如何做UITextView滚动检测和更改图像

Question

It looks like this :

(I can't show image please I don't have 10 prestiges)

let departmentMessage = UITextView(frame: CGRect(x: 25, y: 1500 /      2, width: UIScreen.main.bounds.size.width - 50, height: (UIScreen.main.bounds.size.height - 50)/4 ))
    showBlshText()
    departmentMessage.isScrollEnabled = true
    departmentMessage.isPagingEnabled = true
    departmentMessage.isEditable = false
    departmentMessage.isSelectable = true
    departmentMessage.dataDetectorTypes = UIDataDetectorTypes.link 
    departmentMessage.textColor = UIColor.darkGray

    departmentMessage.textAlignment = .left
    departmentMessage.contentMode = .topLeft

    departmentMessage.backgroundColor = UIColor(displayP3Red: 100, green: 100, blue: 100, alpha: 20)
    departmentMessage.font = UIFont(name: "Helvetica-Light", size: 20)
    self.view.addSubview(departmentMessage)
    departmentMessage.removeFromSuperview()

I expect the output of the word to change, but the actual output isn't work.

Answer 1

UITextView is a subclass of UIScrollView . So everything that a scrollView does a textView can do also. In you case, it seems that you want to do some action when the textView is scrolled. You should look the UIScrollViewDelegate documentation which describes how you can monitor a scrollView to see when it is scrolled. There are a few tips to know:

• the delegate is not called when you set the content offset programatically.
• scrollViewDidEndDecelerating: is not called when scrollViewDidEndDragging:willDecelerate: is called with NO for the willDecelerate value.

So just set your viewController as the delegate, implement the appropriate methods, and change your UI accordingly.

Also, you might have better luck using a UICollectionView or a UITableView. Even if every row is just a label, it is far easier to track what indexPath is at the top of the collectionView then what text is at the top of textView. But without knowing exactly what you are doing it is hard to say.