SOLVED: Help me understand the View protocol

@dper1994

Jun '23

I'm trying to understand a little how the View protocol from SwiftUI works. So we have this:

protocol View {
associatedType Body: View

var body: Self.Body {get}
}

I have two questions about this:

Is Body placeholder replaced with the actual View type (for example Text, Button, Image, VStack, etc?)

What does "Self.Body" means?

Give me some examples please.

2

@Greenamberred HWS+

Jun '23

Maybe this will help - Self vs self

So if you pass 'Text' to the 'View', 'Self.Body' will be essentially the same as 'Text.Body', and you say you can pass anything that conforms to the 'View' protocol.

2

@dper1994

Jun '23

I think Self always refer to the conforming Type of the protocol, for example:

struct MyCustomView: View {
var body: some View {
    Text("Hello World")
   }
}

Here, Self.Body would be MyCustomView.Body

But I dont understand why they refer to var: Self.Body instead of just var: Body

2

@roosterboy HWS+

Jun '23

But I dont understand why they refer to var: Self.Body instead of just var: Body

If you have a type somewhere else in your code called Body, how is the compiler to know which Body you are referring to?

By using Self.Body, the compiler knows you are referring to the associatedType Body of the type that conforms to the View protocol.

Is Body placeholder replaced with the actual View type (for example Text, Button, Image, VStack, etc?)

Yes, and those types can get very complicated very fast.

This View:

struct ContentView: View {
    @State var counter = 0 

    var body: some View {
        VStack {
            Button(action: { counter += 1 }, label: {
                Text("Tap me!")
                    .padding() 
                    .background(Color(.tertiarySystemFill))
                    .cornerRadius(5)
            })
            if counter > 0 {
                Text("You've tapped \(counter) times")
            } else {
                Text("You've not yet tapped")
            }
        } 
    }
}

has a body whose type is this:

VStack<TupleView<(Button<ModifiedContent<ModifiedContent<ModifiedContent<Text,_PaddingLayout>,_BackgroundModifier<Color>>,_ClipEffect<RoundedRectangle>>>,_ConditionalContent<Text, Text>)>>

* example from Thinking in SwiftUI v2.0 by Chris Eidhof and Florian Kugler

4

@dper1994

Jun '23

Thank you very much, now is clear for me, I didn't know Swift would confuse if I have something else called Body. Now it makes sense. SwiftUI is making sure that Body is coming from "MyCustomView.Body" and not some independent Body type.

2

	@dper1994 Jun '23 I'm trying to understand a little how the View protocol from SwiftUI works. So we have this: `protocol View { associatedType Body: View var body: Self.Body {get} }` I have two questions about this: Is Body placeholder replaced with the actual View type (for example Text, Button, Image, VStack, etc?) What does "Self.Body" means? Give me some examples please. 2
	@Greenamberred HWS+ Jun '23 Maybe this will help - Self vs self So if you pass 'Text' to the 'View', 'Self.Body' will be essentially the same as 'Text.Body', and you say you can pass anything that conforms to the 'View' protocol. 2
	@dper1994 Jun '23 I think Self always refer to the conforming Type of the protocol, for example: `struct MyCustomView: View { var body: some View { Text("Hello World") } }` Here, `Self.Body` would be `MyCustomView.Body` But I dont understand why they refer to `var: Self.Body` instead of just `var: Body` 2
	@roosterboy HWS+ Jun '23 But I dont understand why they refer to `var: Self.Body` instead of just `var: Body` If you have a type somewhere else in your code called `Body`, how is the compiler to know which `Body` you are referring to? By using `Self.Body`, the compiler knows you are referring to the associatedType `Body` of the type that conforms to the `View` protocol. Is Body placeholder replaced with the actual View type (for example Text, Button, Image, VStack, etc?) Yes, and those types can get very complicated very fast. This `View`: `struct ContentView: View { @State var counter = 0 var body: some View { VStack { Button(action: { counter += 1 }, label: { Text("Tap me!") .padding() .background(Color(.tertiarySystemFill)) .cornerRadius(5) }) if counter > 0 { Text("You've tapped \(counter) times") } else { Text("You've not yet tapped") } } } }` has a `body` whose type is this: `VStack<TupleView<(Button<ModifiedContent<ModifiedContent<ModifiedContent<Text,_PaddingLayout>,_BackgroundModifier<Color>>,_ClipEffect<RoundedRectangle>>>,_ConditionalContent<Text, Text>)>>` * example from Thinking in SwiftUI v2.0 by Chris Eidhof and Florian Kugler 4
	@dper1994 Jun '23 Thank you very much, now is clear for me, I didn't know Swift would confuse if I have something else called Body. Now it makes sense. SwiftUI is making sure that Body is coming from "MyCustomView.Body" and not some independent Body type. 2

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