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;

}