如何读取项目根目录中的文本文件？

You have to use absolute path in this case. But if you set the CopyToOutputDirectory = CopyAlways, it will work as you are doing it.

From Solution Explorer, right click on myfile.txt and choose "Properties"

From there, set the Build Action to content and Copy to Output Directory to either Copy always or Copy if newer

You can use the following to get the root directory of a website project:

String FilePath;
FilePath = Server.MapPath("/MyWebSite");

Or you can get the base directory like so:

AppDomain.CurrentDomain.BaseDirectory

Add a Resource File to your project (Right Click Project->Properties->Resources). Where it says "strings", you can switch to be "files". Choose "Add Resource" and select your file.

You can now reference your file through the Properties.Resources collection.

You can have it embedded (build action set to Resource) as well, this is how to retrieve it from there:

private static UnmanagedMemoryStream GetResourceStream(string resName)
{
var assembly = Assembly.GetExecutingAssembly();
var strResources = assembly.GetName().Name + ".g.resources";
var rStream = assembly.GetManifestResourceStream(strResources);
var resourceReader = new ResourceReader(rStream);
var items = resourceReader.OfType<DictionaryEntry>();
var stream = items.First(x => (x.Key as string) == resName.ToLower()).Value;
return (UnmanagedMemoryStream)stream;
}


private void Button1_Click(object sender, RoutedEventArgs e)
{
string resName = "Test.txt";
var file = GetResourceStream(resName);
using (var reader = new StreamReader(file))
{
var line = reader.ReadLine();
MessageBox.Show(line);
}
}

(Some code taken from this answer by Charles)

private string _filePath = Path.GetDirectoryName(System.AppDomain.CurrentDomain.BaseDirectory);

The method above will bring you something like this:

"C:\Users\myuser\Documents\Visual Studio 2015\Projects\myProjectNamespace\bin\Debug"

From here you can navigate backwards using System.IO.Directory.GetParent:

_filePath = Directory.GetParent(_filePath).FullName;

1 time will get you to \bin, 2 times will get you to \myProjectNamespace, so it would be like this:

_filePath = Directory.GetParent(Directory.GetParent(_filePath).FullName).FullName;

Well, now you have something like "C:\Users\myuser\Documents\Visual Studio 2015\Projects\myProjectNamespace", so just attach the final path to your fileName, for example:

_filePath += @"\myfile.txt";
TextReader tr = new StreamReader(_filePath);

Hope it helps.

In this code you access to root directory project:

 string _filePath = Path.GetDirectoryName(System.AppDomain.CurrentDomain.BaseDirectory);

then:

StreamReader r = new StreamReader(_filePath + "/cities2.json"))