Sometimes when add child view controller programmatically and just add subview fill all container. You have to add constraint again and again. This snip set code will help you add by one line of code.

addContraint.m

//
//  CommonAutolayoutUtils.h
//  Vien Vu
//
//  Created by Vien Vu  on 1/8/16.
//  Copyright © 2016 Vien Vu. All rights reserved.
//

#import <Foundation/Foundation.h>
#import <UIKit/UIKit.h>

@interface CommonAutolayoutUtils : NSObject

+ (void)addConstraintsChildToContainer:(UIView *) parent childView:(UIView *)child;
+ (void)addConstraintsChildToContainer:(UIView *) parent childView:(UIView *)child insets:(UIEdgeInsets)inset;

@end

.m File

//
//  CommonAutolayoutUtils.m
//  Vien Vu
//
//  Created by Vien Vu  on 1/8/16.
//  Copyright © 2016 Vien Vu. All rights reserved.
//

#import "CommonAutolayoutUtils.h"

@implementation CommonAutolayoutUtils


+ (void)addConstraintsChildToContainer:(UIView *)parent childView:(UIView *)child {
    NSDictionary *views =@{@"childView": child,@"container": parent};
    //Horizontal constraints
    NSArray *horizontalConstraints = [NSLayoutConstraint constraintsWithVisualFormat:@"H:|[childView]|" options:0 metrics:nil views:views];
    
    [parent addConstraints:horizontalConstraints];
    //Vertical constraints
    NSArray *verticalConstraints = [NSLayoutConstraint constraintsWithVisualFormat:@"V:|[childView]|" options:0 metrics:nil views:views];
    
    [parent addConstraints:verticalConstraints];
    
}

+ (void)addConstraintsChildToContainer:(UIView *)parent childView:(UIView *)child insets:(UIEdgeInsets)inset {
    NSDictionary *views =@{@"childView": child,@"container": parent};
    //Horizontal constraints
    NSArray *horizontalConstraints = [NSLayoutConstraint constraintsWithVisualFormat:[NSString stringWithFormat:@"H:|-%f-[childView]-%f-|", inset.left, inset.right] options:0 metrics:nil views:views];
    
    [parent addConstraints:horizontalConstraints];
    //Vertical constraints
    NSArray *verticalConstraints = [NSLayoutConstraint constraintsWithVisualFormat:[NSString stringWithFormat:@"V:|-%f-[childView]-%f-|", inset.top, inset.bottom] options:0 metrics:nil views:views];
    
    [parent addConstraints:verticalConstraints];
}

@end