iOS task list hint

BackgroundHint.m

//
//  BackgroundHint.m
//  Zus
//
//  Created by Lex on 4/13/16.
//  Copyright © 2016 lex.sh. All rights reserved.
//

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

@interface BackgroundHint : NSObject

@end

@implementation BackgroundHint

static const UInt8 kBackgroundHintTag = 45;

+ (void) load {

    [[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(showHint)
                                                 name:UIApplicationDidEnterBackgroundNotification
                                               object:nil];

    [[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(hideHint)
                                                 name:UIApplicationDidBecomeActiveNotification
                                               object:nil];

    [[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(hideHint)
                                                 name:UIApplicationWillEnterForegroundNotification
                                               object:nil];
}

+ (UIImageView *) hintImageView {
    UIImageView *view = [[UIImageView alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
    view.autoresizingMask = UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleHeight;
    view.image = [UIImage imageNamed:@"background_hint"];
    view.tag = kBackgroundHintTag;
    [view setContentMode:UIViewContentModeScaleAspectFill];
    return view;
}

+ (void) showHint {
    UIView *view = [[UIApplication sharedApplication] keyWindow].subviews.lastObject;
    [view addSubview: [self hintImageView]];
}

+ (void) hideHint {
    UIView *view = [[UIApplication sharedApplication] keyWindow].subviews.lastObject;
    UIView *hintView = [view viewWithTag:kBackgroundHintTag];
    [hintView removeFromSuperview];
}

@end