StreamReader.ReadLineAsync Method
Definition
Important
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Overloads
ReadLineAsync() |
Reads a line of characters asynchronously from the current stream and returns the data as a string. |
ReadLineAsync(CancellationToken) |
Reads a line of characters asynchronously from the current stream and returns the data as a string. |
ReadLineAsync()
- Source:
- StreamReader.cs
- Source:
- StreamReader.cs
- Source:
- StreamReader.cs
Reads a line of characters asynchronously from the current stream and returns the data as a string.
public:
override System::Threading::Tasks::Task<System::String ^> ^ ReadLineAsync();
public override System.Threading.Tasks.Task<string> ReadLineAsync ();
public override System.Threading.Tasks.Task<string?> ReadLineAsync ();
[System.Runtime.InteropServices.ComVisible(false)]
public override System.Threading.Tasks.Task<string> ReadLineAsync ();
override this.ReadLineAsync : unit -> System.Threading.Tasks.Task<string>
[<System.Runtime.InteropServices.ComVisible(false)>]
override this.ReadLineAsync : unit -> System.Threading.Tasks.Task<string>
Public Overrides Function ReadLineAsync () As Task(Of String)
Returns
A task that represents the asynchronous read operation. The value of the TResult
parameter contains the next line from the stream, or is null
if all the characters have been read.
- Attributes
Exceptions
The number of characters in the next line is larger than Int32.MaxValue.
The stream has been disposed.
The reader is currently in use by a previous read operation.
Examples
The following example shows how to read the first line of a file by using the ReadLineAsync() method.
using System;
using System.IO;
namespace ConsoleApplication
{
class Program
{
static async Task Main()
{
await ReadCharacters();
}
static async Task ReadCharacters()
{
String result;
using (StreamReader reader = File.OpenText("existingfile.txt"))
{
Console.WriteLine("Opened file.");
result = await reader.ReadLineAsync();
Console.WriteLine("First line contains: " + result);
}
}
}
}
Imports System.IO
Module Module1
Sub Main()
ReadCharacters()
End Sub
Async Sub ReadCharacters()
Dim result As String
Using reader As StreamReader = File.OpenText("existingfile.txt")
Console.WriteLine("Opened file.")
result = Await reader.ReadLineAsync()
Console.WriteLine("First line contains: " + result)
End Using
End Sub
End Module
Remarks
This method stores in the task it returns all non-usage exceptions that the method's synchronous counterpart can throw. If an exception is stored into the returned task, that exception will be thrown when the task is awaited. Usage exceptions, such as ArgumentException, are still thrown synchronously. For the stored exceptions, see the exceptions thrown by ReadLine().
Applies to
ReadLineAsync(CancellationToken)
- Source:
- StreamReader.cs
- Source:
- StreamReader.cs
- Source:
- StreamReader.cs
Reads a line of characters asynchronously from the current stream and returns the data as a string.
public:
override System::Threading::Tasks::ValueTask<System::String ^> ReadLineAsync(System::Threading::CancellationToken cancellationToken);
public override System.Threading.Tasks.ValueTask<string?> ReadLineAsync (System.Threading.CancellationToken cancellationToken);
override this.ReadLineAsync : System.Threading.CancellationToken -> System.Threading.Tasks.ValueTask<string>
Public Overrides Function ReadLineAsync (cancellationToken As CancellationToken) As ValueTask(Of String)
Parameters
- cancellationToken
- CancellationToken
The token to monitor for cancellation requests.
Returns
A value task that represents the asynchronous read operation. The value of the TResult
parameter contains the next line from the stream, or is null
if all of the characters have been read.
Exceptions
The number of characters in the next line is larger than Int32.MaxValue.
The stream reader has been disposed.
The reader is currently in use by a previous read operation.
The cancellation token was canceled. This exception is stored into the returned task.
Remarks
If this method is canceled via cancellationToken
, some data that has been read from the current Stream but not stored (by the StreamReader) or returned (to the caller) may be lost.
This method stores in the task it returns all non-usage exceptions that the method's synchronous counterpart can throw. If an exception is stored into the returned task, that exception will be thrown when the task is awaited. Usage exceptions, such as ArgumentException, are still thrown synchronously. For the stored exceptions, see the exceptions thrown by ReadLine().
Applies to
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