UIResponder of UIKit framework

In the previous blog, the touch event mentioned the response event and the responder chain, and it is UIResponder that manages the responder chain.
1. Code

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions

{

   

    NSLog(@"window:%@",[self.window nextResponder]);

    NSLog(@"AppDelegate: %@",[self nextResponder]);

    return YES;

}

 

//

//  ViewController.m

//  UIResponder

//

//  Created by cyw on 15-5-16.

//  Copyright (c) 2015  cyw. All rights reserved.

//



#import "ViewController.h"



@interface ViewController ()<UITextFieldDelegate>



@end



@implementation ViewController



- (void)viewDidLoad

{

    [super viewDidLoad];

    UITextField *textField=[[UITextField alloc]init];

    textField.frame=CGRectMake(100, 100, 100, 40);

    textField.borderStyle=UITextBorderStyleLine;

    textField.backgroundColor=[UIColor redColor];

    textField.delegate=self;

    textField.tag=10001;

    BOOL canBecomeFirstResponder=[textField canBecomeFirstResponder     ];

    BOOL canResignFirstResponder=[textField canResignFirstResponder];

    NSLog(@"%d  %d",canBecomeFirstResponder,canResignFirstResponder);

    [textField becomeFirstResponder];

    [self.view addSubview:textField];

    

    UITextField *textField1=[[UITextField alloc]init];

    textField1.frame=CGRectMake(100, 200, 100, 40);

    textField1.borderStyle=UITextBorderStyleLine;

    textField1.backgroundColor=[UIColor redColor];

    textField1.delegate=self;

    textField1.tag=10002;

    [self.view addSubview:textField1];

    

     UIResponder *responder1= [textField nextResponder];

     UIResponder *responder2=[self nextResponder];

     UIResponder *responder3=[self.view nextResponder];

     NSLog(@"textField:%@
ViewController:%@
self.view:%@",responder1,responder2,responder3);



}

- (void)textFieldDidBeginEditing:(UITextField *)textField

{

       BOOL isFirstResponder= [textField isFirstResponder];

        NSLog(@"textField%d isFirstResponder %d:",textField.tag,isFirstResponder);

}



- (void)didReceiveMemoryWarning

{

    [super didReceiveMemoryWarning];

    // Dispose of any resources that can be recreated.

}



@end

2. Results

2015-05-17 00:30:02.427 UIResponder[1132:60b] window:<UIApplication: 0x8d71b80>

2015-05-17 00:30:02.437 UIResponder[1132:60b] AppDelegate: (null)

2015-05-17 00:30:02.446 UIResponder[1132:60b] 1  1

2015-05-17 00:30:02.449 UIResponder[1132:60b] textField:<UIView: 0x8e742d0; frame = (0 0; 320 480); autoresize = RM+BM; layer = <CALayer: 0x8e739e0>>

ViewController:(null)

self.view:<ViewController: 0x8c9b8c0>

2015-05-17 00:30:02.463 UIResponder[1132:60b] textField10001 isFirstResponder 1:

3. From the above output results, I am a little puzzled, why ViewController returns NULL? I thought about it for a long time and couldn't think of any reason, please give pointers to experts
Fourth, in fact, UIResponder is not only these, you can refer to: http://southpeak.github.io/blog/2015/03/07/uiresponder/?utm_source=tuicool