How to update constrain when textField have input text - ios

Question

I have a question right now. I have a textField, a tableView and a label. When textField text is empty,the tableView is hidden.But when user input something in textField, the list of tableView will show on the View. TableView's position is between textField and label. How to update this constrain? I try to do this, but it doesn't work for me. Thanks.
class ViewController: UIViewController, UITextFieldDelegate,UITableViewDelegate,UITableViewDataSource {
var tableView: UITableView = UITableView()
var textField: UITextField = UITextField()
var label:UILabel = UILabel()
var haveText:Bool = false
var autoCompletePossibilities = ["Wand","Wizard","Test","1","12","123","1234","12345"]
var autoComplete = [String]()
var tableviewHeightConstraint:NSLayoutConstraint?
override func loadView() {
super.loadView()
tableView.translatesAutoresizingMaskIntoConstraints = false
textField.translatesAutoresizingMaskIntoConstraints = false
label.translatesAutoresizingMaskIntoConstraints = false
loadContent()
}
override func viewWillLayoutSubviews() {
super.viewWillLayoutSubviews()
loadVFL()
}
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view, typically from a nib.
textField.delegate = self
tableView.delegate = self
tableView.dataSource = self
textField.backgroundColor = UIColor.lightGray
tableView.backgroundColor = UIColor.brown
label.backgroundColor = UIColor.cyan
label.text = "hello I'm beginner.Nice."
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}
func DictionaryOfInstanceVariables(_ container:AnyObject, objects: String ...) -> [String:AnyObject] {
var views = [String:AnyObject]()
for objectName in objects {
guard let object = object_getIvar(container, class_getInstanceVariable(type(of: container), objectName)) else {
assertionFailure("\(objectName) is not an ivar of: \(container)");
continue
}
views[objectName] = object as AnyObject?
}
return views
}
func loadContent() {
view.addSubview(textField)
view.addSubview(tableView)
view.addSubview(label)
}
func loadVFL() {
let views = DictionaryOfInstanceVariables(self, objects:
"textField"
,"label"
,"tableView"
)
let metrics = ["padding":15]
self.view.addConstraints(NSLayoutConstraint.constraints(withVisualFormat: "H:|[textField]|", options: [], metrics: metrics, views: views))
self.view.addConstraints(NSLayoutConstraint.constraints(withVisualFormat: "H:|[label]|", options: [], metrics: metrics, views: views))
self.view.addConstraints (NSLayoutConstraint.constraints(withVisualFormat: "H:|[tableView]|", options: [], metrics: metrics, views: views))
//declare tableview height constraints and init here
tableviewHeightConstraint = NSLayoutConstraint.init(item: view,
attribute: .height,
relatedBy: .equal,
toItem: nil,
attribute: .notAnAttribute,
multiplier: 1,
constant: 0) // init it with a 0 height
tableView.addConstraint(tableviewHeightConstraint!) // add the constraint to the tableView
self.view.addConstraints (NSLayoutConstraint.constraints(withVisualFormat: "V:|-50-[textField(60.0)][tableView][label(30.0)]", options: [], metrics: metrics, views: views))
}
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = UITableViewCell()
let index = indexPath.row as Int
cell.textLabel?.text = autoComplete[index]
cell.backgroundColor = UIColor.green
return cell
}
func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return autoComplete.count
}
func textFieldShouldBeginEditing(_ textField: UITextField) -> Bool {
tableviewHeightConstraint?.constant = 160; // required height
UIView.animate(withDuration: 0.5) { // animate so it will be pretty
self.view.layoutIfNeeded()
}
return true
}
func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
let subString = (textField.text! as NSString).replacingCharacters(in: range, with: string)
searchAutocompleteEntriesWithSubString(subString: subString)
return true
}
func searchAutocompleteEntriesWithSubString(subString:String)
{
autoComplete.removeAll(keepingCapacity: false)
for key in autoCompletePossibilities {
let myString:NSString = key as NSString
let subStringRange:NSRange = myString.range(of: subString)
if subStringRange.location == 0 {
autoComplete.append(key)
}
}
tableView.reloadData()
}
}
log print:
Probably at least one of the constraints in the following list is one you don't want.
Try this:
(1) look at each constraint and try to figure out which you don't expect;
(2) find the code that added the unwanted constraint or constraints and fix it.
(
"NSLayoutConstraint:0x60800009be40 V:[UITextField:0x7fc04db09e10]-(0)-[UITableView:0x7fc04e81e400] (active)",
"NSLayoutConstraint:0x60800009bf30 UITableView:0x7fc04e81e400.height == 150 (active)",
"NSLayoutConstraint:0x60800009d4c0 V:[UITableView:0x7fc04e81e400]-(0)-[UILabel:0x7fc04be057c0'hello I'm beginner.Nice.'] (active)",
"NSLayoutConstraint:0x600000281360 V:[UITextField:0x7fc04db09e10]-(0)-[UILabel:0x7fc04be057c0'hello I'm beginner.Nice.'] (active)"
)
Will attempt to recover by breaking constraint
NSLayoutConstraint:0x60800009d4c0 V:[UITableView:0x7fc04e81e400]-(0)-[UILabel:0x7fc04be057c0'hello I'm beginner.Nice.'] (active)
Make a symbolic breakpoint at UIViewAlertForUnsatisfiableConstraints to catch this in the debugger.
The methods in the UIConstraintBasedLayoutDebugging category on UIView listed in <UIKit/UIView.h> may also be helpful.
2017.06.16 UPdate new crash log:
crash log here.
2017.06.16 Finally successful code:
class ViewController: UIViewController, UITextFieldDelegate,UITableViewDelegate,UITableViewDataSource {
var tableView: UITableView = UITableView()
var textField: UITextField = UITextField()
var label:UILabel = UILabel()
var haveText:Bool = false
var autoCompletePossibilities = ["Wand","Wizard","Test","1","12","123","1234","12345"]
var autoComplete = [String]()
var tableviewHeightConstraint:NSLayoutConstraint?
override func loadView() {
super.loadView()
tableView.translatesAutoresizingMaskIntoConstraints = false
textField.translatesAutoresizingMaskIntoConstraints = false
label.translatesAutoresizingMaskIntoConstraints = false
loadContent()
loadVFL()
}
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view, typically from a nib.
textField.delegate = self
tableView.delegate = self
tableView.dataSource = self
textField.backgroundColor = UIColor.lightGray
tableView.backgroundColor = UIColor.brown
label.backgroundColor = UIColor.cyan
label.text = "hello I'm beginner.Nice."
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}
func DictionaryOfInstanceVariables(_ container:AnyObject, objects: String ...) -> [String:AnyObject] {
var views = [String:AnyObject]()
for objectName in objects {
guard let object = object_getIvar(container, class_getInstanceVariable(type(of: container), objectName)) else {
assertionFailure("\(objectName) is not an ivar of: \(container)");
continue
}
views[objectName] = object as AnyObject?
}
return views
}
func loadContent() {
view.addSubview(textField)
view.addSubview(tableView)
view.addSubview(label)
}
func loadVFL() {
let views = DictionaryOfInstanceVariables(self, objects:
"textField"
,"label"
,"tableView"
)
let metrics = ["padding":15]
tableviewHeightConstraint = NSLayoutConstraint.init(item: tableView,
attribute: .height,
relatedBy: .equal,
toItem: nil,
attribute: .height,
multiplier: 1,
constant: 0) // init it with a 0 height
tableView.addConstraint(tableviewHeightConstraint!) // add the constraint to the tableView
self.view.addConstraints(NSLayoutConstraint.constraints(withVisualFormat: "H:|[textField]|", options: [], metrics: metrics, views: views))
self.view.addConstraints(NSLayoutConstraint.constraints(withVisualFormat: "H:|[label]|", options: [], metrics: metrics, views: views))
self.view.addConstraints(NSLayoutConstraint.constraints(withVisualFormat: "H:|[tableView]|", options: [], metrics: metrics, views: views))
self.view.addConstraints(NSLayoutConstraint.constraints(withVisualFormat: "V:|-50.0-[textField(60.0)][tableView][label(30.0)]", options: [], metrics: metrics, views: views))
}
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = UITableViewCell()
let index = indexPath.row as Int
cell.textLabel?.text = autoComplete[index]
cell.backgroundColor = UIColor.green
return cell
}
func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return autoComplete.count
}
func textFieldShouldBeginEditing(_ textField: UITextField) -> Bool {
super.updateViewConstraints()
tableView.removeConstraints(tableView.constraints)
tableviewHeightConstraint = NSLayoutConstraint(item: tableView, attribute: .height, relatedBy: .equal , toItem: nil, attribute: .height, multiplier: 1, constant: 160.0)
tableView.addConstraint(tableviewHeightConstraint!) // add the constraint to the tableView
UIView.animate(withDuration: 0.5) { // animate so it will be pretty
self.updateViewConstraints()
self.view.layoutIfNeeded()
}
return true
}
func textFieldShouldReturn(_ textField: UITextField) -> Bool {
super.updateViewConstraints()
textField.resignFirstResponder()
tableView.removeConstraints(tableView.constraints)
tableviewHeightConstraint = NSLayoutConstraint(item: tableView, attribute: .height, relatedBy: .equal , toItem: nil, attribute: .height, multiplier: 1, constant: 0.0)
tableView.addConstraint(tableviewHeightConstraint!) // add the constraint to the tableView
UIView.animate(withDuration: 0.5) { // animate so it will be pretty
self.updateViewConstraints()
self.view.layoutIfNeeded()
}
return true
}
func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
let subString = (textField.text! as NSString).replacingCharacters(in: range, with: string)
searchAutocompleteEntriesWithSubString(subString: subString)
return true
}
func searchAutocompleteEntriesWithSubString(subString:String)
{
autoComplete.removeAll(keepingCapacity: false)
for key in autoCompletePossibilities {
let myString:NSString = key as NSString
let subStringRange:NSRange = myString.range(of: subString)
if subStringRange.location == 0 {
autoComplete.append(key)
}
}
tableView.reloadData()
}
}
(IMAGE) Finally View like this.

Answer 1

My approach will be loading all the needed constraints on loadVFL.
func loadVFL() {
let views = DictionaryOfInstanceVariables(self, objects:
"textField"
,"tableView"
,"label"
)
let metrics = ["padding":15]
self.view.addConstraints (NSLayoutConstraint.constraints(withVisualFormat: "H:|[textField]|", options: [], metrics: metrics, views: views))
self.view.addConstraints (NSLayoutConstraint.constraints(withVisualFormat: "H:|[tableView]|", options: [], metrics: metrics, views: views))
self.view.addConstraints (NSLayoutConstraint.constraints(withVisualFormat: "H:|[label]|", options: [], metrics: metrics, views: views))
//declare tableview height constraints and init here
tableviewHeightConstraint = NSLayoutConstraint.init(item: tableView,
attribute: .height,
relatedBy: .equal,
toItem: nil,
attribute: .notAnAttribute,
multiplier: 1,
constant: 0) // init it with a 0 height
tableView.addConstraint(tableviewHeightConstraint) // add the constraint to the tableView
self.view.addConstraints (NSLayoutConstraint.constraints(withVisualFormat: "V:|-50-[textField(60.0)][tableView][label(30.0)]", options: [], metrics: metrics, views: views))
}
After initialising in your textShouldBeginEditing function activate your tableview constraint:
func textFieldShouldBeginEditing(_ textField: UITextField) -> Bool {
tableviewHeightConstraint.constant = 160; // required height
UIView.animateWithDuration(0.5) { // animate so it will be pretty
self.view.layoutIfNeeded()
}
return true
}
If you want to hide to it on some function you call when you are done searching. Just set the constant back to 0
I think that should work. Give it a try and let me know