IOS AutoLayout Encoding

// Do not define the Frame in this place. The following Visual Format defines the Frame.

UIView * redView = [[UIView alloc] init];

RedView. backgroundColor = [UIColor redColor];

// Set NO according to the Apple Doc to prevent the autoresize conflict between the Constraint and View.

[RedView setTranslatesAutoresizingMaskIntoConstraints: NO];

[Self. view addSubview: redView];

UIView * blueView = [[UIView alloc] init];

BlueView. backgroundColor = [UIColor blueColor];

[BlueView setTranslatesAutoresizingMaskIntoConstraints: NO];

[Self. view addSubview: blueView];

// Bind two views

NSDictionary * views = NSDictionaryOfVariableBindings (redView, blueView );

// The constraint is used to define the horizontal direction correlation (x, width) of the Frame)

[Self. view addConstraints: [NSLayoutConstraint constraintsWithVisualFormat: @ "H: |-(> = 10)-[redView (200)]"

Options: 0

Metrics: nil

Views: views];

// The constraint is used to define the vertical correlation (y, height) of the Frame)

[Self. view addConstraints: [NSLayoutConstraint constraintsWithVisualFormat: @ "V: |-(> = 240)-[redView (100)]"

Options: 0

Metrics: nil

Views: views];

[Self. view addConstraints: [NSLayoutConstraint constraintsWithVisualFormat: @ "H: [blueView (= redView)]"

Options: 0

Metrics: nil

Views: views];

[Self. view addConstraints: [NSLayoutConstraint constraintsWithVisualFormat: @ "V: |-(40)-[blueView (= redView)]"

Options: 0

Metrics: nil

Views: views];

// The constraint here is used to describe the relationship between the two views.

[Self. view addConstraint: [NSLayoutConstraint constraintWithItem: blueView

Attribute: NSLayoutAttributeLeft

RelatedBy: NSLayoutRelationEqual

ToItem: redView

Attribute: NSLayoutAttributeLeft

Multiplier: 1

Constant: 0];

Above.

Method and Macro do not provide an explanation. Please refer to the Apple Doc.