Enemy following player in XNA and stop within 20 pixels

Question

I'm trying to get my enemies to follow the player and stop within 20 pixels, I have tried a number of algorithms including the Vector2.Lerp(); method to try and fix this but it keeps breaking the build. Any help would be greatly appreciated. The code is below.

public void Update(GameTime gameTime)
{
    if (this.IsAlive)
    {
        float elapsed = (float)gameTime.ElapsedGameTime.TotalSeconds;
        double distanceToPlayer = Math.Sqrt(Math.Pow(Level.Player.Position.X - this.Position.X, 2) + Math.Pow(Level.Player.Position.Y - this.Position.Y, 2));

        // Calculate tile position based on the side we are walking towards.
        float posX = Position.X + localBounds.Width / 2 * (int)direction;
        int tileX = (int)Math.Floor(posX / Tile.Width) - (int)direction;
        int tileY = (int)Math.Floor(Position.Y / Tile.Height);

        if (waitTime > 0)
        {
            // Wait for some amount of time.
            waitTime = Math.Max(0.0f, waitTime - (float)gameTime.ElapsedGameTime.TotalSeconds);
            if (waitTime <= 0.0f)
            {
                // Then turn around.
                direction = (FaceDirection)(-(int)direction);
            }
        }
        else
        {
            // If we are about to run into a wall or off a cliff, start waiting.
            if (Level.GetCollision(tileX + (int)direction, tileY - 1) == TileCollision.Impassable || Level.GetCollision(tileX + (int)direction, tileY) == TileCollision.Passable) //is the enemy is close and is not attacking, attack and turn!
            {
                waitTime = MaxWaitTime;
            }
            else
            {
                // Move in the current direction.
                Vector2 velocity = new Vector2((int)direction * MoveSpeed * elapsed, 0.0f);
                position = position + velocity;
            }
        }
        dtAttack += gameTime.ElapsedGameTime;
        AttackPlayer();
    }
    else
    {
        dt += gameTime.ElapsedGameTime;
        if (dt.TotalSeconds > (sprite.Animation.FrameCount * sprite.Animation.FrameTime))
            this.Remove = true;
    }
}

Answer 1

Does it have to be 20 pixels on the screen? Seems strange. You could try to calculate the euclidean distance between the player and the enemy, using the Vector2.Distance method. If the distance is 20 or lower, stop the enemy. If not, keep following the player.