这里说明下 网络加载启动图这个说法是不对的。这个叫iOS闪屏
转载http://www.starming.com/index.php?v=index&view=21

在- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions 里添加
//加一张自定义的图就实现了。就这么简单。当然复杂的你可以自己在这里实现下
self.window.rootViewController.view.alpha = 0;
UIImageView *splashImageView = [[UIImageView alloc]initWithImage:[UIImage imageNamed:@"splash"]];
[self.window addSubview:splashImageView];
[UIView animateWithDuration:0.7 animations:^{
    self.window.rootViewController.view.alpha = 1.0;
} completion:^(BOOL finished) {
    [addSubview:splashImageView removeFromSuperview];
}];