App中遇到需要用户打开设置界面的需求时，可以友好的引导用户去设置界面设置，而不是只是添加个提示，让用户自己去设置（可能他们也不知道怎么设置）
这样提示用户是不是很友好呢，那如何实现呢
UIAlertController * controller = [UIAlertController alertControllerWithTitle:@"提示" message:@"123456" preferredStyle:UIAlertControllerStyleAlert];
UIAlertAction * action = [UIAlertAction actionWithTitle:@"Settiogs" style:UIAlertActionStyleDefault handler:^(UIAlertAction * _Nonnull action) {
NSURL * appSettings = [NSURL URLWithString:UIApplicationOpenSettingsURLString];
[[UIApplication sharedApplication] openURL:appSettings];
}];
[controller addAction:action];
[self presentViewController:controller animated:YES completion:nil];
我开始在Appdelegate是这样写的（TextViewController * vc = [[TextViewController alloc]init];self.window.rootViewController = vc;（这个controller是根controller上发现界面不显示 出现这个错误Attempt to presentonwhose view is not in the window hierarchy!）当我变成这样写时
TextViewController * vc = [[TextViewController alloc]init];
UINavigationController * nav = [[UINavigationController alloc]initWithRootViewController:vc];
self.window.rootViewController = nav; 就ok了
非常重要的代码是NSURL * appSettings = [NSURL URLWithString:UIApplicationOpenSettingsURLString];
[[UIApplication sharedApplication] openURL:appSettings];
}]；
可以打开设置
