主线程，异步线程切换

//TODO:切换到异步线程

• (void) operationOnAnshyThread:(dispatch_block_t)actionBlock{
  if ([NSThread currentThread].isMainThread) {
  dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
  if (actionBlock) {
  actionBlock();
  }
  });
  return;
  }
  if (actionBlock) {
  actionBlock();
  }
  }
  //TODO:切回主线程操作
• (void) operationOnMainThread:(dispatch_block_t)actionBlock{
  if ([NSThread currentThread].isMainThread) {
  if (actionBlock) {
  actionBlock();
  }
  return;
  }
  dispatch_async(dispatch_get_main_queue(), ^{
  if (actionBlock) {
  actionBlock();
  }
  });
  }