func callAsFunction () async
Overview 概要
When the refresh
environment value contains an instance of this structure, certain built-in views in the corresponding Environment
begin offering a refresh capability. They apply the instance’s handler to any refresh operation that the user initiates. By default, the environment value is nil
, but you can use the refreshable(action:)
modifier to create and store a new refresh action that uses the handler that you specify:
List(mailbox.conversations) { conversation in
ConversationCell(conversation)
}
.refreshable {
await mailbox.fetch()
}
On iOS and iPadOS, the List
in the example above offers a pull to refresh gesture because it detects the refresh action. When the user drags the list down and releases, the list calls the action’s handler. Because SwiftUI declares the handler as asynchronous, it can safely make long-running asynchronous calls, like fetching network data.
Refreshing Custom Views
You can also offer refresh capability in your custom views. Read the refresh
environment value to get the Refresh
instance for a given Environment
. If you find a non-nil
value, change your view’s appearance or behavior to offer the refresh to the user, and call the instance to conduct the refresh. You can call the refresh instance directly because it defines a call
method that Swift calls when you call the instance:
struct RefreshableView: View {
private var refresh (\.refresh)
var body: some View {
Button("Refresh") {
Task {
await refresh?()
}
}
.disabled(refresh == nil)
}
}
Be sure to call the handler asynchronously by preceding it with await
. Because the call is asynchronous, you can use its lifetime to indicate progress to the user. For example, you might reveal an indeterminate Progress
before calling the handler, and hide it when the handler completes.
If your code isn’t already in an asynchronous context, create a Task
for the method to run in. If you do this, consider adding a way for the user to cancel the task. For more information, see Concurrency in The Swift Programming Language.