QGraphicsItems not showing up QGraphicsScene

Question

我正在尝试构建一个带有QGraphicsScene的自定义小部件。

class Graphics:public QWidget{
public:
Graphis();
}
Graphics::Graphics(){
QGraphicsScene* scene = new QGraphicsScene(this);


QGridLayout* grid = new QGridLayout;


QGraphicsView* view = new QGraphicsView(this);


QGraphicsLineItem* y = new QGraphicsLineItem(scene->width()/2, 0, scene->width() / 2, scene->height());
QGraphicsLineItem* x = new QGraphicsLineItem(0, scene->height() / 2, scene->width(), scene->height() / 2);
scene->addItem(y);
scene->addItem(x);


grid->addWidget(view, 0, 0, 1, 1);
setLayout(grid);
view->setScene(scene);
view->show();
}

但是当我运行小部件时，主小部件内的QGraphicsView小部件中只显示了一个空场景。

Answer 1

试试这样;我认为一个问题是scene->width()和scene->height()很可能都返回 0，至少在您第一次调用它们时是这样，因为sceneRect()默认返回一个足够大的 QRect 以适应场景的当前内容(最初是空的(：

Graphics::Graphics(){
QGraphicsScene* scene = new QGraphicsScene(this);
QGridLayout* grid = new QGridLayout(this);
QGraphicsView* view = new QGraphicsView(scene, this);
scene->setSceneRect(0, 0, 200, 200);
QGraphicsLineItem* y = new QGraphicsLineItem(scene->width()/2, 0, scene->width() / 2, scene->height());
QGraphicsLineItem* x = new QGraphicsLineItem(0, scene->height() / 2, scene->width(), scene->height() / 2);
scene->addItem(y);
scene->addItem(x);
grid->addWidget(view, 0, 0, 1, 1);
}