获取时间戳
- (NSString*)simulateAndRenderScene
{
NSDate* dat = [NSDate dateWithTimeIntervalSinceNow:0];
NSTimeInterval a=[dat timeIntervalSince1970]*1000;
NSString *timeString = [NSString stringWithFormat:@"%f", a];
NSLog(@"stringTime = %@",stringTime);
return timeString;
}