返回仅包含列表框项的字符串行

Question

I am trying to retrieve lines of data from a text file that contain items I added to a listbox, but it just keeps returning all lines of data from my test file:

foreach (var item in searchValList.Items)
{
    while ((line = file.ReadLine()) != null)
    {
        if (line.Contains(searchValList.Text))
        {
           sb.AppendLine(line.ToString());
           resultsTextBox.Text = sb.ToString();
        }
        else
        {
           resultsTextBox.Text = "The value was not found in this file";
        }
    }
}

Answer 1

You are searching for the same value in all the lines, (and virtually your outer loop is meaningless)

Change following

 if (line.Contains(searchValList.Text))

to

 if (item.Text != null && line.Contains(item.Text.ToString()))

Answer 2

I think it should be this way since you have a listbox. Try this :

foreach (var item in searchValList.Items)
{
    while ((line = file.ReadLine()) != null)
    {
        if (line.Contains(item.ToString()))
        {
           sb.AppendLine(line.ToString());
           resultsTextBox.Text = sb.ToString();
        }
        else
        {
           resultsTextBox.Text = "The value was not found in this file";
        }
    }
}

Answer 3

I see several problems in your code.

1. searchValList.Text has to be item.ToString();
2. Inner while loop spins till EOF for fisrt iteration, in second Iteration it will always return null since EOF already reached.
3. In all the else part inside the loop you're setting "The value was not found in this file" that is completely wrong

It should be something like this.

string[] lines = File.ReadAllLines("...");
var listboxItems = searchValList.Cast<object>().Select(x=> x.ToString()).ToList();

foreach (var line in lines)
{
    if (listboxItems.Any(x=> line.Contains(x)))
    {
        sb.AppendLine(line);
    }     
}

if(sb.Length > 0)
{
    resultsTextBox.Text = sb.ToString();
}
else
{
     resultsTextBox.Text = "The value was not found in this file";
}