

[anoraxis]

I'm using a QProgressDialog with the limits (0, 0) to show something during a sqlite query and preparing the results to show. The QProgressDialog window stays in blank all the time, not matter if the process took 1 second or minute. My code is something like:

QProgressDialog dialog(this);
    dialog.setLabelText("Updating");
    dialog.setMinimun(0)
    dialog.setMaximum(0);
    dialog.show();
    try
    {
        // here I call a function that executes a sql query to a sqlite database and then updates the whole interface with the result.
        dialog.accept();
    }
    catch (QString e)
    {
        QMessageBox::critical(this, "Error - " + qApp->applicationName(), e);
        qApp->exit(1);
    }

QProgressDialog dialog(this);
    dialog.setLabelText("Updating");
    dialog.setMinimun(0)
    dialog.setMaximum(0);
    dialog.show();
    try
    {
        // here I call a function that executes a sql query to a sqlite database and then updates the whole interface with the result.
        dialog.accept();
    }
    catch (QString e)
    {
        QMessageBox::critical(this, "Error - " + qApp->applicationName(), e);
        qApp->exit(1);
    }

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Reading other post I have seen that in cases of a long during process is better to use another thread instead of the main one. It's this correct? Can I block the program during the process so the user can't interact with it when using another thread?

[wysota]

Sql query blocks your application so that the progress bar doesn't have a chance to update itself. You can experiment with executing the query in a thread.

[mvuori]

As far as I understand, at least the title should appear before going into the blocking part.

Perhaps the UI operations are cached and need some extra help. I have sometimes added a xxxxx.update() after a xxxxx.show() to make a widget visible.

[wysota]

As far as I understand, at least the title should appear before going into the blocking part.

No. For the window to appear, events need to be processed.

[Lesiok]

As far as I understand, at least the title should appear before going into the blocking part.

Perhaps the UI operations are cached and need some extra help. I have sometimes added a xxxxx.update() after a xxxxx.show() to make a widget visible.

After widget show add QCoreApplication::processEvents. But the best solution is to move SQL operations to another thread.

[anoraxis]

Ok, thanks. I will the sql part to another thread.

Another thing, in my case the title of the QProgressDialog is the only element that appears, the rest of the dialog is blank.