Swift – How to assign an optional Binding parameter in SwiftUI

bindingswiftswiftui

I'm trying to build a custom NavBar with some optional Views, like a searchbar (but only if the view needs to display it).

I need to pass some @State properties with @Binding down the views, basically. But I also need them to be Optional parameters.

Here's an example:

struct NavBar: View {
    
    var isSearchable: Bool?
    
    @Binding var searchTxt: String
    @Binding var searchIsOn: Bool
    
    var navBarTitle: String
    var navBarAction: (() -> Void)?
    var navBarImage: String?
    
    init(navBarTitle: String, navBarAction: (() -> Void)? = nil, navBarImage: String? = nil, isSearchable: Bool? = false, searchTxt: (Binding<String>)?, searchIsOn : (Binding<Bool>)?) {
        self.navBarTitle = navBarTitle
        if(navBarAction != nil) {
            self.navBarAction = navBarAction!
        }
        if(navBarImage != nil) {
            self.navBarImage = navBarImage!
        }
        self.isSearchable = isSearchable
        
        self._searchTxt = (searchTxt != nil) ? (searchTxt!).binding : nil
        self._searchIsOn = (searchIsOn != nil) ? (searchIsOn!).binding : nil
        
        assert((navBarAction != nil) ? navBarImage != nil : true)
        assert((isSearchable! == true) ? (searchTxt!.value.count > 0) : true)
    }
// var body ....

}

The properties I'm talking about are searchIsOn and searchTxt.
But doing the assignment self._searchTxt = searchTxt or self._searchIsOn = searchIsOn throws a compile error:

Cannot assign value of type 'Binding?' to type 'Binding'

Do you know how could I resolve this issue?

Or is there a better way to do what I'm trying to do?

Best Answer

@Binding var searchTxt: String?

init(searchTxt: Binding<String?>?) {
    self._searchTxt = searchTxt ?? Binding.constant(nil)
}

Or consider this: TextField("", text: $text ?? "default value")

https://stackoverflow.com/a/61002589/4728060

func ??<T>(lhs: Binding<Optional<T>>, rhs: T) -> Binding<T> {
    Binding(
        get: { lhs.wrappedValue ?? rhs },
        set: { lhs.wrappedValue = $0 }
    )
}

Related Solutions

Ios – Initializer for conditional binding must have Optional type, not ‘AnyObject – Approach

No need to unwrap the result from try. It is not an optional. You do need to cast the result from try to an NSDictionary. Use as? to downcast it.

Best practice: full access to returned error for good error handling

func parseData2(){
    var data:NSData?

    if let data2 = data  {
        do {
            let details = try NSJSONSerialization.JSONObjectWithData(data2, options: .AllowFragments)

            if let detailsDict = details as? NSDictionary {
                print("Parse Data")
            } else if let detailsArray = details as? NSArray {
                print("array")
            }

        } catch {
            print("Error \(error)")
        }
    }
}

Quick and dirty: error handling is not for me!

func parseData2(){
    var data:NSData?

    if let data2 = data  {

        let details = try? NSJSONSerialization.JSONObjectWithData(data2, options: .AllowFragments)

        if let detailsDict = details as? NSDictionary {
            print("Parse Data")
        } else {
            print("details might be nil, or not an NSDictionary")
        }
    }
}

Bad Ass Mode: crashes are features

func parseData2(){
    var data:NSData?

    if let data2 = data  {

        let details = try! NSJSONSerialization.JSONObjectWithData(data2, options: .AllowFragments) as! NSDictionary

    }
}

Some extra info on multiple unwraps : Drop the code below in a playground.

struct SomeStruct {
    var anOptional : Int?
    init() {
    }
}

func unwrapWithIfLet() {

    if let unWrappedStruct = myStruct, let unWrappedSomething = unWrappedStruct.anOptional {
        print("multiple optional bindings succeeded")
        // both unWrappedStruct and unWrappedSomething are available here
    } else {
        print("something is nil")
    }
}

func unwrapWithGuard() {

    guard let unWrappedStruct = myStruct, let unWrappedSomething = unWrappedStruct.anOptional else {
        print("something is nil")
        return
    }
    print("multiple optional bindings succeeded")
    // both unWrappedStruct and unWrappedSomething are available here
}


var myStruct : SomeStruct?

//unwrapWithGuard()
//unwrapWithIfLet()

myStruct = SomeStruct()
myStruct!.anOptional = 1

unwrapWithGuard()
unwrapWithIfLet()

Swift – How to pass one SwiftUI View as a variable to another View struct

To sum up everything I read here and the solution which worked for me and on iOS14:

struct ContainerView<Content: View>: View {
    @ViewBuilder var content: Content
    
    var body: some View {
        content
    }
}

This not only allows you to put simple Views inside, but also, thanks to @ViewBuilder, use if-else and switch-case blocks:

struct SimpleView: View {
    var body: some View {
        ContainerView {
            Text("SimpleView Text")
        }
    }
}

struct IfElseView: View {
    var flag = true
    
    var body: some View {
        ContainerView {
            if flag {
                Text("True text")
            } else {
                Text("False text")
            }
        }
    }
}

struct SwitchCaseView: View {
    var condition = 1
    
    var body: some View {
        ContainerView {
            switch condition {
            case 1:
                Text("One")
            case 2:
                Text("Two")
            default:
                Text("Default")
            }
        }
    }
}

Bonus: If you want a greedy container, which will claim all the possible space (in contrary to the container above which claims only the space needed for its subviews) here it is:

struct GreedyContainerView<Content: View>: View {
    @ViewBuilder let content: Content
    
    var body: some View {
        Color.clear
            .overlay(content)
    }
}

Best Answer

Related Solutions

Ios – Initializer for conditional binding must have Optional type, not ‘AnyObject – Approach

Swift – How to pass one SwiftUI View as a variable to another View struct

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