title: Cannot select/edit text in UITextView within UIScrollView
body: <p>I have setup my UIScrollView with subviews like so using Masonry:</p>
  
  <pre><code>- (void)setupViews {
      self.view.backgroundColor = [UIColor Background];
      self.scrollView = [UIScrollView new];
      self.scrollView.alwaysBounceVertical = YES;
      [self.view addSubview:self.scrollView];
      [self.scrollView mas_makeConstraints:^(MASConstraintMaker *make) {
          make.edges.equalTo(self.view);
      }];
      self.contentView = [UIView new];
      [self.scrollView addSubview:self.contentView];
      self.scrollView.backgroundColor = [UIColor clearColor];
      [self.contentView mas_makeConstraints:^(MASConstraintMaker *make) {
          make.edges.equalTo(self.scrollView);
          make.left.and.right.equalTo(self.view);
      }];
      self.imageButton = [UIButton buttonWithType:UIButtonTypeCustom];
      [self.imageButton sd_setImageWithURL:[NSURL URLWithString:self.card.cardImageURL] forState:UIControlStateNormal];
      [self.imageButton.imageView setContentMode:UIViewContentModeScaleAspectFill];
      [self.contentView addSubview:self.imageButton];
      [self.imageButton mas_makeConstraints:^(MASConstraintMaker *make) {
          make.left.top.and.right.equalTo(self.contentView);
          make.height.equalTo(self.imageButton.mas_width).multipliedBy(3/4.0);
      }];
      self.textField = [UITextField new];
      self.textField.backgroundColor = [UIColor whiteColor];
      self.textField.font = kFontRegular(14);
      self.textField.text = self.card.cardTitle;
      [self.contentView addSubview:self.textField];
      [self.textField mas_makeConstraints:^(MASConstraintMaker *make) {
          make.left.equalTo(self.contentView).with.offset(8);
          make.top.equalTo(self.imageButton.mas_bottom).with.offset(8);
          make.right.equalTo(self.contentView).with.offset(-8);
          make.height.equalTo(@(45));
      }];
  }
  </code></pre>
  
  <p>but it will not let me interact with the UITextField. what element here is preventing user interaction?
  <a href="https://i.stack.imgur.com/FoGXc.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/FoGXc.png" alt="Screenshot"></a></p>