Task<TResult>.Result 属性
定义
重要
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获取此 Task<TResult> 的结果值。
public:
property TResult Result { TResult get(); };public TResult Result { get; }member this.Result : 'ResultPublic ReadOnly Property Result As TResult属性值
- TResult
此 Task<TResult>结果值，其类型与任务的类型参数相同。
例外
已取消任务。 InnerExceptions 集合包含 TaskCanceledException 对象。
- 或 - 执行任务期间引发了一个异常。 InnerExceptions 集合包含一个或多个异常的相关信息。
示例
以下示例是一个命令行实用工具，用于计算每个目录中的字节数，其名称作为命令行参数传递。 如果目录包含文件，它将执行 lambda 表达式，该表达式实例化 FileStream 目录中每个文件的对象，并检索其 FileStream.Length 属性的值。 如果目录不包含任何文件，则只需调用 FromResult 该方法来创建其属性为零 (0) 的任务 Task<TResult>.Result 。 任务完成后，可从该属性获取 Result 所有目录文件中的总字节数。
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
注解
访问属性的 get 访问器会阻止调用线程，直到异步操作完成;它等效于调用 Wait 该方法。
操作的结果可用后，将存储该操作，并在对属性的后续调用 Result 时立即返回。 请注意，如果在任务操作期间发生异常，或者任务已取消，则 Result 属性不会返回值。 相反，尝试访问属性值会引发异常 AggregateException 。