Qt使用QPixmap小坑

#include <QApplication>
#include <QPushButton>

const QPixmap pixmap(":/image/car.png");

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

    QPushButton button;
    button.setIcon(QIcon(pixmap));
    button.show();

    return a.exec();
}

QPixmap: Must construct a QGuiApplication before a QPixmap.
QPixmap：必须在QPixmap之前构造一个QGuiApplication。

Note: When using the native X11 graphics system, the pixmap becomes invalid when the QApplication instance is destroyed.
注意：使用本机X11图形系统时，销毁QApplication实例后，像素图将会无效。

Warning: Qt requires that a QGuiApplication object exists before any paint devices can be created. Paint devices access window system resources, and these resources are not initialized before an application object is created.
警告：在创建任何绘画设备之前，Qt要求先存在QGuiApplication对象。
绘图设备访问窗口系统资源，并且在创建应用程序对象之前是不会初始化这些资源。

QPixmap::QPixmap(const QString& fileName,...)
    : QPaintDevice()
{
    ...
    if (!qt_pixmap_thread_test())
        return;

    ...
}

static bool qt_pixmap_thread_test()
{
    if (Q_UNLIKELY(!QCoreApplication::instance())) {
        qFatal("QPixmap: Must construct a QGuiApplication before a QPixmap");
        return false;
    }

    ...
    return true;
}

#include <QApplication>
#include <QPushButton>

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

    const QPixmap pixmap(":/Image/backspace.png");

    QPushButton button;
    button.setIcon(QIcon(pixmap));
    button.show();

    return a.exec();
}

QImage
QOpenGLPaintDevice
QPagedPaintDevice
QPaintDeviceWindow
QPicture
QPixmap

QIcon