Instance Method インスタンスメソッド

task(priority:_:)

Adds an asynchronous task to perform when this view appears.

Declaration 宣言

func task(priority: TaskPriority = .userInitiated, _ action: @escaping () async -> Void) -> some View

Return Value 戻り値

A view that runs the specified action asynchronously when the view appears.

Parameters パラメータ

priority: The task priority to use when creating the asynchronous task. The default priority is userInitiated.
action: A closure that SwiftUI calls as an asynchronous task when the view appears. SwiftUI automatically cancels the task if the view disappears before the action completes.

Discussion 議論

Use this modifier to perform an asynchronous task with a lifetime that matches that of the modified view. If the task doesn’t finish before SwiftUI removes the view or the view changes identity, SwiftUI cancels the task.

Use the await keyword inside the task to wait for an asynchronous call to complete, or to wait on the values of an AsyncSequence instance. For example, you can modify a Text view to start a task that loads content from a remote resource:

let url = URL(string: "https://example.com")!
@State private var message = "Loading..."


var body: some View {
    Text(message)
        .task {
            do {
                var receivedLines = [String]()
                for try await line in url.lines {
                    receivedLines.append(line)
                    message = "Received \(receivedLines.count) lines"
                }
            } catch {
                message = "Failed to load"
            }
        }
}

This example uses the lines method to get the content stored at the specified URL as an asynchronous sequence of strings. When each new line arrives, the body of the for-await-in loop stores the line in an array of strings and updates the content of the text view to report the latest line count.