gistfile1.txt

    /*
        Creates a green btn and sets its position equal to a rect of {50.0f, 50.0f, 200.0f, 300.0f}
    */
    
    UIButton *btn       = [[UIButton alloc] init];
    btn.backgroundColor = [UIColor greenColor];
    [btn setTranslatesAutoresizingMaskIntoConstraints:NO];
    [self.view addSubview:btn];
    
    NSLayoutConstraint *widthConstraint  = [NSLayoutConstraint constraintWithItem:btn attribute:NSLayoutAttributeWidth relatedBy:NSLayoutRelationEqual toItem:nil attribute:0 multiplier:0.0 constant:200];
    NSLayoutConstraint *heightConstraint = [NSLayoutConstraint constraintWithItem:btn attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:nil attribute:0 multiplier:0.0 constant:300];
    NSLayoutConstraint *vertConstraint   = [NSLayoutConstraint constraintWithItem:btn attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeTop multiplier:0.0 constant:50];
    NSLayoutConstraint *horizConstraint  = [NSLayoutConstraint constraintWithItem:btn attribute:NSLayoutAttributeLeft relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeLeft multiplier:0.0 constant:50];
    [self.view addConstraints:@[widthConstraint, heightConstraint, vertConstraint, horizConstraint]];