QDialogs

Remarks#

The QDialog class is the base class of dialog windows. A dialog window is a top-level window mostly used for short-term tasks and brief communications with the user. QDialogs may be modal or modeless.

Note that QDialog (and any other widget that has type Qt::Dialog) uses the parent widget slightly differently from other classes in Qt. A dialog is always a top-level widget, but if it has a parent, its default location is centered on top of the parent’s top-level widget (if it is not top-level itself). It will also share the parent’s taskbar entry.

A modal dialog is a dialog that blocks input to other visible windows in the same application. Dialogs that are used to request a file name from the user or that are used to set application preferences are usually modal. Dialogs can be application modal (the default) or window modal.

The most common way to display a modal dialog is to call its exec() function. When the user closes the dialog, exec() will provide a useful return value.

A modeless dialog is a dialog that operates independently of other windows in the same application. Modeless dialogs are displayed using show(), which returns control to the caller immediately.

MyCompareFileDialog.h

#ifndef MYCOMPAREFILEDIALOG_H
#define MYCOMPAREFILEDIALOG_H

#include <QtWidgets/QDialog>

class MyCompareFileDialog : public QDialog
{
    Q_OBJECT

public:
    MyCompareFileDialog(QWidget *parent = 0);
    ~MyCompareFileDialog();
};


#endif // MYCOMPAREFILEDIALOG_H

MyCompareFileDialogDialog.cpp

#include "MyCompareFileDialog.h"
#include <QLabel>

MyCompareFileDialog::MyCompareFileDialog(QWidget *parent)
: QDialog(parent)
{
    setWindowTitle("Compare Files");
    setWindowFlags(Qt::Dialog);
    setWindowModality(Qt::WindowModal);

    resize(300, 100);
    QSizePolicy sizePolicy(QSizePolicy::Preferred, QSizePolicy::Preferred);
    setSizePolicy(sizePolicy);
    setMinimumSize(QSize(300, 100));
    setMaximumSize(QSize(300, 100));

    QLabel* myLabel = new QLabel(this);
    myLabel->setText("My Dialog!");
}

MyCompareFileDialog::~MyCompareFileDialog()
{ }

MainWindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>

namespace Ui {
class MainWindow;
}

class MyCompareFileDialog;

class MainWindow : public QMainWindow
{
    Q_OBJECT

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

private:
    Ui::MainWindow *ui;
    MyCompareFileDialog* myDialog;
};

#endif // MAINWINDOW_H

MainWindow.cpp

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include "mycomparefiledialog.h"

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

    myDialog = new MyCompareFileDialog(this);

    connect(ui->pushButton,SIGNAL(clicked()),myDialog,SLOT(exec()));
}

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

main.cpp

#include "mainwindow.h"
#include <QApplication>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;
    w.show();

    return a.exec();
}

mainwindow.ui

<?xml version="1.0" encoding="UTF-8"?>
<ui version="4.0">
 <class>MainWindow</class>
 <widget class="QMainWindow" name="MainWindow">
  <property name="geometry">
   <rect>
    <x>0</x>
    <y>0</y>
    <width>400</width>
    <height>300</height>
   </rect>
  </property>
  <property name="windowTitle">
   <string>MainWindow</string>
  </property>
  <widget class="QWidget" name="centralWidget">
   <widget class="QPushButton" name="pushButton">
    <property name="geometry">
     <rect>
      <x>140</x>
      <y>80</y>
      <width>111</width>
      <height>23</height>
     </rect>
    </property>
    <property name="text">
     <string>Show My Dialog</string>
    </property>
   </widget>
  </widget>
  <widget class="QMenuBar" name="menuBar">
   <property name="geometry">
    <rect>
     <x>0</x>
     <y>0</y>
     <width>400</width>
     <height>21</height>
    </rect>
   </property>
  </widget>
  <widget class="QToolBar" name="mainToolBar">
   <attribute name="toolBarArea">
    <enum>TopToolBarArea</enum>
   </attribute>
   <attribute name="toolBarBreak">
    <bool>false</bool>
   </attribute>
  </widget>
  <widget class="QStatusBar" name="statusBar"/>
 </widget>
 <layoutdefault spacing="6" margin="11"/>
 <resources/>
 <connections/>
</ui>