ObjC, revert to interface builder autolayout constraints, after adding / removing programmatically?

问题

I have a free version of my app and I remove + add autolayout constraints (to hide a premium feature), however if the user purchases my app I'd like to revert back to to the constraints set by interface builder.

I'm hoping there's a method which will achieve this, but I haven't been able to find it so far?

Here's what I have

if (!purchased) {

[self.tblOtherAccounts addConstraints:[NSLayoutConstraint
   constraintsWithVisualFormat:@"V:[tblOtherAccounts(==0)]"
   options:0
   metrics:nil
   views:NSDictionaryOfVariableBindings(tblOtherAccounts)]];


NSDictionary *views = @{ @"tblOtherAccounts" : self.tblOtherAccounts, 
   @"butBackAllAc" : butBackAllAc  };

[self.view removeConstraints:[NSLayoutConstraint 
   constraintsWithVisualFormat:@"V:[tblOtherAccounts]-(12)-[butBackAllAc]"
   options:0
   metrics:nil
   views:views]];

[self.view addConstraints:[NSLayoutConstraint 
   constraintsWithVisualFormat:@"V:[tblOtherAccounts]-(0)-[butBackAllAc]"
   options:0
   metrics:nil
   views:views]];
}

回答1:

Add an IBOutlet to store your constraint in your ViewController :

@property (weak, nonatomic) IBOutlet NSLayoutConstraint *myConstraint;

Then update its value :

_myConstraint.constant = 100.0f;
[_myView setNeedsUpdateConstraints];
[_myView layoutIfNeeded];

Regarding your comment on setting the relation to "equals", I don't think you'll be able to do that.

One thing you can do though is use your storyboard-generated constraint as a placeholder :

NSLayoutConstraint *newConstraint = [NSLayoutConstraint constraintWithItem:_myConstraint.firstItem
                                                                 attribute:_myConstraint.firstAttribute
                                                                 relatedBy:_myConstraint.relation
                                                                    toItem:_myConstraint.secondItem
                                                                 attribute:_myConstraint.secondAttribute
                                                                multiplier:_myConstraint.multiplier
                                                                  constant:_myConstraint.constant];

[_myConstraint.secondItem removeConstraint:_myConstraint];
[constraint.secondItem addConstraint:newConstraint];

Of course the code above will create an exact duplicate of your constraint, but you can edit it to change the appropriate values to fit your needs.

回答2:

I think, you cannot do exactly that. You need to perform that logic in code. I.e. apply some constraints, then, on user action, apply another set of constraints.

Example: You have 2 constraints:

@property ... topConstraint;
@property ... leadingConstraint;

At the start you assign them some values:

topConstraint.constant = 100;
leadingConstraint.constant = 100;

After some user action, modify them:

topConstraint.constant = 150;
leadingConstraint.constant = 150;

来源：https://stackoverflow.com/questions/30433439/objc-revert-to-interface-builder-autolayout-constraints-after-adding-removin

标签

ios

objective-c

cocoa-touch

autolayout

ios7.1