关于 QQuickImageProvider 官方的描述
The QQuickImageProvider class provides an interface for supporting pixmaps and threaded image requests in QML.

有时候希望将QPixmap或者QImage中的图像显示到Qml中, 这时候就需要用到QQuickImageProvider了
继承QQuickImageProvider 新建一个类:

```
class ImageProvider : public QQuickImageProvider
{
public:
ImageProvider::ImageProvider(ImageType type, Flags flags = Flags()) :
QQuickImageProvider(type, flags)
{
}
~ImageProvider(){}
QPixmap requestPixmap(const QString &id, QSize *size, const QSize &requestedSize)
{
QString strFileName = QCoreApplication::applicationDirPath() + "/" + id;
qDebug()