Toggle sorting in List View - json

Question

I use 'Api' as an ObervableObject and inside there's #Published var isAscd to be toggled. Function getPost fetch JSON data from web and populate is List View. I use a button in HeaderView to toggle the sorting method. Compiling is succeeded but button takes no action. I don't know what goes wrong?
class Api: ObservableObject {
#Published var posts: [Post] = []
#Published var isAscd: Bool = false
func getPosts(completion: #escaping ([Post]) -> ()) {
guard let url = URL(string: getListURLString) else { return }
URLSession.shared.dataTask(with: url) { (data, _, _) in
let posts = try! JSONDecoder().decode([Post].self, from: data!)
DispatchQueue.main.async {
completion(posts)
}
}
.resume()
}
}
struct HeaderView: View {
var holding: String = "市值/數量"
var earning: String = "現價/成本"
var profit: String = "持倉賺蝕"
#ObservedObject var api = Api()
var body: some View {
HStack{
Button(action: {
self.api.isAscd.toggle()
if self.api.isAscd {
self.api.posts.sort { $0.stockcode > $1.stockcode}
} else { self.api.posts.sort { $0.stockcode < $1.stockcode}
}
print(self.api.posts.count)
print(self.api.isAscd)
}.......}
List {
Section(header: HeaderView())
{
ForEach(posts)
{ post in
HStack {
VStack(alignment: .leading)
..........
}
}.frame(minWidth: 0, maxWidth: .infinity, minHeight: 0, maxHeight: 250, alignment: .center)
.onAppear {
Api().getPosts {(posts) in
self.posts = posts
//self.apr.isAscd.toggle()
}
}
}