Task.FromResult<TResult>(TResult) メソッド

定義

指定した結果で成功した Task<TResult> を作成します。Creates a Task<TResult> that's completed successfully with the specified result.

public:
generic <typename TResult>
 static System::Threading::Tasks::Task<TResult> ^ FromResult(TResult result);
public static System.Threading.Tasks.Task<TResult> FromResult<TResult> (TResult result);
static member FromResult : 'Result -> System.Threading.Tasks.Task<'Result>
Public Shared Function FromResult(Of TResult) (result As TResult) As Task(Of TResult)

型パラメーター

TResult

タスクによって返される結果の型。The type of the result returned by the task.

パラメーター

result
TResult

完了したタスクに格納する結果。The result to store into the completed task.

戻り値

正常に完了したタスク。The successfully completed task.

次の例は、コマンドライン引数として渡された名前を持つ各ディレクトリ内のファイルのバイト数を計算するコマンドラインユーティリティです。The following example is a command-line utility that calculates the number of bytes in the files in each directory whose name is passed as a command-line argument. この例では、FileStream オブジェクトをインスタンス化し、ディレクトリ内の各ファイルの FileStream.Length プロパティの値を取得する長いコードパスを実行するのではなく、単純に FromResult メソッドを呼び出して、ディレクトリにファイルがない場合に Task<TResult>.Result プロパティがゼロ (0) のタスクを作成します。Rather than executing a longer code path that instantiates a FileStream object and retrieves the value of its FileStream.Length property for each file in the directory, the example simply calls the FromResult method to create a task whose Task<TResult>.Result property is zero (0) if a directory has no files.

using System;
using System.Collections.Generic;
using System.IO;
using System.Threading;
using System.Threading.Tasks;

public class Example
{
   public static void Main()
   {
      string[] args = Environment.GetCommandLineArgs();
      if (args.Length > 1) {
         List<Task<long>> tasks = new List<Task<long>>();
         for (int ctr = 1; ctr < args.Length; ctr++)
            tasks.Add(GetFileLengthsAsync(args[ctr]));

         try {
            Task.WaitAll(tasks.ToArray());
         }
         // Ignore exceptions here.
         catch (AggregateException) {}

         for (int ctr = 0 ; ctr < tasks.Count; ctr++) {
            if (tasks[ctr].Status == TaskStatus.Faulted)
               Console.WriteLine("{0} does not exist", args[ctr + 1]);
            else
               Console.WriteLine("{0:N0} bytes in files in '{1}'",
                                 tasks[ctr].Result, args[ctr + 1]);
         }
      }
      else {
         Console.WriteLine("Syntax error: Include one or more file paths.");
      }
   }

   private static Task<long> GetFileLengthsAsync(string filePath)
   {
      if (! Directory.Exists(filePath)) {
         return Task.FromException<long>(
                     new DirectoryNotFoundException("Invalid directory name."));
      }
      else {
         string[] files = Directory.GetFiles(filePath);
         if (files.Length == 0)
            return Task.FromResult(0L);
         else
            return Task.Run( () => { long total = 0;
                                     Parallel.ForEach(files, (fileName) => {
                                                 var fs = new FileStream(fileName, FileMode.Open,
                                                                         FileAccess.Read, FileShare.ReadWrite,
                                                                         256, true);
                                                 long length = fs.Length;
                                                 Interlocked.Add(ref total, length);
                                                 fs.Close(); } );
                                     return total;
                                   } );
      }
   }
}
// When launched with the following command line arguments:
//      subdir . newsubdir
// the example displays output like the following:
//       0 bytes in files in 'subdir'
//       2,059 bytes in files in '.'
//       newsubdir does not exist
Imports System.Collections.Generic
Imports System.IO
Imports System.Threading
Imports System.Threading.Tasks

Module Example
   Public Sub Main()
      Dim args() As String = Environment.GetCommandLineArgs()
      If args.Length > 1 Then
         Dim tasks As New List(Of Task(Of Long))
         For ctr = 1 To args.Length - 1
            tasks.Add(GetFileLengthsAsync(args(ctr)))
         Next
         Try
            Task.WaitAll(tasks.ToArray())
         ' Ignore exceptions here.
         Catch e As AggregateException
         End Try

         For ctr As Integer = 0 To tasks.Count - 1
            If tasks(ctr).Status = TaskStatus.Faulted Then
               Console.WriteLine("{0} does not exist", args(ctr + 1))
            Else
               Console.WriteLine("{0:N0} bytes in files in '{1}'",
                                 tasks(ctr).Result, args(ctr + 1))
            End If
         Next
      Else
         Console.WriteLine("Syntax error: Include one or more file paths.")
      End If
   End Sub
   
   Private Function GetFileLengthsAsync(filePath As String) As Task(Of Long)
      If Not Directory.Exists(filePath) Then
         Return Task.FromException(Of Long)(
                     New DirectoryNotFoundException("Invalid directory name."))
      Else
         Dim files As String() = Directory.GetFiles(filePath)
         If files.Length = 0 Then
            Return Task.FromResult(0L)
         Else
            Return Task.Run( Function()
                                Dim total As Long = 0
                                Dim lockObj As New Object
                                Parallel.ForEach(files, Sub(fileName)
                                                           Dim fs As New FileStream(fileName, FileMode.Open,
                                                                     FileAccess.Read, FileShare.ReadWrite,
                                                                     256, True)
                                                           Dim length As Long = fs.Length
                                                           Interlocked.Add(total, length)
                                                           fs.Close()
                                                        End Sub)
                                Return total
                             End Function )
         End If
      End If
   End Function
End Module
' When launched with the following command line arguments:
'      subdir . newsubdir
' the example displays output like the following:
'       0 bytes in files in 'subdir'
'       2,059 bytes in files in '.'
'       newsubdir does not exist

注釈

このメソッドは、Task<TResult>.Result プロパティが resultStatus プロパティが RanToCompletionである Task<TResult> オブジェクトを作成します。This method creates a Task<TResult> object whose Task<TResult>.Result property is result and whose Status property is RanToCompletion. メソッドは、タスクの戻り値が、長いコードパスを実行せずにすぐにわからない場合によく使用されます。The method is commonly used when the return value of a task is immediately known without executing a longer code path. 具体的な例を次に示します。The example provides an illustration.

値を返さないタスクオブジェクトを作成するには、CompletedTask プロパティからタスクオブジェクトを取得します。To create a Task object that does not return a value, retrieve the Task object from the CompletedTask property.

適用対象

こちらもご覧ください