Text Files

File.ReadLines

more efficient than using ReadAllLines for large files.
Returns an IEnumerable<string> of all the lines of code.

IEnumerable<string> enumLines; 
string[] lines; 

enumLines = System.IO.File.ReadLines(@"C:\\temp\\myfile.txt", Encoding.UTF8);

lines = enumLines.ToArray();

foreach (string line in lines) 
{ 
}

File.ReadAllLines

Added in .NET 4.0
Reads each line into a string array.

string[] lines; 
lines = System.IO.File.ReadAllLines(@"C:\\temp\\myfile.txt"); 
foreach (string line in lines) 
{ 
}

Reads each line into a collection

System.Collections.Generic.List<string> myList; 
myList = System.IO.File.ReadAllLines("C:\temp\SavedLists.txt");

File.ReadAllText

Should only be used on very small, basic files

string sWholeFile; 
string[] lines; 

sWholeFile = System.IO.File.ReadAllText(@"C:\\temp\\myfile.txt"); 
lines = sWholeFile.Split(Environment.NewLine);

StreamReader.ReadToEnd

System.IO.StreamReader oStreamReader; 
string sWholeFile; 

oStreamReader = System.IO.StreamReader(@"C:\\temp\\myfile.txt"); 
sWholeFile = oStreamReader.ReadToEnd;

StreamReader.ReadToEndAsync

System.IO.StreamReader oStreamReader; 
string sWholeFile; 

oStreamReader = System.IO.StreamReader(@"C:\\temp\\myfile.txt"); 
using (oStreamReader) 
{ 
   sWholeFile = await oStreamReader.ReadToEndAsync(); 
}

StreamReader.ReadLine

Reads each line into a string array.

System.IO.StreamReader oStreamReader; 
string sWholeFile; 

oStreamReader = System.IO.StreamReader(@"C:\\temp\\myfile.txt"); 
while ( (line = oStreamReader.ReadLine() ) != null) 
{ 
}

Writing Files from Arrays

This creates a file asynchronously and write

public static async Task Method_WriteTextToFile() 
{ 
   string[] myText = { "Monday", "Tuesday", "Wednesday" }; 

   await System.IO.File.WriteAllLinesAsync("C:\temp\myTextFile.txt", myText); 
}

Writing Files from Collections

Available in .NET 4.0

System.Collections.Generic.List<string> myList; 
System.IO.File.WriteAllLines("C:\temp\SavedLists.txt", myList);

Prioir to .NET 4.0 you needed to use a StreamWriter