問題描述

我有以下代碼來設置 QGraphicsScene.我希望單擊場景并在我單擊的位置繪制一個點.我怎么能這樣做?這是我當前的代碼:

I have the following code to set up a QGraphicsScene. I wish to click on the scene and draw a point at the location I've clicked. How could I do this? This is my current code:

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);

    QGraphicsScene *scene;
    QGraphicsView *view = new QGraphicsView(this);

    view->setGeometry(QRect(20, 50, 400, 400));
    scene = new QGraphicsScene(50, 50, 350, 350);
    view->setScene(scene);
}

推薦答案

UPDATE:有一個名為 QGraphicsSceneMouseEvent 的新類，它使這更容易一些.我剛剛在這里完成了一個使用它的例子:

UPDATE: There is a new class called QGraphicsSceneMouseEvent that makes this a little easier. I just finished an example using it here:

https://stackoverflow.com/a/26903599/999943

它與下面的答案的不同之處在于它子類化 QGraphicsScene，而不是 QGraphicsView，并且它使用 mouseEvent->scenePos() 所以無需手動映射坐標.

It differs with the answer below in that it subclasses QGraphicsScene, not QGraphicsView, and it uses mouseEvent->scenePos() so there isn't a need to manually map coordinates.

您走在正確的軌道上，但您還有一些路要走.

You are on the right track, but you still have a little more to go.

您需要子類化 QGraphicsView 才能使用 QMouseEvent 通過鼠標按下或釋放鼠標來執行某些操作.

You need to subclass QGraphicsView to be able to do something with mouse presses or with mouse releases using QMouseEvent.

    #include <QGraphicsView>
    #include <QGraphicsScene>
    #include <QGraphicsEllipseItem>
    #include <QMouseEvent>

    class MyQGraphicsView : public QGraphicsView
    {
        Q_OBJECT
    public:
        explicit MyQGraphicsView(QWidget *parent = 0);

    signals:

    public slots:
        void mousePressEvent(QMouseEvent * e);
        // void mouseReleaseEvent(QMouseEvent * e);
        // void mouseDoubleClickEvent(QMouseEvent * e);
        // void mouseMoveEvent(QMouseEvent * e);
    private:
        QGraphicsScene * scene;
    };

QGraphicsView 本身沒有無量綱點.您可能希望使用 QGraphicsEllipse 項目或簡單地使用半徑非常小的 scene->addEllipseItem().

QGraphicsView doesn't natively have dimension-less points. You will probably want to use QGraphicsEllipse item or simply, scene->addEllipseItem() with a very small radius.

    #include "myqgraphicsview.h"
    #include <QPointF>

    MyQGraphicsView::MyQGraphicsView(QWidget *parent) :
        QGraphicsView(parent)
    {
        scene = new QGraphicsScene();
        this->setSceneRect(50, 50, 350, 350);
        this->setScene(scene);
    }

    void MyQGraphicsView::mousePressEvent(QMouseEvent * e)
    {
        double rad = 1;
        QPointF pt = mapToScene(e->pos());
        scene->addEllipse(pt.x()-rad, pt.y()-rad, rad*2.0, rad*2.0, 
            QPen(), QBrush(Qt::SolidPattern));
    }

注意 mapToScene() 的用法，使事件的 pos() 正確映射到鼠標在場景上點擊的位置.

Note the usage of mapToScene() to make the pos() of the event map correctly to where the mouse is clicked on the scene.

如果要使用表單，則需要將子類 QGraphicsView 的實例添加到 ui 的 centralWidget 布局中.

You need to add an instance of your subclassed QGraphicsView to the centralWidget's layout of your ui if you are going to use a form.

    QGridLayout * gridLayout = new QGridLayout(ui->centralWidget);
    gridLayout->addWidget( new MyQGraphicsView() );

或者如果您的 ui 已經有布局，它將如下所示:

or if your ui has a layout already it will look like this:

    ui->centralWidget->layout()->addWidget( new MyGraphicsView() );

如果你不使用 QMainWindow 和一個表單，你可以將它添加到一個 QWidget 如果你為它設置一個布局然后添加你的 QGraphicsView 以類似的方式到該布局.如果您不想在 QGraphicsView 周圍留出邊距，只需調用 show 即可，不要將其放在不同的布局中.

If you don't use a QMainWindow and a form, you can add it to a QWidget if you set a layout for it and then add your QGraphicsView to that layout in a similar manner. If you don't want a margin around your QGraphicsView, just call show on it and don't put it inside a different layout.

    #include <QtGui/QApplication>
    #include "myqgraphicsview.h"

    int main(int argc, char *argv[])
    {
        QApplication a(argc, argv);

        MyQGraphicsView view;
        view.show();

        return a.exec();
    }

就是這樣.現在您對 QGraphicsView 及其與鼠標的交互很危險.

And that's it. Now you are dangerous with QGraphicsView's and their interaction with the mouse.

請務必閱讀和研究 Qt 的圖形視圖框架和相關examples在使用QGraphicsView 和 QGraphicsScene.它們是非常強大的 2D 圖形工具，可能需要一些學習曲線，但它們值得.