C＃中隐藏的“GDI +钩子窗口”是什么？

每当任何C＃应用程序在进程中打开包含控件的第一个窗体时，将打开一个名为“G”的隐藏窗口，其类名称为“GDI + Hook窗口类” ，如下面的应用程序所示：

这里是使用的代码：

using System; using System.Text; using System.Diagnostics; using System.Drawing; using System.Runtime.InteropServices; using System.Windows.Forms; namespace WindowsFormsApplication1 { public class Form1 : Form { private delegate bool EnumThreadDelegate(IntPtr hWnd, IntPtr lParam); private EnumThreadDelegate showWindowName; private Button button1; private string windowList = string.Empty; private Button button2; private int increment; [DllImport("user32.dll")] private static extern bool EnumThreadWindows(int dwThreadId, EnumThreadDelegate lpfn, IntPtr lParam); [DllImport("user32.dll", CharSet = CharSet.Unicode, SetLastError = false)] private static extern IntPtr SendMessage(IntPtr hWnd, UInt32 Msg, IntPtr wParam, IntPtr lParam); [DllImport("user32.dll", CharSet = CharSet.Unicode)] private static extern int GetWindowText(IntPtr hWnd, StringBuilder lpString, int nMaxCount); [DllImport("user32.dll", SetLastError = true, CharSet = CharSet.Unicode)] private static extern int GetClassName(IntPtr hWnd, StringBuilder lpClassName, int nMaxCount); public Form1() { showWindowName = ShowWindowName; InitializeComponent(); SetStyle(ControlStyles.OptimizedDoubleBuffer | ControlStyles.UserPaint | ControlStyles.AllPaintingInWmPaint, true); } [STAThread] public static void Main() { Application.EnableVisualStyles(); Application.SetCompatibleTextRenderingDefault(false); Application.Run(new Form1()); } protected override void OnShown(EventArgs e) { base.OnShown(e); button1_Click(null, null); } private bool ShowWindowName(IntPtr hWnd, IntPtr lParam) { increment++; StringBuilder windowName = new StringBuilder(65535); GetWindowText(hWnd, windowName, 65535); StringBuilder className = new StringBuilder(65535); GetClassName(hWnd, className, 65535); windowList += "Window " + increment + ":\n\tTitle: " + windowName + "\n\tClass Name: " + className + "\n\n"; Invalidate(false); return true; } protected override void OnPaint(PaintEventArgs e) { base.OnPaint(e); e.Graphics.DrawString(windowList, Font, Brushes.Black, PointF.Empty); } private void button1_Click(object sender, EventArgs e) { increment = 0; windowList = string.Empty; foreach (ProcessThread thread in Process.GetCurrentProcess().Threads) EnumThreadWindows(thread.Id, showWindowName, IntPtr.Zero); } private void button2_Click(object sender, EventArgs e) { foreach (ProcessThread thread in Process.GetCurrentProcess().Threads) EnumThreadWindows(thread.Id, (hwnd, lParam) => { StringBuilder windowName = new StringBuilder(65535); GetWindowText(hwnd, windowName, 65535); if (windowName.ToString() == "G") SendMessage(hwnd, 0x10, IntPtr.Zero, IntPtr.Zero); return false; }, IntPtr.Zero); button1_Click(null, null); } private void InitializeComponent() { this.button1 = new System.Windows.Forms.Button(); this.button2 = new System.Windows.Forms.Button(); this.SuspendLayout(); // // button1 // this.button1.Dock = System.Windows.Forms.DockStyle.Bottom; this.button1.Location = new System.Drawing.Point(0, 379); this.button1.Name = "button1"; this.button1.Size = new System.Drawing.Size(504, 23); this.button1.TabIndex = 0; this.button1.Text = "Reload"; this.button1.UseVisualStyleBackColor = true; this.button1.Click += new System.EventHandler(this.button1_Click); // // button2 // this.button2.Dock = System.Windows.Forms.DockStyle.Right; this.button2.Location = new System.Drawing.Point(429, 0); this.button2.Name = "button2"; this.button2.Size = new System.Drawing.Size(75, 379); this.button2.TabIndex = 1; this.button2.Text = "Kill G Window"; this.button2.UseVisualStyleBackColor = true; this.button2.Click += new System.EventHandler(this.button2_Click); // // Form1 // this.ClientSize = new System.Drawing.Size(504, 402); this.Controls.Add(this.button2); this.Controls.Add(this.button1); this.Name = "Form1"; this.Text = "Form1"; this.ResumeLayout(false); } } } 

如果我以编程方式closures窗口（通过单击“K窗口”button），窗口closures，但程序的forms保持正常运行，似乎完全不受影响。

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这个神秘窗口的目的和function是什么？