WifiManager单元对WIFI_STATE_CHANGED_ACTION的解释:
Broadcast intent action indicating that Wi-Fi has been enabled, disabled,
* enabling, disabling, or unknown. One extra provides this state as an int.
* Another extra provides the previous state, if available.
即WiFi的打开关闭等相关变化的广播
STATE_CHANGE则是指WiFi连接到一个ssid后的广播