C＃文件行用arraylist删除

Question

I am trying to make a class which will help me delete one specific line from a file. So I came up with the idea to put all lines in an arraylist, remove from the list the line i don't need, wipe clear my .txt file and write back the remaining objects of the list. My problem is that I encounter some sort of logical error i can't fint, that doesn't remove the line from the arraylist and writes it back again. Here's my code:

public class delete
{
    public void removeline(string line_to_delete)
    {
        string[] lines = File.ReadAllLines("database.txt");
        ArrayList list = new ArrayList(lines);
        list.Remove(line_to_delete);
        File.WriteAllText("database.txt", String.Empty);
        using (var writer = new StreamWriter("database.txt"))
        {
            foreach (object k in lines)
            {
                writer.WriteLine(k);
            }
        }
    }
}

What is that I am missing? I tried lots of things on removing a line from a text file that did not work. I tried this because it has the least file operations so far.

Thanks!

Answer 1

You can do:

var line_to_delete = "line to delete";
var lines = File.ReadAllLines("database.txt");
File.WriteAllLines("database.txt", lines.Where(line => line != line_to_delete));

File.WriteAllLines will overwrite the existing file.

Do not use ArrayList , there is a generic alternative List<T> . Your code is failing due to the use of ArrayList as it can only remove a single line matching the criteria. With List<T> you can use RemoveAll to remove all the lines matching criteria.

If you want to do the comparison with ignore case you can do:

File.WriteAllLines("database.txt", lines.Where(line => 
            !String.Equals(line, line_to_delete, StringComparison.InvariantCultureIgnoreCase)));

Answer 2

I believe you're intending:

public static void RemoveLine(string line)
{
     var document = File.ReadAllLines("...");
     document.Remove(line);
     document.WriteAllLines("..");
}

That would physically remove the line from the collection. Another approach would be to simply filter out that line with Linq:

var filter = document.Where(l => String.Compare(l, line, true) == 0);

You could do the Remove in an ArrayList proper documentation on how is here . Your code should actually work, all of these answers are more semantic oriented. The issue could be due to actual data, could you provide a sample? I can't reproduce with your code.