MqttServer.cpp:125:43: No viable conversion from 'std::string' (aka 'basic_string<char>') to 'const QByteArray' qbytearray.h:181:5: candidate constructor not viable: no known conversion from 'std::string' (aka 'basic_string<char>') to 'const char *' for 1st argument qbytearray.h:189:12: candidate constructor not viable: no known conversion from 'std::string' (aka 'basic_string<char>') to 'QByteArray &&' for 1st argument qbytearray.h:463:12: candidate constructor not viable: no known conversion from 'std::string' (aka 'basic_string<char>') to 'QByteArrayDataPtr' for 1st argument qbytearray.h:524:20: candidate constructor not viable: no known conversion from 'std::string' (aka 'basic_string<char>') to 'const QByteArray &' for 1st argument qbytearray.h:405:67: passing argument to parameter 'hexEncoded' here

这个错误的意思是说，你正在尝试将一个`std::string`类型的变量转换为`QByteArray`类型，但是`QByteArray`没有一个可以接受`std::string`类型参数的构造函数。

要解决这个问题，你需要将`std::string`类型转换为`QByteArray`类型。你可以使用`QByteArray::fromStdString()`函数来实现这一点，例如：

std::string myString = "hello";
QByteArray myByteArray = QByteArray::fromStdString(myString);

这将把`myString`转换为一个`QByteArray`类型的变量`myByteArray`。你可以在你的代码中使用类似的方法来解决这个问题。