Task<TResult> Constructors
Definition
Important
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Initializes a new Task<TResult> object.
Overloads
Task<TResult>(Func<TResult>)
- Source:
- Future.cs
- Source:
- Future.cs
- Source:
- Future.cs
Initializes a new Task<TResult> with the specified function.
public:
Task(Func<TResult> ^ function);public Task (Func<TResult> function);new System.Threading.Tasks.Task<'Result> : Func<'Result> -> System.Threading.Tasks.Task<'Result>Public Sub New (function As Func(Of TResult))Parameters
- function
- Func<TResult>
The delegate that represents the code to execute in the task. When the function has completed, the task's Result property will be set to return the result value of the function.
Exceptions
The function argument is null.
The function argument is null.
Examples
The following example counts the approximate number of words in text files that represent published books. Each task is responsible for opening a file, reading its entire contents asynchronously, and calculating the word count by using a regular expression. The Task.WaitAll(Task[]) method is called to ensure that all tasks have completed before displaying the word count of each book to the console.
Object instantiation is separated from object execution in this example so that the example can ensure that each file exists. If they do not, it displays the name of the missing file. Otherwise, it calls the Task.Start method to launch each task.
using System;
using System.IO;
using System.Text.RegularExpressions;
using System.Threading.Tasks;
public class Example
{
public static async Task Main()
{
string pattern = @"\p{P}*\s+";
string[] titles = { "Sister Carrie", "The Financier" };
Task<int>[] tasks = new Task<int>[titles.Length];
for (int ctr = 0; ctr < titles.Length; ctr++) {
string s = titles[ctr];
tasks[ctr] = new Task<int>( () => {
// Number of words.
int nWords = 0;
// Create filename from title.
string fn = s + ".txt";
StreamReader sr = new StreamReader(fn);
string input = sr.ReadToEndAsync().Result;
sr.Close();
nWords = Regex.Matches(input, pattern).Count;
return nWords;
} );
}
// Ensure files exist before launching tasks.
bool allExist = true;
foreach (var title in titles) {
string fn = title + ".txt";
if (! File.Exists(fn)) {
allExist = false;
Console.WriteLine("Cannot find '{0}'", fn);
break;
}
}
// Launch tasks
if (allExist) {
foreach (var t in tasks)
t.Start();
await Task.WhenAll(tasks);
Console.WriteLine("Word Counts:\n");
for (int ctr = 0; ctr < titles.Length; ctr++)
Console.WriteLine("{0}: {1,10:N0} words", titles[ctr], tasks[ctr].Result);
}
}
}
// The example displays the following output:
// Sister Carrie: 159,374 words
// The Financier: 196,362 words
Imports System.IO
Imports System.Text.RegularExpressions
Imports System.Threading.Tasks
Module Example
Public Sub Main()
Dim pattern As String = "\p{P}*\s+"
Dim titles() As String = { "Sister Carrie",
"The Financier" }
Dim tasks(titles.Length - 1) As Task(Of Integer)
For ctr As Integer = 0 To titles.Length - 1
Dim s As String = titles(ctr)
tasks(ctr) = New Task(Of Integer)( Function()
' Number of words.
Dim nWords As Integer = 0
' Create filename from title.
Dim fn As String = s + ".txt"
Dim sr As New StreamReader(fn)
Dim input As String = sr.ReadToEndAsync().Result
sr.Close()
nWords = Regex.Matches(input, pattern).Count
Return nWords
End Function)
Next
' Ensure files exist before launching tasks.
Dim allExist As Boolean = True
For Each title In titles
Dim fn As String = title + ".txt"
If Not File.Exists(fn) Then
allExist = false
Console.WriteLine("Cannot find '{0}'", fn)
Exit For
End If
Next
' Launch tasks
If allExist Then
For Each t in tasks
t.Start()
Next
Task.WaitAll(tasks)
Console.WriteLine("Word Counts:")
Console.WriteLine()
For ctr As Integer = 0 To titles.Length - 1
Console.WriteLine("{0}: {1,10:N0} words", titles(ctr), tasks(ctr).Result)
Next
End If
End Sub
End Module
' The example displays the following output:
' Sister Carrie: 159,374 words
' The Financier: 196,362 words
The regular expression pattern \p{P}*\s+ matches zero, one, or more punctuation characters followed by one or more white-space characters. It assumes that the total number of matches equals the approximate word count.
Remarks
This constructor should only be used in advanced scenarios where it is required that the creation and starting of the task is separated.
Rather than calling this constructor, the most common way to instantiate a Task<TResult> object and launch a task is by calling the static Task.Run<TResult>(Func<TResult>) and TaskFactory<TResult>.StartNew(Func<TResult>) methods.
If a task with no action is needed just for the consumer of an API to have something to await, a TaskCompletionSource<TResult> should be used.
See also
Applies to
Task<TResult>(Func<Object,TResult>, Object)
- Source:
- Future.cs
- Source:
- Future.cs
- Source:
- Future.cs
Initializes a new Task<TResult> with the specified function and state.
public:
Task(Func<System::Object ^, TResult> ^ function, System::Object ^ state);public Task (Func<object,TResult> function, object state);public Task (Func<object?,TResult> function, object? state);new System.Threading.Tasks.Task<'Result> : Func<obj, 'Result> * obj -> System.Threading.Tasks.Task<'Result>Public Sub New (function As Func(Of Object, TResult), state As Object)Parameters
The delegate that represents the code to execute in the task. When the function has completed, the task's Result property will be set to return the result value of the function.
- state
- Object
An object representing data to be used by the action.
Exceptions
The function argument is null.
The function argument is null.
Remarks
Rather than calling this constructor, the most common way to instantiate a Task<TResult> object and launch a task is by calling the static TaskFactory<TResult>.StartNew(Func<Object,TResult>, Object) method. The only advantage offered by this constructor is that it allows object instantiation to be separated from task invocation.
See also
Applies to
Task<TResult>(Func<TResult>, CancellationToken)
- Source:
- Future.cs
- Source:
- Future.cs
- Source:
- Future.cs
Initializes a new Task<TResult> with the specified function.
public:
Task(Func<TResult> ^ function, System::Threading::CancellationToken cancellationToken);public Task (Func<TResult> function, System.Threading.CancellationToken cancellationToken);new System.Threading.Tasks.Task<'Result> : Func<'Result> * System.Threading.CancellationToken -> System.Threading.Tasks.Task<'Result>Public Sub New (function As Func(Of TResult), cancellationToken As CancellationToken)Parameters
- function
- Func<TResult>
The delegate that represents the code to execute in the task. When the function has completed, the task's Result property will be set to return the result value of the function.
- cancellationToken
- CancellationToken
The CancellationToken to be assigned to this task.
Exceptions
The CancellationTokenSource that created cancellationToken has already been disposed.
The function argument is null.
The function argument is null.
Remarks
Rather than calling this constructor, the most common way to instantiate a Task<TResult> object and launch a task is by calling the static Task.Run<TResult>(Func<TResult>, CancellationToken) and TaskFactory<TResult>.StartNew(Func<TResult>, CancellationToken) methods. The only advantage offered by this constructor is that it allows object instantiation to be separated from task invocation.
See also
Applies to
Task<TResult>(Func<TResult>, TaskCreationOptions)
- Source:
- Future.cs
- Source:
- Future.cs
- Source:
- Future.cs
Initializes a new Task<TResult> with the specified function and creation options.
public:
Task(Func<TResult> ^ function, System::Threading::Tasks::TaskCreationOptions creationOptions);public Task (Func<TResult> function, System.Threading.Tasks.TaskCreationOptions creationOptions);new System.Threading.Tasks.Task<'Result> : Func<'Result> * System.Threading.Tasks.TaskCreationOptions -> System.Threading.Tasks.Task<'Result>Public Sub New (function As Func(Of TResult), creationOptions As TaskCreationOptions)Parameters
- function
- Func<TResult>
The delegate that represents the code to execute in the task. When the function has completed, the task's Result property will be set to return the result value of the function.
- creationOptions
- TaskCreationOptions
The TaskCreationOptions used to customize the task's behavior.
Exceptions
The creationOptions argument specifies an invalid value for TaskCreationOptions.
The function argument is null.
The function argument is null.
Remarks
Rather than calling this constructor, the most common way to instantiate a Task<TResult> object and launch a task is by calling the static TaskFactory<TResult>.StartNew(Func<TResult>, TaskCreationOptions) method. The only advantage offered by this constructor is that it allows object instantiation to be separated from task invocation.
See also
Applies to
Task<TResult>(Func<Object,TResult>, Object, CancellationToken)
- Source:
- Future.cs
- Source:
- Future.cs
- Source:
- Future.cs
Initializes a new Task<TResult> with the specified action, state, and options.
public:
Task(Func<System::Object ^, TResult> ^ function, System::Object ^ state, System::Threading::CancellationToken cancellationToken);public Task (Func<object,TResult> function, object state, System.Threading.CancellationToken cancellationToken);public Task (Func<object?,TResult> function, object? state, System.Threading.CancellationToken cancellationToken);new System.Threading.Tasks.Task<'Result> : Func<obj, 'Result> * obj * System.Threading.CancellationToken -> System.Threading.Tasks.Task<'Result>Public Sub New (function As Func(Of Object, TResult), state As Object, cancellationToken As CancellationToken)Parameters
The delegate that represents the code to execute in the task. When the function has completed, the task's Result property will be set to return the result value of the function.
- state
- Object
An object representing data to be used by the function.
- cancellationToken
- CancellationToken
The CancellationToken to be assigned to the new task.
Exceptions
The CancellationTokenSource that created cancellationToken has already been disposed.
The function argument is null.
The function argument is null.
Remarks
Rather than calling this constructor, the most common way to instantiate a Task<TResult> object and launch a task is by calling the static TaskFactory<TResult>.StartNew(Func<Object,TResult>, Object, CancellationToken) method. The only advantage offered by this constructor is that it allows object instantiation to be separated from task invocation.
See also
Applies to
Task<TResult>(Func<Object,TResult>, Object, TaskCreationOptions)
- Source:
- Future.cs
- Source:
- Future.cs
- Source:
- Future.cs
Initializes a new Task<TResult> with the specified action, state, and options.
public:
Task(Func<System::Object ^, TResult> ^ function, System::Object ^ state, System::Threading::Tasks::TaskCreationOptions creationOptions);public Task (Func<object,TResult> function, object state, System.Threading.Tasks.TaskCreationOptions creationOptions);public Task (Func<object?,TResult> function, object? state, System.Threading.Tasks.TaskCreationOptions creationOptions);new System.Threading.Tasks.Task<'Result> : Func<obj, 'Result> * obj * System.Threading.Tasks.TaskCreationOptions -> System.Threading.Tasks.Task<'Result>Public Sub New (function As Func(Of Object, TResult), state As Object, creationOptions As TaskCreationOptions)Parameters
The delegate that represents the code to execute in the task. When the function has completed, the task's Result property will be set to return the result value of the function.
- state
- Object
An object representing data to be used by the function.
- creationOptions
- TaskCreationOptions
The TaskCreationOptions used to customize the task's behavior.
Exceptions
The creationOptions argument specifies an invalid value for TaskCreationOptions.
The function argument is null.
The function argument is null.
Remarks
Rather than calling this constructor, the most common way to instantiate a Task<TResult> object and launch a task is by calling the static TaskFactory<TResult>.StartNew(Func<Object,TResult>, Object, TaskCreationOptions) method. The only advantage offered by this constructor is that it allows object instantiation to be separated from task invocation.
See also
Applies to
Task<TResult>(Func<TResult>, CancellationToken, TaskCreationOptions)
- Source:
- Future.cs
- Source:
- Future.cs
- Source:
- Future.cs
Initializes a new Task<TResult> with the specified function and creation options.
public:
Task(Func<TResult> ^ function, System::Threading::CancellationToken cancellationToken, System::Threading::Tasks::TaskCreationOptions creationOptions);public Task (Func<TResult> function, System.Threading.CancellationToken cancellationToken, System.Threading.Tasks.TaskCreationOptions creationOptions);new System.Threading.Tasks.Task<'Result> : Func<'Result> * System.Threading.CancellationToken * System.Threading.Tasks.TaskCreationOptions -> System.Threading.Tasks.Task<'Result>Public Sub New (function As Func(Of TResult), cancellationToken As CancellationToken, creationOptions As TaskCreationOptions)Parameters
- function
- Func<TResult>
The delegate that represents the code to execute in the task. When the function has completed, the task's Result property will be set to return the result value of the function.
- cancellationToken
- CancellationToken
The CancellationToken that will be assigned to the new task.
- creationOptions
- TaskCreationOptions
The TaskCreationOptions used to customize the task's behavior.
Exceptions
The CancellationTokenSource that created cancellationToken has already been disposed.
The creationOptions argument specifies an invalid value for TaskCreationOptions.
The function argument is null.
The function argument is null.
Remarks
Rather than calling this constructor, the most common way to instantiate a Task<TResult> object and launch a task is by calling the static TaskFactory.StartNew<TResult>(Func<TResult>, CancellationToken, TaskCreationOptions, TaskScheduler) method. The only advantage offered by this constructor is that it allows object instantiation to be separated from task invocation.
See also
Applies to
Task<TResult>(Func<Object,TResult>, Object, CancellationToken, TaskCreationOptions)
- Source:
- Future.cs
- Source:
- Future.cs
- Source:
- Future.cs
Initializes a new Task<TResult> with the specified action, state, and options.
public:
Task(Func<System::Object ^, TResult> ^ function, System::Object ^ state, System::Threading::CancellationToken cancellationToken, System::Threading::Tasks::TaskCreationOptions creationOptions);public Task (Func<object,TResult> function, object state, System.Threading.CancellationToken cancellationToken, System.Threading.Tasks.TaskCreationOptions creationOptions);public Task (Func<object?,TResult> function, object? state, System.Threading.CancellationToken cancellationToken, System.Threading.Tasks.TaskCreationOptions creationOptions);new System.Threading.Tasks.Task<'Result> : Func<obj, 'Result> * obj * System.Threading.CancellationToken * System.Threading.Tasks.TaskCreationOptions -> System.Threading.Tasks.Task<'Result>Public Sub New (function As Func(Of Object, TResult), state As Object, cancellationToken As CancellationToken, creationOptions As TaskCreationOptions)Parameters
The delegate that represents the code to execute in the task. When the function has completed, the task's Result property will be set to return the result value of the function.
- state
- Object
An object representing data to be used by the function.
- cancellationToken
- CancellationToken
The CancellationToken to be assigned to the new task.
- creationOptions
- TaskCreationOptions
The TaskCreationOptions used to customize the task's behavior.
Exceptions
The CancellationTokenSource that created cancellationToken has already been disposed.
The creationOptions argument specifies an invalid value for TaskCreationOptions.
The function argument is null.
The function argument is null.
Remarks
Rather than calling this constructor, the most common way to instantiate a Task<TResult> object and launch a task is by calling the static TaskFactory<TResult>.StartNew(Func<Object,TResult>, Object, CancellationToken, TaskCreationOptions, TaskScheduler) method. The only advantage offered by this constructor is that it allows object instantiation to be separated from task invocation.
See also
Applies to
.NET