windows - SHGetDriveMedia 和同步

Question

识别我使用的媒体SHGetDriveMedia；在我传递的第二个参数上pdwMediaContent作为参考，api 插入内容的类型。但是，识别是异步完成的。我怎么知道api什么时候完成了识别？

Answer 1

它不是异步的。当您在将磁盘放入驱动器后立即调用它时，它处于“嗅探阶段”，试图确定应该使用哪种自动播放磁盘的方法。当函数返回时，可以在ARCONTENT标志中返回几个检测阶段：

ARCONTENT_PHASE_UNKNOWN (0x00000000)
  Introduced in Windows Vista. AutoPlay is searching the media. The phase of the 
  search (presniff, sniffing, or final) is unknown.

ARCONTENT_PHASE_PRESNIFF (0x10000000)
  Introduced in Windows Vista. The contents of the media are known before the 
  media is searched, due to the media type; for instance, audio CDs and DVD movies.

ARCONTENT_PHASE_SNIFFING (0x20000000)
  Introduced in Windows Vista. AutoPlay is currently searching the media. Any 
  results reported during this phase should be considered a partial list as more 
  content types might still be found.

ARCONTENT_PHASE_FINAL (0x40000000)
  Introduced in Windows Vista. AutoPlay has finished searching the media. Results 
  reported are final.

ARCONTENT_PHASE_MASK (0x70000000)
  Introduced in Windows Vista. A mask that denotes valid ARCONTENT_PHASE values.

这似乎表明（基于上面的文本ARCONTENT_PHASE_FINAL）您应该期望需要多次调用此函数，直到您在返回的标志中收到该值，此时您可以检查磁盘标志中的其他值类型。