为UITextView添加通知..来检测UITextView内容的改变

self.mTextView =[[UITextView alloc]initWithFrame:CGRectMake(0, 0, SCREEN_WIDTH - 100, 28)];
    self.mTextView.backgroundColor =[UIColor whiteColor];
    self.mTextView.delegate = self;
    self.mTextView.text = @"我来说几句....";

[self.mSecondaryBackView addSubview:self.mTextView];

[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(textDidChanged:) name:UITextViewTextDidChangeNotification object:nil];

- (void)textDidChanged:(NSNotification *)notif //监听文字改变 换行时要更改输入框的位置
{
    CGSize contentSize = self.mTextView.contentSize;
    UILabel *holdPlace = (UILabel *)[self.mTextView viewWithTag:1500];
    if (holdPlace) {
            holdPlace.text = @"";
    }

if (contentSize.height > 140){
        return;
    }
    CGFloat minus = 3;
    CGRect selfFrame = self.mBackView.frame;
    CGFloat selfHeight = self.mTextView.superview.frame.origin.y * 2 + contentSize.height - minus + 2 * 2;
    CGFloat selfOriginY = selfFrame.origin.y - (selfHeight - selfFrame.size.height);
    selfFrame.origin.y = selfOriginY;
    selfFrame.size.height = selfHeight;
    self.mBackView.frame = selfFrame;
    self.mSecondaryBackView.frame =CGRectMake(10, 10, 230, selfHeight-20);
    NSLog(@"文字改变");

}