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Task(Of TResult).Result Property

Gets the result value of this Task(Of TResult).

Namespace:  System.Threading.Tasks
Assemblies:   System.Threading.Tasks (in System.Threading.Tasks.dll)
  mscorlib (in mscorlib.dll)

'Declaration
Public ReadOnly Property Result As TResult

Property Value

Type: TResult
The result value of this Task(Of TResult), which is the same type as the task's type parameter.

ExceptionCondition
AggregateException

The task was canceled. The AggregateException.InnerExceptions collection contains a TaskCanceledException object.

-or-

An exception was thrown during the execution of the task. The AggregateException.InnerExceptions collection contains information about the exception or exceptions.

Accessing the property's get accessor blocks the calling thread until the asynchronous operation is complete; it is equivalent to calling the Wait method.

Once the result of an operation is available, it is stored and is returned immediately on subsequent calls to the Result property. 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. Instead, attempting to access the property value throws an AggregateException exception.

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. If the directory contains files, it executes a lambda expression that instantiates a FileInfo object for each file in the directory and retrieves the value of its FileInfo.Length property. If a directory contains no files, it simply calls the FromResult(Of TResult) method to create a task whose Task(Of TResult).Result property is zero (0). When the tasks finish, the total number of bytes in all a directory's files is available from the Result property.

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 filePath.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
                                                           total = 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

.NET Framework

Supported in: 4.6, 4.5, 4

.NET Framework Client Profile

Supported in: 4

Portable Class Library

Supported in: Portable Class Library

Supported in: Windows Phone 8.1

Supported in: Windows Phone Silverlight 8.1

Supported in: Windows Phone Silverlight 8
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