How to Turn a UITextView into "Pages" like an E-reader [closed] - swift

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I have a Text View that contains a long passage. Rather than have a user scroll to keep reading, I want to separate the text into pages.
The screen would take up the full amount of text it can, and then the user can click a next or previous page. In other words, the behavior of any e-reader on the market.
I really am not sure where to start with. I would assume a few things I would have to do:
Get the character count of the string that will go in the text view.
Get the view width and height of the user's text view on his device
Figure out how many characters from the character count can be displayed on the text view based on the user's device dimensions.
With whatever formula I come up with, dynamically choose the text amount based on this.
let count = str.count
let userWidth = UIScreen.main.bounds.size.width
let userHeight = UIScreen.main.bounds.size.height
However, there is nothing I can come up with that works, and even this doesn't seem like it is the right path.
Any advice on how to start on creating e-reader page turning functionality? I can use a UIWebView instead of a UITextView if that makes it easier.
Thanks!

Answer 1

You're on the right track, but your implementation will only work for monospaced fonts (Menlo, Courier, etc) because the letter widths of proportional fonts (Helvetica, Times, etc) vary from letter to letter. Also, your plan would have the text breaking in the middle of words, which is probably sub-optimal.
TextKit has tools to make all this easier for you. If you want to do standard pagination, with wrapping at word boundaries instead of inside them, you can use the NSLayoutManager to do this for you.
A few notes:
You can't use the screen width to accurately calculate the size of the view, because you need to account for safe areas and the textContainerInset of the UITextView.
I'll leave pagination to you. You can either calculate the pages up from, or simple move forward or backwards through the ranges by trimming the previous page from the string.
func stringThatFitsOnScreen(originalString: String) -> String? {
// the visible rect area the text will fit into
let userWidth = textView.bounds.size.width - textView.textContainerInset.right - textView.textContainerInset.left
let userHeight = textView.bounds.size.height - textView.textContainerInset.top - textView.textContainerInset.bottom
let rect = CGRect(x: 0, y: 0, width: userWidth, height: userHeight)
// we need a new UITextView object to calculate the glyphRange. This is in addition to
// the UITextView that actually shows the text (probably a IBOutlet)
let tempTextView = UITextView(frame: self.textView.bounds)
tempTextView.font = textView.font
tempTextView.text = originalString
// get the layout manager and use it to layout the text
let layoutManager = tempTextView.layoutManager
layoutManager.ensureLayout(for: tempTextView.textContainer)
// get the range of text that fits in visible rect
let rangeThatFits = layoutManager.glyphRange(forBoundingRect: rect, in: tempTextView.textContainer)
// convert from NSRange to Range
guard let stringRange = Range(rangeThatFits, in: originalString) else {
return nil
}
// return the text that fits
let subString = originalString[stringRange]
return String(subString)
}
There are more complex ways to mix and match text views, layout managers, and text containers. You can investigate it as you get a handle on the easy stuff.