通过代码自动布局问题？

Question

i use autolayout without sb and xib.But i have some problems recently.

i don't understand which view should i use to implement the following two methods

- (void)addConstraint:(NSLayoutConstraint *)constraint

- (void)addConstraints:(NSArray<__kindof NSLayoutConstraint *> *)constraints

for example,i have a super view as following:

_menuView = [[UIScrollView alloc] init];
_menuView.translatesAutoresizingMaskIntoConstraints = NO;
[self.view addSubview:_menuView];
[self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"H:|-0-[_menuView]-0-|" options:0 metrics:nil views:NSDictionaryOfVariableBindings(_menuView)]];
[self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"V:|-0-[_menuView(40)]" options:0 metrics:nil views:NSDictionaryOfVariableBindings(_menuView)]];

and two subViews:view1,view2.When i use autolayout to add constraints to describe view1 and view2,

[WHICHVIEW addConstraint:<#(nonnull NSLayoutConstraint *)#>];

or [WHICHVIEW addConstraints:<#(nonnull NSArray<__kindof NSLayoutConstraint *> *)#>];

what should WHICHVIEW should be? Let me put it another way,is WHICHVIEW depend on the relationship between view1 and view2?what if view1 is not the same hierarchy as view2?

Answer 1

Do not use any WHICHVIEW . Do not call addConstraints: . Call NSLayoutConstraint.activateConstraints instead. It has the advantage that it does all that work for you - it adds the constraints to the correct views, automatically.

Answer 2

WHICHVIEW should be a parent of [all] the items you are trying to constrain. So if you are adding a number of views to a scrollview and trying to constrain them, with respect to themselves and to the scrollview, the scrollview should be WHICHVIEW. If view1 and view2 are not at all in the same hierarchy, then you cannot add a constraint between the two.