How to change or update NSLayoutConstraint programmatically
I have implemented AutoLayout programmatically using the Code :
- (void)addConstraintWithListNavigationViewController:(UIView *)listViewNavigation y:(CGFloat)y height:(CGFloat)height
{
//WIDTH_ListTableView = 0.4
//set x = 0;
NSLayoutConstraint *constraintToAnimate1 = [NSLayoutConstraint constraintWithItem:listViewNavigation
attribute:NSLayoutAttributeLeft
relatedBy:NSLayoutRelationEqual
toItem:self.view
attribute:NSLayoutAttributeLeft
multiplier:0.00
constant:0];
[self.view addConstraint:constraintToAnimate1];
//set y = y;
NSLayoutConstraint *constraintToAnimate2 = [NSLayoutConstraint constraintWithItem:listViewNavigation
attribute:NSLayoutAttributeTop
relatedBy:NSLayoutRelationEqual
toItem:self.view
attribute:NSLayoutAttributeBottom
multiplier:0.00
constant:y];
[self.view addConstraint:constraintToAnimate2];
//set Width = self.view.frame.size.width*0.4
NSLayoutConstraint *constraintToAnimate3 = [NSLayoutConstraint constraintWithItem:listViewNavigation
attribute:NSLayoutAttributeWidth
relatedBy:NSLayoutRelationEqual
toItem:self.view
attribute:NSLayoutAttributeWidth
multiplier:1-WIDTH_ListTableView
constant:0.0];
[self.view addConstraint:constraintToAnimate3];
//Set height = height
NSLayoutConstraint *constraintToAnimate4 = [NSLayoutConstraint constraintWithItem:listViewNavigation
attribute:NSLayoutAttributeHeight
relatedBy:NSLayoutRelationEqual
toItem:nil
attribute:NSLayoutAttributeNotAnAttribute
multiplier:0.00
constant:height];
[self.view addConstraint:constraintToAnimate4];
}
And this works perfect, but every-time this ViewController receives a Notification, it will run:
[self.view layoutIfNeeded];
But I want to set the width of listViewNavigation according a boolean variable connected.
if(connected){
listViewNavigation.view.frame.size.width = 0.4 * self.view.frame.size.width;
}
else{
listViewNavigation.view.frame.size.width = 0.6 * self.view.frame.size.width;
}
But i do not know how can I update the NSLayoutConstraint :
NSLayoutConstraint *constraintToAnimate3 = [NSLayoutConstraint constraintWithItem:PreView
attribute:NSLayoutAttributeWidth
relatedBy:NSLayoutRelationEqual
toItem:self.view
attribute:NSLayoutAttributeWidth
multiplier:1 - WIDTH_ListTableView
constant:0.0];
[self.view addConstraint:constraintToAnimate3];
when this ViewController receive the notification.
Answer
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