你好，我创建了 3 个 viewModel，想要将它们连接到单个视图（UI），但不能

Question

我有 3 个视图模型（AdminViewModel、StudentViewModel、ProfessorViewModel），我有一个用户登录数据库的 UI，我创建了一个名为 ExtractRole 的方法，它扮演当前从数据库登录的用户的角色。我正在尝试为了在用户登录后完成他的角色，并根据角色调用并可视化三个 ViewModel 之一。我不知道如何“绑定”ViewModel，以便可以调用它

这就是我制作 LoginView.xaml.cs 的方式 ”

   public partial class LoginView : Window
{   
    private string _databasePath;

    public LoginView() 
        { 
          InitializeComponent(); _databasePath = System.IO.Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.Desktop), "Welcome.db"); 
         }

    private bool isLoggedIn = false;
    private void LoginBtn_Click(object sender, RoutedEventArgs e)
    {
        // Perform validation against the database
        bool isValidUser = ValidateUser(LoginTextBox.Text, PasswordTextBox.Password);
        if (!isLoggedIn)
        {
            if (isValidUser)
            {
                // Navigate to the StudentsList page

                string role = ExtractRole(LoginTextBox.Text, PasswordTextBox.Password);

                MessageBox.Show($"Your role is: {role}");
                StudentsList studentsList = new StudentsList();
                // Add the StudentsList UserControl to a container (e.g., a Grid)
                // Assuming you have a Grid called "mainGrid" defined in your LoginView.xaml
                mainGrid.Children.Clear(); // Clear existing content
                mainGrid.Children.Add(studentsList);
                isLoggedIn = true;
                LoginBtn.Content = "Exit"; // Change button text to "Exit"
            }
            else
            {
                MessageBox.Show("Invalid username or password! Please try again!");
            }
        }
        else
        {
            isLoggedIn = false;


            // Optionally, you can open a new instance of the login window
            LoginView loginView = new LoginView();
            loginView.Show();
            // Close the current window
            Window.GetWindow(this).Close();
            LoginBtn.Content = "Login"; // Change button text to "Login"
        }

        // Prevent the button click event from bubbling up and closing the window
        e.Handled = true;
    }


    // Method to validate user credentials (dummy implementation)
    private bool ValidateUser(string username, string password)
    {
        
        // Construct the connection string to the SQLite database
        string connectionString = $"Data Source={_databasePath};";


        using (SqliteConnection connection = new SqliteConnection(connectionString))
        {
            connection.Open();

            // SQL query to check if the provided username and password exist in the Users table
            string query = "SELECT COUNT (*) FROM Users WHERE Name = @Name AND Password = @Password";

            // Create a command object with the query and connection
            using (SqliteCommand command = new SqliteCommand(query, connection))
            {
                // Add parameters to the query to prevent SQL injection
                command.Parameters.AddWithValue("@Name", username);
                command.Parameters.AddWithValue("@Password", password);

                long result = (long)command.ExecuteScalar();
                int count = Convert.ToInt32(result);
                connection.Close();
                return count > 0;
            }



        }
    }

    private string ExtractRole(string username, string password)
    {
        string role = null;
        string connectionString = $"Data Source={_databasePath};";
        using (SqliteConnection connection = new SqliteConnection(connectionString))
        {
            connection.Open();

            string query = "SELECT Role FROM Users WHERE Name = @Name AND Password =@Password";
            using (SqliteCommand command = new SqliteCommand(query, connection))
            {
                command.Parameters.AddWithValue("@Name", username);
                command.Parameters.AddWithValue("@Password", password);

                object roleObject = command.ExecuteScalar();

                if(roleObject != null) 
                {
                    role = roleObject.ToString();
                }
            }
        }

        return role;
    }
}

这是我的 StudentViewModel 的例子： ”

  namespace Welcome.ViewModel
    { 

public class StudentViewModel: UserViewModel
    { 

private Model.User _user;  

 public StudentViewModel(Model.User user) : base(user)
    {
        _user = user;
    }

    public StudentGradeStatus GradeStatus 
    {
        get {return _user.GradeStatus;}
        set{_user.GradeStatus = value; }
    }

    public DateTime BirthDay
    {
        get { return _user.BirthDay; }
        set { _user.BirthDay = value; }
    }

    public string FNomer
    {
        get { return _user.FNomer; }
        set { _user.FNomer = value; }
    }

    public UserGender Gender
    {
        get { return _user.Gender; }
        set { _user.Gender = value; }   
    }
  }

我尝试在 LoginView.xaml 中使用：

xmlns:local1="clr-namespace:Welcome.ViewModel;assembly=Welcome"

<Window.Resources>

<DataTemplate DataType="{x:Type local1:AdminViewModel}">

<local1:StudentViewModel/>

</DataTemplate>

但收到：” 严重性代码 说明 项目文件行抑制状态 错误 XLS0414 未找到类型“local1:ProfessorViewModel”。验证您没有缺少程序集引用并且所有引用的程序集均已构建。”

Answer 1

在您的 xaml 中，您需要定义在提供特定视图模型时应使用的视图。这看起来像：

<DataTemplate DataType="{x:Type local1:AdminViewModel"}">
  <local1:MyViewForAll/>
</DataTemplate>
<DataTemplate DataType="{x:Type local1:StudentViewModel"}">
  <local1:MyViewForAll/>
</DataTemplate>
<DataTemplate DataType="{x:Type local1:ProfessorViewModel"}">
  <local1:MyViewForAll/>
</DataTemplate>

要显示内容，我将使用 ContentControl，它绑定到一个对象或所有 3 个不同 ViewModel 共享的基类。

<ContentControl Content="{Binding CurrentViewModel}" x:Name="mainContent"/>

在视图模型或代码隐藏中，您可以根据登录的用户类型将正确的 ViewModelType 分配给 ContentControl。这可能类似于：

switch(role)
{
  case "admin":
    CurrentViewModel = new AdminViewModel();
    break;
  case "professor":
    CurrentViewModel = new ProfessorViewModel();
    break;
  case "student":
    CurrentViewModel = new StudentViewModel();
    break;
  default:
    throw new ArgumentException("case not found");
}