TextReader Class

Definition

Namespace:

System.IO

Assembly:

System.Runtime.dll

Source:

TextReader.cs

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

public ref class TextReader abstract : MarshalByRefObject, IDisposable

public abstract class TextReader : MarshalByRefObject, IDisposable

type TextReader = class
    inherit MarshalByRefObject
    interface IDisposable

Public MustInherit Class TextReader
Inherits MarshalByRefObject
Implements IDisposable

Inheritance

Object

MarshalByRefObject

TextReader

Derived

System.IO.StreamReader

System.IO.StringReader

Implements

IDisposable

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.

Notes to Implementers

A derived class must minimally implement the Peek() and Read() methods to make a useful instance of TextReader.

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.
CreateObjRef(Type)	Creates an object that contains all the relevant information required to generate a proxy used to communicate with a remote object. (Inherited from MarshalByRefObject)
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.
Equals(Object)	Determines whether the specified object is equal to the current object. (Inherited from Object)
GetHashCode()	Serves as the default hash function. (Inherited from Object)
GetLifetimeService()	Obsolete. Retrieves the current lifetime service object that controls the lifetime policy for this instance. (Inherited from MarshalByRefObject)
GetType()	Gets the Type of the current instance. (Inherited from Object)
InitializeLifetimeService()	Obsolete. Obtains a lifetime service object to control the lifetime policy for this instance. (Inherited from MarshalByRefObject)
MemberwiseClone()	Creates a shallow copy of the current Object. (Inherited from Object)
MemberwiseClone(Boolean)	Creates a shallow copy of the current MarshalByRefObject object. (Inherited from MarshalByRefObject)
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.
Read(Span<Char>)	Reads the characters from the current reader and writes the data to the specified buffer.
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.
ReadAsync(Memory<Char>, CancellationToken)	Asynchronously reads the characters from the current stream into a memory block.
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.
ReadBlock(Span<Char>)	Reads the characters from the current stream and writes the data to a buffer.
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.
ReadBlockAsync(Memory<Char>, CancellationToken)	Asynchronously reads the characters from the current stream and writes the data to a buffer.
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.
ReadLineAsync(CancellationToken)	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.
ReadToEndAsync(CancellationToken)	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.
ToString()	Returns a string that represents the current object. (Inherited from Object)

See also

• StringReader
• StreamReader
• File and Stream I/O
• How to: Read Text from a File
• How to: Write Text to a File
• How to: Read and Write to a Newly Created Data File