Kdevelop5 doesn't hint the class members automatically

I use Kdevelop5 on OpenSUSE leap 15.1 and I am conducting the numerical computation with the "armadillo" library. I have included the head file of the "armadillo" library But I found Kdevelop5 doesn't hint the class members automatically. For example, in the following program.

#include <armadillo>
#include <iostream>
using namespace std;
int main(int argc, char** argv) {
  
    arma::mat A;
    arma::vec So  
    return 0;
}

If I input "A. ", it should give me all the class members of the "arm::A" class. I have run the same program in NetBeans c++, NetBeans c++ can give me right hint. Could you please give me some suggestions. Regards