What is Geometry Reader in SwiftUI?

Question

I am learning SwiftUI. And I come across to \"GeometryReader\". And I want to know why and when to use it?

Answer 1

What is called Reader in The SwiftUI?

In addition to the kontiki's answer, Readers are container views that define their content as a function. So they can have some access and abilities about their parent. They are generic structs if you look more closely and there is 2 readers available now in SwiftUI 2.0:

_{Note that it's just a convention, they're not conforming special protocl more of the View protocl}.

GeometryReader

struct GeometryReader : View

This is A container view that defines its content as a function of its own size and coordinate space. So you can detect frame and position changes and the current state of any view withing a GeometryReader. One of the popular usage of this reader that when you need separate views in separate stacks have the same (or relative) sizes.

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ScrollViewReader

struct ScrollViewReader : View

This is view whose child is defined as a function of a ScrollViewProxy targeting the scrollable views within the child. So you can have some access to the scrollview like scrolling to a specific item in a list or similar stuff.

_{To minimalizing the duplication, I didn't post examples, you can check the link for more information if you want}