Custom UITableViewCell Constraints - swift

Question

I'm creating a chat using a UITable with custom cells for the chat bubbles. Like WhatsApp, I want some bubbles to be on the left, and some to be on the right.
I'm using dequeueReusableCell(withIdentifier identifier: String) -> UITableViewCell?, which calls the cell's init(style:reuseIdentifier:) method so setup my cell with:
override init(style: UITableViewCell.CellStyle, reuseIdentifier: String?) {
cellBackground = UIView()
super.init(style: style, reuseIdentifier: reuseIdentifier)
backgroundColor = .clear
setupConstraints()
}
func setupConstraints() {
NSLayoutConstraint.activate([
cellBackground.topAnchor.constraint(equalTo: contentView.topAnchor),
cellBackground.bottomAnchor.constraint(equalTo: contentView.bottomAnchor),
cellBackground.leadingAnchor.constraint(equalTo: contentView.leadingAnchor),
cellBackground.widthAnchor.constraint(equalTo: contentView.widthAnchor, multiplier: 0.5)
])
}
but this isn't satisfactory. The cell is always on the left, due to the leadingAnchor constraint - when the cell is on the right it needs to be a trailingAnchor constraint.
If I use a setup function for the cell, should setupConstraints be called there, or should the init setup the constraints it knows about at that time? Alternatively, should these constraints all be set up in layoutSubviews()?

Answer 1

Add 2 instance variables as a references to the leading and trailing constraints inside the cell custom class
var leadCon,traCon:NSLayoutConstraint!
Then inside init also but out of the activate
leadCon = cellBackground.leadingAnchor.constraint(equalTo: contentView.leadingAnchor)
leadCon.isActive = true
And
traCon = cellBackground.trailingAnchor.constraint(equalTo: contentView.trailingAnchor)
traCon.isActive = true
According to what you need add a func
func toLeft(_ value:Bool) {
if value {
leadCon.isActive = true
traCon.isActive = false
}
else {
leadCon.isActive = false
traCon.isActive = true
}
}
And call it after dequeue line in cellForRowAt