Visual C# 何时需要 Close() 和 Dispose()？

Question

I am new to Visual C# and don't understand when I need to use the Close() and Dispose() methods on FileStream and StreamReader objects. In the code snippet below, I open a file, read the first line, and validate that it is what is expected. Do I need all of the Close() and Dispose() calls shown? If not, when are they needed? Thank you!

        FileStream fs = null;
        StreamReader sr = null;

        try
        {
            fs = new FileStream(txtMstrFile.Text, FileMode.Open, FileAccess.Read);
            using (sr = new StreamReader(fs))
            {
                if (String.IsNullOrEmpty(sLine = sr.ReadLine()))
                {
                    MessageBox.Show(Path.GetFileName(txtMstrFile.Text) + " is an empty file.", "Empty Master File", MessageBoxButtons.OK,
                        MessageBoxIcon.Information);
                    sr.Close();
                    fs.Close();
                    fs.Dispose();
                    return;
                }
                if(!String.Equals(sLine, "Master File"))
                {
                    MessageBox.Show(Path.GetFileName(txtMstrFile.Text) + " has an invalid format.", "Master File is Invalid", MessageBoxButtons.OK,
                        MessageBoxIcon.Error);
                    sr.Close();
                    fs.Close();
                    fs.Dispose();
                    return;
                }
        // Code to process sLine here
                sr.Close();
            }
            fs.Close();
            fs.Dispose();
        }
        catch (IOException ex)
        {
            MessageBox.Show(Path.GetFileName(txtMstrFile.Text) + "\r\n" + ex.ToString(), "File Access Error", MessageBoxButtons.OK,
                MessageBoxIcon.Error);
            sr.Close();
            fs.Close();
            fs.Dispose();
            return;
        }
        sr.Close();
        fs.Close();
        fs.Dispose();

Answer 1

Explicit Dispose() and Close() are rare avises in the typical code: using will do it for you:

   try {
     using (var sr = new StreamReader(new FileStream(txtMstrFile.Text, 
                                                     FileMode.Open, 
                                                     FileAccess.Read))) {
       string sLine = sr.ReadLine(); 

       if (String.IsNullOrEmpty(sLine)) {
         MessageBox.Show($"{Path.GetFileName(txtMstrFile.Text)} is an empty file.", 
                          "Empty Master File", 
                           MessageBoxButtons.OK,
                           MessageBoxIcon.Information);

         return;
       }
     
       if (!String.Equals(sLine, "Master File")) {
         MessageBox.Show($"{Path.GetFileName(txtMstrFile.Text)} has an invalid format.", 
                          "Empty Master File", 
                           MessageBoxButtons.OK,
                           MessageBoxIcon.Information);

         return;
       }  
     }  
   }
   catch (IOException ex) {
     MessageBox.Show($"{Path.GetFileName(txtMstrFile.Text)}\r\n{ex}", 
                      "File Access Error", 
                       MessageBoxButtons.OK,
                       MessageBoxIcon.Error);

     return;
   }   

Please, don't concatenate string when creating messages, string interpolation : $"... " often is much more readable .

Edit: You can totally get rid of Stream s and StreamReader s:

   try {
     // That's enough to read the 1st file's line
     string sLine = File.ReadLines(txtMstrFile.Text).First();

     if (String.IsNullOrEmpty(sLine)) {
       MessageBox.Show($"{Path.GetFileName(txtMstrFile.Text)} is an empty file.", 
                        "Empty Master File", 
                         MessageBoxButtons.OK,
                         MessageBoxIcon.Information);

       return;
     }
     
     if (!String.Equals(sLine, "Master File")) {
       MessageBox.Show($"{Path.GetFileName(txtMstrFile.Text)} has an invalid format.", 
                        "Empty Master File", 
                         MessageBoxButtons.OK,
                         MessageBoxIcon.Information);

       return;
     }
   }
   catch (IOException ex) {
     MessageBox.Show($"{Path.GetFileName(txtMstrFile.Text)}\r\n{ex}", 
                      "File Access Error", 
                       MessageBoxButtons.OK,
                       MessageBoxIcon.Error);

     return;
   } 

Answer 2

Some computer languages leave memory management to the programmer so freeing up memory that is no longer required is known as garbage collection. Dispose is the programmer's way of saying "clean up now". Close is for closing things like connections to databases. Close says "write any unwritten data to the file now" and is a safety measure that ensures that your file data is saved if your computer crash.