您不需要私人API，只需在您的applicationDidFinishLaunching方法中尝试。

  controller = [[UITabBarController alloc] initWithNibName：nil bundle：nil]; 

 HeadlinesViewController * headlines = [[HeadlinesViewController alloc] init]; 
 OpinionsViewController * opinion = [[OpinionsViewController alloc] init]; 

 controller.viewControllers = [NSArray arrayWithObjects：headlines，opinion，nil]; 

 //设置你的位置，宽度和高度
 controller.tabBar.frame = CGRectMake（0，20，320，50）; 
 [window addSubview：controller.view]; 
 [window makeKeyAndVisible]; 
 

This looks like a long shot, but does anyone know of a way to:

1. Position a UITabBar on the top part of the screen
2. Change it's height

You are welcome to suggest private API methods

you don't need private API, just try this in your applicationDidFinishLaunching method.

controller = [[UITabBarController alloc] initWithNibName:nil bundle:nil];

HeadlinesViewController *headlines = [[HeadlinesViewController alloc] init];
OpinionsViewController *opinions = [[OpinionsViewController alloc] init];

controller.viewControllers = [NSArray arrayWithObjects:headlines, opinions, nil];

    // set your position , width and height there
controller.tabBar.frame = CGRectMake(0, 20, 320, 50);
[window addSubview:controller.view ];
[window makeKeyAndVisible];