问WP8游戏中的System.InvalidOperationException (MonoGame )

EN

using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Graphics;

namespace GameName2
{
     public class Game1 : Game
     {
         GraphicsDeviceManager _graphics;
         SpriteBatch _spriteBatch;
         Texture2D _bg;

         public Game1()
         {
             _graphics = new GraphicsDeviceManager(this);
             Content.RootDirectory = "Content";
         }

         protected override void Initialize()
         {
             // TODO: Add your initialization logic here

             base.Initialize();
         }

         protected override void LoadContent()
         {
             // Create a new SpriteBatch, which can be used to draw textures.
             _spriteBatch = new SpriteBatch(GraphicsDevice);

             _bg = Content.Load<Texture2D>(@"Loading");
             // TODO: use this.Content to load your game content here
         }

         protected override void UnloadContent()
         {
             // TODO: Unload any non ContentManager content here
         }


         protected override void Update(GameTime gameTime)
         {
             // TODO: Add your update logic here

             base.Update(gameTime);
         }


         protected override void Draw(GameTime gameTime)
         {
             GraphicsDevice.Clear(Color.CornflowerBlue);

             // TODO: Add your drawing code here

             _spriteBatch.Draw(_bg,
                 new Rectangle(0, 0, Window.ClientBounds.Width, Window.ClientBounds.Height),
                 null,
                 Color.White,
                 0,
                 Vector2.Zero,
                 SpriteEffects.None,
                 0);

             base.Draw(gameTime);
         }
     }
 }

protected override void Draw(GameTime gameTime)
     {
         GraphicsDevice.Clear(Color.CornflowerBlue);

         // TODO: Add your drawing code here

         _spriteBatch.Draw(_bg,
             new Rectangle(0, 0, Window.ClientBounds.Width, Window.ClientBounds.Height),
             null,
             Color.White,
             0,
             Vector2.Zero,
             SpriteEffects.None,
             0);

         base.Draw(gameTime);
     }