监听textView文字改变的通知

/**
 *  添加textView
 */
- (void)setupTextView
{
    //1.添加
    TextView *textView = [[TextView alloc] init];
    textView.font = [UIFont systemFontOfSize:15];
    textView.frame = self.view.bounds;
    [self.view addSubview:textView];
    self.textView = textView;
    
    //2.监听textView文字改变的通知
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(textDidChange) name:UITextViewTextDidChangeNotification object:textView];
}

/**
 *  监听textView文字改变
 */
- (void)textDidChange
{
    self.navigationItem.rightBarButtonItem.enabled = (self.textView.text.length != 0);
}
- (void)dealloc
{
    //移除监听
    [[NSNotificationCenter defaultCenter] removeObserver:self];
}


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