iOS: update constraints programmatically - ios

Question

I have this code to update constraints for a UITextFiled
- (void)updateUIOnePassword {
NSLayoutConstraint *fullTextField = [NSLayoutConstraint constraintWithItem:self.passwordTextField attribute:NSLayoutAttributeTrailing relatedBy:NSLayoutRelationEqual toItem:self.userIdTextField attribute:NSLayoutAttributeTrailing multiplier:1.0f constant:0.0f];
NSLayoutConstraint *cutTextField = [NSLayoutConstraint constraintWithItem:self.passwordTextField attribute:NSLayoutAttributeTrailing relatedBy:NSLayoutRelationEqual toItem:self.userIdTextField attribute:NSLayoutAttributeTrailing multiplier:1.0f constant:-60.0f];
if ([self isOnepasswordAvailable]) {
self.onepasswordButton.alpha = 1.0f;
[self.view removeConstraint:fullTextField];
[self.view addConstraint:cutTextField];
} else {
self.onepasswordButton.alpha = 0.0f;
[self.view addConstraint:fullTextField];
[self.view updateConstraints];
}
[self.view setNeedsUpdateConstraints];
[self.view layoutIfNeeded];
}
when isOnepasswordAvailable is TRUE at start, it works fine, after when I delete OP app and isOnepasswordAvailable is FALSE works well again, but when I enter again in isOnepasswordAvailable when id TRUE the constraints don't work fine anymore and I have some warning in the consolle.
Do you know why?
Thanks

Answer 1

Though I always prefer having an IBOutlet to constraint, you have created a constraint programmatically I believe there must be a good reason for that :)
Couple of issues I noticed,
1> I checked both of your constraints, only thing those constraints vary is in their constant values. I believe you dont have to create two different constraint and add and remove them based on condition. Looks very much complicated.
you can have a property named
#property (nonatomic,strong) NSLayoutConstraint *textFieldConstraint;
and in viewWillAppear
if ([self isOnepasswordAvailable]) {
self.textFieldConstraint = [NSLayoutConstraint constraintWithItem:self.passwordTextField attribute:NSLayoutAttributeTrailing relatedBy:NSLayoutRelationEqual toItem:self.userIdTextField attribute:NSLayoutAttributeTrailing multiplier:1.0f constant:0.0f];
}
else {
self.textFieldConstraint = [NSLayoutConstraint constraintWithItem:self.passwordTextField attribute:NSLayoutAttributeTrailing relatedBy:NSLayoutRelationEqual toItem:self.userIdTextField attribute:NSLayoutAttributeTrailing multiplier:1.0f constant:-60.0f];
}
[self.view addConstraint:self.textFieldConstraint];
[self.view layoutIfNeeded];
2> Update the method updateUIOnePassword as
- (void)updateUIOnePassword {
if ([self isOnepasswordAvailable]) {
self.onepasswordButton.alpha = 1.0f;
self.textFieldConstraint.constant = 0.0f;
} else {
self.onepasswordButton.alpha = 0.0f;
self.textFieldConstraint.constant = -0.60f;
}
[self.view layoutIfNeeded];
}
This should do the job :) Have look buddy :)

Answer 2

- (void)updateUIOnePassword {
NSLayoutConstraint *fullTextField = [NSLayoutConstraint constraintWithItem:self.passwordTextField attribute:NSLayoutAttributeTrailing relatedBy:NSLayoutRelationEqual toItem:self.userIdTextField attribute:NSLayoutAttributeTrailing multiplier:1.0f constant:0.0f];
NSLayoutConstraint *cutTextField = [NSLayoutConstraint constraintWithItem:self.passwordTextField attribute:NSLayoutAttributeTrailing relatedBy:NSLayoutRelationEqual toItem:self.userIdTextField attribute:NSLayoutAttributeTrailing multiplier:1.0f constant:-60.0f];
if ([self isOnepasswordAvailable]) {
self.onepasswordButton.alpha = 1.0f;
[self.view removeConstraint:fullTextField]; //Invalid statement
[self.view addConstraint:cutTextField];
} else {
self.onepasswordButton.alpha = 0.0f;
[self.view addConstraint:fullTextField];
[self.view updateConstraints];
}
[self.view setNeedsUpdateConstraints];
[self.view layoutIfNeeded];
}
You have an invalid statement. - updateUIOnePassword() gets called fullTextField is not have added as constrain and its just an allocation.
meaning you are trying to remove the object which does not present in the array (Array of constraints)
Now my suggestion is, Make a class level instance of cutTextField and fullTextField add them only once.
when you don't need it
[fullTextField setActive:NO];
When you need to modify
[fullTextField setActive:YES]; //if already set to NO
[fullTextField setConstant:100];