拖放面板控件由于索引不正确而重叠

Question

我正在试验一个包含一些垂直堆叠面板的表单，我正在尝试实现一些拖放，以便它们可以重新排序。到目前为止，它运行得很好，除了一个我无法找出的bug。
前提是它是一个文件列表，必须保持垂直堆叠，但可以在用户认为合适的时候重新排序，以形成我稍后生成的文档的页面列表。

试一下下面的代码，你应该得到一个有6个堆叠面板的表单。点击并拖动其中任何一个向上或向下，它们将重新排序。

问题是如果你快速上下拖动一个它们开始相互重叠。
我在这里放了快捷键CTRL + B，可以在任何给定时间列出当前面板顶部的位置，你会看到你得到了重复的数字，当你不应该。

问题出在MouseMove事件上。我敢肯定这有点像竞态条件，字典跟不上或者索引计算不够快，但我很挠头。我试过把它们锁起来，但是没有用。
我相信有更好的方法来实现这一点，所以我愿意接受建议，但考虑到这永远不会超过30个面板，这符合我的需求。

很抱歉这么乱，我打算稍后再收拾!

public Form1()
{
    InitializeComponent();
    this.SuspendLayout();
    this.AutoScaleDimensions = new System.Drawing.SizeF(6F, 13F);
    this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
    this.ClientSize = new System.Drawing.Size(284, 601);
    this.DoubleBuffered = true;
    this.FormBorderStyle = System.Windows.Forms.FormBorderStyle.FixedSingle;
    this.MaximizeBox = false;
    this.MaximumSize = new System.Drawing.Size(300, 640);
    this.MinimumSize = new System.Drawing.Size(300, 640);
    this.Name = "Form1";
    this.StartPosition = System.Windows.Forms.FormStartPosition.CenterScreen;
    this.Text = "Form1";
    this.Load += new System.EventHandler(this.Form1_Load);
    this.KeyDown += new System.Windows.Forms.KeyEventHandler(this.Form1_KeyDown);
    this.ResumeLayout(false);
}
Dictionary<int, Panel> panelPositions = new Dictionary<int, Panel>();
static Random rnd = new Random();
int y;
int start;
static int index, previndex, currentindex, newindex, maxindex;
bool isDragging;
Panel currentPanel;
static readonly object Lock = new Object();
private void Form1_Load(object sender, EventArgs e)
{
    Width = 300;
    Height = 640;
    int count = 5;
    int currentTop = 0;
    for (int i = 0; i <= count; i++)
    {
        Panel panel = new Panel();
        panel.Width = 300;
        panel.Height = 100;
        panel.Top = currentTop;
        panel.BackColor = RandomColor();
        panel.Margin = Padding.Empty;
        panel.Padding = Padding.Empty;
        panel.BorderStyle = BorderStyle.None;
        Label label = new Label();
        label.Font = new Font("Segoe UI", 24.0f);
        label.Text = (i + 1).ToString();
        label.Top = 20;
        label.Left = 20;
        label.AutoSize = true;
        panel.Controls.Add(label);
        panel.MouseDown += new MouseEventHandler(MouseisDown);
        panel.MouseMove += new MouseEventHandler(MouseMoves);
        panel.MouseUp += new MouseEventHandler(MouseisUp);
        lock (Lock)
        {
            panelPositions.Add(i, panel);
        }
        Controls.Add(panel);
        currentTop += 100;
    }
    lock (Lock)
    {
        maxindex = panelPositions.Count - 1;
    }
}
private void MouseisUp(object sender, MouseEventArgs e)
{
    if (isDragging)
    {
        if (newindex < maxindex)
        {
            currentPanel.Top = newindex * 100;
        }
        else
        {
            currentPanel.Top = maxindex * 100;
        }
    }
    isDragging = false;
}
// I'M SURE THE PROBLEM IS IN HERE SOMEWHERE.
private void MouseMoves(object sender, MouseEventArgs e)
{
    // CHECK THE MOUSE IS STILL DOWN
    if (isDragging)
    {
        // DRAG PANEL VERTICALLY WITH MOUSE
        currentPanel.Location = new Point(currentPanel.Left, e.Y + currentPanel.Top - y);
        // WORK OUT NEW INDEX POSITION
        newindex = 0;
        if ((currentPanel.Top + e.Y) > 0)
        {
            newindex = ((currentPanel.Top + e.Y) / 100);
        }
        // NEW POSITION?
        if (currentindex != newindex)
        {
            // TRACK CHANGES
            previndex = currentindex;
            currentindex = newindex;
            /* PRETTY SURE IT'S THIS BIT THAT'S WRONG */
            // CHECK WE'RE NOT OUT OF BOUNDS
            if (currentindex <= maxindex)
            {
                lock (Lock)
                {
                    // RE-ARRANGE PANEL INDEX
                    panelPositions[previndex] = panelPositions[currentindex];
                    panelPositions[currentindex] = currentPanel;
                    panelPositions[previndex].Top = previndex * 100;
                }
            }
        }
    }
}
private void MouseisDown(object sender, MouseEventArgs e)
{
    if (e.Button == MouseButtons.Left)
    {
        currentPanel = sender as Panel;
        isDragging = true;
        currentPanel.BringToFront();
        y = e.Y;
        start = currentPanel.Top;
        int i = 0;
        if (currentPanel.Top > 0)
        {
            i = currentPanel.Top;
            i = (i / 100);
        }
        index = i;
        previndex = i;
        currentindex = i;
    }
    else
    {
        isDragging = false;
    }
}
private Color RandomColor()
{
    Color randColor;
    randColor = Color.FromArgb(RandomRGB(), RandomRGB(), RandomRGB());
    return randColor;
}
private int RandomRGB()
{
    return rnd.Next(1, 256);
}
private void Form1_KeyDown(object sender, KeyEventArgs e)
{
    if (e.Control && e.KeyCode == Keys.B)
    {
        string message = string.Empty;
        int count = panelPositions.Count;
        for (int i = 0; i < count; i++)
        {
            message += @"Panel " + i.ToString() + @": " + panelPositions[i].Top.ToString() + Environment.NewLine;
        }
        MessageBox.Show(message);
    }
}

谢谢!

编辑:我认为这是与当面板超出表单的底部边界有关。如果在窗体内拖动，则不会出现问题。我想是和前面的索引有关，但是我看不出来

Answer 1

变化

    // NEW POSITION?
    if (currentindex != newindex)

    // NEW POSITION?
    if (currentindex != newindex && newindex <= maxindex)

我想你知道为什么:)

p。s:你的"编辑"部分有点误导人。