可以不可以这样理解：
MSGpkt = (afIncomingMSGPacket_t *)osal_msg_receive( SampleApp_TaskID );这个条语句只是接收到一个消息，还不知道是什么消息
switch( MSGpkt->hdr.event ) {
caseKEY_CHANGE: //这里发现是一条按键消息， SampleApp_HandleKeys( ((keyChange_t *)MSGpkt)->state, ((keyChange_t *)MSGpkt)->keys );那么上面接收到的消息的内容就是
typedefstruct{ osal_event_hdr_t hdr; uint8 state; // shift uint8 keys; // keys} keyChange_t;这个结构体的内容，如果按照
typedefstruct{ osal_event_hdr_t hdr; /* OSAL Message header */ uint16 groupId; /* Message's group ID - 0 if not set */ uint16 clusterId; /* Message's cluster ID */ afAddrType_t srcAddr; /* Source Address, if endpoint is STUBAPS_INTER_PAN_EP, it's an InterPAN message */ uint16 macDestAddr; /* MAC header destination short address */ uint8 endPoint; /* destination endpoint */ uint8 wasBroadcast; /* TRUE if network destination was a broadcast address */ uint8 LinkQuality; /* The link quality of the received data frame */ uint8 correlation; /* The raw correlation value of the received data frame */ int8 rssi; /* The received RF power in units dBm */ uint8 SecurityUse; /* deprecated */ uint32 timestamp; /* receipt timestamp from MAC */ afMSGCommandFormat_t cmd; /* Application Data */} afIncomingMSGPacket_t;这个结构体访问的话，其实中的uint16 groupId;就是
uint8 state; // shiftuint8 keys; // keys这两个变量的值？