- (void)showOrHideNavPrompt{
BOOL show = YES;
double delayInSeconds =1.0;
dispatch_time_t popTime =dispatch_time(DISPATCH_TIME_NOW, (int64_t)(delayInSeconds * NSEC_PER_SEC));
dispatch_after(popTime,dispatch_get_main_queue(), ^(void){
if(show) {
[self.navigationItemsetPrompt:@"Add photos with faces to Googlyify them!"]; }else {
[self.navigationItemsetPrompt:nil];
} });}
看 https://github.com/nixzhu/dev-blog/blob/master/2014-04-19-grand-central-dispatch-in-depth-part-1.md GCD深入理解时发现的。
