Question

我正在尝试做简单的KVO示例，但我遇到了问题。

这是我的* .m文件：

#import "KVO_ViewController.h"

@interface KVO_ViewController ()

@property NSUInteger number;

@end

@implementation KVO_ViewController

- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.

    [self addObserver:self forKeyPath:@"number" options:NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld context:nil];
}

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

- (IBAction)incNumber:(id)sender
{
    _number++;
    NSLog(@"%d", _number);
}

-(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{
    NSLog(@"From KVO");

    if([keyPath isEqualToString:@"number"])
    {
        id oldC = [change objectForKey:NSKeyValueChangeOldKey];
        id newC = [change objectForKey:NSKeyValueChangeNewKey];

        NSLog(@"%@ %@", oldC, newC);
    }
}

@end

注意：我有一个按钮，点击该按钮会增加number属性。
我想在number属性更改时收到通知。

代码无效，我无法理解为什么。

Answer 1

KVO适用于setter和getter，incNumber您正在直接访问iVar，而不是使用self.number

- (IBAction)incNumber:(id)sender
{
    self.number++;
    NSLog(@"%d", self.number);
}

Answer 2

而不是：

_number++;

尝试：

[self willChangeValueForKey:@"number"];
_number++;
[self didChangeValueForKey:@"number"];

或者更好的只是：

self.number++

让系统处理willChangeValueForKey:和didChangeValueForKey:方法。

Answer 3

@interface TraineeLocationCell : UIView
@property (strong, nonatomic) NSString *traineeAddress;
@end

@implementation

// in textview delgate method  i am setting traineeAddress string value
- (void)textViewDidEndEditing:(UITextView *)textView
{
    if (textView.text.length >0)
    [self setValue:textView.text forKey:@"traineeAddress"];

}

@end

以及我正在使用此课程的其他课程

 TraineeLocationCell *locationView;//create object here
 [locationView addObserver:self forKeyPath:@"traineeAddress" options:NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld context:nil];//observing the key in this class

//这是代理方法，它处理的值是否改变

-(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{
   if([keyPath isEqualToString:@"traineeAddress"]){
        if (!settingsValues.address)
            settingsValues.address = [[NSMutableArray alloc]initWithObjects:[change valueForKey:@"new"], nil];

        else
            [settingsValues.address replaceObjectAtIndex:0 withObject:[change valueForKey:@"new"]];
    }
}

简单的KVO例子

3 个答案: