A small code snippet to show small in-app notifications on iOS. These notifications cover the Status Bar.

StatusBarNotificationManager.h

//
//  StatusBarNotificationManager.h
//
//  Created by Rahul Jiresal on 2015-09-23.
//

#import <Foundation/Foundation.h>
#import <UIKit/UIKit.h>

@interface StatusBarNotificationManager : NSObject

+ (void)showWithMessage:(NSString*)message backgroundColor:(UIColor*)bgColor autoHide:(BOOL)autoHide;
+ (void)hide;
+ (UIColor*)errorColor;
+ (UIColor*)warningColor;
+ (UIColor*)successColor;


@end

StatusBarNotificationManager.m

//
//  StatusBarNotificationManager.m
//
//  Created by Rahul Jiresal on 2015-09-23.
//

#import "StatusBarNotificationManager.h"

@interface StatusBarNotificationManager ()

@property (strong, nonatomic) UIWindow* notificationWindow;
@property (strong, nonatomic) UILabel* notificationLabel;
@property BOOL currentlyShowing;

@end

@implementation StatusBarNotificationManager

static StatusBarNotificationManager *STATUSBARNOTIFICATIONMANAGER_SINGLETON = nil;
static bool isFirstAccess = YES;

+ (id)sharedInstance
{
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        isFirstAccess = NO;
        STATUSBARNOTIFICATIONMANAGER_SINGLETON = [[super allocWithZone:NULL] init];
    });
    
    return STATUSBARNOTIFICATIONMANAGER_SINGLETON;
}

#pragma mark - Life Cycle

+ (id) allocWithZone:(NSZone *)zone {
    return [self sharedInstance];
}

+ (id)copyWithZone:(struct _NSZone *)zone {
    return [self sharedInstance];
}

+ (id)mutableCopyWithZone:(struct _NSZone *)zone {
    return [self sharedInstance];
}

- (id)copy {
    return [[StatusBarNotificationManager alloc] init];
}

- (id)mutableCopy {
    return [[StatusBarNotificationManager alloc] init];
}

- (id) init {
    if(STATUSBARNOTIFICATIONMANAGER_SINGLETON){
        return STATUSBARNOTIFICATIONMANAGER_SINGLETON;
    }
    if (isFirstAccess) {
        [self doesNotRecognizeSelector:_cmd];
    }
    self = [super init];
    return self;
}


+ (void)showWithMessage:(NSString*)message backgroundColor:(UIColor*)bgColor autoHide:(BOOL)autoHide {
    [[StatusBarNotificationManager sharedInstance] showWithMessage:message backgroundColor:bgColor];
    if (autoHide) {
        dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(0.5 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
            [[StatusBarNotificationManager sharedInstance] hideAnimated:YES];
        });
    }
}

+ (void)hide {
    [[StatusBarNotificationManager sharedInstance] hideAnimated:YES];
}

+ (UIColor*)errorColor {
    return [UIColor colorWithRed:249.0/255.0 green:83.0/255.0 blue:114.0/255.0 alpha:1.0];
}

+ (UIColor*)warningColor {
    return [UIColor colorWithRed:255.0/255.0 green:153.0/255.0 blue:0.0/255.0 alpha:1.0];
}

+ (UIColor*)successColor {
    return [UIColor colorWithRed:29.0/255.0 green:156.0/255.0 blue:90.0/255.0 alpha:1.0];
}

- (void)showWithMessage:(NSString*)message backgroundColor:(UIColor*)bgColor {
    if (!self.notificationWindow) {
        self.notificationWindow = [[UIWindow alloc] initWithFrame:CGRectMake(0, -[UIApplication sharedApplication].statusBarFrame.size.height, [[UIScreen mainScreen] bounds].size.width, [UIApplication sharedApplication].statusBarFrame.size.height)];
        [self.notificationWindow setWindowLevel:UIWindowLevelStatusBar + 1];
        self.notificationLabel = [[UILabel alloc] initWithFrame:CGRectMake(0, 0, [[UIScreen mainScreen] bounds].size.width, [UIApplication sharedApplication].statusBarFrame.size.height)];
        [self.notificationLabel setTextAlignment:NSTextAlignmentCenter];
        [self.notificationLabel setTextColor:[UIColor whiteColor]];
        [self.notificationLabel setFont:[UIFont systemFontOfSize:12.0]];
        [self.notificationWindow addSubview:self.notificationLabel];
    }
    
    if (self.currentlyShowing) {
        [self hideAnimated:NO];
    }
    
    [self.notificationWindow setBackgroundColor:bgColor];
    [self.notificationLabel setText:message];
    [self.notificationWindow setHidden:NO];

    [UIView animateWithDuration:0.1 animations:^{
        [self.notificationWindow setFrame:CGRectMake(0, 0, [[UIScreen mainScreen] bounds].size.width, [UIApplication sharedApplication].statusBarFrame.size.height)];
    }];
}

- (void)hideAnimated:(BOOL)animated {
    if (animated) {
        [UIView animateWithDuration:0.1 animations:^{
            [self.notificationWindow setFrame:CGRectMake(0, -[UIApplication sharedApplication].statusBarFrame.size.height, [[UIScreen mainScreen] bounds].size.width, [UIApplication sharedApplication].statusBarFrame.size.height)];
        } completion:^(BOOL finished) {
            [self.notificationWindow setHidden:YES];
        }];
    }
    else {
        [self.notificationWindow setHidden:YES];
        [self.notificationWindow setFrame:CGRectMake(0, -[UIApplication sharedApplication].statusBarFrame.size.height, [[UIScreen mainScreen] bounds].size.width, [UIApplication sharedApplication].statusBarFrame.size.height)];
    }
}

@end