Async.Catch<'T> 方法 (F#)
建立會執行指定計算的非同步計算。如果這個計算順利完成，這個方法會將 Choice1Of2 與傳回值一起傳回。如果這個計算在完成之前引發例外狀況，則會傳回具有所引發例外狀況的 Choice2Of2。
**命名空間/模組路徑：**Microsoft.FSharp.Control
組件：FSharp.Core (在 FSharp.Core.dll 中)
// Signature:
static member Catch : Async<'T> -> Async<Choice<'T,exn>>
// Usage:
Async.Catch (computation)
參數
computation
型別：Async<'T>傳回型別 'T 的輸入計算。
傳回值
傳回型別 T 之選項或例外狀況的計算。
範例
下列程式碼範例示範如何使用 Async.Catch 執行可能擲回例外狀況的非同步計算。
open System
open System.IO
let writeToFile filename numBytes =
async {
use file = File.Create(filename)
printfn "Writing to file %s." filename
do! file.AsyncWrite(Array.zeroCreate<byte> numBytes)
}
let readFile filename numBytes =
async {
use file = File.OpenRead(filename)
printfn "Reading from file %s." filename
do! file.AsyncRead(numBytes) |> Async.Ignore
}
let filename = "BigFile.dat"
let numBytes = 100000000
let result1 = writeToFile filename numBytes
|> Async.Catch
|> Async.RunSynchronously
match result1 with
| Choice1Of2 _ -> printfn "Successfully wrote to file."; ()
| Choice2Of2 exn ->
printfn "Exception occurred writing to file %s: %s" filename exn.Message
// Start these next two operations asynchronously, forcing an exception due
// to trying to access the file twice simultaneously.
Async.Start(readFile filename numBytes)
let result2 = writeToFile filename numBytes
|> Async.Catch
|> Async.RunSynchronously
match result2 with
| Choice1Of2 buffer -> printfn "Successfully read from file."
| Choice2Of2 exn ->
printfn "Exception occurred reading from file %s: %s" filename (exn.Message)
平台
Windows 8 中， Windows 7， Windows Server 2012 上， Windows Server 2008 R2
版本資訊
F# 核心程式庫版本
支援版本:2.0， 4.0，可攜式執行檔 (PE)。