WPF C# - DataGrid select item on user keypress

Question

I made this function to select the item on DataGrid on user keypress. If the user key is "A" it will select the first item where username starts with letter "A". If the user key is again "A" it will select the next item where username starts with letter "A" and so on. The function works great, but what I want is when there are no more items where username starts with "A" to start over (select the first item), it currently remains on the last item where username start with letter "A".

private static Key lastKey;
private static int lastFoundIndex = 0;

public static void AccountsDataGrid_SearchByKey(object sender, KeyEventArgs e)
{
    DataGrid dataGrid = sender as DataGrid;

    if ((dataGrid.Items.Count == 0) && !(e.Key >= Key.A && e.Key <= Key.Z))
    {
        return;
    }

    if ((lastKey != e.Key) || (lastFoundIndex == dataGrid.Items.Count - 1))
    {
        lastFoundIndex = 0;
    }

    for (int i = lastFoundIndex; i < dataGrid.Items.Count; i++)
    {
        if (dataGrid.SelectedIndex == i)
        {
            continue;
        }

        Account account = dataGrid.Items[i] as Account;

        if (account.Username.StartsWith(e.Key.ToString(), true, CultureInfo.CurrentCulture))
        {
            dataGrid.ScrollIntoView(account);
            dataGrid.SelectedItem = account;

            lastFoundIndex = i;

            break;
        }
    }

    lastKey = e.Key;
}

Update (with solution):

Inspired by Danielle's idea, I have changed my code like below, works like a charm.

private static Key lastKey;
private static int lastFoundIndex = 0;

public static void AccountsDataGrid_SearchByKey(object sender, KeyEventArgs e)
{
    DataGrid dataGrid = sender as DataGrid;

    if ((dataGrid.Items.Count == 0) && !(e.Key >= Key.A && e.Key <= Key.Z))
    {
        return;
    }

    if ((lastKey != e.Key) || (lastFoundIndex == dataGrid.Items.Count - 1))
    {
        lastFoundIndex = 0;
    }

    Func<object, bool> itemCompareMethod = (item) =>
    {
        Account account = item as Account;

        if (account.Username.StartsWith(e.Key.ToString(), true, CultureInfo.CurrentCulture))
        {
            return true;
        }

        return false;
    };

    lastFoundIndex = FindDataGridRecordWithinRange(dataGrid, lastFoundIndex, dataGrid.Items.Count, itemCompareMethod);

    if (lastFoundIndex == -1)
    {
        lastFoundIndex = FindDataGridRecordWithinRange(dataGrid, 0, dataGrid.Items.Count, itemCompareMethod);
    }

    if (lastFoundIndex != -1)
    {
        dataGrid.ScrollIntoView(dataGrid.Items[lastFoundIndex]);
        dataGrid.SelectedIndex = lastFoundIndex;
    }

    if (lastFoundIndex == -1)
    {
        lastFoundIndex = 0;
        dataGrid.SelectedItem = null;
    }

    lastKey = e.Key;
}

private static int FindDataGridRecordWithinRange(DataGrid dataGrid, int min, int max, Func<object, bool> itemCompareMethod)
{
    for (int i = min; i < max; i++)
    {
        if (dataGrid.SelectedIndex == i)
        {
            continue;
        }

        if (itemCompareMethod(dataGrid.Items[i]))
        {
            return i;
        }
    }

    return -1;
}

Answer 1

The solution you wound up with is needlessly complex and checks rows it doesn't need to check. The two static variables to maintain state are not needed either. Try this instead:

    public void MainGrid_SearchByKey(object sender, KeyEventArgs e)
    {
        DataGrid dataGrid = sender as DataGrid;
        if (dataGrid.Items.Count == 0 || e.Key < Key.A || e.Key > Key.Z)
        {
            return;
        }

        Func<object, bool> doesItemStartWithChar = (item) =>
        {
            Account account = item as Account;
            return account.Username.StartsWith(e.Key.ToString(), true, CultureInfo.InvariantCulture);
        };

        int currentIndex = dataGrid.SelectedIndex;
        int foundIndex = currentIndex;

        // Search in following rows
        foundIndex = FindMatchingItemInRange(dataGrid, currentIndex, dataGrid.Items.Count - 1, doesItemStartWithChar);

        // If not found, search again in the previous rows
        if (foundIndex == -1)
        {
            foundIndex = FindMatchingItemInRange(dataGrid, 0, currentIndex - 1, doesItemStartWithChar);
        }

        if (foundIndex > -1) // Found
        {
            dataGrid.ScrollIntoView(dataGrid.Items[foundIndex]);
            dataGrid.SelectedIndex = foundIndex;
        }
    }

    private static int FindMatchingItemInRange(DataGrid dataGrid, int min, int max, Func<object, bool> doesItemStartWithChar)
    {
        for (int i = min; i <= max; i++)
        {
            if (dataGrid.SelectedIndex == i) // Skip the current selection
            {
                continue;
            }

            if (doesItemStartWithChar(dataGrid.Items[i])) // If current item matches the string, return index
            {
                return i;
            }
        }

        return -1;
    }

Regarding your comment, just add this check:

        if (Keyboard.Modifiers.HasFlag(ModifierKeys.Control))
        {
            return;
        }

Answer 2

Your code says that to start searching again from the beginning, the lastFoundIndex should be equal to dataGrid.Items.Count - 1 (supposing the same key was pressed again). But your last found Account may be not at the end of the Items collection, so that the lastFoundIndex was not set to dataGrid.Items.Count - 1 when the previous key was pressed. In this case your condition to start over again is not fulfilled.

Try changing the last-found checking and the "for" loop like this:

bool found = false; 
bool lastFound = true;

if (lastKey != e.Key || lastFound)
{
    lastFoundIndex = 0;
}

for (int i = lastFoundIndex; i < dataGrid.Items.Count; i++)
{
    if (dataGrid.SelectedIndex == i)
    {
        continue;
    }

    Account account = dataGrid.Items[i] as Account;

    if (account.Username.StartsWith(e.Key.ToString(), true, CultureInfo.CurrentCulture))
    {
        if (!found)
        {
            dataGrid.ScrollIntoView(account);
            dataGrid.SelectedItem = account;

            lastFoundIndex = i;
            found = true;
        }
        else
        {
            lastFound = false;
            break;
        }
    }
}

Basically it will try to find one more item to see if it was the last match or not.

Answer 3

if i change my function like below, it will stay 2 times on the last item for letter "A" before going to the first item with letter "A" (assuming the user key is still "A").

    private static Key lastKey;
    private static int lastFoundIndex = 0;

    public static void AccountsDataGrid_SearchByKey(object sender, KeyEventArgs e)
    {
        DataGrid dataGrid = sender as DataGrid;

        if ((dataGrid.Items.Count == 0) && !(e.Key >= Key.A && e.Key <= Key.Z))
        {
            return;
        }

        if ((lastKey != e.Key) || (lastFoundIndex == dataGrid.Items.Count - 1))
        {
            lastFoundIndex = 0;
        }

        for (int i = lastFoundIndex; i < dataGrid.Items.Count; i++)
        {
            if ((lastFoundIndex > 0) && (lastFoundIndex == i))
            {
                lastFoundIndex = 0;
            }

            if (dataGrid.SelectedIndex == i)
            {
                continue;
            }

            Account account = dataGrid.Items[i] as Account;

            if (account.Username.StartsWith(e.Key.ToString(), true, CultureInfo.CurrentCulture))
            {
                dataGrid.ScrollIntoView(account);
                dataGrid.SelectedItem = account;

                lastFoundIndex = i;

                break;
            }
        }

        lastKey = e.Key;
    }

Answer 4

You could extract your for-loop into a separate method that determines if another item was found.

public int FindRecordWithinRange(DataGrid dataGrid, int min, int max)
{
    for (int i = min; i < max; i++)
    {
        if (dataGrid.SelectedIndex == i)
            continue;

        Account account = dataGrid.Items[i] as Account;

        if (account.Username.StartsWith(e.Key.ToString(), true, CultureInfo.CurrentCulture))
        {
            dataGrid.ScrollIntoView(account);
            dataGrid.SelectedItem = account;

            return i;
        }
    }

    return -1;
}

And call into it using something like this:

lastFoundIndex = FindRecordWithinRange(dataGrid, lastFoundIndex, dataGrid.Items.Count);
if (lastFoundIndex == -1)
    lastFoundIndex = FindRecordWithinRange(dataGrid, 0, dataGrid.Items.Count);
if (lastFoundIndex == -1)
    dataGrid.SelectedItem = null;

This would basically attempt to search the list from the beginning and would also handle the case where no items were found by clearing out the selection. You might also want to scroll to the beginning in this case, handling at this point is dependent on what you want to do.

Another thing you might want to do here is extract your ScrollIntoView and Selection logic and handle that after the index has been determined.