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

Srujan

Hi, I am new to QT. Here I just want to place QT GUI part like dialogs/windows in my library.
For that I have build my library by creating a new workspace under QT library.
Now I have created qt designer form that represents dialog part. But not able to access dialog part.
Here my code

//
//dialog.h
//
#ifndef DIALOG_H
#define DIALOG_H

#include <QDialog>

namespace Ui {
class Dialog;
}

class Dialog : public QDialog
{
    Q_OBJECT

public:
    explicit Dialog(QWidget *parent = 0);
    ~Dialog();

private:
    Ui::Dialog *ui;
};

#endif // DIALOG_H

//
// dialog.cpp
//
#include "dialog.h"
#include "ui_dialog.h"

Dialog::Dialog(QWidget *parent) :
    QDialog(parent),
    ui(new Ui::Dialog)
{
    ui->setupUi(this);
}// Dialog()

Dialog::~Dialog()
{
    delete ui;
}

//
// helper.h
//
#ifndef HELPER_H
#define HELPER_H

#include"dialog.h"

void show_dialog1( );

#endif // HELPER_H

//
// helper.cpp
//
#include"helper.h"

void show_dialog1( )
{
    Ui:Dialog *uiTestDlg;
    uiTestDlg->show();
}// show_dialog1()

when I tried to call this show_dialog1(), instead of invoking dialogs its getting crash..
Any suggestions for proper way of invoking qt gui from shared library..

Thanks in advance

jsulm

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

void show_dialog1( )
{
Ui:Dialog *uiTestDlg;
uiTestDlg->show();
}

Well, you are dereferencing a dangling pointer. You did not create any instance of Dialog. It should be:

void show_dialog1( )
{
    Ui::Dialog *uiTestDlg = new Ui::Dialog();
    uiTestDlg->show();
}

Srujan

This post is deleted!

Srujan

@jsulm I agree, but now getting error like-
invalid use of incomplete type..

mrjj

Hi
That means it want the include file

#include "dialog.h"
in same cpp file where u have
void show_dialog1( )

Srujan

@mrjj already made that update by referring from this link that you have answered earlier..
https://forum.qt.io/topic/58057/solved-invalid-use-of-incomplete-type-class-ui-mainwindow
Still getting same error...

mrjj

@Srujan
ok. then something is really wrong :)

Just to be 1000% sure. it still say same error if u do :

void show_dialog1( )
{
Dialog *uiTestDlg = new Dialog();
uiTestDlg->show();
}

and then
Build->clean all
Build->qmake
Build->Rebuild all.

Srujan

@mrjj
Able to build, but when trying to access from app its again getting crash..
And in console its showing error like "QWidget: Must construct a QApplication before a QWidget"

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 ?