从其课外访问小部件？

Question

Qt Creator中，我有几个小部件的声明如下所示：

头文件：

class MapViewer : public QGraphicsView 
{ 
    Q_OBJECT 

public: 
    explicit MapViewer(QGraphicsScene *scene, QWidget *parent = 0); 
    ~MapViewer(); 

public slots: 
    void mousePressEvent(QMouseEvent *event); 

}; 

// Declaration for the map editor window. 
class MapEditor : public QMainWindow 
{ 
    Q_OBJECT 

public: 
    explicit MapEditor(QWidget *parent = 0); 
    ~MapEditor(); 

public: 
    QLayout *editorLayout; 
    QPushButton *btn; 
    QGraphicsScene *mapScene; 
    MapViewer *mapView; 

private: 
    Ui::MapEditor *ui; 
}; 

CPP文件：

MapEditor::MapEditor(QWidget *parent) : 
    QMainWindow(parent), 
    ui(new Ui::MapEditor) 
{ 

    ui->setupUi(this); 
    this->setWindowTitle("2DXY :: Map Editor"); 
    this->setGeometry(10,10,1170,750); 
    editorLayout = new QVBoxLayout; // Create a new layout 
    this->setLayout(editorLayout); // Set the widget's layout to our newly created layout. 

    mapScene = new QGraphicsScene(); // Create a new graphics scene to draw upon. 

    mapView = new MapViewer(mapScene,this); // Create a new graphics view to display our scene - set its parent to 'this' so that it doesn't open in a new window. 
    mapView->setHorizontalScrollBarPolicy(Qt::ScrollBarAlwaysOff); 
    mapView->setVerticalScrollBarPolicy(Qt::ScrollBarAlwaysOff); 
    mapView->setGeometry(20,20,1178,546); // Width first, then height. 

AND：

void MapViewer::mousePressEvent(QMouseEvent *event) 
{ 
    // Show an empty message box, just to check that the event handler works! 
    QMessageBox *notification = new QMessageBox(); 
    notification->show(); 
    notification->exec(); 
    // Some how access the same QGraphicsScene and View (mapScene, mapView) as above, so 
    // I can update their contents on the open form/window. 

} 

而且正如你所看到的，我希望再次访问图形场景来更新它，然后重绘i吨（或其他）。但是我根本无法访问图形场景，尽管用不同的方式声明小部件需要几个小时的试验和错误。我知道监听器本身是可以工作的，因为如果它设置为打开一个新的消息框，或者输出到调试窗口，那么它就可以工作，这只是我不能访问我已经定义的小部件。

我觉得这个问题有一个（相对）简单的解决方案，而且我只是错过了一些明显的东西。

Answer 1

void MapViewer::mousePressEvent(QMouseEvent *event) 
{ 
    // Show an empty message box, just to check that the event handler works! 
    QMessageBox *notification = new QMessageBox(); 
    notification->show(); 
    notification->exec(); 

    // To add something whenever the user clicks, you don't need the view, 
    // just the scene. 
    scene()->addItem(new MyItem()); 
} 

记住MapViewer从QGraphicsView派生，并认为必须知道它属于现场 - 所以它有一个scene()方法返回它，你继承。

Answer 2

您将QGraphicsScene传递给您的MapRender对象的构造函数。你在构造函数中如何处理这个场景？理想情况下，您应该将其存储为MapRender的数据成员。例如：

class MapRender { 
public: 
    MapRender(QGraphicsScene* scene) 
     : scene_(scene) 
    { 
    } 

public slots: 
    void mousePressEvent(QMouseEvent *event); 

private: 
    QGraphicsScene* scene_; 
} 

现在，在您执行mousePressEvent，您可以访问到现场成员：

void MapRender::mousePressEvent(QMouseEvent *event) { 
    int CursorX = event->globalX(); 
    int CursorY = event->globalY(); 

    QGraphicsRectItem *clickedBox = new QGraphicsRectItem(40,40,32,32); 
    clickedBox->setBrush(QBrush(Qt::blue)); 

    scene_->addItem(clickedBox); 
} 

请记住，您最好应该把构造函数的实现在你的CPP文件，但我的例子在简明声明中就是这样做的。