CGRectMake标签没有出现

Question

I've just started to make a new app with a navigation bar. I made the first view with the navigation in the AppDelegate.m .

AppDelegate.m :

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    sleep(2);
    self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
    // Override point for customization after application launch.
    self.window.backgroundColor = [UIColor whiteColor];
    UINavigationController* nav = [[UINavigationController alloc] initWithRootViewController:[[HomeViewController alloc] initWithNibName:@"HomeViewController" bundle:nil]];
    self.window.rootViewController = nav;
    [self.window makeKeyAndVisible];
    return YES;
}

Then, I making the view of the HomeViewController inside loadView method.

LoadView of HomeViewController :

- (void)loadView
{
    self.view = [[UIView alloc] init];
    self.view.backgroundColor = [UIColor whiteColor];
    self.searchPoiInstructionsLabel = [[UILabel alloc] initWithFrame:CGRectMake(0, 0, 50, 20)];
    self.searchPoiInstructionsLabel.layer.borderColor = [UIColor blackColor].CGColor;
    self.searchPoiInstructionsLabel.layer.borderWidth = 2.0f;
    self.searchPoiInstructionsLabel.text = @"HELLO WORLD";
    [self.view addSubview:self.searchPoiInstructionsLabel];
}

My label Hello World doesn't appear...

For the frame, if I set CGRectMake(0, 65, 50, 20) , 65 for y , my "Hello World" appears... (I know, I have to increase the width :) )

I just don't understand the origins of my view... If someone can explain me please.

Thanks

Answer 1

This is iOS7 baggage. If you run your app under iOS6, you will see the label as you expect/intend.

Under iOS7, your view originates under the navigation bar which is why you don't see the label when you set the frame to originate at 0,0. If you look really closely, you can actually see the blurred label behind the Carrier indicator in the status bar.

There are multiple ways to work with this:

If the UINavigationBar is not translucent, then the 0,0 origin will work.

You can update the labels frame using topLayoutGuide

You could use a UIScrollView instead of UIView

Answer 2

---

Origin in iOS 7 is kind of different. In a Navigation Controller, things below Navigation bar can be showed a little with blur effect. So the label's origin in the Navigation Controller is up-left (0, 0) point below the Navigation bar instead of the leftest point under the Navigation bar. Here a demo for you.

Answer 3

- (void)viewDidLoad
{
    [super viewDidLoad];
    if ([[[[UIDevice currentDevice]systemVersion] componentsSeparatedByString:@"."][0] intValue] >=7)    {
      if ([self respondsToSelector:@selector(edgesForExtendedLayout)]) {
        self.edgesForExtendedLayout = UIRectEdgeNone;
      }
    }
}