Task<TResult>.Result 屬性

定義

取得這個 Task<TResult> 的結果值。Gets the result value of this Task<TResult>.

public:
 property TResult Result { TResult get(); };
public TResult Result { get; }
member this.Result : 'Result
Public ReadOnly Property Result As TResult

屬性值

TResult

這個Task<TResult>的結果值, 與工作的型別參數屬於相同的型別。The result value of this Task<TResult>, which is of the same type as the task's type parameter.

例外狀況

工作已取消。The task was canceled. InnerExceptions 集合包含 TaskCanceledException 物件。The InnerExceptions collection contains a TaskCanceledException object.

-或--or- 在工作執行期間擲回例外狀況。An exception was thrown during the execution of the task. InnerExceptions 集合包含例外狀況的相關資訊。The InnerExceptions collection contains information about the exception or exceptions.

範例

下列範例是一個命令列公用程式, 它會計算每個目錄中, 檔案中的位元組數目, 而這些檔案的名稱會當做命令列引數傳遞。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. 如果目錄包含檔案, 它會執行 lambda 運算式, 將目錄中FileStream每個檔案的物件具現化, 並抓取其FileStream.Length屬性的值。If the directory contains files, it executes a lambda expression that instantiates a FileStream object for each file in the directory and retrieves the value of its FileStream.Length property. 如果目錄未包含任何檔案, 它只會呼叫FromResult方法來建立其Task<TResult>.Result屬性為零 (0) 的工作。If a directory contains no files, it simply calls the FromResult method to create a task whose Task<TResult>.Result property is zero (0). 當工作完成時, 就可以從Result屬性取得所有目錄檔案中的位元組總數。When the tasks finish, the total number of bytes in all a directory's files is available from the Result property.

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

備註

存取屬性的 get 存取子會封鎖呼叫執行緒, 直到非同步作業完成為止;這相當於呼叫Wait方法。Accessing the property's get accessor blocks the calling thread until the asynchronous operation is complete; it is equivalent to calling the Wait method.

一旦作業的結果可供使用之後, 就會加以儲存, 並在後續呼叫Result屬性時立即傳回。Once the result of an operation is available, it is stored and is returned immediately on subsequent calls to the Result property. 請注意, 如果在工作的作業期間發生例外狀況, 或工作已取消, 則Result屬性不會傳回值。Note that, if an exception occurred during the operation of the task, or if the task has been cancelled, the Result property does not return a value. 相反地, 嘗試存取屬性值AggregateException會擲回例外狀況。Instead, attempting to access the property value throws an AggregateException exception.

適用於

另請參閱