监听textView的属性的改变，用通知，代理不好用

/**
*  添加textView
*/
- (void)setupTextView
{
// 1.添加
IWTextView *textView = [[IWTextView 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];
}

- (void)dealloc
{
[[NSNotificationCenter defaultCenter] removeObserver:self];
}

/**
*  监听文字改变
*/
- (void)textDidChange
{
self.navigationItem.rightBarButtonItem.enabled = (self.textView.text.length != 0);
}