C# 中的 TextReader 用於從文字檔案讀取文字或連續的字元序列。 TextReader 類別位於 System.IO 命名空間下。它是StreamReader和StringReader的抽象基底類，分別用於從流和字串中讀取字元。我們無法建立 TextReader 的對象，因為它是一個抽象類別。預設情況下，TextReader 不是線程安全的。派生 TextReader 類別的類別需要至少實作 Peek() 和 Read() 方法才能建立有用的 TextReader 實例。
文法：
建立TextReader的語法如下：
TextReader text_reader = File.OpenText(file_path);
上述語句將在「file_path」指定的位置開啟一個檔案。然後，在 text_reader 的幫助下，我們可以使用 TextReader 類別的方法來從檔案中讀取內容。
我們也可以藉助「using」區塊建立 TextReader，如下所示：
using(TextReader text_reader = File.OpenText(file_path))
{
//user code
}使用「using」區塊的優點是，當物件的工作完成並且不再需要該物件時，它會釋放其中指定的物件所獲取的記憶體。
為了使用 TextReader，有必要在我們的程式碼中匯入 System.IO 命名空間。由於 TextReader 是一個抽象類，我們不能直接使用 new 關鍵字來建立它的實例，但我們可以使用 File 類別的 OpenText() 方法來實現，如下所示：
TextReader text_reader = File.OpenText(file_path);
OpenText() 方法將檔案的位置作為輸入，然後在同一位置開啟現有的 UTF-8 編碼文字檔案進行讀取。
File.OpenText() 方法傳回 StreamReader 類別的對象，該類別是 TextReader 的衍生類，因此有助於在程式碼中建立 TextReader 類別的有用實例。此實例可用於呼叫 TextReader 類別的方法來從檔案中讀取內容。 TextReader 類別衍生自抽象類別 MarshalByRefObject。其繼承層次如下圖所示：
物件 → MarshalByRefObject → TextReader
我們可以在 TextReader 的兩個衍生類別（即 StreamReader 和 StringReader）的協助下使用 TextReader。
TextReader的一些重要方法請參考下表：
| Method | Description |
| Close() | It is used to close the TextReader and to release any system resources associated with it. |
| Dispose() | It is used to release all the resources used by an object of TextReader. |
| Peek() | It is used to read the next character without changing the state of the reader and it returns the next available character without actually reading it from the reader. |
| Read() | It is used to read the next character from the text reader and it also advances the character position by one character. |
| ReadLine() | It is used to read a line of characters from the text reader and it also returns the data as a string. |
| ReadToEnd() | It is used to read all characters from the current position to the end of the text reader and it returns them as one string. |
We can pass a text file name in a TextReader constructor to create an object. Following are the different examples of TextReader in C#.
Reading a line of a file using the ReadLine() method of TextReader.
Code:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.IO;
namespace ConsoleApp3
{
public class Program
{
public static void Main()
{
string file = @"E:\Content\TextReader.txt";
try
{
if (File.Exists(file))
{
// opening the text file and reading a line
using (TextReader textReader = File.OpenText(file))
{
Console.WriteLine(textReader.ReadLine());
}
}
else
{
Console.WriteLine("File does not exist!");
}
Console.ReadKey();
}
catch (Exception ex)
{
Console.WriteLine(ex.Message);
}
}
}
}Output:
Reading five characters from a file using the ReadBlock() method of TextReader.
Code:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.IO;
namespace ConsoleApp3
{
public class Program
{
public static void Main()
{
string file = @"E:\Content\TextReader.txt";
try
{
if (File.Exists(file))
{
//Opening the text file and reading 5 characters
using (TextReader textReader = File.OpenText(file))
{
char[] ch = new char[5];
textReader.ReadBlock(ch, 0, 5);
Console.WriteLine(ch);
}
}
else
{
Console.WriteLine("File does not exist!");
}
Console.ReadKey();
}
catch (Exception ex)
{
Console.WriteLine(ex.Message);
}
}
}
}Output:
Reading the whole content of a text file using the ReadToEnd() method of TextReader.
Code:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.IO;
namespace ConsoleApp3
{
public class Program
{
public static void Main()
{
string file = @"E:\Content\TextReader.txt";
string content = String.Empty;
try
{
if (File.Exists(file))
{
//Opening a text file and reading the whole content
using (TextReader tr = File.OpenText(file))
{
content = tr.ReadToEnd();
Console.WriteLine(content);
}
}
else
{
Console.WriteLine("File does not exist!");
}
Console.ReadKey();
}
catch (Exception ex)
{
Console.WriteLine(ex.Message);
}
}
}
}Output:
Reading the content of a text file using TextReader and writing it to another file.
Code:
using System;
using System.Text;
using System.Threading.Tasks;
using System.IO;
namespace ConsoleApp3
{
public class Program
{
public static void Main()
{
string fileToRead = @"E:\Content\TextReader.txt";
string fileToWrite = @"E:\Content\TextReaderAndWriter.txt";
StringBuilder content = new StringBuilder();
string str = String.Empty;
try
{
//checking if the file exists to read
if (File.Exists(fileToRead))
{
//Opening a text file and reading the whole content
using (TextReader textReader = File.OpenText(fileToRead))
{
while ((str = textReader.ReadLine()) != null)
{
content.Append("\n" + str);
}
}
}
else
{
Console.WriteLine("File does not exist!");
}
//checking if the file to write content already exists
if (File.Exists(fileToWrite))
{
File.Delete(fileToWrite);
}
//creating file if it does not exist
using (TextWriter textWriter = File.CreateText(fileToWrite))
{
textWriter.WriteLine(content);
}
Console.ReadKey();
}
catch (Exception ex)
{
Console.WriteLine(ex.Message);
}
}
}
}Output:
以上是C# 中的文字閱讀器的詳細內容。更多資訊請關注PHP中文網其他相關文章！
