How can I access control created within if-statement from outside if-statement in C# WinForms?

Question

I'm loading music playlist from disk to C# ListView control. I'm using ListViewGroups to separate albums, and there can be several albums in playlist.

Playlists are saved in following text format: (not the greatest way, I know, but works for this example)

|album|name of album
track 1 fsdfsfasf.mp3
track 2 fdsgfgfdhhh.mp3
track 3 gfdgsdgsdfgs.mp3

When I'm loading playlist to ListView, I test if string "|album|" is found from the beginning of line, and use that line for group header text. Code sample below:

using (StreamReader reader = File.OpenText("playlist.txt"))
{
    while (reader.Peek() >= 0)
    {
        result = reader.ReadLine();

        if (result.Substring(0, 7) == "|album|")
        {
            ListViewGroup group = new ListViewGroup();
            group.Header = result.Substring(7);
            lstPlaylist.Groups.Add(group); // lstPlaylist is existing ListView control for playlist
        }

        else
        {
            ListViewItem item = new ListViewItem(result, 0, group);
            lstPlaylist.Items.Add(item);
        }
    }
}

If "|album|" string is found, then I create new ListViewGroup. But that group is inaccessible inside else-statement (I can't assign item to group), because it's out of scope. How can I create new ListViewGroup inside if-statement and use it outside that if-statement?

Answer 1

You need to declare the variable outside the if statement so that it is available in the else clause. You also need to handle the case when a track is found before an album, unless you have already validated the source file.

using (StreamReader reader = File.OpenText("playlist.txt"))
        {
            ListViewGroup group = null;
            while (reader.Peek() >= 0)
            {
                result = reader.ReadLine();
                if (result.Substring(0, 7) == "|album|")
                {
                    group = new ListViewGroup();
                    group.Header = result.Substring(7);
                    lstPlaylist.Groups.Add(group); // lstPlaylist is existing ListView control for playlist
                }

                else
                {
                    if (group != null)
                    {
                        ListViewItem item = new ListViewItem(result, 0, group);
                        lstPlaylist.Items.Add(item);
                    } 
                    else
                    {
                        // you are trying to add a track before any group has been created.
                        // handle this error condition
                    }
                }
            }
        }

Answer 2

You have to first declare the variable outside the if statement and then give it whatever values inside the if statement. Or outside if you want the same value in both the if and else.

Basically what is happening is that the variable is never being made if you go to the else portion of your code because it is created and initialized in the if portion.

Good Luck!

Answer 3

Looking at your logic, you need to initialize ListViewGroup in either case. If you find the word "|album|" then you also assign a property value. So an easy fix is to move the variable up to increase it's scope:

ListViewGroup group = new ListViewGroup();//move to here
if (result.Substring(0, 7) == "|album|")
        {

            group.Header = result.Substring(7);
            lstPlaylist.Groups.Add(group); // lstPlaylist is existing ListView control for playlist
        }

        else
        {
            ListViewItem item = new ListViewItem(result, 0, group);//now group is initialized here as well
            lstPlaylist.Items.Add(item);
        }