Explain Aspect Ratio and respective terms in iOS? - ios

Question

I want to understand Aspect Ratio.
Here, I am setting Aspect Ratio of an UIImageView.
These are options when I click this constraint.
How this constraint works and what are "PRESETS", Reverse Multiplier and Convert to Decimal.
Thanks.

Answer 1

Aspect ratio constraint is used to control the width and height of a view as per a aspect ratio that you set here. There are some standard presets such as 1:1 which means width will be equal to height. Similarly other presets calculates the dimensions based on a ratio
Reverse Multiplier is just used to reverse the ratio. E.g. 4:3 will be 3:4
Convert to decimal just represents the ratio as a decimal. E.g. 4:3 will be 1.33
If you want a view to always maintain an aspect ratio then you can use this constraint. In your case if its image view and you know the aspect ratio of the image that will be set then you can set that aspect ratio as the constraint so that the image is always sized according to the image that is set to that image view,

Answer 2

If you select Aspect Ratio for a single item, the width of the item is
used as the numerator for the ratio, and the height is used for the
denominator. If you select Aspect Ratio for multiple items, Auto
Layout chooses the width of one of the items for the numerator and the
height of another item for the denominator. To change the initial
aspect ratio, edit the Multiplier field of the Attributes inspector
for the constraint. To change which item to use for the width or the
height, use the First Item and Second Item pop-up menus in the
Attributes inspector.
Read more here

Answer 3

Constraints are something like equations in maths.
Ex:
let
X- known value (20)
Y- Unknown value (?)
m- multiplier (like 2 or 3 times)
C- constant (+3 or -3)
to find Y value we use this equation.
Y = m * X + C
Y = 2 * 20 + 3
Y = 43
Constraint equation:
First Object = (Multipler * Second Object ) + constant
width = (0.5 * Height) + 20
In Aspect Ratio condition
Note : one value should be fixed ( Height or width )
A) PRESETS
1)Width = 1 * Height
Width/ Height = 1/1 (1:1)
2)Width = 3/4 * height
Width / Height = 3 / 4 (3:4)
B) REVERSE MULTIPLIER
Before Reverse
Width = 1/2 * Height (1:2)
After Reverse
Width = 2/1 * Height (2:1)
C) CONVERT TO DECIMAL
Before conversion
Width = 1/2 * Height
After Conversion
Width = 0.5 * Height (0.5)