case "学生": stundetwin s = new stundetwin(); s.Show(); MessageBox.Show("登录成功"); break; case "老师": MainWindow M = new MainWindow(); M.Show();MessageBox.Show("登录成功"); break;

这段代码是switch语句中根据下拉框选中的文本值执行的代码块。根据不同的文本值，执行不同的操作。

如果cb_load.Text等于"学生"，则创建了一个名为s的stundetwin窗口，并使用Show()方法显示该窗口。同时，使用MessageBox.Show()方法在屏幕上显示一条消息框，提示用户登录成功。最后使用break语句跳出switch语句。

如果cb_load.Text等于"老师"，则创建了一个名为M的MainWindow窗口，并使用Show()方法显示该窗口。同时，使用MessageBox.Show()方法在屏幕上显示一条消息框，提示用户登录成功。最后使用break语句跳出switch语句。

需要注意的是，创建窗口并显示时，需要确保该窗口已经定义并实现了相关的操作，否则程序会出现错误。同时，在使用MessageBox.Show()方法显示消息框时，需要注意该方法会阻塞程序的执行，直到用户关闭消息框为止。

相关问题

C# 一次性将所有MessageBox弹窗置顶

如果你想要一次性将所有的MessageBox弹窗置顶，你可以使用一个自定义的MessageBox类来代替原生的MessageBox类。这个自定义类将会在每次调用时创建一个新的窗口，并将其置顶。

以下是一个示例代码：

public static class CustomMessageBox
{
    [DllImport("user32.dll", SetLastError = true)]
    public static extern IntPtr SetForegroundWindow(IntPtr hWnd);

    public static DialogResult Show(string text, string caption, MessageBoxButtons buttons, MessageBoxIcon icon)
    {
        var topMostMessageBox = new Form
        {
            TopMost = true,
            MaximizeBox = false,
            MinimizeBox = false,
            ShowInTaskbar = false,
            FormBorderStyle = FormBorderStyle.FixedDialog,
            StartPosition = FormStartPosition.CenterScreen,
            AutoSize = true,
            AutoSizeMode = AutoSizeMode.GrowAndShrink
        };

        topMostMessageBox.Controls.Add(new Label { Text = text, Dock = DockStyle.Fill, Margin = new Padding(10) });

        switch (buttons)
        {
            case MessageBoxButtons.OKCancel:
                {
                    var okButton = new Button
                    {
                        DialogResult = DialogResult.OK,
                        Text = "OK",
                        Dock = DockStyle.Bottom,
                        Margin = new Padding(10)
                    };
                    topMostMessageBox.Controls.Add(okButton);

                    var cancelButton = new Button
                    {
                        DialogResult = DialogResult.Cancel,
                        Text = "Cancel",
                        Dock = DockStyle.Bottom,
                        Margin = new Padding(10)
                    };
                    topMostMessageBox.Controls.Add(cancelButton);

                    topMostMessageBox.AcceptButton = okButton;
                    topMostMessageBox.CancelButton = cancelButton;

                    break;
                }
            case MessageBoxButtons.YesNo:
                {
                    var yesButton = new Button
                    {
                        DialogResult = DialogResult.Yes,
                        Text = "Yes",
                        Dock = DockStyle.Bottom,
                        Margin = new Padding(10)
                    };
                    topMostMessageBox.Controls.Add(yesButton);

                    var noButton = new Button
                    {
                        DialogResult = DialogResult.No,
                        Text = "No",
                        Dock = DockStyle.Bottom,
                        Margin = new Padding(10)
                    };
                    topMostMessageBox.Controls.Add(noButton);

                    topMostMessageBox.AcceptButton = yesButton;
                    topMostMessageBox.CancelButton = noButton;

                    break;
                }
            case MessageBoxButtons.OK:
            default:
                {
                    var okButton = new Button
                    {
                        DialogResult = DialogResult.OK,
                        Text = "OK",
                        Dock = DockStyle.Bottom,
                        Margin = new Padding(10)
                    };
                    topMostMessageBox.Controls.Add(okButton);

                    topMostMessageBox.AcceptButton = okButton;

                    break;
                }
        }

        topMostMessageBox.Text = caption;
        topMostMessageBox.ShowIcon = icon == MessageBoxIcon.None ? false : true;
        topMostMessageBox.Icon = SystemIcons.Question;

        SetForegroundWindow(topMostMessageBox.Handle);

        return topMostMessageBox.ShowDialog();
    }
}

然后，你可以像这样调用它：

CustomMessageBox.Show("This is a message", "Caption", MessageBoxButtons.OK, MessageBoxIcon.Information);

程序模仿实现Windows自带记事本功能：新建文件、保存、编辑、格式、帮助等功能。

实现Windows自带记事本的功能，需要用到一些GUI库，这里我推荐使用Python自带的GUI库tkinter来实现。

以下是一个简单的代码示例，实现了新建、保存、编辑、格式和帮助等基本功能：

import tkinter as tk
from tkinter import messagebox, filedialog

class Notepad:
    def __init__(self, master):
        self.master = master
        self.master.title("记事本")
        self.textpad = tk.Text(self.master, undo=True)
        self.textpad.pack(expand=True, fill="both")
        self.filename = None
        
        # 创建菜单栏
        self.menu_bar = tk.Menu(self.master)
        
        # 创建文件菜单
        self.file_menu = tk.Menu(self.menu_bar, tearoff=0)
        self.file_menu.add_command(label="新建", accelerator="Ctrl+N", command=self.new_file)
        self.file_menu.add_command(label="打开", accelerator="Ctrl+O", command=self.open_file)
        self.file_menu.add_command(label="保存", accelerator="Ctrl+S", command=self.save_file)
        self.file_menu.add_command(label="另存为", accelerator="Ctrl+Shift+S", command=self.save_as_file)
        self.file_menu.add_separator()
        self.file_menu.add_command(label="退出", command=self.exit)
        self.menu_bar.add_cascade(label="文件", menu=self.file_menu)
        
        # 创建编辑菜单
        self.edit_menu = tk.Menu(self.menu_bar, tearoff=0)
        self.edit_menu.add_command(label="撤销", accelerator="Ctrl+Z", command=self.textpad.edit_undo)
        self.edit_menu.add_command(label="恢复", accelerator="Ctrl+Y", command=self.textpad.edit_redo)
        self.edit_menu.add_separator()
        self.edit_menu.add_command(label="剪切", accelerator="Ctrl+X", command=self.cut)
        self.edit_menu.add_command(label="复制", accelerator="Ctrl+C", command=self.copy)
        self.edit_menu.add_command(label="粘贴", accelerator="Ctrl+V", command=self.paste)
        self.edit_menu.add_separator()
        self.edit_menu.add_command(label="查找", accelerator="Ctrl+F", command=self.find)
        self.edit_menu.add_command(label="替换", accelerator="Ctrl+H", command=self.replace)
        self.menu_bar.add_cascade(label="编辑", menu=self.edit_menu)
        
        # 创建格式菜单
        self.format_menu = tk.Menu(self.menu_bar, tearoff=0)
        self.format_menu.add_command(label="字体", command=self.choose_font)
        self.menu_bar.add_cascade(label="格式", menu=self.format_menu)
        
        # 创建帮助菜单
        self.help_menu = tk.Menu(self.menu_bar, tearoff=0)
        self.help_menu.add_command(label="关于", command=self.about)
        self.menu_bar.add_cascade(label="帮助", menu=self.help_menu)
        
        self.master.config(menu=self.menu_bar)
        
        # 创建快捷键
        self.master.bind("<Control-n>", lambda event: self.new_file())
        self.master.bind("<Control-o>", lambda event: self.open_file())
        self.master.bind("<Control-s>", lambda event: self.save_file())
        self.master.bind("<Control-S>", lambda event: self.save_as_file())
        self.master.bind("<Control-z>", lambda event: self.textpad.edit_undo())
        self.master.bind("<Control-y>", lambda event: self.textpad.edit_redo())
        self.master.bind("<Control-x>", lambda event: self.cut())
        self.master.bind("<Control-c>", lambda event: self.copy())
        self.master.bind("<Control-v>", lambda event: self.paste())
        self.master.bind("<Control-f>", lambda event: self.find())
        self.master.bind("<Control-h>", lambda event: self.replace())
        
    def new_file(self):
        self.textpad.delete(1.0, tk.END)
        self.filename = None
        
    def open_file(self):
        self.filename = filedialog.askopenfilename(defaultextension=".txt", filetypes=[("All Files", "*.*"), ("Text Documents", "*.txt")])
        if self.filename:
            self.textpad.delete(1.0, tk.END)
            with open(self.filename, "r") as f:
                self.textpad.insert(1.0, f.read())
    
    def save_file(self):
        if self.filename:
            with open(self.filename, "w") as f:
                f.write(self.textpad.get(1.0, tk.END))
        else:
            self.save_as_file()
    
    def save_as_file(self):
        self.filename = filedialog.asksaveasfilename(defaultextension=".txt", filetypes=[("All Files", "*.*"), ("Text Documents", "*.txt")])
        if self.filename:
            with open(self.filename, "w") as f:
                f.write(self.textpad.get(1.0, tk.END))

    def exit(self):
        self.master.quit()
    
    def cut(self):
        self.textpad.event_generate("<<Cut>>")
    
    def copy(self):
        self.textpad.event_generate("<<Copy>>")
    
    def paste(self):
        self.textpad.event_generate("<<Paste>>")
    
    def find(self):
        find_dialog = tk.Toplevel(self.master)
        find_dialog.title("查找")
        find_dialog.transient(self.master)
        tk.Label(find_dialog, text="查找:").grid(row=0, column=0, sticky="e")
        find_entry = tk.Entry(find_dialog, width=30)
        find_entry.grid(row=0, column=1, padx=2, pady=2, sticky="we")
        find_entry.focus_set()
        case_var = tk.IntVar()
        tk.Checkbutton(find_dialog, text="区分大小写", variable=case_var).grid(row=1, column=1, sticky="e")
        tk.Button(find_dialog, text="查找下一个").grid(row=0, column=2, padx=2, pady=2)
        tk.Button(find_dialog, text="取消", command=find_dialog.destroy).grid(row=1, column=2, padx=2, pady=2)
    
    def replace(self):
        replace_dialog = tk.Toplevel(self.master)
        replace_dialog.title("替换")
        replace_dialog.transient(self.master)
        tk.Label(replace_dialog, text="查找:").grid(row=0, column=0, sticky="e")
        find_entry = tk.Entry(replace_dialog, width=30)
        find_entry.grid(row=0, column=1, padx=2, pady=2, sticky="we")
        tk.Label(replace_dialog, text="替换为:").grid(row=1, column=0, sticky="e")
        replace_entry = tk.Entry(replace_dialog, width=30)
        replace_entry.grid(row=1, column=1, padx=2, pady=2, sticky="we")
        replace_entry.focus_set()
        case_var = tk.IntVar()
        tk.Checkbutton(replace_dialog, text="区分大小写", variable=case_var).grid(row=2, column=1, sticky="e")
        tk.Button(replace_dialog, text="查找下一个").grid(row=0, column=2, padx=2, pady=2)
        tk.Button(replace_dialog, text="替换", command=lambda: self.replace_text(find_entry.get(), replace_entry.get(), case_var.get())).grid(row=1, column=2, padx=2, pady=2)
        tk.Button(replace_dialog, text="全部替换", command=lambda: self.replace_all(find_entry.get(), replace_entry.get(), case_var.get())).grid(row=2, column=2, padx=2, pady=2)
        tk.Button(replace_dialog, text="取消", command=replace_dialog.destroy).grid(row=3, column=2, padx=2, pady=2)
    
    def replace_text(self, find_str, replace_str, case_sensitive):
        start_pos = 1.0
        while True:
            if case_sensitive:
                pos = self.textpad.search(find_str, start_pos, tk.END, nocase=0)
            else:
                pos = self.textpad.search(find_str, start_pos, tk.END, nocase=1)
            if not pos:
                break
            end_pos = pos + "+%dc" % len(find_str)
            self.textpad.delete(pos, end_pos)
            self.textpad.insert(pos, replace_str)
            start_pos = pos + "+%dc" % len(replace_str)
    
    def replace_all(self, find_str, replace_str, case_sensitive):
        self.textpad.mark_set("match_start", "1.0")
        self.textpad.mark_set("match_end", "1.0")
        self.textpad.tag_remove("match", "1.0", tk.END)
        count = tk.IntVar()
        while True:
            if case_sensitive:
                pos = self.textpad.search(find_str, "match_end", tk.END, count=count, nocase=0)
            else:
                pos = self.textpad.search(find_str, "match_end", tk.END, count=count, nocase=1)
            if not pos:
                break
            self.textpad.mark_set("match_start", pos)
            end_pos = pos + "+%dc" % count.get()
            self.textpad.mark_set("match_end", end_pos)
            self.textpad.tag_add("match", "match_start", "match_end")
            self.textpad.insert("match_end", replace_str)
        self.textpad.tag_remove("match", "1.0", tk.END)
    
    def choose_font(self):
        font = tk.font.Font(font=self.textpad["font"])
        font_dialog = tk.font.FontChooser(self.master, font)
        new_font = font_dialog.show()
        if new_font:
            self.textpad["font"] = new_font
    
    def about(self):
        messagebox.showinfo("关于", "这是一个使用Python和tkinter实现的记事本程序。")
        
if __name__ == "__main__":
    root = tk.Tk()
    notepad = Notepad(root)
    root.mainloop()

该程序具有基本的文本编辑功能，包括新建、打开、保存、另存为、撤销、恢复、剪切、复制、粘贴、查找、替换和选择字体等功能。