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。

代码

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：