How to change or update NSLayoutConstraint programmatically
OK, I figure out.
[self.view removeConstraint:self.constraintOld];
[self.view addConstraint:self.constraintNew];
[UIView animateWithDuration:time animations:^{
[self.view layoutIfNeeded];
}];
I think you have 2 options.
Option 1 Keep a property
@property (strong,nonatomic)NSLayoutConstraint *constraintToAnimate3;
Then use this property to
self.constraintToAnimate3 = [NSLayoutConstraint constraintWithItem:PreView
attribute:NSLayoutAttributeWidth
relatedBy:NSLayoutRelationEqual
toItem:self.view
attribute:NSLayoutAttributeWidth
multiplier:1
constant:-1 * 0.4 * self.view.frame.size.width];
[self.view addConstraint:self.constraintToAnimate3];
When you want to change
if(connected){
self.constraintToAnimate3.constant = -1 *0.6 * self.view.frame.size.width;
}
else{
self.constraintToAnimate3.constant = -1 *0.4 * self.view.frame.size.width;
}
[UIView animateWithDuration:yourduration animations:^{
[self.view layoutIfNeeded];
}];
Option 2 Set an identifier of constraintToAnimate3
constraintToAnimate3.identifier = @"1234"
Then search to get the constraint
NSLayoutConstraint * constraint3 = nil;
NSArray * constraints = self.view.constraints;
for (NSLayoutConstraint * constraint in constraints) {
if ([constraint.identifier isEqualToString:@"1234"]) {
constraint3 = constraint;
break;
}
}
Then change the constant as shown in Option1
Update: If use constant in the code I post
PreView.frame.size.with = self.view.size.width * multiplier + constant