TextReader Class

Definition

Represents a reader that can read a sequential series of characters.

[System.Runtime.InteropServices.ComVisible(true)]
public abstract class TextReader : MarshalByRefObject, IDisposable
Inheritance
Derived
System.IO.StreamReader
System.IO.StringReader
Attributes
Implements

Inherited Members

System.MarshalByRefObject

System.Object

Examples

The TextReader class is an abstract class. Therefore, you do not instantiate it in your code. The StreamReader class derives from TextReader and provides implementations of the members for reading from a stream. The following example shows how to read all the characters in a file by using the StreamReader.ReadAsync(Char[], Int32, Int32) method. It checks whether each character is a letter, digit, or white space before adding the character to an instance of the StringBuilder class.

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

namespace WpfApplication
{
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
        }

        private async void Button_Click_1(object sender, RoutedEventArgs e)
        {
            string filename = @"C:\Example\existingfile.txt";
            char[] result;
            StringBuilder builder = new StringBuilder();

            using (StreamReader reader = File.OpenText(filename))
            {
                result = new char[reader.BaseStream.Length];
                await reader.ReadAsync(result, 0, (int)reader.BaseStream.Length);
            }
           
            foreach (char c in result)
            {
                if (char.IsLetterOrDigit(c) || char.IsWhiteSpace(c))
                {
                    builder.Append(c);
                }
            }
            FileOutput.Text = builder.ToString();
        }
    }
}
Imports System.Text
Imports System.IO

Class MainWindow

    Private Async Sub Button_Click_1(sender As Object, e As RoutedEventArgs)
        Dim filename As String = "C:\Example\existingfile.txt"
        Dim result() As Char
        Dim builder As StringBuilder = New StringBuilder()

        Using reader As StreamReader = File.OpenText(filename)
            ReDim result(reader.BaseStream.Length)
            Await reader.ReadAsync(result, 0, reader.BaseStream.Length)
        End Using

        For Each c As Char In result
            If (Char.IsLetterOrDigit(c) Or Char.IsWhiteSpace(c)) Then
                builder.Append(c)
            End If
            Next
        FileOutput.Text = builder.ToString()
    End Sub
End Class

Remarks

TextReader is the abstract base class of StreamReader and StringReader, which read characters from streams and strings, respectively. Use these derived classes to open a text file for reading a specified range of characters, or to create a reader based on an existing stream.

Important

This type implements the IDisposable interface. When you have finished using any type that derives from this type, you should dispose of it either directly or indirectly. To dispose of the type directly, call its Dispose method in a try/catch block. To dispose of it indirectly, use a language construct such as using (in C#) or Using (in Visual Basic). For more information, see Dispose and the "Using an Object that Implements IDisposable" section in the IDisposable interface topic.

Constructors

TextReader()

Initializes a new instance of the TextReader class.

Fields

Null

Provides a TextReader with no data to read from.

Methods

Close()

Closes the TextReader and releases any system resources associated with the TextReader.

Dispose()

Releases all resources used by the TextReader object.

Dispose(Boolean)

Releases the unmanaged resources used by the TextReader and optionally releases the managed resources.

Peek()

Reads the next character without changing the state of the reader or the character source. Returns the next available character without actually reading it from the reader.

Read()

Reads the next character from the text reader and advances the character position by one character.

Read(Char[], Int32, Int32)

Reads a specified maximum number of characters from the current reader and writes the data to a buffer, beginning at the specified index.

ReadAsync(Char[], Int32, Int32)

Reads a specified maximum number of characters from the current text reader asynchronously and writes the data to a buffer, beginning at the specified index.

ReadBlock(Char[], Int32, Int32)

Reads a specified maximum number of characters from the current text reader and writes the data to a buffer, beginning at the specified index.

ReadBlockAsync(Char[], Int32, Int32)

Reads a specified maximum number of characters from the current text reader asynchronously and writes the data to a buffer, beginning at the specified index.

ReadLine()

Reads a line of characters from the text reader and returns the data as a string.

ReadLineAsync()

Reads a line of characters asynchronously and returns the data as a string.

ReadToEnd()

Reads all characters from the current position to the end of the text reader and returns them as one string.

ReadToEndAsync()

Reads all characters from the current position to the end of the text reader asynchronously and returns them as one string.

Synchronized(TextReader)

Creates a thread-safe wrapper around the specified TextReader.