How to add constraints programmatically in ios

Question

I created my UI elements programmatically in ios. Everything is fine in all iphone sices but my buttons get streched.

btnLogin=[[UIButton alloc] initWithFrame:CGRectMake(80, h-90, w-160, 40)]; This is the way Icreated my button. I know In interface builder we can use auto layout. But how can I add constraints to this button programmatically?

Because now the button width changing according to the screen size although the left and right side edges are fixed. How can I avoide the element streatching according to the device and also I want to manage the same gap between left and right side between the button and the parent view border.

How can I do this? Please help me Thanks

Answer 1

This is what you want

 UIButton * button = [[UIButton alloc] init];
button.backgroundColor = [UIColor redColor];
[self.view addSubview:button];

NSDictionary * buttonDic = NSDictionaryOfVariableBindings(button);
button.translatesAutoresizingMaskIntoConstraints = NO;

NSArray * hConstraints = [NSLayoutConstraint constraintsWithVisualFormat:@"H:|-80-[button]-80-|"
                                                                 options:0
                                                                 metrics:nil
                                                                    views:buttonDic];
[self.view addConstraints:hConstraints];

NSArray * vConstraints = [NSLayoutConstraint constraintsWithVisualFormat:@"V:[button(40)]-90-|"
                                                                 options:0
                                                                 metrics:nil
                                                                   views:buttonDic];
[self.view addConstraints:vConstraints];

Screenshot iphone 6

iPhone 6p

Update:

H:|-80-[button]-80-|,this create constraints at horizontal,button left and right to superview keeps to 80

"V:[button(40)]-90-|",this create constraints at Vertical，button height keeps to 40 and bottoms to superview bottoms keeps to 90