XNA游戏开发之(二)——IsFixedTimeStep

　　【原创】Alex
        默认情况下Update方法每秒调用60次，或者说每隔16.667毫秒更新一次。可以通过改变TargetElapsedTime变量改变更新频率： this.TargetElapsedTime = TimeSpan.FromSeconds(1.0f / 1500.0f); 当调用到这行代码时，XNA会以每秒1500次的频率调用Update方法。

　　可以让XNA不按固定时间间隔调用Update方法，要做到这点，需要将Is FixedTimeStep变量设置为false。

using System;

using System.Collections.Generic;

using System.Linq;

using Microsoft.Xna.Framework;

using Microsoft.Xna.Framework.Audio;

using Microsoft.Xna.Framework.Content;

using Microsoft.Xna.Framework.GamerServices;

using Microsoft.Xna.Framework.Graphics;

using Microsoft.Xna.Framework.Input;

using Microsoft.Xna.Framework.Media;

using Microsoft.Xna.Framework.Net;

using Microsoft.Xna.Framework.Storage;



namespace Alex

{

    /// <summary>

    /// This is the main type for your game

    /// </summary>

    public class AlexGame : Microsoft.Xna.Framework.Game

    {

        GraphicsDeviceManager graphics;

        SpriteBatch spriteBatch;

        int updateCount = 0;

        public AlexGame()

        {

            graphics = new GraphicsDeviceManager(this);

            Content.RootDirectory = "Content";

        }



        /// <summary>

        /// Allows the game to perform any initialization it needs to before starting to run.

        /// This is where it can query for any required services and load any non-graphic

        /// related content.  Calling base.Initialize will enumerate through any components

        /// and initialize them as well.

        /// </summary>

        protected override void Initialize()

        {

            // TODO: Add your initialization logic here

            //设置刷新次数

            this.TargetElapsedTime = TimeSpan.FromSeconds(1.0f / 1500.0f);

            //调用该方法刷新次数失效

            this.IsFixedTimeStep = false;

            base.Initialize();

        }



        /// <summary>

        /// LoadContent will be called once per game and is the place to load

        /// all of your content.

        /// </summary>

        protected override void LoadContent()

        {

            // Create a new SpriteBatch, which can be used to draw textures.

            spriteBatch = new SpriteBatch(GraphicsDevice);



            // TODO: use this.Content to load your game content here

        }



        /// <summary>

        /// UnloadContent will be called once per game and is the place to unload

        /// all content.

        /// </summary>

        protected override void UnloadContent()

        {

            // TODO: Unload any non ContentManager content here

        }



        /// <summary>

        /// Allows the game to run logic such as updating the world,

        /// checking for collisions, gathering input, and playing audio.

        /// </summary>

        /// <param name="gameTime">Provides a snapshot of timing values.</param>

        protected override void Update(GameTime gameTime)

        {

            // Allows the game to exit

            if (GamePad.GetState(PlayerIndex.One).Buttons.Back == ButtonState.Pressed)

            {

                this.Exit();

            }

            if (Keyboard.GetState().IsKeyDown(Keys.Escape))

            {

                this.Exit();

            }

            updateCount=updateCount+1;

            this.Window.Title =updateCount.ToString();



            // TODO: Add your update logic here



            base.Update(gameTime);

        }



        /// <summary>

        /// This is called when the game should draw itself.

        /// </summary>

        /// <param name="gameTime">Provides a snapshot of timing values.</param>

        protected override void Draw(GameTime gameTime)

        {

            GraphicsDevice.Clear(Color.CornflowerBlue);



            // TODO: Add your drawing code here



            base.Draw(gameTime);

        }

    }

}
运行结果：