如何使用kvo来观察文本文件的文本更改? [英] how to use kvo to observer textfiled's text change?

问题描述

演示非常简单

// add a textField to viewController's view 
UITextField *textField = [[UITextField alloc] initWithFrame:CGRectMake(0, 30, 375, 40)];

self.textField = textField;

textField.placeholder = @"Please input text";

// add observer for textField's attribute "text"
[textField addObserver:self forKeyPath:@"text" options:NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld context:nil];

[self.view addSubview:textField];

然后实现该方法:

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary<NSString *,id> *)change context:(void *)context {


NSLog(@"----  text changed"); 
}

在dealloc方法中:

at the dealloc method :

- (void)dealloc {

[_textField removeObserver:self forKeyPath:@"text"];
}

但是当我输入text时，方法watchValueForKeyPath:ofObject:change:context:不执行

but when i input text , the method observeValueForKeyPath:ofObject:change:context: do not execute

我不知道为什么

推荐答案

您只需要为UITextView事件中的UIControlEventEditingChanged事件向自己添加目标.请参见下面的示例:

You just need to add a target to self for the UIControlEventEditingChanged event to the UITextView. See the example below:

[textField addTarget:self 
              action:@selector(textFieldDidChange:) 
    forControlEvents:UIControlEventEditingChanged];

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