Software Defined Networking (SDN) is an emerging technology that is replacing traditional networks in many advanced applications such as network virtualization and cloud computing. Recently, SDN has been proposed for wireless networks to add flexibility to incorporate exponentially increasing wireless traffic and to adapt network configurations on the fly, and it is known as Software Defined Wireless Networking or SDWN. There have been several methods proposed for SDWN because of the benefits it offers such as flexibility, manageability and having greater control over the network. In this paper, we present a comprehensive study of different approaches for SDWN along with its challenges and benefits. We also outline current state of the research and future perspectives. With this paper, readers can have a more thorough understanding of SDWN and the research trends in this area.