Photoelectron diffraction theory is applied to the investigation of the dependence of magnetic dichroism and spin polarization on the emission direction of photoelectrons in angle-resolved core-level photoemission. It is shown that photoelectron diffraction effects may cause significant modulations in the angular dependence of magnetic dichroism in angle-resolved core-level photoemission. Furthermore, it is pointed out that both magnetic dichroism and spin polarization should show the same angular dependence on the electron emission direction. Results of photoelectron diffraction theory are discussed in detail for p-type core-level photoemission in comparison with those of the single-atom approach. The applied theory gives a good explanation of the experimental data of Fe 3p and Co 2p photoelectrons excited in thin Fe and Co films, respectively.