Qt新手在这里遇到一个问题，它声称我没有声明一个我很确定已宣布的类。
我不能为我的生活弄清楚这一点。请帮忙。
在Connection.h和.cpp中注释出有问题的行会产生可编译的输出。
这是我的代码的精简版本，问题仍然存在：
顺便说一句，Map.ui只有拖入图形视图。
错误讯息：
In file included from ../Map/Map.h:17:0,
from ../Map/City.cpp:1:
../Map/Connection.h:14:11: error: 'City' was not declared in this scope
QPair<City*, City*> cities;
^
../Map/Connection.h:14:18: error: 'City' was not declared in this scope
QPair<City*, City*> cities;
^
../Map/Connection.h:14:23: error: template argument 1 is invalid
QPair<City*, City*> cities;
^
../Map/Connection.h:14:23: error: template argument 2 is invalid
../Map/Connection.h:19:22: error: 'City' was not declared in this scope
Connection(QPair<City*, City*> cities, int cost);
^
../Map/Connection.h:19:29: error: 'City' was not declared in this scope
Connection(QPair<City*, City*> cities, int cost);
^
../Map/Connection.h:19:34: error: template argument 1 is invalid
Connection(QPair<City*, City*> cities, int cost);
Map.pro：
QT += core gui
greaterThan(QT_MAJOR_VERSION, 4): QT += widgets
TARGET = Map
TEMPLATE = app
SOURCES +=\
City.cpp \
Connection.cpp \
Map.cpp \
Driver.cpp
HEADERS += \
City.h \
Connection.h \
Map.h
FORMS += \
Map.ui
Map.h：
#ifndef MAP_H
#define MAP_H
#include <QApplication>
#include <QGraphicsItem>
#include <QMainWindow>
#include <QtCore>
#include <QtGui>
#include <QGraphicsScene>
#include <QGraphicsEllipseItem>
#include <QDebug>
#include <QPainter>
#include <QString>
#include <QVector>
#include "ui_Map.h"
#include "Connection.h"
#include "City.h"
namespace Ui
{
class Map;
}
class Map : public QMainWindow
{
Q_OBJECT
public:
explicit Map(QWidget *parent = 0);
~Map();
private:
Ui::Map *ui;
QGraphicsScene *scene;
};
#endif // MAP_H
Map.cpp：
#include "Map.h"
#include "ui_Map.h"
Map::Map(QWidget *parent) : QMainWindow(parent), ui(new Ui::Map)
{
ui->setupUi(this);
scene = new QGraphicsScene(this);
ui->graphicsView->setScene(scene);
City *c1 = new City(30, 30, 30, "K");
City *c2 = new City(30, 90, 30, "O");
Connection *conn1 = new Connection(45, 45, 45, 105, 1);
c1->setZValue(4);
c2->setZValue(4);
conn1->setZValue(2);
scene->addItem(c1);
scene->addItem(c2);
scene->addItem(conn1);
}
Map::~Map()
{
delete ui;
}
City.h：
#ifndef CITY_H
#define CITY_H
#include "Map.h"
class City : public QGraphicsItem
{
private:
int x;
int y;
int r;
QString name;
QRectF bounds;
QVector<QPair<City*, int> > neighbors;
public:
City();
City(int x, int y, int r, QString name);
int getX() { return this->x; }
int getY() { return this->y; }
int getR() { return this->r; }
QString getName() { return this->name; }
QVector<QPair<City*, int> > getNeighbors() { return this->neighbors; }
void setNeighbors(QVector<QPair<City*, int> >) { this->neighbors = neighbors; }
QRectF boundingRect() const;
void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget);
};
#endif // CITY_H
City.cpp：
#include "Map.h"
City::City()
{
this->bounds = QRectF(0, 0, 0, 0);
}
City::City(int x, int y, int r, QString name)
{
this->x = x;
this->y = y;
this->r = r;
this->name = name;
this->bounds = QRectF(x, y, r, r);
}
QRectF City::boundingRect() const
{
return QRectF(x, y, r, r);
}
void City::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget)
{
QRectF rec;
if (this->bounds == QRectF(0, 0, 0, 0))
rec = boundingRect();
else
rec = this->bounds;
QBrush brush(Qt::blue);
QPen pen(Qt::blue);
painter->setBrush(brush);
painter->setPen(pen);
painter->drawEllipse(rec);
}
Connection.h：
#ifndef CONNECTION_H
#define CONNECTION_H
#include "Map.h"
class Connection : public QGraphicsItem
{
private:
int x1, x2;
int y1, y2;
int cost;
QRectF bounds;
QPair<City*, City*> cities; // PROBLEMATIC LINE -- CLAIMS CITY WAS NOT DECLARED
public:
Connection();
Connection(int x1, int y1, int x2, int y2, int cost);
Connection(QPair<City*, City*> cities, int cost); // PROBLEMATIC LINE -- CLAIMS CITY WAS NOT DECLARED
int getCost() { return this->cost; }
QRectF boundingRect() const;
void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget);
};
#endif // CONNECTION_H
Connection.cpp：
#include "Map.h"
Connection::Connection()
{
this->bounds = QRectF(0, 0, 0, 0);
}
Connection::Connection(int x1, int y1, int x2, int y2, int cost)
{
this->x1 = x1;
this->x2 = x2;
this->y1 = y1;
this->y2 = y2;
this->bounds = QRectF(x1, x2, y1, y2);
}
Connection::Connection(QPair<City*, City*> cities, int cost) // PROBLEMATIC BLOCK
{
int r = cities.first->getR();
this->x1 = cities.first->getX() + r/2;
this->x2 = cities.second->getX() + r/2;
this->y1 = cities.first->getY() + r/2;
this->y2 = cities.second->getY() + r/2;
this->cost = cost;
this->bounds = QRectF(x1, x2, y1, y2);
}
QRectF Connection::boundingRect() const
{
return QRectF(0, 0, 0, 0);
}
void Connection::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget)
{
QRectF rec;
if (this->bounds == QRectF(0, 0, 0, 0))
rec = boundingRect();
else
rec = this->bounds;
QBrush brush(Qt::red);
QPen pen(Qt::red);
painter->setPen(pen);
painter->drawLine(QLine(this->x1, this->y1, this->x2, this->y2));
}
Driver.cpp：
#include "Map.h"
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
Map w;
w.show();
return a.exec();
}
感谢您抽出宝贵时间来看看这个。我感谢任何反馈。有问题的线条可以编译一段时间，但似乎添加某些东西“打破”它。
this线程的答案让我觉得它可能是愚蠢的，但我改变事物顺序的尝试并没有解决它。
答案 0 :(得分：3)
只要查看错误消息，就可以看到City类确实没有在Connection中定义。
In file included from ../Map/Map.h:17:0,
from ../Map/City.cpp:1:
City.cpp以#include "Map.h"开始，这是奇怪的，因为cpp文件中没有对Map类型的引用。 City.cpp应该以{{1}}开头。
City.h以#include "City.h"开头，这甚至更奇怪，因为City类没有提到Map。
所以此时City.cpp：1 - ＆gt; Map.h：17你包括“Connection.h”。此时，没有已定义的类型。不是城市，而不是地图。编译器在没有定义类型的情况下接近 Connection 类。
很难猜测你的依赖关系实际上是什么样的，但这个特定包含的一个解决方案可能是。
#include "Map.h"。#include "X.h"。#include "Map.h"。所以要么做前瞻声明，要么做“#include”City.h“总之：只包含您的类实际需要的标头中的文件。在相应的cpp中，首先包括标题。实现还需要头部所需的任何类型。之后，您将包含实现所需的其他类型。