这是我在UIViewController类别中的东西。对很多事情都很有用，包括获取第一响应者。积木很棒!

- (UIView*) enumerateAllSubviewsOf: (UIView*) aView UsingBlock: (BOOL (^)( UIView* aView )) aBlock {

 for ( UIView* aSubView in aView.subviews ) {
  if( aBlock( aSubView )) {
   return aSubView;
  } else if( ! [ aSubView isKindOfClass: [ UIControl class ]] ){
   UIView* result = [ self enumerateAllSubviewsOf: aSubView UsingBlock: aBlock ];

   if( result != nil ) {
    return result;
   }
  }
 }    

 return nil;
}

- (UIView*) enumerateAllSubviewsUsingBlock: (BOOL (^)( UIView* aView )) aBlock {
 return [ self enumerateAllSubviewsOf: self.view UsingBlock: aBlock ];
}

- (UIView*) findFirstResponder {
 return [ self enumerateAllSubviewsUsingBlock:^BOOL(UIView *aView) {
  if( [ aView isFirstResponder ] ) {
   return YES;
  }

  return NO;
 }];
}

而不是遍历视图集合寻找设置了isFirstResponder的视图，我也将消息发送给nil，但我存储了消息的接收器，以便我可以返回它并对它做任何我想做的事情。

此外，我将在调用本身的deferred语句中保存找到的responder的optional归零。这确保在调用结束时没有引用保留——即使是弱引用。

import UIKit

private var _foundFirstResponder: UIResponder? = nil

extension UIResponder {

    static var first:UIResponder? {

        // Sending an action to 'nil' implicitly sends it to the first responder
        // where we simply capture it and place it in the _foundFirstResponder variable.
        // As such, the variable will contain the current first responder (if any) immediately after this line executes
        UIApplication.shared.sendAction(#selector(UIResponder.storeFirstResponder(_:)), to: nil, from: nil, for: nil)

        // The following 'defer' statement runs *after* this getter returns,
        // thus releasing any strong reference held by the variable immediately thereafter
        defer {
            _foundFirstResponder = nil
        }

        // Return the found first-responder (if any) back to the caller
        return _foundFirstResponder
    }

    // Make sure to mark this with '@objc' since it has to be reachable as a selector for `sendAction`
    @objc func storeFirstResponder(_ sender: AnyObject) {

        // Capture the recipient of this message (self), which is the first responder
        _foundFirstResponder = self
    }
}

有了上面的，我可以通过简单地这样做辞去第一响应者…

UIResponder.first?.resignFirstResponder()

但由于我的API实际上交还了第一个responder是什么，我可以对它做任何我想做的事情。

下面是一个示例，它检查当前的第一个响应器是否是一个带有helpMessage属性设置的UITextField，如果是，则在控件旁边的帮助气泡中显示它。我们通过屏幕上的“Quick Help”按钮来调用它。

func showQuickHelp(){

    if let textField = UIResponder?.first as? UITextField,
       let helpMessage = textField.helpMessage {
    
        textField.showHelpBubble(with:helpMessage)
    }
}

对上述的支持在UITextField上的扩展中定义，就像这样…

extension UITextField {
    var helpMessage:String? { ... }
    func showHelpBubble(with message:String) { ... }
}

现在要支持这个功能，我们所要做的就是决定哪些文本字段有帮助消息，UI会为我们处理其余的事情。

这是递归的一个很好的候选!不需要添加一个类别到UIView。

用法(来自你的视图控制器):

UIView *firstResponder = [self findFirstResponder:[self view]];

代码:

// This is a recursive function
- (UIView *)findFirstResponder:(UIView *)view {

    if ([view isFirstResponder]) return view; // Base case

    for (UIView *subView in [view subviews]) {
        if ([self findFirstResponder:subView]) return subView; // Recursion
    }
    return nil;
}

这是一个类别，允许您通过调用[UIResponder currentFirstResponder]快速找到第一个响应器。只需添加以下两个文件到您的项目:

UIResponder + FirstResponder.h:

#import <Cocoa/Cocoa.h>
@interface UIResponder (FirstResponder)
    +(id)currentFirstResponder;
@end

UIResponder + FirstResponder.m:

#import "UIResponder+FirstResponder.h"
static __weak id currentFirstResponder;
@implementation UIResponder (FirstResponder)
    +(id)currentFirstResponder {
         currentFirstResponder = nil;
         [[UIApplication sharedApplication] sendAction:@selector(findFirstResponder:) to:nil from:nil forEvent:nil];
         return currentFirstResponder;
    }
    -(void)findFirstResponder:(id)sender {
        currentFirstResponder = self;
    }
@end

这里的技巧是将一个动作发送给nil将它发送给第一个响应者。

(我最初在这里发表了这个答案:https://stackoverflow.com/a/14135456/322427)

这是我所做的，当用户单击ModalViewController中的Save/Cancel时，找到什么UITextField是第一个responder:

    NSArray *subviews = [self.tableView subviews];

for (id cell in subviews ) 
{
    if ([cell isKindOfClass:[UITableViewCell class]]) 
    {
        UITableViewCell *aCell = cell;
        NSArray *cellContentViews = [[aCell contentView] subviews];
        for (id textField in cellContentViews) 
        {
            if ([textField isKindOfClass:[UITextField class]]) 
            {
                UITextField *theTextField = textField;
                if ([theTextField isFirstResponder]) {
                    [theTextField resignFirstResponder];
                }

            }
        }

    }

}

下面是一个基于Jakob Egger最优秀的答案在Swift中实现的扩展:

import UIKit

extension UIResponder {
    // Swift 1.2 finally supports static vars!. If you use 1.1 see: 
    // http://stackoverflow.com/a/24924535/385979
    private weak static var _currentFirstResponder: UIResponder? = nil
    
    public class func currentFirstResponder() -> UIResponder? {
        UIResponder._currentFirstResponder = nil
        UIApplication.sharedApplication().sendAction("findFirstResponder:", to: nil, from: nil, forEvent: nil)
        return UIResponder._currentFirstResponder
    }
    
    internal func findFirstResponder(sender: AnyObject) {
        UIResponder._currentFirstResponder = self
    }
}

斯威夫特4

import UIKit    

extension UIResponder {
    private weak static var _currentFirstResponder: UIResponder? = nil
    
    public static var current: UIResponder? {
        UIResponder._currentFirstResponder = nil
        UIApplication.shared.sendAction(#selector(findFirstResponder(sender:)), to: nil, from: nil, for: nil)
        return UIResponder._currentFirstResponder
    }
    
    @objc internal func findFirstResponder(sender: AnyObject) {
        UIResponder._currentFirstResponder = self
    }
}