/// <summary>
        /// Carga inicial dos elementos e resources do jogo
        /// </summary>
        protected override void LoadContent()
        {
            spriteBatch = new SpriteBatch(GraphicsDevice);
            menuinicial = new MenuInicial(
                this,
                spriteBatch,
                Content.Load <SpriteFont>("Tela/menufont"),
                Content.Load <Texture2D>("Tela/01_menu"));
            comandosp1 = Content.Load <Texture2D>("imagens/posp1");
            comandosp2 = Content.Load <Texture2D>("imagens/posp2");
            somtiro    = Content.Load <SoundEffect>("audios/somtiro");
            rocket     = Content.Load <SoundEffect>("audios/rocket");
            colisao    = Content.Load <SoundEffect>("audios/colisao");
            explode    = Content.Load <SoundEffect>("audios/explode");
            flare      = Content.Load <SoundEffect>("audios/flare");
            musica     = Content.Load <Song>("audios/musica");

            Components.Add(menuinicial);
            menuinicial.Hide();

            configuranaves = new ConfiguraNaves(
                this,
                spriteBatch,
                Content.Load <Texture2D>("Tela/02_telaEscolha"));
            Components.Add(configuranaves);
            configuranaves.Hide();

            level1 = new Level1(
                this,
                spriteBatch,
                Content.Load <Texture2D>("Tela/03_jogo"),
                configuranaves);
            Components.Add(level1);
            level1.Hide();

            activeScreen = menuinicial;
            activeScreen.Show();
        }
        /// <summary>
        /// Logica principal do jogo
        /// </summary>
        /// <param name="gameTime">Imagem do tempo de jogo</param>
        protected override void Update(GameTime gameTime)
        {
            keyboardState = Keyboard.GetState();
            if (GamePad.GetState(PlayerIndex.One).Buttons.Back == ButtonState.Pressed)
            {
                this.Exit();
            }

            if (playsong == 0)
            {
                MediaPlayer.Play(musica);
                playsong = 1;
            }

            if (activeScreen == menuinicial)
            {
                if (CheckKey(Keys.Enter))
                {
                    explode.Play();
                    configuranaves.Limpar();
                    if (menuinicial.SelectedIndex == 0)
                    {
                        activeScreen.Hide();
                        activeScreen = configuranaves;
                        activeScreen.Show();
                    }
                    if (menuinicial.SelectedIndex == 1)
                    {
                        this.Exit();
                    }
                }
                // Efeito sonoro
                if (CheckKey(Keys.Up))
                {
                    flare.Play();
                }
                if (CheckKey(Keys.Down))
                {
                    flare.Play();
                }
            }
            if (activeScreen == configuranaves)
            {
                if (configuranaves.iniciolistanave > 1)
                {
                    level1.Limpar();
                    level1.configuranaves = this.configuranaves;
                    activeScreen.Hide();
                    activeScreen = level1;
                    activeScreen.Show();
                }
            }
            if (activeScreen == level1)
            {
                if (CheckKey(Keys.Enter) && level1.acabouJogo)
                {
                    configuranaves.Hide();
                    activeScreen = menuinicial;
                    activeScreen.Show();
                }
                // Efeito sonoro som dos tiros
                if (CheckKey(Keys.RightShift))
                {
                    somtiro.Play();
                }
                if (CheckKey(Keys.R))
                {
                    somtiro.Play();
                }
                if (CheckKey(Keys.T))
                {
                    rocket.Play();
                }
                if (CheckKey(Keys.Down))
                {
                    flare.Play();
                }
            }

            base.Update(gameTime);
            oldKeyboardState = keyboardState;
        }