Is it possible in SwiftUI to have an optional @ViewBuilder
closure? For example, let's say I want to develop a custom view that takes two view builder closures like this:
import SwiftUI
struct TopAndBottomView<Content>: View where Content: View {
let topContent: () -> Content
let bottomContent: () -> Content
init(@ViewBuilder topContent: @escaping () -> Content, @ViewBuilder bottomContent: @escaping () -> Content) {
self.topContent = topContent
self.bottomContent = bottomContent
}
var body: some View {
VStack {
topContent()
Spacer()
bottomContent()
}
}
}
struct TopAndBottomView_Previews: PreviewProvider {
static var previews: some View {
TopAndBottomView(topContent: {
Text("TOP")
}, bottomContent: {
Text("BOTTOM")
})
}
}
But I'd like the bottom view to be optional. I tried with:
struct TopAndBottomView<Content>: View where Content: View {
let topContent: () -> Content
let bottomContent: (() -> Content)?
init(@ViewBuilder topContent: @escaping () -> Content, @ViewBuilder bottomContent: (() -> Content)? = nil) {
self.topContent = topContent
self.bottomContent = bottomContent
}
var body: some View {
VStack {
topContent()
Spacer()
if bottomContent != nil {
bottomContent!()
}
}
}
}
but I get this error:
Function builder attribute 'ViewBuilder' can only be applied to a parameter of function type.
Thanks.
Taking into account buildIf
feature of ViewBuilder
the following approach is possible that allows to keep ViewBuilder
in init
(that is preferable)
Tested & works with Xcode 11.2 / iOS 13.2
struct TopAndBottomView<Content>: View where Content: View {
let topContent: () -> Content
let bottomContent: () -> Content?
init(@ViewBuilder topContent: @escaping () -> Content,
@ViewBuilder bottomContent: @escaping () -> Content? = { nil }) {
self.topContent = topContent
self.bottomContent = bottomContent
}
var body: some View {
VStack {
topContent()
Spacer()
bottomContent()
}
}
}
So works as this one
struct TopAndBottomView_Previews: PreviewProvider {
static var previews: some View {
TopAndBottomView(topContent: {
Text("TOP")
}, bottomContent: {
Text("BOTTOM")
})
}
}
and this one
struct TopAndBottomView_Previews: PreviewProvider {
static var previews: some View {
TopAndBottomView(topContent: {
Text("TOP")
})
}
}