Question

我正在使用Head First C＃书学习C＃。在构建Greyhound Racing游戏的第一个实验室中，我遇到了一些行为，我不明白为什么我的代码呈现的方式。在第一次点击Race按钮时，匹马跑到赛道的尽头，但是它们被渲染成使得它们各自在它们后面创建先前图像的踪迹，直到它们到达轨道的末端，之后前面的图像最终消失。在随后单击Race按钮时，会发生同样的事情，但它也无法从终点线擦除每只狗的PictureBox，直到当前比赛完成。 enter image description here

这是一段短短19秒的视频，展示了我的意思：Example of trailing images

为什么比赛期间狗会“追踪”，为什么在下一场比赛结束后再次开始比赛之前他们不会从终点线上消失？我认为当狗在TakeStartingPosition()重新定位时，它们会被移动，而不是重新绘制。与Run()相同，我认为每个新位置都是一个移动，而不是重绘，但它似乎是在每个移动步骤重绘图像，而不是在比赛结束时擦拭旧的。我做错了什么？

Greyhound.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;


namespace RaceTrackSimulator
{
    class Greyhound
    {
        public int StartingPosition;
        public int RacetrackLength;
        public PictureBox MyPictureBox = null;
        public int Location = 0;
        public Random Randomizer;

        public bool Run()
        {
            // Move forward either 1, 2, 3 or 4 spaces at random
            int moveSpaces = Randomizer.Next(1, 4);


            // Update the position of my Picturebox on the form like this:
            //  MyPictureBox.Left = StartingPosition + Location;
            MyPictureBox.Left = StartingPosition + Location;

            // Return true if I won the race
            if (Location >= RacetrackLength)
            {
                return true;
            }
            else
            {
                Location += moveSpaces;
                return false;
            }
        }

        public void TakeStartingPosition()
        {
            // Reset my location to 0 and my PictureBox to starting position
            Location = 0;
            MyPictureBox.Left = StartingPosition;

        }
    }
}

Form1.cs的

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace RaceTrackSimulator
{
    public partial class Form1 : Form
    {
        Greyhound[] Dogs;

        public Form1()
        {
            InitializeComponent();
            Random MyRandomizer = new Random();

            // Initialize Dogs
            Dogs = new Greyhound[4];

            Dogs[0] = new Greyhound()
            {
                MyPictureBox = pictureBox2,
                StartingPosition = racetrackPictureBox.Left,
                RacetrackLength = racetrackPictureBox.Width - pictureBox2.Width,
                Randomizer = MyRandomizer
            };

            Dogs[1] = new Greyhound()
            {
                MyPictureBox = pictureBox3,
                StartingPosition = racetrackPictureBox.Left,
                RacetrackLength = racetrackPictureBox.Width - pictureBox3.Width,
                Randomizer = MyRandomizer
            };

            Dogs[2] = new Greyhound()
            {
                MyPictureBox = pictureBox4,
                StartingPosition = racetrackPictureBox.Left,
                RacetrackLength = racetrackPictureBox.Width - pictureBox4.Width,
                Randomizer = MyRandomizer
            };

            Dogs[3] = new Greyhound()
            {
                MyPictureBox = pictureBox5,
                StartingPosition = racetrackPictureBox.Left,
                RacetrackLength = racetrackPictureBox.Width - pictureBox5.Width,
                Randomizer = MyRandomizer
            };
        }

        private void raceButton_Click(object sender, EventArgs e)
        {
            bool winner = false;
            int winningDog = 0;

            for (int eachDog = 0; eachDog < Dogs.Length; eachDog++)
            {
                Dogs[eachDog].TakeStartingPosition();
            }

            while (!winner)
            {
                for (int i = 0; i < 4; i++)
                {
                    if (Dogs[i].Run())
                    {
                        winner = true;
                        winningDog = i+1;
                    }
                    System.Threading.Thread.Sleep(1);
                }
            }

            MessageBox.Show("Winning Dog is #" + winningDog);
        }
    }
}

Form1.Designer.cs

namespace RaceTrackSimulator
{
    partial class Form1
    {
        /// <summary>
        /// Required designer variable.
        /// </summary>
        private System.ComponentModel.IContainer components = null;

        /// <summary>
        /// Clean up any resources being used.
        /// </summary>
        /// <param name="disposing">true if managed resources should be disposed; otherwise, false.</param>
        protected override void Dispose(bool disposing)
        {
            if (disposing && (components != null))
            {
                components.Dispose();
            }
            base.Dispose(disposing);
        }

        #region Windows Form Designer generated code

        /// <summary>
        /// Required method for Designer support - do not modify
        /// the contents of this method with the code editor.
        /// </summary>
        private void InitializeComponent()
        {
            this.pictureBox2 = new System.Windows.Forms.PictureBox();
            this.racetrackPictureBox = new System.Windows.Forms.PictureBox();
            this.pictureBox3 = new System.Windows.Forms.PictureBox();
            this.pictureBox4 = new System.Windows.Forms.PictureBox();
            this.pictureBox5 = new System.Windows.Forms.PictureBox();
            this.raceButton = new System.Windows.Forms.Button();
            ((System.ComponentModel.ISupportInitialize)(this.pictureBox2)).BeginInit();
            ((System.ComponentModel.ISupportInitialize)(this.racetrackPictureBox)).BeginInit();
            ((System.ComponentModel.ISupportInitialize)(this.pictureBox3)).BeginInit();
            ((System.ComponentModel.ISupportInitialize)(this.pictureBox4)).BeginInit();
            ((System.ComponentModel.ISupportInitialize)(this.pictureBox5)).BeginInit();
            this.SuspendLayout();
            // 
            // pictureBox2
            // 
            this.pictureBox2.Image = global::RaceTrackSimulator.Properties.Resources.dog;
            this.pictureBox2.Location = new System.Drawing.Point(13, 22);
            this.pictureBox2.Name = "pictureBox2";
            this.pictureBox2.Size = new System.Drawing.Size(75, 20);
            this.pictureBox2.SizeMode = System.Windows.Forms.PictureBoxSizeMode.AutoSize;
            this.pictureBox2.TabIndex = 2;
            this.pictureBox2.TabStop = false;
            // 
            // racetrackPictureBox
            // 
            this.racetrackPictureBox.Image = global::RaceTrackSimulator.Properties.Resources.racetrack;
            this.racetrackPictureBox.Location = new System.Drawing.Point(13, 12);
            this.racetrackPictureBox.Name = "racetrackPictureBox";
            this.racetrackPictureBox.Size = new System.Drawing.Size(600, 200);
            this.racetrackPictureBox.SizeMode = System.Windows.Forms.PictureBoxSizeMode.AutoSize;
            this.racetrackPictureBox.TabIndex = 0;
            this.racetrackPictureBox.TabStop = false;
            // 
            // pictureBox3
            // 
            this.pictureBox3.Image = global::RaceTrackSimulator.Properties.Resources.dog;
            this.pictureBox3.Location = new System.Drawing.Point(13, 74);
            this.pictureBox3.Name = "pictureBox3";
            this.pictureBox3.Size = new System.Drawing.Size(75, 20);
            this.pictureBox3.SizeMode = System.Windows.Forms.PictureBoxSizeMode.AutoSize;
            this.pictureBox3.TabIndex = 3;
            this.pictureBox3.TabStop = false;
            // 
            // pictureBox4
            // 
            this.pictureBox4.Image = global::RaceTrackSimulator.Properties.Resources.dog;
            this.pictureBox4.Location = new System.Drawing.Point(13, 126);
            this.pictureBox4.Name = "pictureBox4";
            this.pictureBox4.Size = new System.Drawing.Size(75, 20);
            this.pictureBox4.SizeMode = System.Windows.Forms.PictureBoxSizeMode.AutoSize;
            this.pictureBox4.TabIndex = 4;
            this.pictureBox4.TabStop = false;
            // 
            // pictureBox5
            // 
            this.pictureBox5.Image = global::RaceTrackSimulator.Properties.Resources.dog;
            this.pictureBox5.Location = new System.Drawing.Point(13, 178);
            this.pictureBox5.Name = "pictureBox5";
            this.pictureBox5.Size = new System.Drawing.Size(75, 20);
            this.pictureBox5.SizeMode = System.Windows.Forms.PictureBoxSizeMode.AutoSize;
            this.pictureBox5.TabIndex = 5;
            this.pictureBox5.TabStop = false;
            // 
            // raceButton
            // 
            this.raceButton.Location = new System.Drawing.Point(538, 377);
            this.raceButton.Name = "raceButton";
            this.raceButton.Size = new System.Drawing.Size(75, 23);
            this.raceButton.TabIndex = 6;
            this.raceButton.Text = "RACE!";
            this.raceButton.UseVisualStyleBackColor = true;
            this.raceButton.Click += new System.EventHandler(this.raceButton_Click);
            // 
            // Form1
            // 
            this.AutoScaleDimensions = new System.Drawing.SizeF(6F, 13F);
            this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
            this.ClientSize = new System.Drawing.Size(625, 412);
            this.Controls.Add(this.raceButton);
            this.Controls.Add(this.pictureBox5);
            this.Controls.Add(this.pictureBox4);
            this.Controls.Add(this.pictureBox3);
            this.Controls.Add(this.pictureBox2);
            this.Controls.Add(this.racetrackPictureBox);
            this.Name = "Form1";
            this.Text = "Form1";
            ((System.ComponentModel.ISupportInitialize)(this.pictureBox2)).EndInit();
            ((System.ComponentModel.ISupportInitialize)(this.racetrackPictureBox)).EndInit();
            ((System.ComponentModel.ISupportInitialize)(this.pictureBox3)).EndInit();
            ((System.ComponentModel.ISupportInitialize)(this.pictureBox4)).EndInit();
            ((System.ComponentModel.ISupportInitialize)(this.pictureBox5)).EndInit();
            this.ResumeLayout(false);
            this.PerformLayout();

        }

        #endregion

        private System.Windows.Forms.PictureBox racetrackPictureBox;
        private System.Windows.Forms.PictureBox pictureBox2;
        private System.Windows.Forms.PictureBox pictureBox3;
        private System.Windows.Forms.PictureBox pictureBox4;
        private System.Windows.Forms.PictureBox pictureBox5;
        private System.Windows.Forms.Button raceButton;
    }
}

Answer 1

您正在按钮单击处理程序处理程序中运行紧密循环，该处理程序独占主UI线程。当狗向前移动时，由形状重新表现为“擦除”狗以前所在的位置。但是，由于代码卡在循环中，因此无法重绘。同样，当比赛重新开始时，由于同样的原因，狗不会从终点线消失。

一种可能的“快速修复”是在代码中调用Application.DoEvents();以允许表单自行更新。这看起来像这样：

    private void raceButton_Click(object sender, EventArgs e)
    {
        bool winner = false;
        int winningDog = 0;

        for (int eachDog = 0; eachDog < Dogs.Length; eachDog++)
        {
            Dogs[eachDog].TakeStartingPosition();
        }
        Application.DoEvents();

        while (!winner)
        {
            for (int i = 0; i < 4; i++)
            {
                if (Dogs[i].Run())
                {
                    winner = true;
                    winningDog = i+1;
                }
                Application.DoEvents();
                System.Threading.Thread.Sleep(1);
            }
        }

        MessageBox.Show("Winning Dog is #" + winningDog);
    }

然而，这只是一个真正问题之上的创可贴：你不应该在按钮点击处理程序中使用长时间循环来独占主UI线程。

一种可能的解决方案是在按钮点击处理程序中重置狗，然后启动计时器。在Timer（）的Tick（）事件中，您将调用每个狗Run（）方法并检查获胜者。赢得比赛后，关闭计时器。

移动到新位置时，PictureBox仍保留在旧位置

1 个答案: