关于z-stack结构体默认对齐方式与强制转换问题，急，求大神回答

搞不懂以下这两个结构体为什么可以转换

uint16 SampleApp_ProcessEvent( uint8 task_id, uint16 events )
{
  afIncomingMSGPacket_t * MSGpkt;

  if ( events & SYS_EVENT_MSG )
  {
    MSGpkt = (afIncomingMSGPacket_t *)osal_msg_receive( SampleApp_TaskID );
    while ( MSGpkt )
    {
      switch ( MSGpkt->hdr.event )
      {
        
        case KEY_CHANGE:
          SampleApp_HandleKeys( ((keyChange_t *)MSGpkt)->state, ((keyChange_t *)MSGpkt)->keys );
          break;

1
typedef struct
{
  osal_event_hdr_t hdr;
  uint8             state; // shift
  uint8             keys;  // keys
} keyChange_t;


typedef struct
{
  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;

消息头一直，第一次转换 一般只取消息头信息

 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