A device includes a mounting apparatus and a supporting apparatus. The mounting apparatus includes a fixing bracket, an engaging member slidably mounted to the fixing bracket, and an operation member mounted to the engaging member. The fixing bracket defines first and second engaging holes. The supporting apparatus includes a connecting bracket detachably mounted to the fixing bracket. The fixing bracket defines a connecting hole. The connecting bracket comprises a hook. The engaging member comprises a stop piece. The operation member forms a projection. When the engaging member is slid to engage the projection into the first engaging hole, the stop piece moves away from the connecting hole and the first hook extends through the connecting hole. The engaging member is slid to engage the projection in the second engaging hole, the stop piece moves between the connecting hole and the hook to engage with the hook.