#include <QApplication>
#include <QWidget>
#include <QPushButton>
#include <QPainter>

class MyWidget : public QWidget {
    Q_OBJECT

public:
    MyWidget(QWidget *parent = nullptr) : QWidget(parent), displayText("Hello, World!") {
        // 创建一个按钮并连接槽函数
        QPushButton *button = new QPushButton("Change Text", this);
        button->setGeometry(50, 150, 100, 30);
        connect(button, &QPushButton::clicked, this, &MyWidget::changeText);
    }

protected:
    void paintEvent(QPaintEvent *event) override {
        QPainter painter(this);

        // 设置字体大小
        painter.setFont(QFont("Arial", 24));
  
        // 在窗口中央绘制当前文本
        painter.drawText(rect(), Qt::AlignCenter, displayText);
    }

private slots:
    void changeText() {
        // 改变要显示的文本
        displayText = "Text Changed!";

        // 请求重绘，触发 paintEvent()
        update();
    }

private:
    QString displayText;  // 显示的文本
};

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

    MyWidget widget;
    widget.resize(400, 300);
    widget.show();
  
    return app.exec();

}

#include "main.moc"