Q:

How to add Equal Spacing and equal width for button in iOS Auto layout

Am new to Auto layout constraints in Xcode. I have one Bottom View like UITabBar with 6 UIButtons. Without constraints I aligned those buttons with 5 space padding with each buttons and each buttons has 50 width. 
Now,I am trying to make it by using Auto layout to support all Screen sizes. 

In Storyboard constrains I set equal width for 6 buttons and I made 60
  space between each buttons. I set first button 0 to leading space and
  I set the last button 0 to tail constraints.

I want the buttons with equal width and flexible spaces between views in all device sizes. 
Can anyone pleas help me? Looking for the help. Thanks in advance.
 

A:

check this image and made your constraints like below...  

RESULT:- preview in different sizes  

With Stackview (For iOS 9.0 and above)

NOTE: If you have to make app for iOS 9 and later then UIStackView is another option for you

A:

With iOS 9 and Xcode 7, you can now have the expected result with UIStackView and only 3 or 4 auto layout constraints.
The following step by step uses Storyboard.

Create 6 UIButtons and 5 UIViews. Align them horizontally. Give some color to your views.

Select all your views and buttons and click on the Stack button. You will have all your buttons and colored views aligned in a UIStackView.

Select your stack view, go to the Utilities panel and select the Attributes Inspector item. There, click on the Distribution button and select "Fill Equally".

For now, your stack view's height relies on your buttons intrinsic content size. If you're fine with it, you can go to step 5. However, if needed, you can give your stack view a height constraint. Select your stack view, click on the Pin button, check the Height button, add the required value and click on the Add 1 Constraint button.

As an alternative, If you want each element of your stack view to have its height matching its width, select the first button of your stack view, click on the Pin button, select Aspect Ratio and click on the Add 1 Constraint button.

You can check that your aspect ratio constraint is correct in your Document outline (left panel) and, if you need, you can change it with a different constraint in the Attribute inspector (right panel).

Now, it's time to give some external constraints to your stack view. Select your stack view. Click on the pin button, make sure the Constrain to margin button is not select and set leading, trailing and bottom constraints to zero. Make sure that the bottom constraint is related to your view controller's view. Then, change the Update Frames button to "All Frames in Container". You can now click on the Add 3 Constraints button.

Your stack view is now set.

Further remark:
If you don't need your colored views width to match your buttons width, you can build a stack view with only UIButtons and simply add spacing to your stack view in the Attribute inspector. However, you will have to find a way to add a background color behind your stack view. Apple states about it in the UIKit Framework Reference:

The UIStackView is a nonrendering subclass of UIView. It does not
  provide any user interface of its own. Instead, it just manages the
  position and size of its arranged views. As a result, some properties
  (like backgroundColor) have no affect on the stack view.

I've build a Xcode project with 4 different stack views:

one with colored views and relying on the embedded UIButtons intrinsic content size for its height,
one with colored views and with a UIButton "equal width and height" constraint,
one with colored views and with its own height constraint,
one without colored views but with spacing and embedded inside a colored view.

You can find this project on this GitHub repo.

