displaying second form called by first form with database table of mysql.

[high_flyer]

and.... what is the problem you are facing?

[rahulvishwakarma]

sorry i lost my project when my system (computer) suddenly crashed. but same thing i made up and found this problem:
thsi is my myappmainwindow.cpp :-

#include "myappmainwindow.h"
#include "ui_myappmainwindow.h"
 
MyappMainWindow::MyappMainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MyappMainWindow)
{
    ui->setupUi(this);
 
    db = new QSqlDatabase(QSqlDatabase::addDatabase("QMYSQL"));
    db->setHostName("oracle");
    db->setDatabaseName("test");
    db->setUserName("rahul");
    db->setPassword("rahul");
    db->setPort(3306);
 
    query = new QSqlQuery(*db);
}
 
MyappMainWindow::~MyappMainWindow()
{
    db->close();
    delete ui;
}
 
void MyappMainWindow::on_pushButtonLogin_clicked()
{
    QString su = ui->lineEditUserName->text().trimmed();
    QString sp = ui->lineEditPassword->text().trimmed();
 
    dlg = new sqlqueymodelDialog();
 
    if(db->open())
    {
 
        QString strquery = "select * form artist";
            dlg->model = new QSqlQueryModel();
            dlg->model->setQuery(strquery);
 
            dlg->tableiew->setModel(model);//here program crashes
            dlg->show();
            dlg->exec();
    }
}

#include "myappmainwindow.h"
#include "ui_myappmainwindow.h"

MyappMainWindow::MyappMainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MyappMainWindow)
{
    ui->setupUi(this);

    db = new QSqlDatabase(QSqlDatabase::addDatabase("QMYSQL"));
    db->setHostName("oracle");
    db->setDatabaseName("test");
    db->setUserName("rahul");
    db->setPassword("rahul");
    db->setPort(3306);

    query = new QSqlQuery(*db);
}

MyappMainWindow::~MyappMainWindow()
{
    db->close();
    delete ui;
}

void MyappMainWindow::on_pushButtonLogin_clicked()
{
    QString su = ui->lineEditUserName->text().trimmed();
    QString sp = ui->lineEditPassword->text().trimmed();

    dlg = new sqlqueymodelDialog();

    if(db->open())
    {

        QString strquery = "select * form artist";
            dlg->model = new QSqlQueryModel();
            dlg->model->setQuery(strquery);

            dlg->tableiew->setModel(model);//here program crashes
            dlg->show();
            dlg->exec();
    }
}

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this is myappmainwindow.h

#ifndef MYAPPMAINWINDOW_H
#define MYAPPMAINWINDOW_H
 
#include <QMainWindow>
#include "sqlqueymodeldialog.h"
#include <QtSql>
#include <QMessageBox>
 
namespace Ui {
class MyappMainWindow;
}
 
class MyappMainWindow : public QMainWindow
{
    Q_OBJECT
 
public:
    explicit MyappMainWindow(QWidget *parent = 0);
    ~MyappMainWindow();
 
private slots:
    void on_pushButtonLogin_clicked();
 
private:
    Ui::MyappMainWindow *ui;
    sqlqueymodelDialog * dlg;
    QSqlDatabase *db;
    QSqlQuery *query;
    //QSqlQueryModel *model;
 
};
 
#endif // MYAPPMAINWINDOW_H

#ifndef MYAPPMAINWINDOW_H
#define MYAPPMAINWINDOW_H

#include <QMainWindow>
#include "sqlqueymodeldialog.h"
#include <QtSql>
#include <QMessageBox>

namespace Ui {
class MyappMainWindow;
}

class MyappMainWindow : public QMainWindow
{
    Q_OBJECT

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

private slots:
    void on_pushButtonLogin_clicked();

private:
    Ui::MyappMainWindow *ui;
    sqlqueymodelDialog * dlg;
    QSqlDatabase *db;
    QSqlQuery *query;
    //QSqlQueryModel *model;

};

#endif // MYAPPMAINWINDOW_H

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here is sqlquerymodel.h

#ifndef SQLQUEYMODELDIALOG_H
#define SQLQUEYMODELDIALOG_H
 
#include <QDialog>
#include <QtSql>
#include <QtWidgets>
 
namespace Ui {
class sqlqueymodelDialog;
}
 
class sqlqueymodelDialog : public QDialog
{
    Q_OBJECT
 
public:
    explicit sqlqueymodelDialog(QWidget *parent = 0);
    ~sqlqueymodelDialog();
 
private:
    Ui::sqlqueymodelDialog *ui;
 
protected:
     QSqlQueryModel  *model;
 
public:
   // QTableView *tableView;
 
};
 
#endif // SQLQUEYMODELDIALOG_H

#ifndef SQLQUEYMODELDIALOG_H
#define SQLQUEYMODELDIALOG_H

#include <QDialog>
#include <QtSql>
#include <QtWidgets>

namespace Ui {
class sqlqueymodelDialog;
}

class sqlqueymodelDialog : public QDialog
{
    Q_OBJECT

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

private:
    Ui::sqlqueymodelDialog *ui;

protected:
     QSqlQueryModel  *model;

public:
   // QTableView *tableView;

};

#endif // SQLQUEYMODELDIALOG_H

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now how can i access dlg(second dialog) gui component(for example tableviewloginform added using Qt Creator) from myappmainwoindow.cpp.

[d_stranz]

//here program crashes

The code you have posted won't even compile, much less run. Your SQL query has a typo ("form" instead of "from") so it won't execute anyway.

If you want to give a pointer to the model to your dialog, then simply implement a public method in the dialog class (setModel( QSqlQueryModel * ) or something like that) and call it from your main window class.

This is a basic C++ issue. Surely when you learned C++, you were taught about classes, encapsulation, member variables, and member functions. If you don't remember, then go back and study some more.

[rahulvishwakarma]

I added public function :-

void setmodel(QSqlQueryModel *model);

void setmodel(QSqlQueryModel *model);

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in sqlquerymodelDialog.h

and in CPP file
---
i added :-

void sqlqueymodelDialog::setmodel(QSqlQueryModel *model)
{
    ui->tableviewforms->setModel(model);
}

void sqlqueymodelDialog::setmodel(QSqlQueryModel *model)
{
    ui->tableviewforms->setModel(model);
}

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in file myappmainwindows.cpp
----------------------------

this shows only sqlqueymodelDialog form but without having mysql database table in it's tableviewLoginForm( QTableview component);
i wanto show sqlsqlquerymodel.ui calling from myappaminwindows.cpp, with dataqbase query fired by myappaminwindows object like this :

void MyappMainWindow::on_pushButtonLogin_clicked()
{
    QString su = ui->lineEditUserName->text().trimmed();
    QString sp = ui->lineEditPassword->text().trimmed();
 
    if(db->open())
    {
        dlg = new sqlqueymodelDialog(this);
        model = new QSqlQueryModel();//   QSqlQueryModel *model as private 
         query = new QSqlQuery("select * from artist");
         model->setQuery(*query);
         dlg->setmodel(model);
 
           // dlg->exec();
            dlg->show();
            dlg->activateWindow();
   }
}

void MyappMainWindow::on_pushButtonLogin_clicked()
{
    QString su = ui->lineEditUserName->text().trimmed();
    QString sp = ui->lineEditPassword->text().trimmed();

    if(db->open())
    {
        dlg = new sqlqueymodelDialog(this);
        model = new QSqlQueryModel();//   QSqlQueryModel *model as private 
         query = new QSqlQuery("select * from artist");
         model->setQuery(*query);
         dlg->setmodel(model);

           // dlg->exec();
            dlg->show();
            dlg->activateWindow();
   }
}

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[high_flyer]

Try getting the last error after setQuery(), may be this will give you a hint where the problem is.
http://doc.qt.io/qt-5/qsqlquerymodel.html#setQuery

lastError() can be used to retrieve verbose information if there was an error setting the query.

P.S
Your code leaks memory like a net trying to hold water.
Make sure you know what happens with each object you allocate on the heap and remember that any QObject can be assigned another QObject as parent which will ensure that when a parent is destroyed, all its children are destroyed as well saving you a lot of pointer house keeping.