QTableView派生类中的paintEvent:绘制设备返回的引擎== 0，类型:1

问题描述

作为 Qt加载指示器的后续措施动画图像(又称预加载器)还是替代图像?我尝试在QTableView内绘画.但是，当我初始化QPainter时，会收到以下警告.

As a follow up of Qt load indicator by animated image (aka preloader) or alternative? I try to paint inside a QTableView. But when I initialize the QPainter I get the following warnings.

QWidget::paintEngine: Should no longer be called
QPainter::begin: Paint device returned engine == 0, type: 1

这是代码(SO答案，带有按钮的按钮似乎起作用):

Here is the code (SO answer, with a button it seems to work):

    void CDerivedFromQTableView::paintEvent(QPaintEvent *event)
    {
        QTableView::paintEvent(event); // draw original content
        QPainter p(this); // Problem: QPainter::begin: Paint device returned engine == 0, type: 1
        const QPixmap pm(QPixmap::grabWidget(this->m_loadIndicator));
        QPoint middle = this->geometry().center();
        int x = middle.x() - pm.width() / 2;
        int y = middle.y() - pm.height() / 2;
        p.drawPixmap(QPoint(x, y), pm); // draw load indicator inside QTableView
    }

我很惊讶创建QPainter失败，为什么会这样.我在做什么错了?

I am surprised creating the QPainterfails, so why is that. What am I doing wrong?

简化版仍会发出警告

        QPainter p(this);
        QTableView::paintEvent(event);
        return;

当我注释掉QPainter时，警告(当然)消失了，所以这似乎确实是根本原因，但是为什么?

Warning (of course) gone when I comment out QPainter, so it really seems to be the root cause, but why?

推荐答案

由于QTableView是QAbstractScrollArea的子类，因此应在其视口中打开QPainter:

As QTableView is a subclass of QAbstractScrollArea you should open QPainter on its viewport:

void CDerivedFromQTableView::paintEvent(QPaintEvent *event)
{
    QTableView::paintEvent(event); // draw original content

    QPainter p(this->viewport());
    p.drawRect(0, 0, 20, 20);
}

文档说:

注意:如果您打开一个画家，请确保在viewport()上将其打开.

Note: If you open a painter, make sure to open it on the viewport().

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