C# XNA :Snake Game, direction problem

Question

I am trying to do a snake game in XNA but I have some little problems...

I explain :

The Snake has a direction (Enum Type : Haut(=up), Bas(=down), Droite(=right), Gauche(=left)) When the player press a direction key this funcion is used :

public void SetDirection(Direction newDirection) // Teste les directions impossibles => impossible de faire un demi tour
{
    if (_direction == Direction.Haut && newDirection == Direction.Bas)
    {
        return;
    }
    else if (_direction == Direction.Bas && newDirection == Direction.Haut)
    {
        return;
    }
    else if (_direction == Direction.Gauche && newDirection == Direction.Droite)
    {
        return;
    }
    else if (_direction == Direction.Droite && newDirection == Direction.Gauche)
    {
        return;
    }
    _direction = newDirection;
}

In theory, the snake can't make a U-turn. But it does not work properly (I will try to explain why) :

The snake moves each 100ms. while these 100ms, the snake is waiting for a direction. BUT if the snake goes up for example, and if the user presses {Droite(=right), Bas(=down)} or {Gauche(=left), Bas(=down)} while these 100ms, the snake makes a U-turn, and die because he cuts himself.

As a consequence, the user loose the game...

I can't see how to solve this problem.

If I am not clear or if you need any other information, please let me know.

Thanks in advance for your help

PS : I am sorry for the grammar faults but I don't speak perfectly english... :)

PPS : Here is the call to setDirection :

case GameState.Infini:
    if (newKeyboardState.IsKeyDown(Keys.Escape))
    {
        CurrentGameState = GameState.Pause;
    }
    else if (newKeyboardState.IsKeyDown(Keys.Up))
    {
        _snake.SetDirection(Direction.Haut);
    }
    else if (newKeyboardState.IsKeyDown(Keys.Down))
    {
        _snake.SetDirection(Direction.Bas);
    }
    else if (newKeyboardState.IsKeyDown(Keys.Left))
    {
        _snake.SetDirection(Direction.Gauche);
    }
    else if (newKeyboardState.IsKeyDown(Keys.Right))
    {
        _snake.SetDirection(Direction.Droite);
    }

Answer 1

I finally succeeded to get rid of this behaviour. (Thanks @Jon !)

"Don't let the snake change its direction if it heads backward from its current heading. " It actually works :)

Example with 'Up' Direction :

int X = _snake._parts.Last().X;
int Y = _snake._parts.Last().Y;
if (newDirection == Direction.Haut)
{
    Rectangle test = new Rectangle(X, Y - _blocCorps.Height, _blocCorps.Width, _blocCorps.Height);
    if (test.Intersects(_snake._parts.ElementAt(_snake._parts.Count - 2)))
    {
        return; 
    }
}

Thank to everyone who took some time to help me !

Answer 2

Not sure if this will work but I did a few tests and it seems to be fine. Define your enum like this :

enum Directions
    {
        Up = 1,
        Down = ~Up,
        Right = 2,
        Left = ~Right
    };

Now you can a check about the current direction and next direction like this

    if(currDit == ~nextDir)
    {
    //the snake will go into itself
    }else
    {
    //change the direction
    }

Again I'm not 100% sure that this will work. Someone correct me if I'm wrong.