“这个类不是密钥值编码兼容的密钥号码。”

Question

我刚刚开始使用iOS开发，并认为一个好的第一个应用程序将是一个简单的计算器。不幸的是，每当我尝试运行该应用程序时，它都会崩溃，并显示错误“此类不是密钥值编码兼容密钥numberFour”。

这是ViewController.h：

#import <UIKit/UIKit.h>

 @interface ViewController : UIViewController
- (IBAction)numberZero:(id)sender;
- (IBAction)numberOne:(id)sender;
- (IBAction)numberTwo:(id)sender;
- (IBAction)numberThree:(id)sender;
- (IBAction)numberFour:(id)sender;
- (IBAction)numberFive:(id)sender;
- (IBAction)numberSix:(id)sender;
- (IBAction)numberSeven:(id)sender;
- (IBAction)numberNine:(id)sender;
- (IBAction)numberEight:(id)sender;
@property (weak, nonatomic) IBOutlet UILabel *expressionView;

-(void)updateExpressionView; 

@property NSNumber *operandOne;
@property NSNumber *operandTwo;
@property NSNumber *one;
@property NSNumber *two;
@property NSNumber *three;
@property NSNumber *four;
@property NSNumber *five;
@property NSNumber *six;
@property NSNumber *seven;
@property NSNumber *eight;
@property NSNumber *nine;
@property NSNumber *zero;

@property NSMutableArray *expression; 

@end

这是ViewController.m：

#import "ViewController.h"



@interface ViewController ()

@end

@implementation ViewController


- (void)viewDidLoad
 {
    [super viewDidLoad];
     // Do any additional setup after loading the view, typically from a nib.
     self.one = [NSNumber numberWithInt: 1];
     self.two = [NSNumber numberWithInt:2];
     self.three = [NSNumber numberWithInt:3];
     self.four = [NSNumber numberWithInt: 4];
     self.five = [NSNumber numberWithInt:5];
     self.six = [NSNumber numberWithInt: 6];
     self.seven = [NSNumber numberWithInt:7];
     self.eight = [NSNumber numberWithInt:8];
     self.nine = [NSNumber numberWithInt: 9];
     self.zero = [NSNumber numberWithInt:0];

 }

- (void)didReceiveMemoryWarning
{
     [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

- (IBAction)numberOne:(id)sender {
    [self.expression addObject:self.one];
    [self updateExpressionView];

}

 - (IBAction)numberTwo:(id)sender {
     [self.expression addObject: self.two];
     [self updateExpressionView];


}

- (IBAction)numberThree:(id)sender {
    [self.expression addObject: self.three];
    [self updateExpressionView];

}

- (IBAction)numberFour:(id)sender {
     [self.expression addObject: self.four];
     [self updateExpressionView];

      }

  - (IBAction)numberFive:(id)sender {
     [self.expression addObject: self.five];
     [self updateExpressionView];


  }

  - (IBAction)numberSix:(id)sender {
      [self.expression addObject:self.six];
      [self updateExpressionView];

  } 

 - (IBAction)numberSeven:(id)sender {
     [self.expression addObject: self.seven];
     [self updateExpressionView];

 }

 - (IBAction)numberNine:(id)sender {
     [self.expression addObject: self.nine];
     [self updateExpressionView];

 }
 - (IBAction)numberZero:(id)sender {
     [self.expression addObject: self.zero];
     [self updateExpressionView];

 }

 - (IBAction)numberEight:(id)sender {
     [self.expression addObject: self.eight];
     [self updateExpressionView];

 }

 -(void)updateExpressionView {
      NSString *expressionNSString = (NSString *)self.expression;
      self.expressionView.text = expressionNSString;
  }
 @end

Answer 1

在xib或storyboard中，此场景没有正确指定View Controller的类型。当您为计算器选择场景时，可以在界面构建器中找到它，并检查其属性（请参见附图）。您需要将该类设置为从UIViewController继承的自定义类的名称（在本例中为ViewController）。

Answer 2

您的.xib或storyboard文件中没有连接numberFour，或者文件所有者更可能不是ViewController类型。

Answer 3

很抱歉没有将此作为评论添加，我没有足够的声誉（最低要求50分）。

之前已经问过这个问题，请看SO：What does this mean? "'NSUnknownKeyException', reason: … this class is not key value coding-compliant for the key X"就是一个例子。

1. 您是否检查过您的视图（在故事板中）使用了正确的控制器ViewController？
2. 您是否正确地将故事板中的IBAction与实际视图相关联？ （如果nr.1是正确的，根据我的经验，这通常不重要。）

Answer 4

您确定所有IBAction都是xib上的链接或故事板中的视图吗？

在添加对象之前，您还需要初始化数组：

self.expression = [[NSMutableArray alloc] init]; // add this line just after [super viewDidLoad];