ios 简单的 KVO 示例
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Simple KVO example
提问by WebOrCode
I am trying to do simple KVO example, but I am having problems.
我正在尝试做简单的 KVO 示例，但我遇到了问题。
This is my *.m file:
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
Note:I have a button which when clicked it will increment the numberproperty.
I want to be notified when numberproperty is changed.
注意：我有一个按钮，单击它会增加number属性。
我想在number属性更改时收到通知。
The code is not working and I can not figure it why.
代码不起作用，我不知道为什么。
采纳答案by codester
KVO works with setter and getter and in incNumberyou are directly accessing iVar so instead of that use self.number
KVO 与 setter 和 getter 一起使用，并且incNumber您直接访问 iVar，而不是使用self.number
- (IBAction)incNumber:(id)sender
{
self.number++;
NSLog(@"%d", self.number);
}
回答by Abizern
Rather than:
而不是：
_number++;
Try:
尝试：
[self willChangeValueForKey:@"number"];
_number++;
[self didChangeValueForKey:@"number"];
or ever better just:
或者更好的是：
self.number++
And let the system take care of the willChangeValueForKey:and didChangeValueForKey:methods.
并让系统照顾willChangeValueForKey:和didChangeValueForKey:方法。
回答by parvind
@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
and in other class where i am using this class
在我使用这个课程的其他课程中
TraineeLocationCell *locationView;//create object here
[locationView addObserver:self forKeyPath:@"traineeAddress" options:NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld context:nil];//observing the key in this class
//this is the delegate method which take care of value is changed or not
//这是处理值是否改变的委托方法
-(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"]];
}
}
