Issue with autoLayout and constraints - ios

Question

I have an issue with iOS and AutoLayout...it is a testing application where I have replicated the problem. It consists in a simple view controller, containing a fixed UIButton; when user clicks this button, the delegate have to create a custom view, apply it positioning constraints; the view has then a method to build his content views, and the child views are placed with constraints too.
Here is the code:
//MyViewController.m
#implementation MyViewController
- (void)viewDidLoad
{
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
UIButton *start_but = [[UIButton alloc] initWithFrame:CGRectMake(10, 10, 100, 40)];
[start_but setTitle:#"Draw" forState:UIControlStateNormal];
[start_but setTitleColor:[UIColor yellowColor] forState:UIControlStateNormal];
[start_but addTarget:self action:#selector(clickAction:) forControlEvents:UIControlEventTouchUpInside];
[self.view addSubview:start_but];
}
- (void)didReceiveMemoryWarning
{
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
- (void)clickAction: (id)sender
{
localView = [[MyView alloc] initWithFrame:CGRectMake(0, 0, 400, 300)];
UIView *superview = (UIView*)localView;
superview.translatesAutoresizingMaskIntoConstraints = NO;
[self.view addSubview:localView];
NSLayoutConstraint *constr = [NSLayoutConstraint constraintWithItem:localView
attribute:NSLayoutAttributeTop
relatedBy:NSLayoutRelationEqual
toItem:self.view
attribute:NSLayoutAttributeTop
multiplier:1.0
constant:100.0];
[self.view addConstraint:constr];
constr = [NSLayoutConstraint constraintWithItem:localView
attribute:NSLayoutAttributeRight
relatedBy:NSLayoutRelationEqual
toItem:self.view
attribute:NSLayoutAttributeRight
multiplier:1.0
constant:-50.0];
[self.view addConstraint:constr];
[localView CreateGuiInterface];
}
#end
//MyView.m
#implementation MyView
- (id)initWithFrame:(CGRect)frame
{
self = [super initWithFrame:frame];
if (self)
{
// Initialization code
}
return self;
}
-(void)CreateGuiInterface
{
UIView *superview = self;
self.backgroundColor = [UIColor redColor];
UIButton *but1 = [[UIButton alloc] init];
[but1 setTitle:#"Button" forState:UIControlStateNormal];
[but1 setTitleColor:[UIColor blackColor] forState:UIControlStateNormal];
but1.backgroundColor = [UIColor yellowColor];
but1.translatesAutoresizingMaskIntoConstraints = NO;
[superview addSubview:but1];
NSLayoutConstraint *constraint = [NSLayoutConstraint constraintWithItem:but1
attribute:NSLayoutAttributeRight
relatedBy:NSLayoutRelationEqual
toItem:superview
attribute:NSLayoutAttributeRight multiplier:1.0
constant:-20.0];
[superview addConstraint:constraint];
constraint = [NSLayoutConstraint constraintWithItem:but1
attribute:NSLayoutAttributeTop
relatedBy:NSLayoutRelationEqual
toItem:superview
attribute:NSLayoutAttributeTop
multiplier:1.0
constant:50.0];
[superview addConstraint:constraint];
UILabel *label = [[UILabel alloc] init];
label.text = #"Label";
label.backgroundColor = [UIColor greenColor];
label.textColor = [UIColor blackColor];
label.translatesAutoresizingMaskIntoConstraints = NO;
[superview addSubview:label];
constraint = [NSLayoutConstraint constraintWithItem:label
attribute:NSLayoutAttributeRight
relatedBy:NSLayoutRelationEqual
toItem:but1
attribute:NSLayoutAttributeLeft
multiplier:1.0
constant:-40.0];
[superview addConstraint:constraint];
constraint = [NSLayoutConstraint constraintWithItem:label
attribute:NSLayoutAttributeTop
relatedBy:NSLayoutRelationEqual
toItem:but1
attribute:NSLayoutAttributeBottom
multiplier:1.0
constant:20.0];
[superview addConstraint:constraint];
}
#end
So, the problem is that when i click iOS seems to have problem to draw the view background color. It is strange, 'cause if i don't use superview.translatesAutoresizingMaskIntoConstraints = NO and put the view in a fixed place (with initWithFrame:CGRect(100,200,300,400) for example) without using constraints, it works fine: can there be problems using constraints in child and parent views? AppleDoc said that the constraints cannot pass throughout the view barrier; so i've written my app with local-view oriented constraints....
can somebody help me?
thanks in advice

Answer 1

The intent with autoLayout is to never have to setFrame on any of your views. If you want to place your view programatically within your superview, you will provide constraints for that. The changes I made you will see the background red as intended. I didn't change your MyView implementation (simply added -(void)CreateGuiInterface;
within MyView.h). The changes I made to demonstrate are within your MyViewController implementation.
Try the following code in place of your viewController:
#interface MyViewController ()
#property (nonatomic, strong) MyView* localView;
#end
#implementation MyViewController
- (void)viewDidLoad
{
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
UIButton *start_but = [[UIButton alloc] init];
start_but.translatesAutoresizingMaskIntoConstraints = NO;
[start_but setTitle:#"Draw" forState:UIControlStateNormal];
[start_but setTitleColor:[UIColor yellowColor] forState:UIControlStateNormal];
[start_but addTarget:self action:#selector(clickAction:) forControlEvents:UIControlEventTouchUpInside];
[self.view addSubview:start_but];
// The following constraints simply place the initial start button in the top left
NSDictionary* views = NSDictionaryOfVariableBindings(start_but);
NSString* format = #"H:|-[start_but]";
NSArray* constraints = [NSLayoutConstraint constraintsWithVisualFormat:format
options:0
metrics:nil
views:views];
[self.view addConstraints:constraints];
format = #"V:|-[start_but]";
constraints = [NSLayoutConstraint constraintsWithVisualFormat:format
options:0
metrics:nil
views:views];
[self.view addConstraints:constraints];
}
- (void)clickAction: (id)sender
{
self.localView = [[MyView alloc] init];
UIView *superview = (UIView*)self.localView;
superview.translatesAutoresizingMaskIntoConstraints = NO;
[self.view addSubview:self.localView];
// Here I'm placing your parent view (MyView) 50 points on right of the superview with
// a width of 400 points
NSDictionary* views = NSDictionaryOfVariableBindings(superview);
NSString* format = #"H:[superview(==400)]-(50)-|";
NSArray* constraints = [NSLayoutConstraint constraintsWithVisualFormat:format
options:0
metrics:nil
views:views];
[self.view addConstraints:constraints];
// Vertically 100 points from the top of the superview with a height of 300 points
format = #"V:|-(100)-[superview(==300)]";
constraints = [NSLayoutConstraint constraintsWithVisualFormat:format
options:0
metrics:nil
views:views];
[self.view addConstraints:constraints];
[self.localView CreateGuiInterface];
}
#end