Question

I am currently working on a C# WPF project. I have a list which uses a class to store multiple values. The class is called DBTables and has the following inside:

class DBTables
{
 public string selDatabase { get; set; }
 public string selTable { get; set; }
}

I am creating a new instance of the list with the following code

List<DBTables> tableArr = new List<DBTables>();

I am adding new items to the List without any problems but the problem I am having is when it comes to removing an item from the list.

A an item is added to the list when a checkbox is selected the item is added and when the checkbox is unchecked the item needs to be removed. Each time the checkbox is checked two values are added using the following code:

private void addBackupArray(string table)
{
    backupArr.Add(new DBTables
    {
        selDatabase = selectedDatabase,
        selTable = table
    });
}

When the check box is unchecked the values at the position need to be removed and I have sort of got it working but after it has removed the item it then displays the error ‘InvalidOperationException, collection was modified; enumeration may not execute’.

Below is the code that I am currently using to remove the item from the list.

private void removeBackupArray(string table)
{
    int i = 0;
    foreach (DBTables tables in backupArr)
    {
        if (selectedDatabase == tables.selDatabase && table == tables.selTable)
        {
            backupArr.RemoveAt(i);
            i = 0;
        }
        i++;
    }
}

The code above iterates through the values in the list and based on an if statement of whether the two variables match the value found in the list it removes it at the current position of the counter i.

How can I get round this issue so I can remove the item without getting the error.

Thanks for any help you can provide.

Answer 1

Change the foreach to normal for loop will fix the issue:

for (int tablesIndex = 0; tablesIndex < backupArr.Count; tablesIndex++)
{
    var tables = backupArr[tablesIndex];

    if (selectedDatabase == tables.selDatabase && table == tables.selTable)
    {
        backupArr.RemoveAt(tablesIndex);
        tablesIndex--;
    }
}