Writing List<String> contents to text file after deleting string

问题

I'm trying to get the contents of a Text File, delete a line of string, and re-write back to the Text File, deleting the line of string. I'm using StreamReader to get the text, importing into a List, removing the string, then rewriting using StreamWriter. My problems arises somewhere around the removing or writing of the string. Instead of writing back the existing, non deleted contents to the text file, all the text is replaced with :

System.Collections.Generic.List`1[System.String]

My code for this function is as follows:

{
            for (int i = deleteDevice.Count - 1; i >= 0; i--)
            {
                string split = "";
                //deleteDevice[i].Split(',').ToString();
                List<string> parts = split.Split(',').ToList();

                if (parts.Contains(deviceList.SelectedItem.ToString()))
                {

                    deleteDevice.Remove(i.ToString());
                }

            }
            if (deleteDevice.Count != 0) //Error Handling
            {

                writer.WriteLine(deleteDevice);

            }
        }

        deviceList.Items.Remove(deviceList.SelectedItem);
    }

I would just like the script to write back any string that isn't deleted (If there is any), without replacing it. Any help is appreciated, Cheers

回答1:

You can read all the info from the text file into a list and then remove from the list and rewrite that to the text file.

I would change the list 'deleteDevice' to store a string array instead and use the code below to determine which item to remove.

        List<int> toRemove = new List<int>();
        int i = 0;
        /*build a list of indexes to remove*/
        foreach (string[] x in deleteDevice)
        {
            if (x[0].Contains(deviceList.SelectedItem.ToString()))
            {
                toRemove.Add(i);
            }
            i++;
        }

        /*Remove items from list*/
        foreach (int fd in toRemove)
             deleteDevice.RemoveAt(fd);

        /*write to text file*/
        using (StreamWriter writer = new StreamWriter("Devices.txt"))
        {
            if (deleteDevice.Count != 0) //Error Handling
            {
                foreach (string[] s in deleteDevice)
                {
                    StringBuilder sb = new StringBuilder();
                    for (int fds = 0; fds < s.Length; fds++ )
                    {
                       sb.Append(s[fds] + ",");
                    }
                    string line = sb.ToString();
                    writer.WriteLine(line.Substring(0, line.Length - 1));
                }
            }
        }

This isn't the best solution but should work for your needs. There's probably a much easier way of doing this.

回答2:

The problem is in the following line:

writer.WriteLine(deleteDevice);

You're writing deleteDevice (I assume this is of type List). List.ToString() returns the type name of the list, because this has no specific implementation. What you want is

foreach(String s in deleteDevice)
{
    writer.WriteLine(s);
}

回答3:

Problems

deleteDevice is of type List<string>, and because it also doesn't overload ToString(), the default behaviour of List<string>.ToString() is to return the name of the type.

Hence your line writer.WriteLine(deleteDevice); writes the string System.Collections.Generic.List1[System.String]`.

Other than that, there are many things wrong with your code...

For example, you do this:

string split = "";

and then on the line afterwards you do this:

List<string> parts = split.Split(',').ToList();

But because split is "", this will always return an empty list.

---

Solution

To simplify the code, you could first write a helper method that will remove from a file all the lines that match a specified predicate:

public void RemoveUnwantedLines(string filename, Predicate<string> unwanted)
{
    var lines = File.ReadAllLines(filename);
    File.WriteAllLines(filename, lines.Where(line => !unwanted(line)));
}

Then you can write the predicate something like this (this might not be quite right; I don't really know exactly what your code is doing because it's not compilable and omits some of the types):

string filename = "My Filename";
string deviceToRemove= deviceList.SelectedItem.ToString();

Predicate<string> unwanted = line => 
    line.Split(new [] {','})
    .Contains(deviceToRemove);

RemoveUnwantedLines(filename, unwanted);

来源：https://stackoverflow.com/questions/19560703/writing-liststring-contents-to-text-file-after-deleting-string