找不到标识 horizontalScrollBar-QT开发中文网

如果在你的代码中找不到 horizontalScrollBar() 的标识，可能是因为你没有将滚动条与画布关联或者没有正确访问到滚动区域的滚动条。以下是如何修复这个问题并确保能够访问水平和垂直滚动条。

你可以通过在 QScrollArea 对象上调用 horizontalScrollBar() 和 verticalScrollBar() 方法来获取滚动条。这需要确保你在合适的上下文中进行操作。下面是一个更新后的示例，其中包括了如何正确使用这些滚动条：

#include <QApplication>
#include <QMainWindow>
#include <QScrollArea>
#include <QFrame>
#include <QVBoxLayout>
#include <QPainter>
#include <QMouseEvent>

class CanvasFrame : public QFrame {
    Q_OBJECT

public:
    CanvasFrame(QWidget *parent = nullptr) : QFrame(parent) {
        setMinimumSize(500, 500);
        setMouseTracking(true);
        dragging = false;
    }

protected:
    void paintEvent(QPaintEvent *event) override {
        Q_UNUSED(event);
        
        QPainter painter(this);
        
        // 设置线条颜色和宽度
        painter.setPen(QPen(Qt::gray, 1));

        int gridSize = 100;
        
        // 绘制横向网格线
        for (int i = 0; i <= height(); i += gridSize) {
            painter.drawLine(0, i, width(), i);
        }
        
        // 绘制纵向网格线
        for (int j = 0; j <= width(); j += gridSize) {
            painter.drawLine(j, 0, j, height());
        }
    }

    void mousePressEvent(QMouseEvent *event) override {
        if (event->button() == Qt::LeftButton) {
            lastMousePos = event->pos();
            dragging = true;
            setCursor(Qt::ClosedHandCursor); // 更换光标为抓手形状
        }
    }

    void mouseMoveEvent(QMouseEvent *event) override {
        if (dragging && event->buttons() & Qt::LeftButton) { 
            int dx = event->pos().x() - lastMousePos.x();
            int dy = event->pos().y() - lastMousePos.y();
            
            // 获取父类（scrollArea）的水平和垂直滚动条，并设置值
            QScrollArea* scrollArea = qobject_cast<QScrollArea*>(parentWidget());
            if (scrollArea) {
                scrollArea->horizontalScrollBar()->setValue(scrollArea->horizontalScrollBar()->value() - dx);
                scrollArea->verticalScrollBar()->setValue(scrollArea->verticalScrollBar()->value() - dy);
            }

            lastMousePos = event->pos(); // 更新位置到当前鼠标位置
         }
    }

    void mouseReleaseEvent(QMouseEvent *event) override {
        if (event->button() == Qt::LeftButton) {
            dragging = false;
            unsetCursor(); // 恢复光标
         }
     }

private:
    QPoint lastMousePos;
    bool dragging;
};

class MainWindow : public QMainWindow {
public:
    MainWindow(QWidget *parent = nullptr)
      : QMainWindow(parent)
    {
       setWindowTitle("Grid Example");
       resize(800, 600);

       auto layout = new QVBoxLayout;

       auto leftFrame = new QFrame(this);
       leftFrame->setFixedWidth(200);
       leftFrame->setStyleSheet("background-color: green;");

       auto scrollArea = new QScrollArea(this);
       auto canvas = new CanvasFrame(scrollArea);

       scrollArea->setWidget(canvas);
       scrollArea->setWidgetResizable(true);

       layout->addWidget(leftFrame);
       layout->addWidget(scrollArea);

       QWidget *centralWidget = new QWidget(this);
       centralWidget->setLayout(layout);
       setCentralWidget(centralWidget);
   }
};

int main(int argc, char *argv[]) {
   QApplication a(argc, argv);
   MainWindow w;
   w.show();
   return a.exec();
}