添加项目文件。

SamplePreSystem.UI/ViewModel/Login/LoginViewModel.cs

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+using CommunityToolkit.Mvvm.ComponentModel;
+using CommunityToolkit.Mvvm.Input;
+using SamplePre.ProcessBll.BLL;
+using System;
+using System.Collections.Generic;
+using System.ComponentModel;
+using System.Linq;
+using System.Runtime.CompilerServices;
+using System.Security.Principal;
+using System.Text;
+using System.Threading.Tasks;
+using System.Windows;
+using System.Windows.Input;
+
+namespace SamplePreSystem.UI.ViewModel.Login
+{
+    public partial class LoginViewModel : ObservableObject
+    {
+        
+
+        UsersBll usersBll = new UsersBll();
+
+        /// <summary>
+        /// 关闭委托
+        /// </summary>
+        public Action<bool> ColseAction;
+
+        //保持用户名
+        public Action<string> SaveUserAction;
+
+        public LoginViewModel()
+        {
+            ;
+        }
+
+        [ObservableProperty]
+        public string errInfo = "";
+
+        [ObservableProperty]
+        public bool isSaveUser = false;
+
+        [ObservableProperty]
+        public string userName = "";
+
+
+        [ObservableProperty]
+        public string userPwd = "";
+
+
+
+        public bool UserChecked()
+        {         
+
+            if (usersBll.CheckUser(UserName, UserPwd) == false)
+            {
+               
+                ErrInfo = "登录账号或密码错误！";
+                return false;
+            }
+
+            if (IsSaveUser == true)
+            {
+                SaveUserAction?.Invoke(UserName);
+
+            }
+
+            ColseAction?.Invoke(true);
+
+            return true;
+
+        }
+
+        /// <summary>
+        /// 登录
+        /// </summary>
+        [RelayCommand]
+        public void LoginButtonClick()
+        {
+            UserChecked();
+
+        }
+
+        /// <summary>
+        /// 回车登录
+        /// </summary>
+        /// <param name="e"></param>
+        [RelayCommand]
+        public void PwdKeyDown(KeyEventArgs e)
+        {
+            if (e.Key == Key.Enter)
+            {
+                UserChecked();
+            }
+
+        }
+
+
+
+        /// <summary>
+        /// 退出
+        /// </summary>
+        [RelayCommand]
+        public void CancelClick()
+        {
+            ColseAction?.Invoke(false);
+        }
+
+
+
+
+
+    }
+}