Objective-C加载自定义Xib关联Outlet触发NSUnknownKeyException报错求助

问题场景与报错信息 #

开发Objective-C项目时，自定义CollectionViewCell的Xib并关联Outlet后，出现如下崩溃：

2023-06-07 22:50:32.194106-0700 ProturisApp[91070:2437111] *** Terminating app due to uncaught exception 'NSUnknownKeyException', reason: '[<InputCollectionViewCell 0x10403ee78> setValue:forUndefinedKey:]: this class is not key value coding-compliant for the key brickWall.'

相关代码如下：

UIView分类（NIBLoader） #

@implementation UIView (NIBLoader)
+ (instancetype)fromNib {
    return [[[NSBundle mainBundle] loadNibNamed:NSStringFromClass([self class]) owner:self options:nil] objectAtIndex:0];
}
@end

InputCollectionViewCell实现 #

#import "InputCollectionViewCell.h"
#define IDENTIFFIER @"InputCollectionViewCell"

@implementation InputCollectionViewCell

-(instancetype)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
      if (self) {
          [self loadFromNib];
  
      }
      return self;
}
- (instancetype)initWithCoder:(NSCoder *)coder
{
    self = [super initWithCoder:coder];
       if (self) {
           [self loadFromNib];
           self.userInteractionEnabled = YES;
           
           // Initialize what is needed
       }
       return self;
}

+ (NSString *) identifier {
    return IDENTIFFIER;
}


- (void)loadFromNib {
    UIView *nibView = [[self class] fromNib];
    if (nibView) {
        nibView.frame = self.bounds;
        nibView.autoresizingMask = UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleHeight;
        [self addSubview:nibView];
        nibView.backgroundColor = [UIColor redColor];
    }
}

@end

MainViewController关键代码 #

#import "MainViewController.h"

@interface MainViewController ()

@end

@implementation MainViewController
@synthesize menuCollectionView;

- (void)viewDidLoad {
    [super viewDidLoad];
 
    [self.menuCollectionView registerClass:[InputCollectionViewCell class] forCellWithReuseIdentifier:[InputCollectionViewCell identifier]];

    menuCollectionView.delegate = self;
    menuCollectionView.dataSource = self;
}
- (void)viewWillDisappear:(BOOL)animated
{
    [super viewWillDisappear:animated];
    [InputCollectionViewCell dealloc];
}


- (nonnull __kindof UICollectionViewCell *)collectionView:(nonnull UICollectionView *)collectionView cellForItemAtIndexPath:(nonnull NSIndexPath *)indexPath {
    // Dequeue a reusable cell from the collection view.
    InputCollectionViewCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:[InputCollectionViewCell identifier] forIndexPath:indexPath];
     [cell addBorderAndShadow];

       // Configure the cell with data for the index path.
 //      MyData *data = self.myDataArray[indexPath.item];
    //   [cell configureWithData:data];

       // Return the configured cell.
       return cell;
}
@end

Xib配置截图：

修复步骤 #

1. 检查并修复Outlet关联 #

• 打开对应的Xib文件，找到名为brickWall的控件，右键点击查看连线列表，确认所有连线都指向InputCollectionViewCell类，且该类的.h文件中存在对应的属性声明：

  @property (nonatomic, weak) IBOutlet <控件类型，如UIView/UIImageView> *brickWall;
  

• 如果之前删除过该属性但未清除Xib中的连线，直接删除无效的连线即可。

2. 修正Nib加载的Owner参数 #

当前UIView (NIBLoader)中fromNib方法的owner传的是类对象（self），这会导致KVC关联错误。修改为：

@implementation UIView (NIBLoader)
+ (instancetype)fromNib {
    // 加载Nib时owner设为nil，避免不必要的KVC关联
    return [[[NSBundle mainBundle] loadNibNamed:NSStringFromClass([self class]) owner:nil options:nil] firstObject];
}
@end

或者在InputCollectionViewCell的loadFromNib方法中直接指定owner为当前实例：

- (void)loadFromNib {
    UIView *nibView = [[NSBundle mainBundle] loadNibNamed:NSStringFromClass([self class]) owner:self options:nil].firstObject;
    if (nibView) {
        nibView.frame = self.bounds;
        nibView.autoresizingMask = UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleHeight;
        [self addSubview:nibView];
        nibView.backgroundColor = [UIColor redColor];
    }
}

3. 修正CollectionView的Cell注册方式 #

使用Xib创建的Cell，应该注册Nib而非Class，否则CollectionView会用纯代码创建Cell，导致Xib加载逻辑冲突。修改MainViewController的viewDidLoad：

- (void)viewDidLoad {
    [super viewDidLoad];
 
    // 替换registerClass为registerNib
    UINib *cellNib = [UINib nibWithNibName:[InputCollectionViewCell identifier] bundle:nil];
    [self.menuCollectionView registerNib:cellNib forCellWithReuseIdentifier:[InputCollectionViewCell identifier]];

    menuCollectionView.delegate = self;
    menuCollectionView.dataSource = self;
}

同时，移除InputCollectionViewCell中initWithFrame:和initWithCoder:里的[self loadFromNib]调用，因为注册Nib后CollectionView会自动加载Xib创建Cell，重复加载会导致子视图重复添加及KVC错误。

4. 删除手动调用dealloc的代码 #

viewWillDisappear中的[InputCollectionViewCell dealloc];是错误操作，dealloc由系统自动调用，手动调用会引发内存问题，直接删除该行代码。

内容的提问来源于stack exchange，提问作者Jael Ruvalcaba