请好手分析一下QImageReaderPrivate:initHandler() 返回false的原因

请高手分析一下QImageReaderPrivate::initHandler() 返回false的原因
/*!
    \internal
*/
bool QImageReaderPrivate::initHandler()
{
    // check some preconditions
    if (!device || (!deleteDevice && !device->isOpen() && !device->open(QIODevice::ReadOnly))) {
        imageReaderError = QImageReader::DeviceError;
        errorString = QLatin1String(QT_TRANSLATE_NOOP(QImageReader, "Invalid device"));
        return false;
    }

    // probe the file extension
    if (deleteDevice && !device->isOpen() && !device->open(QIODevice::ReadOnly) && autoDetectImageFormat) {
        QList<QByteArray> extensions = QImageReader::supportedImageFormats();
        if (!format.isEmpty()) {
            // Try the most probable extension first
            int currentFormatIndex = extensions.indexOf(format.toLower());
            if (currentFormatIndex > 0)
                extensions.swap(0, currentFormatIndex);
        }

        int currentExtension = 0;

        QFile *file = static_cast<QFile *>(device);
        QString fileName = file->fileName();

        do {
            file->setFileName(fileName + QLatin1Char('.')
                    + QString::fromLatin1(extensions.at(currentExtension++).constData()));
            file->open(QIODevice::ReadOnly);
        } while (!file->isOpen() && currentExtension < extensions.size());

        if (!device->isOpen()) {
            imageReaderError = QImageReader::FileNotFoundError;
            errorString = QLatin1String(QT_TRANSLATE_NOOP(QImageReader, "File not found"));
            file->setFileName(fileName); // restore the old file name
            return false;
        }
    }

    // assign a handler
    if (!handler && (handler = createReadHandlerHelper(device, format, autoDetectImageFormat, ignoresFormatAndExtension)) == 0) {
        imageReaderError = QImageReader::UnsupportedFormatError;
        errorString = QLatin1String(QT_TRANSLATE_NOOP(QImageReader, "Unsupported image format"));
        return false;
    }
    return true;
}



------解决方案--------------------
朋友，你只有把你的问题写出来，我们才好帮你啊
------解决方案--------------------
设备都打不开，或者没有就绪，当然要返回false了。
最好看看插件之类的装上了没有。