QByteArray::fromHex(hex_str)；报错form_para.cpp:342:68: No viable conversion from 'QString' to 'const QByteArray' qbytearray.h:181:5: candidate constructor not viable: no known conversion from 'QString' to 'const char *' for 1st argument qbytearray.h:189:12: candidate constructor not viable: no known conversion from 'QString' to 'QByteArray &&' for 1st argument qbytearray.h:463:12: candidate constructor not viable: no known conversion from 'QString' to 'QByteArrayDataPtr' for 1st argument qbytearray.h:524:20: candidate constructor not viable: no known conversion from 'QString' to 'const QByteArray &' for 1st argument qbytearray.h:405:67: passing argument to parameter 'hexEncoded' here

根据您提供的信息，这个错误是因为您使用了不同类型的参数。函数QByteArray::fromHex()需要一个十六进制字符串作为输入，而您传递了一个QString类型的参数，导致编译器无法将其转换为QByteArray类型。您需要将QString类型的参数转换为QByteArray类型的十六进制字符串，然后再将其传递给函数QByteArray::fromHex()。您可以使用QString的toUtf8()函数将QString转换为QByteArray类型的十六进制字符串，然后再将其传递给QByteArray::fromHex()函数。例如：

QString hex_str = "616263";
QByteArray hex_data = QByteArray::fromHex(hex_str.toUtf8());