private Button _blankButton;
private Button[] _originalButtons = buttonPanel.Controls.OfType<Button>(); // Store an un-randomized list of them in order
// For checking results later


public void form_load() { // Or whatever it's called
    var numbers = Enumerable.Range(1, 8).OrderBy(x => Guid.NewGuid()).ToList(); // Create/Randomize the number list
    var buttons = _originalButtons.OrderBy(x => Guid.NewGuid()).ToList(); // Randomize the button list
    for (var i = 0; i < buttons.Count-1; i++)
    {
        var button = buttons[i];
        button.Text += numbers[i];
        button.Tag = i; // Tag each button to track what position it has in the array
    }
    _blankButton = buttons[buttons.Count-1]; // Save the blankButton for what it is
    _blankButton.Text = " "; // Give it a value so we can treat each of them as a char
    _blankButton.Tag = buttons.Count-1; // Though they all have to get tagged because it could have a number later

}









button_click(object sender, EventArgs e) // Assign this same event to all of the buttons in the Designer
{
    Button clicked = sender as Button;
    if(!string.IsNullOrWhiteSpace(clicked.Text)) {
        // They clicked a button other than the blank one
        // See if the blank one is adjacent
        // It could be either at buttons[i-1], [i+1], [i-3] or [i+3]
        int startPosition = int.Parse(clicked.Tag); // Remember we stored its array position in Tag earlier
        int blankPosition = int.Parse(_blankButton.Tag);
        // Check our 4 possible positions
        if (blankPosition == startPosition - 1 || blankPosition == startPosition - 3 || blankPosition == startPosition + 1 || blankPosition == startPosition + 3) {
            // They have clicked a number that is adjacent to the blank tile
            // Swap the text from one they clicked with the blank tile.
            _blankButton.Text = clicked.Text;
            clicked.Text = " "; // Must have a space value so we can treat it as a char
            _blankButton = clicked;

            // And then check if they have won
            // Do they win only if the blank is in the top left, or can the blank be anywhere?
            // Assuming top left only

            // We actually don't have to cast them from strings, they will compare properly with their ascii char values
            // And null, space, etc are all sorted before the numbers in ASCII too

            int lastValue = 128;
            bool success = true;
            foreach(var button in _originalButtons) { // Iterate the buttons in their original order (reverse order)
                int value = (int)button.Text[0];
                if(value > lastValue)
                { // If any number on the buttons, in reverse, is higher than a previous one, it's not in order
                    success = false;
                    break;
                }
                else
                    lastValue = value;
                // If all of them are lower than their previous ones, it's in order and success stays true
            }

            if (success) {
                // Do whatever you want to do when they win
            }
        }


    }
}