refresh

Discussion 議論

When this environment value contains an instance of the RefreshAction 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 RefreshAction 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 callAsFunction() method that Swift calls when you call the instance:

struct RefreshableView: View {
    @Environment(\.refresh) private var 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 can reveal an indeterminate ProgressView 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.