To implement modeless dialogs, simply change the exec() method to the show() method.

Click the “new” button of the menu bar will pop up a modeless dialog box function, the code is as follows:

#include "MainWindow.h"
#include "ui_MainWindow.h"
#include <QMenuBar>
#include <QMenu>
#include <QDebug>
#include <QToolBar>
#include <QPushButton>
#include <QStatusBar>
#include <QLabel>
#include <QTextEdit>
#include <QDockWidget>
#include <QDialog>
MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    // This part of the code is omitted. PCreate is the pointer to the QAction object defined in the omitted code
    connect(pCreate,&QAction::triggered,[=](){
        QDialog mDialog;
        mDialog.show(a);qDebug() < <"1111";
    });
 
}
 
MainWindow::~MainWindow()
{
    delete ui;
}
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Effect:

You can see (?) When I click On New, there’s a dialog box that does appear,But then it disappeared. At the same time, the console also prints the contents of “1111”, indicating that modeless dialogs do not need to wait for user feedback before executing the code after the show() method.

But! Why did the dialog box disappear?

This is because the mDialog is defined on the stack and is also a local variable. When it leaves the function body, it is automatically reclaimed by memory, so it no longer exists and therefore disappears.

To solve this problem, the mDialog can be made a member variable of the main window class, or it can be dynamically allocated memory using the new keyword, so that it will only disappear when we manually free the memory using the delete keyword.

#include "MainWindow.h"
#include "ui_MainWindow.h"
#include <QMenuBar>
#include <QMenu>
#include <QDebug>
#include <QToolBar>
#include <QPushButton>
#include <QStatusBar>
#include <QLabel>
#include <QTextEdit>
#include <QDockWidget>
#include <QDialog>
MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    // This part of the code is omitted. PCreate is the pointer to the QAction object defined in the omitted code
    connect(pCreate,&QAction::triggered,[=](){
        QDialog *mDialog=new QDialog(this);    // Dynamically apply for memory
        mDialog->show(a);qDebug() < <"1111";
    });
 
}
 
MainWindow::~MainWindow()
{
    delete ui;
}
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Effect:

So that’s where the dialog stays. When we close the main window, the dialog disappears. At this point, although we do not manually free memory by delete, since its parent element (the main window) is closed, the program ends and its destructor is called, so the destructors of all its children are also called and are destructed before the main window. [See: blog.csdn.net/weixin_4100…]

Note: One disadvantage of using dynamic memory allocation is that it only releases memory at the end of the program. If you click the “New” button too often, you will dynamically allocate memory multiple times, which also causes memory leak problems. Therefore, it is best to define the dialog box as a member variable of the main window class. Or, after dynamically allocating memory space, add a line of code that automatically frees memory each time a dialog box is closed.

QDialog *mDialog=new QDialog(this);         
mDialog->setAttribute(Qt::WA_DeleteOnClose);    // Reclaim memory while closing the dialog box
mDialog->show(a);Copy the code

Standard dialog and file dialog

The about method is used if you want to implement a dialog box that is often used in a program to describe software products to the user and only requires the user to click an “I know” button.

Call the About () function of the QMessageBox class, whose arguments are known from the help documentation as “parent”, “title”, and “content”.

#include "MainWindow.h"
#include <QMenuBar>
#include <QMenu>
#include <QDebug>
#include <QToolBar>
#include <QPushButton>
#include <QStatusBar>
#include <QLabel>
#include <QTextEdit>
#include <QDockWidget>
#include <QDialog>
#include <QMessageBox>    // The header file that must be imported to use the standard dialog box
MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
{
    PCreate is a QAction pointer variable defined in the ellipsis code
        connect(pCreate,&QAction::triggered,[=](){
            QMessageBox::about(this."create"."New");
        });
}
 
MainWindow::~MainWindow() {}Copy the code

Effect:

You can see that clicking the “New” button will bring up a modal dialog box titled “Create” with the content “New”.

P. :

Implementing the standard dialog with the following code looks the same.

connect(pCreate,&QAction::triggered,[=](){    
    QMessageBox pMessageBox;                  
    pMessageBox.about(this."haha"."hoho");    
    / / QMessageBox: : about (this, "create", "new");
});                                           
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File dialog box is also very common, for example, we often need to open an existing project in a program, this time will pop up a file dialog box. When we select the target file and click OK, the complete absolute path to the file is returned to us as a string.

To use the file dialog, you must first import header files.

If we want to get the path to an open file, we call the getOpenFileName method.

P. :

The first parameter, parent, specifies the parent component. Note that many Qt component constructors take the parent argument and provide a default value of 0; The second argument, caption, is the dialog’s title; The third parameter, dir, is the default directory to open when the dialog is displayed.”.” represents the program running directory, and “/” represents the root directory of the current drive letter (on Windows, Linux/is the root directory). It can also be platform-specific, such as “C:\”, etc. For example, if I want to open the Data folder in the program run directory as the default path, I should write it as “./Data/”. If I want to have a file selected by default, I can add the file name after the directory: “./Data/teaser.graph” the fourth parameter filter is the extension name filter of the dialog box. For example, we use “Image Files(.jpg.png)” to make it only display JPG or PNG Files. If you need to use multiple filters, use “;;”. Split, such as “JPEG Files(.jpg); PNG Files (. PNG) “; The fifth parameter, selectedFilter, is the default filter selected; The sixth parameter options, are some of the parameters setting dialog box, only show the folder, and so on, for example, it is the value of enum QFileDialog: : Option, each of these options can be combined in use | operation. What if I want to select multiple files? Qt provides the getOpenFileNames() function, which returns a QStringList. You can think of it as a List that only holds QStrings, the List in the STL.

[From: blog.csdn.net/qq_38400517…]

connect(pCreate,&QAction::triggered,[=](){         
   QFileDialog::getOpenFileName(this."open".".. /");    // Relative path is the parent directory of the current program path
}); 
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Effect:

If we also want to specify a range of file types, we need to set the filter parameter. Different file names of the same type are separated by Spaces, and files of different types are separated by;; Space.

connect(pCreate,&QAction::triggered,[=](){
    QFileDialog::getOpenFileName(this."open".".. /"."source(*.cpp *.h);; image(*.jpg *.bmp);; all(*.*)");
});  
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P.S: if you think the string is too long, you can use the Enter key to wrap it, and C++ will automatically add missing double quotes.

Effect:

P.S: If there is any error, welcome to correct ~