Create By: Osama Sheikh
(S.E) And I,T Expert
_________________________________
Post By: Hanan Mannan
Contact Number: Pak (+92)-321-59-95-634
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iOS - Auto Layouts
Introduction
Auto layouts were introduced in iOS 6.0 and we can support only deployment target of 6.0 and higher. It helps us create interfaces that can be used for multiple orientations and multiple devices.
Goal of our example
We will add two buttons that will be placed a certain distance from the center of screen. We will also try to add a resizable text field that will be placed from a certain distance from above the buttons.
Our Approach
We will add text field and two buttons in code along with their constraints. The constraints of each UI Elements will be created and added to the super view and we will have to disable auto resizing for each of the UI elements we add in order get the desired result.
Steps Involved
1. Create a simple View based application.
2. We will only edit ViewController.m and it is as follows.
#import "ViewController.h"
@interface ViewController ()
@property (nonatomic, strong) UIButton *leftButton;
@property (nonatomic, strong) UIButton *rightButton;
@property (nonatomic, strong) UITextField *textfield;
@end
@implementation ViewController
- (void)viewDidLoad{
[super viewDidLoad];
UIView *superview = self.view;
/*1. Create leftButton and add to our view*/
self.leftButton = [UIButton buttonWithType:UIButtonTypeRoundedRect];
self.leftButton.translatesAutoresizingMaskIntoConstraints = NO;
[self.leftButton setTitle:@"LeftButton" forState:UIControlStateNormal];
[self.view addSubview:self.leftButton];
/* 2. Constraint to position LeftButton's X*/
NSLayoutConstraint *leftButtonXConstraint = [NSLayoutConstraint
constraintWithItem:self.leftButton attribute:NSLayoutAttributeCenterX
relatedBy:NSLayoutRelationGreaterThanOrEqual toItem:superview attribute:
NSLayoutAttributeCenterX multiplier:1.0 constant:-60.0f];
/* 3. Constraint to position LeftButton's Y*/
NSLayoutConstraint *leftButtonYConstraint = [NSLayoutConstraint
constraintWithItem:self.leftButton attribute:NSLayoutAttributeCenterY
relatedBy:NSLayoutRelationEqual toItem:superview attribute:
NSLayoutAttributeCenterY multiplier:1.0f constant:0.0f];
/* 4. Add the constraints to button's superview*/
[superview addConstraints:@[ leftButtonXConstraint,
leftButtonYConstraint]];
/*5. Create rightButton and add to our view*/
self.rightButton = [UIButton buttonWithType:UIButtonTypeRoundedRect];
self.rightButton.translatesAutoresizingMaskIntoConstraints = NO;
[self.rightButton setTitle:@"RightButton" forState:UIControlStateNormal];
[self.view addSubview:self.rightButton];
/*6. Constraint to position RightButton's X*/
NSLayoutConstraint *rightButtonXConstraint = [NSLayoutConstraint
constraintWithItem:self.rightButton attribute:NSLayoutAttributeCenterX
relatedBy:NSLayoutRelationGreaterThanOrEqual toItem:superview attribute:
NSLayoutAttributeCenterX multiplier:1.0 constant:60.0f];
/*7. Constraint to position RightButton's Y*/
rightButtonXConstraint.priority = UILayoutPriorityDefaultHigh;
NSLayoutConstraint *centerYMyConstraint = [NSLayoutConstraint
constraintWithItem:self.rightButton attribute:NSLayoutAttributeCenterY
relatedBy:NSLayoutRelationGreaterThanOrEqual toItem:superview attribute:
NSLayoutAttributeCenterY multiplier:1.0f constant:0.0f];
[superview addConstraints:@[centerYMyConstraint,
rightButtonXConstraint]];
//8. Add Text field
self.textfield = [[UITextField alloc]initWithFrame:
CGRectMake(0, 100, 100, 30)];
self.textfield.borderStyle = UITextBorderStyleRoundedRect;
self.textfield.translatesAutoresizingMaskIntoConstraints = NO;
[self.view addSubview:self.textfield];
//9. Text field Constraints
NSLayoutConstraint *textFieldTopConstraint = [NSLayoutConstraint
constraintWithItem:self.textfield attribute:NSLayoutAttributeTop
relatedBy:NSLayoutRelationGreaterThanOrEqual toItem:superview
attribute:NSLayoutAttributeTop multiplier:1.0 constant:60.0f];
NSLayoutConstraint *textFieldBottomConstraint = [NSLayoutConstraint
constraintWithItem:self.textfield attribute:NSLayoutAttributeTop
relatedBy:NSLayoutRelationGreaterThanOrEqual toItem:self.rightButton
attribute:NSLayoutAttributeTop multiplier:0.8 constant:-60.0f];
NSLayoutConstraint *textFieldLeftConstraint = [NSLayoutConstraint
constraintWithItem:self.textfield attribute:NSLayoutAttributeLeft
relatedBy:NSLayoutRelationEqual toItem:superview attribute:
NSLayoutAttributeLeft multiplier:1.0 constant:30.0f];
NSLayoutConstraint *textFieldRightConstraint = [NSLayoutConstraint
constraintWithItem:self.textfield attribute:NSLayoutAttributeRight
relatedBy:NSLayoutRelationEqual toItem:superview attribute:
NSLayoutAttributeRight multiplier:1.0 constant:-30.0f];
[superview addConstraints:@[textFieldBottomConstraint ,
textFieldLeftConstraint, textFieldRightConstraint,
textFieldTopConstraint]];
}
- (void)didReceiveMemoryWarning
{
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
@end
What we did here?
In steps marked 1, 5 and 8 we just programmatically add two buttons and a text field respectively. In rest of the steps we create constraints and add those constraints to respective super views which are actually self.view. When you look into the one of the left button's constraint as shown below,
NSLayoutConstraint *leftButtonXConstraint = [NSLayoutConstraint
constraintWithItem:self.leftButton attribute:NSLayoutAttributeCenterX
relatedBy:NSLayoutRelationGreaterThanOrEqual toItem:superview attribute:
NSLayoutAttributeCenterX multiplier:1.0 constant:-60.0f];
We actually have constraintWithItem and toItem which decides between which UI element we are creating the constraint. The attribute decides on what basis the two elements have linked together. Related by decides how much the attributes have effect between the elements. Multiplier is the multiplication factor and constant will be added to the multipler. Here we are saying that X of leftButton is always greater than or equal to -60 pixels with respect to the center of the super view. Similarly other constraints are defined.
Output
Now when we run the application we'll get the following output on iPhone simulator.
When we change the orientation of the simulator to landscape we will get following output.
When we run the same application on iPhone 5 simulator we will get the following output.
When we change the orientation of the simulator to landscape we will get following output.
