ViewModifiers can be used in nested parent-child Views for each respective #Preview, making it convenient. This also enhances clarity even further.
🔌 Using as an extension of View
Create a custom ViewModifier.
struct DogDataContainerViewModifier: ViewModifier {
func body(content: Content) -> some View {
content
.modelContainer(try! ModelContainer(for: Dog.self))
}
}
All ViewModifiers will be turned into extensions.
extension View {
func dogDataContainer() -> some View {
modifier(DogDataContainerViewModifier())
}
}
It is used in the implementation of the parent as well as in the #Preview of the child.
struct DogView: View {
// ...
}
#Preview {
DogView()
.dogDataContainer()
}
🔌 Initializing or creating data
Additionally, as there are often data initialization or creation tasks, I'll add those.
This will be in the part with View.onAppear().
We'll use ModelContext to manipulate the data.
struct GenerateDataViewModifier: ViewModifier {
@Environment(\.modelContext) private var modelContext
func body(content: Content) -> some View {
content.onAppear {
DataGeneration.generateAllData(modelContext: modelContext)
}
}
}
This will also be made into an extension.
extension View {
func generateData() -> some View {
modifier(GenerateDataViewModifier())
}
}
Let's add this to the initial code.
struct DogDataContainerViewModifier: ViewModifier {
func body(content: Content) -> some View {
content
.generateData()
.modelContainer(try! ModelContainer(for: Dog.self))
}
}
🔌 Conclusion
I'll summarize it.
struct DogDataContainerViewModifier: ViewModifier {
func body(content: Content) -> some View {
content
.generateData()
.modelContainer(try! ModelContainer(for: Dog.self))
}
}
struct GenerateDataViewModifier: ViewModifier {
@Environment(\.modelContext) private var modelContext
func body(content: Content) -> some View {
content.onAppear {
DataGeneration.generateAllData(modelContext: modelContext)
}
}
}
extension View {
func dogDataContainer() -> some View {
modifier(DogDataContainerViewModifier())
}
}
fileprivate extension View {
func generateData() -> some View {
modifier(GenerateDataViewModifier())
}
}
When using, only basic public extensions are used.
struct DogView: View {
// ...
}
#Preview {
DogView()
.dogDataContainer()
}
It can also be used on the implementation side.
For reference, below is Apple's official sample code.
👉 sample-backyard-birds/BackyardBirdsData/General/BackyardBirdsDataContainer.swift at 1843d5655bf884b501e2889ad9862ec58978fdbe · apple/sample-backyard-birds 
)
