Qt中show()与exec()

1. show()默认显示的是非模态对话框,即此对话框出现后你还可以对其他窗口进行操作,可以用setModal函数进行设置窗口为模态,即无法操作其他窗口,即被阻塞. 而exec()出现的只能是模态对话框.

2. show()显示的窗口无论是否模态,都立刻将操作权返回, 运行下面代码;而exec()则是得等待exec出的窗口关闭后再运行下面代码.

qt帮助文档那个中写的是:Shows the dialog as a modal dialog, blocking until the user closes it. The function returns a DialogCode result., 返回的DialogCode 有QDialog::Accepted和QDialog::Rejected,可以根据返回值来进行判断等操作.

下面是一个小程序:

#ifndef DIALOG1_H
#define DIALOG1_H

#include <QDialog>
#include "ui_dialog1.h"

class dialog1 : public QDialog
{
	Q_OBJECT

public:
	dialog1(QWidget *parent = 0);

protected slots:
		void buttonClicked();

private:
	Ui::dialog1 ui;
};

#endif // DIALOG1_H

</pre><pre name="code" class="cpp">/*multiwindow.h*/

#ifndef MULTIWINDOW_H
#define MULTIWINDOW_H
#include "dialog1.h"
#include <QtWidgets/QMainWindow>
#include "ui_multiwindow.h"

class multiWindow : public QMainWindow
{
	Q_OBJECT

public:
	multiWindow(QWidget *parent = 0);

public slots:
		void button1Clicked();

private:
	Ui::multiWindowClass ui;
	dialog1 *dialog;

};

#endif // MULTIWINDOW_H

/*dialog1.cpp*/

#include "dialog1.h"

dialog1::dialog1(QWidget *parent)
	: QDialog(parent)
{
	ui.setupUi(this);
	connect(ui.pushButton, SIGNAL(clicked()), this, SLOT(buttonClicked()));
}

void dialog1::buttonClicked()
{
	this->close();
}

/*multiwindow.cpp*/

#include "multiwindow.h"

multiWindow::multiWindow(QWidget *parent)
	: QMainWindow(parent)
{
	ui.setupUi(this);
	connect(ui.pushButton, SIGNAL(clicked()), this, SLOT(button1Clicked()));
	connect(ui.pushButton_3, SIGNAL(clicked()), this, SLOT(close()));
	dialog = new dialog1(this);

}

void multiWindow::button1Clicked()
{
	this->hide();
	//dialog->show();
	dialog->exec();
	this->show();
}

/*main.cpp*/

#include "multiwindow.h"
#include <QtWidgets/QApplication>

int main(int argc, char *argv[])
{
	QApplication a(argc, argv);
	multiWindow w;
	w.show();
	return a.exec();
}

重点是multiwindow.cpp中的

 <span style="white-space:pre">	</span>this->hide();
	dialog->exec();
	this->show();

当按下按钮时,先将主窗口隐藏,然后显示exec的模态对话框,不继续执行下面代码,等待对话框的操作, 按下对话框的按钮后,对话框关闭,继续执行主对话框代码,将主对话框显示,即实现对话框的调用.

若将exec替换为show,则会出现两个对话框并存的现象.