qt - QAbstractSocket::UnsupportedSocketOperationError 与 QSslSocket

Question

QAbstractSocketUnsupportedSocketOperationError连接到主机时抛出QSslSocket::connectToHostEncrypted()，

环境：Qt 5.9.3 Ubuntu 16.04（虚拟机）和 Qt 5.9.3 Fedora 26（本机）

_socket = new QSslSocket{this};
connect(_socket, static_cast<void(QAbstractSocket::*) QAbstractSocket::SocketError) (&QAbstractSocket::error), this, &EventResource::streamError);

_socket->connectToHostEncrypted(_device->addressUrl().host(), 443, QSslSocket::ReadWrite, QSslSocket::IPv4Protocol);

void EventResource::streamError(QAbstractSocket::SocketError error)
{
    QDebug() << "Event error: " << error; 
    //QAbstractSocket::UnsupportedSocketOperationError
}

你能帮我么？
我不明白错误以及为什么会发生？