View with a binding and a private property

Question

Created Oct ’20

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Hi,

I'm learning SwiftUI and there are still some things I don't understand very well.

For example, this is compiling correctly:

Code Block struct Test: View {
    private var testPrivateProperty = 1
    var body: some View {
        Text("Test")
    }
}
struct Test_Previews: PreviewProvider {
    static var previews: some View {
        Test()
    }
}

This is also compiling correctly:

Code Block struct Test: View {
    @Binding var testBinding: Bool
    var body: some View {
        Text("Test")
    }
}
struct Test_Previews: PreviewProvider {
    static var previews: some View {
        Test(testBinding: .constant(true))
    }
}

But if I create a View that contain both a binding and a private property:

Code Block struct Test: View {
    @Binding var testBinding: Bool
    private var testPrivateProperty = 1
    var body: some View {
        Text("Test")
    }
}
struct Test_Previews: PreviewProvider {
    static var previews: some View {
        Test(testBinding: .constant(true))
        //Error on the line above.
    }
}

the compiler produce this error:

'Test' initializer is inaccessible due to 'private' protection level

Can anyone help me understand why?

Thank you

Boost

Answer 1

OOPer OP

Oct ’20

Can anyone help me understand why?

An interesting example.

When you define a struct, Swift compiler generates a memberwise initializer implicitly.
(Memberwise Initializers for Structure Types in Comparing Structures and Classes,
SE-0242 Synthesize default values for the memberwise initializer)

Something like:

Code Block     init(testBinding: Binding<Bool>, testPrivateProperty: Int = 1) {
        self._testBinding = testBinding
        self.testPrivateProperty = testPrivateProperty
    }

It seems Swift marks this sort of initializers as private, when any of the properties are private.

You may need to define a non-private initializer yourself, when your View has any private properties.

This behavior is not explicitly stated in the articles linked above. You may send a bug report to swift.org, or start a new thread in forums.swift.org .

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