8. QT-Dialog (modal and non-modal)

Dialog introduction

Dialogs are top-level windows for easy user interaction
QDialog is the parent class of all dialog windows in Qtand is a container type component
QDialog inherits from the QWidget class, as shown in the following figure:

What is the difference between QWidget and QDialog

QDialog:

QDialog is a special QWidget with customized window styles
QDialog can only be used as a dedicated interactive window
QDialog cannot be used as a sub-component , embedded in other containers

QWidget:

If QWidget has no parent component , it will become a main window,
If QWidget has a parent component , it will become a child component of its parent component and embedded in its parent component

Code test: difference between QWidget and QDialog

Code 1:

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    QWidget w;
    w.resize(300,300);

    QDialog d(&w);
    d.resize(150,150);

    w.show();
    d.show();

    return a.exec();
}

Effect:

As you can see, the dialog is always used as an independent interactive window

Code 2:

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    QWidget w1;
    w1.resize(300,300);

    QWidget w2(&w1);
    w2.resize(150,150);

    w1.show();
    w2.show();

    return a.exec();
}

Effect:

You can see that only one window appears, and the second window does not appear

dialog type

modal dialog

It is a blocking call , which means that it is impossible to interact with any other window until the dialog box is closed.
Used for occasions that depend on user selection, such as: option settings, message prompts, font settings, etc.
Creating a modal dialog on the stack is the easiest and most common way
Use exec() to enter the message loop of the dialog box to achieve blocking calls

Experimental code:

int main(int argc, char *argv[])
{

    QApplication a(argc, argv);

    QWidget w;
    w.resize(300,300);
    w.show();

    QDialog  d(&w);
    d.resize(150,150);
    d.exec();          // Enter the message loop of dialog box d to realize blocking call

    return a.exec();
}

Modeless dialog

It is a non-blocking call , indicating that when the dialog box appears, it can also interact with the parent window
Used for special function settings, such as: search operation
In general, non-modal dialogs need to be created on the heap to avoid being automatically destroyed
Modeless dialogs need to specify the Qt::WA_DeleteOnClose attribute through the setAttribute() member function
Qt::WA_DeleteOnClose means: After exiting the window, let Qt automatically destroy the dialog
Use show() to display the dialog window, thus achieving a non-blocking call

Experimental code:

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    QWidget w;
    w.resize(300,300);
    w.show();

    QDialog  *d = new QDialog(&w);

    d->setAttribute(Qt::WA_DeleteOnClose);
    d->resize(150,150);
    d->show();                

    return a.exec();
}

混合模态对话框

在非模态对话框的基础上调用QDialog::setModal(true)成员函数实现

实验代码:

int main(int argc, char *argv[])
{

    QApplication a(argc, argv);

    QWidget w;
    w.resize(300,300);
    w.show();

    QDialog  *d = new QDialog(&w);
    d->setAttribute(Qt::WA_DeleteOnClose);
    d->setModal(true);               
    d->resize(150,150);
    d->show();

    return a.exec();
}

对话框返回值处理

只有模态对话框才有返回值概念
QDialog::exec()的返回值作为交互结果

　　-使用void QDialog::done ( int r ) 作为交互结果,将r值返回给exec()

　　-返回值为QDialog::Accepted时,表示用户操作成功

　　-返回值为QDialog::Rejected时,表示用户操作失败

　　-也可以自定义返回数值

8. QT-Dialog (modal and non-modal)

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