How to add constraints to a dynamically created UITextField? - swift

Question

I have created UITextFields dynamically. Now i want to refer to the TextFields to check for some constraints. How do i do so?
func displayTextBox1(height: Int, placeHolder: String, xtb: Int, ytb: Int, lableName: String, xl: Int, yl: Int) {
DispatchQueue.main.async{
self.textField = UITextField(frame: CGRect(x: xtb, y: ytb, width: 343, height: height))
self.textField.textAlignment = NSTextAlignment.left
self.textField.textColor = UIColor.black
self.textField.borderStyle = UITextBorderStyle.line
self.textField.autocapitalizationType = UITextAutocapitalizationType.words // If you need any capitalization
self.textField.placeholder = placeHolder
print("hi")
self.view.addSubview(self.textField)
self.displayLabel(labelName: lableName, x: xl, y: yl)
}
}

Answer 1

You can set constraints programmaticaly using the sample explained code below:
let constraint = NSLayoutConstraint(item: self.textField, attribute: NSLayoutAttribute.width, relatedBy: NSLayoutRelation.equal, toItem: self.view, attribute: NSLayoutAttribute.width, multiplier: 1, constant: -50)
NSLayoutConstraint.activate([constraint])
As you can see, I am creating a constraint for item textField which width should be equal to width of view multiplied by 1 minus 50. That means the width of your textField will be 50 pixels less than the width of the view. The last line of code activates given set of created constraints.

Answer 2

Welcome to Stackoverflow, and hope you're enjoying learning Swift!
I'm going to make some assumptions based on your code snippet:
the details you need to create the textfield and label (position, placeholder text etc) are coming from some service that operates on a background thread (perhaps a HTTP request?) which is why you're using DispatchQueue.main.async to perform UI events back on the main thread.
there will be multiple textfield/label pairs that you're going to configure and add to the interface (not just a single pair)... perhaps a 'todo' list sort of app where a label and textfield let people enter a note (more on this in part 2 of answer) which is why these views (and constraints) are being created in code rather than in a storyboard.
you want to invest in a constraint-based layout rather than frame-based positioning.
Answer part 1
If any of those assumptions are incorrect, then parts of this answer probably won't be relevant.
But assuming the assumptions are correct I suggest a couple things:
Use a separate helper methods to create a textfield/view and return the result (rather than doing everything in a single method) -- methods that have a single purpose will make more sense and be easier to follow.
Don't use a mixture of setting view position/size with frame and constraints - use one approach or the other (since you're new it will be easier to keep a single mental model of how things are working rather than mixing).
Here's a snippet of what a view controller class might start to look like:
import UIKit
class ViewController: UIViewController {
func triggeredBySomeEvent() {
// assuming that you have some equivilent to `YouBackgroundRequestManager.getTextFieldLabelDetails`
// that grabs the info you need to create the label and textfield on a background thread...
YouBackgroundRequestManager.getTextFieldLabelDetails { tfPlaceholder, tfHeight, tfX, tfY, labelName, labelX, labelY in
// perform UI work on the main thread
DispatchQueue.main.async{
// use our method to dynamically create a textfield
let newTextField: UITextField = self.createTextfield(with: tfPlaceholder, height: tfHeight)
// add textfield to a container view (in this case the view controller's view)
self.view.addSubview(newTextField)
// add constraints that pin the textfield's left and top anchor relative to the left and top anchor of the view
newTextField.leftAnchor.constraint(equalTo: self.view.leftAnchor, constant: tfX).isActive = true
newTextField.topAnchor.constraint(equalTo: self.view.topAnchor, constant: tfY).isActive = true
// repeat for label...
let newLabel: UILabel = self.createLabel(with: labelName)
self.view.addSubview(newLabel)
newLabel.leftAnchor.constraint(equalTo: self.view.leftAnchor, constant: labelX).isActive = true
newLabel.topAnchor.constraint(equalTo: self.view.topAnchor, constant: labelY).isActive = true
}
}
}
// create, configure, and return a new textfield
func createTextfield(with placeholder: String, height: CGFloat) -> UITextField {
let textField = UITextField(frame: .zero) // set the frame to zero because we're going to manage this with constraints
textField.placeholder = placeholder
textField.textAlignment = .left
textField.textColor = .black
textField.borderStyle = .line
textField.autocapitalizationType = .words
// translatesAutoresizingMaskIntoConstraints = false is important here, if you don't set this as false,
// UIKit will automatically create constraints based on the `frame` of the view.
textField.translatesAutoresizingMaskIntoConstraints = false
textField.heightAnchor.constraint(equalToConstant: height).isActive = true
textField.widthAnchor.constraint(equalToConstant: 343.0).isActive = true
return textField
}
// create, configure and return a new label
func createLabel(with labelName: String) -> UILabel {
let label = UILabel()
label.text = labelName
label.translatesAutoresizingMaskIntoConstraints = false
return label
}
}
Answer part 2
I'm struggling to imagine the situation where you actually want to do this. If you are making a UI where elements repeat themselves (like a todo list, or maybe a spreadsheet-type interface) then this approach is not the right way to do.
If you want to create a UI where elements repeat themselves as repeating elements in a single column you should investigate using a UITableViewController where you create a cell that represents a single element, and have a tableview manage that collection of cells.
If you want to create a UI where elements repeat themselves in any other way than a vertical list, then you investigate using UICollectionViewController which is a little more complex, but a lot more powerful.
Apologies if this answer goes off-topic, but hope that inspires some ideas that are useful for you.