How To Overwrite A File If It Already Exists?

问题

I'm making a music player. It has 2 forms; one is the main area where you play music. The second form has a CheckedListBox where you select the mp3s you want. When I click a button, it saves the selection in a .txt file so I can access them in the first form, where I'll put the strings into the paths for music player to find the files.

This is the code in my second form, where I save the selected songs into .txt files.

private void selectbtn_Click(object sender, EventArgs e)
{
    if (File.Exists(@"C:\Users\Me\Desktop\JAM_MACHINE\JAMS\record.txt"))
    {
       File.WriteAllText(@"C:\Users\Me\Desktop\JAM_MACHINE\JAMS\record.txt", String.Empty);
    }

    string[] checkedtitles = new string[checkedListBox1.CheckedItems.Count]; 

    for (int ii = 0; ii < checkedListBox1.CheckedItems.Count; ii++)
    {
        checkedtitles[ii] = checkedListBox1.CheckedItems[ii].ToString();
    }
    string selectedSongs = String.Join(Environment.NewLine, checkedtitles); 

    songRecord.writeRecord(selectedSongs); //I initialised the class containing streamwriter/reader, and called it songRecord
    this.Close();   
}

The problem is, whenever I close the program and open it again, I can't rewrite/clear the .txt file. It just adds on to the existing file. Is there something I'm not doing right?

Here is my streamreader/writer codes. I'm pretty sure I closed it after running too, but perhaps somebody can figure out what's wrong:

namespace songss
{
    class DataRecord
    {
    public void writeRecord(string line)
    {
        StreamWriter sw = null;
        try
        {
            sw = new StreamWriter(@"C:\Users\Me\Desktop\JAM_MACHINE\record.txt", true);
            sw.WriteLine(line);
        }
        catch (FileNotFoundException)
        {
            Console.WriteLine("Error: File not found.");
        }
        catch (IOException)
        {
            Console.WriteLine("Error: IO");
        }
        catch(Exception)
        {
            throw;
        }
        finally
        {
            if (sw != null)
                sw.Close();
        }
        }

 public void readRecord()
    {
        StreamReader sr = null;
        string myInputline;
        try
        {
            sr = new StreamReader(@"C:\Users\Me\Desktop\JAM_MACHINE\record.txt");
            while ((myInputline = sr.ReadLine()) != null) ; //readline reads whole line
            Console.WriteLine(myInputline);
        }
        catch (FileNotFoundException)
        {
            Console.WriteLine("Error: File not found");
        }
        catch(IOException)
        {
            Console.WriteLine("Error: IO");
        }
        catch (Exception)
        {
            throw;
        }
        finally
        {
            if (sr != null)
                sr.Close();
        }
    }
    }
    }

回答1:

WriteAllText

File.WriteAllText should do what you want.

Creates a new file, writes the specified string to the file, and then closes the file. If the target file already exists, it is overwritten.

StreamWriter

The StreamWriter class also has an option to overwrite/append:

Initializes a new instance of the StreamWriter class for the specified file by using the default encoding and buffer size. If the file exists, it can be either overwritten or appended to.

public StreamWriter(
    string path,
    bool append
)

Example:

using (StreamWriter writer = new StreamWriter("test.txt", false)){ 
    writer.Write(textToAdd);
}

Looking at your code, you're passing in true which means append.

sw = new StreamWriter(@"C:\Users\Me\Desktop\JAM_MACHINE\record.txt", true);
sw.WriteLine(line);

.NET Compact Framework

If you're stuck on a .NET version that doesn't support anything (e.g. compact framework), you can also implement WriteAllText yourself:

static void WriteAllText(string path, string txt) {
    var bytes = Encoding.UTF8.GetBytes(txt);
    using (var f = File.Open(path, FileMode.Create)) {
        f.Write(bytes, 0, bytes.Length);
    }
}

回答2:

Use this

File.WriteAllText(@"C:\Users\Me\Desktop\JAM_MACHINE\JAMS\record.txt", line);

instead of

sw = new StreamWriter(@"C:\Users\Me\Desktop\JAM_MACHINE\record.txt", true);
sw.WriteLine(line);

回答3:

Refer this link for Solution Provided by Microsoft: (https://msdn.microsoft.com/en-us/library/system.io.file.appendtext(v=vs.110).aspx)

Here is code to append existing File:

StreamWriter writer = File.AppendText(Filepath);
writer.WriteLine(content);
writer.Close();

来源：https://stackoverflow.com/questions/44235689/how-to-overwrite-a-file-if-it-already-exists

标签

.net

winforms

text-files

streamwriter