基于Qt的Model-View显示树形数据

目标

用qt的模型-视图框架实现树型层次节点的显示，从QAbstractItemModel派生自己的模型类MyTreeItemModel，用boost::property_tree::ptree操作树型数据结构，为了演示，此处只实现了个只读的模型

MyTreeItemModel的定义

#pragma once

#include <QAbstractItemModel>
#include "boost/property_tree/ptree.hpp"

class MyTreeItemModel : public QAbstractItemModel
{
	Q_OBJECT

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

	virtual QModelIndex index(int row, int column,
		const QModelIndex &parent = QModelIndex()) const override;
	virtual QModelIndex parent(const QModelIndex &child) const override;
	virtual int rowCount(const QModelIndex &parent = QModelIndex()) const override;
	virtual int columnCount(const QModelIndex &parent = QModelIndex()) const override;
	virtual QVariant data(const QModelIndex &index, int role = Qt::DisplayRole) const override;
	virtual Qt::ItemFlags flags(const QModelIndex &index) const override;
private:
	const boost::property_tree::ptree* GetParent(const boost::property_tree::ptree* pChild,
		int& nParentRow ) const;

private:
	// 创建一个property_tree
	boost::property_tree::ptree m_TreeItem;
};

MyTreeItemModel的实现

1. 简化代码，直接在构造函数创建出树型数据结构，用的是boost库的property_tree::ptree

   MyTreeItemModel::MyTreeItemModel(QObject *parent)
   	: QAbstractItemModel(parent)
   {
   	// 添加数据
   	m_TreeItem.put("node", "root value");
   	m_TreeItem.put("node.child1", "child1 value1");
   	m_TreeItem.put("node.child2", "child2 value2");
   	m_TreeItem.put("node.child3", "child3 value3");
   
   	// 添加子节点
   	boost::property_tree::ptree child;
   	child.put("grandchild", "grandchild value4");
   	m_TreeItem.add_child("node.child4", child);
   	m_TreeItem.put("node.child4", "child4 value4");
   }

2. 模型类必须实现index虚函数，视图、委托会调用index函数来访问模型数据，具体参看qt帮助文档

   QModelIndex MyTreeItemModel::index(int row, int column,
   	const QModelIndex &parent /*= QModelIndex()*/) const
   {
   	if (!hasIndex(row, column, parent))
   	{
   		return QModelIndex();
   	}
   
   	const boost::property_tree::ptree* pParent = nullptr;
   	if (!parent.isValid())
   	{
   		pParent = &m_TreeItem;
   	}
   	else
   	{
   		pParent = reinterpret_cast<boost::property_tree::ptree*>( parent.internalPointer() );
   	}
   
   	auto it = pParent->begin();
   	it = std::next(it, row);
   	const boost::property_tree::ptree* pThisItem = &(it->second);
   	if (pThisItem)
   	{
   		return createIndex(row, column, (void*)pThisItem);
   	}
   
   	return QModelIndex();
   }

3. 模型类必须实现parent虚函数

   QModelIndex MyTreeItemModel::parent(const QModelIndex &child) const
   {
   	if (!child.isValid())
   		return QModelIndex();
   
   	boost::property_tree::ptree *childItem = static_cast<boost::property_tree::ptree*>(child.internalPointer());
   	
   	int nParentRow = 0;
   	const boost::property_tree::ptree* pParentItem = GetParent(childItem, nParentRow);
   	if (!pParentItem)
   	{
   		Q_ASSERT(false);
   		return QModelIndex();
   	}
   
   	if (pParentItem == &m_TreeItem)
   		return QModelIndex();
   
   	return createIndex(nParentRow, 0, (void *)pParentItem);
   }

4. 模型类必须实现rowCount虚函数

   int MyTreeItemModel::rowCount(const QModelIndex &parent /*= QModelIndex()*/) const
   {
   	if (parent.column() > 0) //第一列才有子节点
   		return 0;
   
   	const boost::property_tree::ptree* pParent = nullptr;
   	if (!parent.isValid())
   		pParent = &m_TreeItem;
   	else
   		pParent = static_cast<const boost::property_tree::ptree*>(parent.internalPointer());
   
   	return pParent->size();
   }

5. 模型类必须实现columnCount虚函数

   int MyTreeItemModel::columnCount(const QModelIndex &parent /*= QModelIndex()*/) const
   {
   	return 1; //只支持一列
   }

6. 模型类必须实现data虚函数，因为是只读，只实现了Qt::DisplayRole

   QVariant MyTreeItemModel::data(const QModelIndex &index, int role /*= Qt::DisplayRole*/) const
   {
   	if (!index.isValid())
   		return QVariant();
   
   	if (role != Qt::DisplayRole)
   		return QVariant();
   
   	auto pTreeItem = static_cast<const boost::property_tree::ptree*>(index.internalPointer());
   	if (!pTreeItem)
   	{
   		Q_ASSERT(false);
   		return QVariant();
   	}
   
   	QString strValue = QString::fromStdString(pTreeItem->data());
   	return QVariant(strValue);
   }

7. 重写flags函数，告诉使用者，本模型只提供只读功能，这里基类QAbstractItemModel的实现正好符合需求，可不重写，我这里写出来只是说明下而已

   Qt::ItemFlags MyTreeItemModel::flags(const QModelIndex &index) const
   {
   	if (!index.isValid())
   		return 0;
   
   	//The base class implementation returns a combination of flags that enables 
   	//the item (ItemIsEnabled) and allows it to be selected (ItemIsSelectable).
   	return QAbstractItemModel::flags(index);
   }

8. boost::property_tree::ptree没有提供访问父节点的功能，故加了个GetParent函数，仅测试用，实际不应该这么用，效率低

   const boost::property_tree::ptree* MyTreeItemModel::GetParent(const boost::property_tree::ptree* pChild,
   	int& nParentRow) const
   {
   	if (!pChild)
   	{
   		return nullptr;
   	}
   
   	std::stack<const boost::property_tree::ptree*> mNodeStack;
   	mNodeStack.push(&m_TreeItem);
   	while (!mNodeStack.empty())
   	{
   		const boost::property_tree::ptree* pParent = mNodeStack.top();
   		mNodeStack.pop();
   		if (!pParent)
   		{
   			continue;
   		}
   
   		//在子节点列表中搜索指定节点
   		int nRow = 0;
   		for (auto it = pParent->begin(); it != pParent->end(); ++it, ++nRow)
   		{
   			const boost::property_tree::ptree* pChildItem = &(it->second);
   			if (pChildItem == pChild)
   			{
   				nParentRow = nRow;
   				return pParent;
   			}
   			
   			mNodeStack.push(pChildItem);
   		}
   	}
   
   	nParentRow = 0;
   	return nullptr;
   }

使用自写的模型类

QtGuiApplication1::QtGuiApplication1(QWidget *parent)
	: QMainWindow(parent)
{
	//ui.setupUi(this);

	auto pCentralWidget = new QWidget(this);
	this->setCentralWidget(pCentralWidget);

	auto pVLayout = new QVBoxLayout();
	QAbstractItemModel *pModel = new MyTreeItemModel();
	QTreeView *pTreeView = new QTreeView();
	pTreeView->setModel(pModel);
	pVLayout->addWidget(pTreeView);
	pCentralWidget->setLayout(pVLayout);
}

运行演示