StringReader.ReadLineAsync 方法

定義

命名空間:
System.IO
組件:
mscorlib.dll, System.IO.dll
組件:
mscorlib.dll
組件:
System.IO.dll
組件:
netstandard.dll

非同步讀取目前字串中的一行字元，並將資料以字串形式回傳。

public:
 override System::Threading::Tasks::Task<System::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)

傳回

Task<String>

一個代表非同步讀取操作的任務。 參數的TResult值包含字串讀取器的下一行，或若所有字元皆已讀取，則為 。null

屬性
ComVisibleAttribute

例外狀況

ArgumentOutOfRangeException

下一行的字元數比 Int32.MaxValue 還多。

ObjectDisposedException

字串讀取器已被處理。

InvalidOperationException

讀取器目前正被先前的讀取操作使用。

範例

以下範例展示了如何非同步地一次讀取一行字串。

using System;
using System.IO;
using System.Text;

namespace ConsoleApplication
{
    class Program
    {
        static void Main(string[] args)
        {
            ReadCharacters();
        }

        static async void ReadCharacters()
        {
            StringBuilder stringToRead = new StringBuilder();
            stringToRead.AppendLine("Characters in 1st line to read");
            stringToRead.AppendLine("and 2nd line");
            stringToRead.AppendLine("and the end");

            string readText;

            using (StringReader reader = new StringReader(stringToRead.ToString()))
            {
                while ((readText = await reader.ReadLineAsync()) != null)
                {
                    Console.WriteLine(readText);
                }
            }
        }
    }
}
// The example displays the following output:
//
// Characters in 1st line to read
// and 2nd line
// and the end
//

Imports System.IO
Imports System.Text

Module Module1

    Sub Main()
        ReadCharacters()
    End Sub

    Async Sub ReadCharacters()
        Dim stringToRead = New StringBuilder()
        stringToRead.AppendLine("Characters in 1st line to read")
        stringToRead.AppendLine("and 2nd line")
        stringToRead.AppendLine("and the end")

        Using reader As StringReader = New StringReader(stringToRead.ToString())
            Dim readText As String = Await reader.ReadLineAsync()
            While Not IsNothing(readText)
                Console.WriteLine(readText)
                readText = Await reader.ReadLineAsync()
            End While
        End Using
    End Sub
End Module
' The example displays the following output:
'
' Characters in 1st line to read
' and 2nd line
' and the end
'

備註

此方法在任務中儲存所有非使用例外，該方法的同步對應程式可拋出這些例外。 如果回傳的任務中儲存了例外，該例外會在等待任務時拋出。 使用例外錯誤，例如 ArgumentException，仍會同步拋出。 關於儲存的例外，請參見由 ReadLine()拋出的例外。

適用於