How to Correctly handle Weak Self in Swift Blocks with Arguments

Question

In my TextViewTableViewCell, I have a variable to keep track of a block and a configure method where the block is passed in and assigned.
Here is my TextViewTableViewCell class:

//
//  TextViewTableViewCell.swift
//

import UIKit

class TextViewTableViewCell: UITableViewCell, UITextViewDelegate {

    @IBOutlet var textView : UITextView

    var onTextViewEditClosure : ((text : String) -> Void)?

    func configure(#text: String?, onTextEdit : ((text : String) -> Void)) {
        onTextViewEditClosure = onTextEdit
        textView.delegate = self
        textView.text = text
    }

    // #pragma mark - Text View Delegate

    func textViewDidEndEditing(textView: UITextView!) {
        if onTextViewEditClosure {
            onTextViewEditClosure!(text: textView.text)
        }
    }
}

When I use the configure method in my cellForRowAtIndexPath method, how do I properly use weak self in the block that I pass in.
Here is what I have without the weak self:

let myCell = tableView.dequeueReusableCellWithIdentifier(textViewCellIdenfitier) as TextViewTableViewCell
myCell.configure(text: body, onTextEdit: {(text: String) in
   // THIS SELF NEEDS TO BE WEAK  
   self.body = text
})
cell = bodyCell

UPDATE: I got the following to work using [weak self]:

let myCell = tableView.dequeueReusableCellWithIdentifier(textViewCellIdenfitier) as TextViewTableViewCell
myCell.configure(text: body, onTextEdit: {[weak self] (text: String) in
        if let strongSelf = self {
             strongSelf.body = text
        }
})
cell = myCell

When I do [unowned self] instead of [weak self] and take out the if statement, the app crashes. Any ideas on how this should work with [unowned self]?

Answer 1

If self could be nil in the closure use [weak self].

If self will never be nil in the closure use [unowned self].

If it's crashing when you use [unowned self] I would guess that self is nil at some point in that closure, which is why you had to go with [weak self] instead.

I really liked the whole section from the manual on using strong, weak, and unowned in closures:

https://developer.apple.com/library/content/documentation/Swift/Conceptual/Swift_Programming_Language/AutomaticReferenceCounting.html

Note: I used the term closure instead of block which is the newer Swift term:

Difference between block (Objective C) and closure (Swift) in ios