Qt多文档程序的一种实现

注：文中所列代码质量不高，但不影响演示我的思路

实现思路说明

实现DemoApplication
相当于MFC中CWinAppEx的派生类，暂时没加什么功能。
DemoApplication.h

#pragma once

#include <QtWidgets/QApplication>


//相当于MFC中CWinAppEx的派生类，
class DemoApplication : public QApplication
{
	Q_OBJECT

public:
	DemoApplication(int &argc, char **argv);
	~DemoApplication();

};

DemoApplication.cpp

#include "DemoApplication.h"


DemoApplication::DemoApplication(int &argc, char **argv)
	: QApplication(argc, argv)
{
}

DemoApplication::~DemoApplication()
{
}

实现DemoDocument
相当与MFC的CDocument。DemoDocument保存了当前所有视图的指针（此处实际是DeomChildWindow*，因为DeomChildWindow与DeomView时1对1关系，根据DeomChildWindow可以获得DemoView指针，简化设计，就这样处理了），实现了增加视图addView、移除视图removeView、获取视图数量getViewCount等函数。
DemoDocument.h

#pragma once

#include <QObject>
#include <list>

class DemoChildWindow;

//相当与MFC的CDocument
class DemoDocument : public QObject
{
	Q_OBJECT

public:
	DemoDocument(QObject *parent = 0);
	~DemoDocument();

	void addView(DemoChildWindow* pChildWindow);
	void removeView(DemoChildWindow* pChildWindow);
	int getViewCount() const;

	unsigned int getId() { return m_nId; }

signals:
	void closedDocument(DemoDocument* pDocument);

private:
	static unsigned int allocId();

private:
	static unsigned int s_NextId;
	unsigned int m_nId = 0;

	std::list<DemoChildWindow*> m_viewList; //视图列表
};

DemoDocument.cpp

#include "DemoDocument.h"


unsigned int DemoDocument::s_NextId = 0;

DemoDocument::DemoDocument(QObject *parent)
	: QObject(parent)
{
	m_nId = allocId();
}

DemoDocument::~DemoDocument()
{
}

unsigned int DemoDocument::allocId()
{
	if (DemoDocument::s_NextId == std::numeric_limits<unsigned int>::max())
	{
		DemoDocument::s_NextId = 0;
	}

	return ++DemoDocument::s_NextId;
}


void DemoDocument::addView(DemoChildWindow* pChildWindow)
{
	m_viewList.push_back(pChildWindow);
}

void DemoDocument::removeView(DemoChildWindow* pChildWindow)
{
	auto it = std::find(m_viewList.begin(), m_viewList.end(), pChildWindow);
	if (it != m_viewList.end() )
	{
		m_viewList.erase(it);
	}

	if (m_viewList.size() == 0)
	{
		emit closedDocument(this);
	}
}

int DemoDocument::getViewCount() const
{
	return int(m_viewList.size());
}

实现DemoMainWindow
相当于MFC中的CMainFrame，派生自CMDIFrameWndEx。此类new了一个QMdiArea对象，通过此对象实现多文档程序的通用功能，如切换窗口、层叠窗口、平铺窗口等。类DemoMainWindow直接管理了所有打开的文档，这点同MFC不一样，MFC是通过文档管理器、文档模版处理的，此处简化下，直接在DemoMainWindow中管理。此处我让DemoMainWindow负责新建、打开、关闭文档。
DemoMainWindow.h

#pragma once

#include <QtWidgets/QMainWindow>
#include <QMdiArea>
#include <list>
#include <memory>


class DemoDocument;

//相当于MFC中的CMainFrame，派生自CMDIFrameWndEx
class DemoMainWindow : public QMainWindow
{
	Q_OBJECT

public:
	DemoMainWindow(QWidget *parent = Q_NULLPTR);
	virtual ~DemoMainWindow();

	DemoDocument* getActiveDocument() const;

protected slots:
	void onSlotNewDocument();
	void onSlotClosedDocument(DemoDocument* pDocument );
	void onSlotNewWindow();

private:
	//创建文档的一个视图（DemoChildWindow-DeomView）
	void createNewWindow(DemoDocument* pDocument );

private:
	QMdiArea* m_pMDIArea = nullptr;
	std::list<DemoDocument*> m_DocList; //文档列表
};

DemoMainWindow.cpp

#include "DemoMainWindow.h"
#include "DemoDocument.h"
#include "DemoChildWindow.h"

#include <QMdiSubWindow>
#include <QMenuBar>


DemoMainWindow::DemoMainWindow(QWidget *parent)
	: QMainWindow(parent)
{
	m_pMDIArea = new QMdiArea();
	this->setCentralWidget(m_pMDIArea);

	//void subWindowActivated(QMdiSubWindow * window)

	//菜单
	QMenu* pFileMenu = menuBar()->addMenu(QStringLiteral("文件"));
	QAction* pNewDocAction = new QAction(QStringLiteral("新建"), this);
	connect(pNewDocAction, SIGNAL(triggered()), this, SLOT(onSlotNewDocument()));
	pFileMenu->addAction(pNewDocAction);
	
	//窗口（实际需要动态添加到菜单栏中，即有视图窗口打开，就加入，否则就移除，此处暂未实现）
	QMenu* pWinMenu = menuBar()->addMenu(QStringLiteral("窗口"));
	QAction* pNewWinAction = new QAction(QStringLiteral("新建"), this);
	connect(pNewWinAction, SIGNAL(triggered()), this, SLOT(onSlotNewWindow()));
	pWinMenu->addAction(pNewWinAction);

}

DemoMainWindow::~DemoMainWindow()
{
	for (auto pDoc : m_DocList)
	{
		delete pDoc;
	}
	m_DocList.clear();
}

void DemoMainWindow::onSlotNewDocument()
{
	auto pNewDoc = new DemoDocument();
	m_DocList.push_back(pNewDoc);
	createNewWindow(pNewDoc);

	connect(pNewDoc, SIGNAL(closedDocument(DemoDocument*)), 
		this, SLOT(onSlotClosedDocument(DemoDocument*)));
}

void DemoMainWindow::onSlotClosedDocument(DemoDocument* pDocument)
{
	auto it = std::find(m_DocList.begin(), m_DocList.end(), pDocument);
	if (it != m_DocList.end())
	{
		auto pDoc = *it;
		delete pDoc;
		m_DocList.erase(it);
	}
}

void DemoMainWindow::onSlotNewWindow()
{
	auto pDocument = getActiveDocument();
	createNewWindow(pDocument);
}

//创建文档的一个视图（DemoChildWindow-DeomView）
void DemoMainWindow::createNewWindow(DemoDocument* pDocument)
{
	if (!pDocument)
	{
		Q_ASSERT(false);
		return;
	}

	auto pChildWnd = new DemoChildWindow(pDocument);

	//自己new QMdiSubWindow时，必须设置Qt::WA_DeleteOnClose，参看文档
	//When you create your own subwindow, you must set the Qt::WA_DeleteOnClose widget 
	//attribute if you want the window to be deleted when closed in the MDI area. 
	//If not, the window will be hidden and the MDI area will not activate the next subwindow.
	//添加方式如下：
//	QMdiSubWindow *pMdiSubWindow = new QMdiSubWindow;
//	pMdiSubWindow->setWidget(pChildWnd);
//	pMdiSubWindow->setAttribute(Qt::WA_DeleteOnClose);
//	m_pMDIArea->addSubWindow(pMdiSubWindow);
//	pMdiSubWindow->show();

	//这中方法更简单
	auto pMdiSubWindow = m_pMDIArea->addSubWindow(pChildWnd);
	pMdiSubWindow->setWindowTitle(QStringLiteral("文档%1:%2").arg(pDocument->getId()).arg(
		pDocument->getViewCount()));
	pMdiSubWindow->show();
}

DemoDocument* DemoMainWindow::getActiveDocument() const
{
	auto pCurMdiSubWindow = m_pMDIArea->currentSubWindow();
	if (!pCurMdiSubWindow)
	{
		return nullptr;
	}

	auto pChildWnd = dynamic_cast<DemoChildWindow*>(pCurMdiSubWindow->widget());
	if (!pChildWnd)
	{
		Q_ASSERT(false);
		return nullptr;
	}

	return pChildWnd->GetDocument();
}

实现DemoChildWindow
相当于MFC中的ChildFrm，派生自CMDIChildWndEx，与文档是n-1关系, 与DemoView时1-1关系。此类负责创建DemoView，并且包含了文档对象的指针。MFC中创建ChildFrm以及CView没那么直接，通过消息触发创建了CView，具体参看MFC即可，我此处就简化处理创建的过程。
DemoChildWindow.h

#pragma once

#include <QWidget>

class DemoDocument;
class DemoView;

//相当于MFC中的ChildFrm，派生自CMDIChildWndEx， 与文档是n-1关系, 与DemoView时1-1关系，
class DemoChildWindow : public QWidget
{
	Q_OBJECT

public:
	DemoChildWindow(DemoDocument* pDoc, QWidget* parent = 0, Qt::WindowFlags f = 0);
	~DemoChildWindow();

	DemoDocument* GetDocument() const;

protected:
	virtual void closeEvent(QCloseEvent * event) override;

private:
	DemoDocument* m_pDoc;
	DemoView* m_pView;
};

DemoChildWindow.cpp

#include "DemoChildWindow.h"
#include "DemoView.h"
#include "DemoDocument.h"
#include <QVBoxLayout>

DemoChildWindow::DemoChildWindow(DemoDocument* pDoc, QWidget *parent, Qt::WindowFlags flags)
	: QWidget(parent, flags)
{
	m_pDoc = pDoc;
	m_pView = new DemoView();
	m_pDoc->addView(this);

	auto pVBoxLayout = new QVBoxLayout();
	pVBoxLayout->addWidget(m_pView);
	this->setLayout(pVBoxLayout);
}

DemoChildWindow::~DemoChildWindow()
{
}

DemoDocument* DemoChildWindow::GetDocument() const
{
	return m_pDoc;
}

void DemoChildWindow::closeEvent(QCloseEvent * event)
{
	m_pDoc->removeView(this);
	return QWidget::closeEvent(event);
}

实现DemoView
相当与MFC中的CView，在DemoView中仅显示了硬编码的文本字符串。
DemoView.h

#pragma once

#include <QWidget>

//相当与MFC中的CView
class DemoView : public QWidget
{
	Q_OBJECT

public:
	DemoView(QWidget *parent = Q_NULLPTR);
	~DemoView();

private:
	//Ui::DemoView ui;
};

DemoView.cpp

#include "DemoView.h"
#include <QVBoxLayout>
#include <QLabel>

DemoView::DemoView(QWidget *parent)
	: QWidget(parent)
{
	auto pVBoxLayout = new QVBoxLayout();
	pVBoxLayout->addWidget(new QLabel(QStringLiteral("视图测试")));
	this->setLayout(pVBoxLayout);
	this->setMinimumSize(300, 200);
}

DemoView::~DemoView()
{
}

main函数

#include "DemoApplication.h"
#include "DemoMainWindow.h"

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