Integrating simultaneous wireless information and power transfer (SWIPT) into cooperative cognitive radio networks (CCRN) can increase both energy and spectral efficiencies. In contrast to most of existing works that only consider relay transmission, this paper studies opportunistic relaying along with dynamic energy harvesting in SWIPT-based CCRN. We first propose a new framework that can unify the direct transmission, relay transmission and energy harvesting. Under the proposed framework, we then formulate the optimization problem of maximizing the ergodic capacity for secondary user (SU) while meeting the ergodic capacity for the primary user (PU) and average harvested energy for SU, by joint transmission mode selection and transmit power splitting ratio selection. The problem is nonconvex and we propose the optimal policy by using the dual Lagrangian method. Simulations validate the effectiveness of the proposed scheme.