This paper investigates the problem of resilient decentralized control for nonlinear interconnected systems with unknown control directions under denial-of-service (DoS) attacks. For each subsystem, a novel switched sampled-data observer and an adaptive control architecture are respectively proposed to deal with the unavailable correction term in the existing results. Then a resilient decentralized adaptive controller is developed by employing the backstepping technique to reduce the negative influences of the system uncertainties and DoS attacks. By using average dwell time (ADT) and piecewise Lyapunov stability theories, one can ensure that the closed-loop system is semiglobally uniformly ultimately bounded (SUUB), while the output reference signal of each subsystem is tracked bounded. Furthermore, this scheme has a better utilization of computing and communication resources. Finally, the proposed scheme is verified by a power network system simulation.