How to access Qt GUI from an library using qt designer form

[mrjj]

"QWidget: Must construct a QApplication before a QWidget"

That often comes from Global variables. Like in main.cpp

And as much as i wish, i cannot guess the reason for crash :)

Please show main.cpp.

[Srujan]

@mrjj
Actually in our case we are using some standard applications like cryptokimanager e.t.c..

[mrjj]

@Srujan said in how to access Qt GUI from an library using qt designer form:

@mrjj
Actually in our case we are using some standard applications like cryptokimanager e.t.c..

Meaning that there should not be any globals variables?
Try google
"QWidget: Must construct a QApplication before a QWidget"
and you see there are various reason for this message.

Most often the use of "extern" or static variables.

[Srujan]

@mrjj
Through normal application I am able to invoke QT GUI part.
Here my application code..

//
//main.cpp
//
#include <QCoreApplication>
#include"helper.h"
#include <QtWidgets/QApplication>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv); // previously its like QCoreApplication

    show_dialog1( );

    return a.exec();
}

//changes in .pro file
QT       += gui

greaterThan(QT_MAJOR_VERSION, 4): QT += widgets

After these changes in application project, able to invoke GUI part in shared library

But through our standard applications not able to invoke.

Any idea-
That what changes required for such applications....!!

Any way thanks for your support....

[SGaist]

Hi,

What are your "standard application" ?

[Srujan]

@SGaist
Its "cryptokimanager"

[SGaist]

Let me rephrase that: what toolkit does it use ?

Is it already using Qt ?

Are you building that app yourself or are you writing a plugin for it and have no access to its internals ?

[Srujan]

@SGaist
Its a tool for managing and validating a pkcs#11 module..
For more info please refer Cryptoki manager

[VRonin]

Can you post your code from which you call show_dialog1( ); ?

[Srujan]

@VRonin
simply I have called 'show_dialog1();' from one of exported functions in shared library..

[VRonin]

I suspect you are not creating the application. try Q_ASSERT(QCoreApplication::instance()); if it asserts (i.e. instance() returns NULL) then it means you simply forgot to crate the QApplication before creating any QWidget

[SGaist]

The question you are not answering is: are you working on that software code source directly ?

[Srujan]

@SGaist
yes

[SGaist]

Ok, then are you converting it to a full-blown Qt application ?

[Srujan]

@SGaist
If you are talking about- Cryptoki manager then i am not working on that application. I working on the library that is used to test with cryptokimanager(thrid party standard application).
As specified earlier, in my library there is a need of dialog part.

[SGaist]

So you are going to call the Cryptoki manager application from your code ?

[Srujan]

@SGaist
yes

[SGaist]

What's still not clear is whether you are writing a full-blown Qt application for that. Is it the case ?

[Srujan]

@SGaist yes now i have created separate qt application and invoking that application from library using pipe mechanism..
Now the issue is 'getting value from that application(what ever entered in qlineedit of dialog box)'

[jsulm]

@Srujan Your Qt application could write to stdout and your library would read stdout of that application and parse it. See the documentation for QProcess.