textfield未输入时有提示文字，一输入显示发布按钮，并隐藏提示文字

#pragma mark- 评论输入change时判断
- (void)textViewDidChange:(UITextView *)textView
{
    if(textView.isFirstResponder){
        if(textView.text == nil || [textView.text isEqualToString:@""]){
            [self.commentsView setPostButtonHidden:YES];
            [self.commentsView setInputPlaceholderEnabled:YES];
        } else {
            [self.commentsView setPostButtonHidden:NO];
            [self.commentsView setInputPlaceholderEnabled:NO];
        }
    }
}

 

#pragma mark- post按钮消失与否的控制
- (void)setPostButtonHidden:(BOOL)hidden
{
    const CGFloat duration = 0.20;
    CGFloat alpha = hidden ? 0 : 1.0;
    CGFloat delay = hidden ? 0 : 0.05;
    
    [UIView animateWithDuration:duration
                          delay:delay
                        options:UIViewAnimationOptionCurveEaseOut
                     animations:^{
                         [self.postButton setAlpha:alpha];
    }completion:nil];
}

- (void)setInputPlaceholderEnabled:(BOOL)enabled
{
    _inputPlaceholderEnabled = enabled;
    [self.commentTextViewPlaceholder setHidden:!enabled];
}

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