C # : 通过多行字符串的行进行循环

You can use a StringReader to read a line at a time:

using (StringReader reader = new StringReader(input))
{
string line = string.Empty;
do
{
line = reader.ReadLine();
if (line != null)
{
// do something with the line
}


} while (line != null);
}

from MSDN for StringReader

    string textReaderText = "TextReader is the abstract base " +
"class of StreamReader and StringReader, which read " +
"characters from streams and strings, respectively.\n\n" +


"Create an instance of TextReader to open a text file " +
"for reading a specified range of characters, or to " +
"create a reader based on an existing stream.\n\n" +


"You can also use an instance of TextReader to read " +
"text from a custom backing store using the same " +
"APIs you would use for a string or a stream.\n\n";


Console.WriteLine("Original text:\n\n{0}", textReaderText);


// From textReaderText, create a continuous paragraph
// with two spaces between each sentence.
string aLine, aParagraph = null;
StringReader strReader = new StringReader(textReaderText);
while(true)
{
aLine = strReader.ReadLine();
if(aLine != null)
{
aParagraph = aParagraph + aLine + " ";
}
else
{
aParagraph = aParagraph + "\n";
break;
}
}
Console.WriteLine("Modified text:\n\n{0}", aParagraph);

I suggest using a combination of StringReader and my LineReader class, which is part of MiscUtil but also available in this StackOverflow answer - you can easily copy just that class into your own utility project. You'd use it like this:

string text = @"First line
second line
third line";


foreach (string line in new LineReader(() => new StringReader(text)))
{
Console.WriteLine(line);
}

Looping over all the lines in a body of string data (whether that's a file or whatever) is so common that it shouldn't require the calling code to be testing for null etc :) Having said that, if you do want to do a manual loop, this is the form that I typically prefer over Fredrik's:

using (StringReader reader = new StringReader(input))
{
string line;
while ((line = reader.ReadLine()) != null)
{
// Do something with the line
}
}

This way you only have to test for nullity once, and you don't have to think about a do/while loop either (which for some reason always takes me more effort to read than a straight while loop).

Here's a quick code snippet that will find the first non-empty line in a string:

string line1;
while (
((line1 = sr.ReadLine()) != null) &&
((line1 = line1.Trim()).Length == 0)
)
{ /* Do nothing - just trying to find first non-empty line*/ }


if(line1 == null){ /* Error - no non-empty lines in string */ }

I know this has been answered, but I'd like to add my own answer:

using (var reader = new StringReader(multiLineString))
{
for (string line = reader.ReadLine(); line != null; line = reader.ReadLine())
{
// Do something with the line
}
}

Try using String.Split Method:

string text = @"First line
second line
third line";


foreach (string line in text.Split('\n'))
{
// do something
}

Sometimes I think we can overcomplicate the solution just to avoid repeating one line of code. This is the reason I landed on this question in the first place.

After thinking about it for a bit I came to the conclusion that the simplest solution is to repeat the ReadLine before and inside the loop.

using (var stringReader = new StringReader(input))
{
var line = await stringReader.ReadLineAsync();


while (line != null)
{
// do something
line = await stringReader.ReadLineAsync();
}
}

I realize this might be considered to not follow the DRY principle, but I think it's worth considering given the simplicity.