界面控件DevExpress WinForms MVVM使用教程（五）：登录表单（上）

1. 您的用户数据库实现方式可能会有所不同，对于示例应用程序，您可以定义以下简单类：

C#

public class User {public string Login { get; set; }public string Password { get; set; }}

VB.NET

Public Class UserPublic Property Login() As StringPublic Property Password() As StringEnd Class

…以及以下存储用户凭据的类。

C#

static class CredentialsSource {static System.Collections.Hashtable credentials;static CredentialsSource() {credentials = new System.Collections.Hashtable();credentials.Add("Guest", GetHash(null));credentials.Add("John", GetHash("qwerty"));credentials.Add("Administrator", GetHash("admin"));credentials.Add("Mary", GetHash("12345"));}internal static bool Check(string login, string pwd) {return object.Equals(credentials[login], GetHash(pwd));}static object GetHash(string password) {return password;}internal static System.Collections.Generic.IEnumerable<string> GetUserNames() {foreach(string item in credentials.Keys)yield return item;}}

VB.NET

Friend NotInheritable Class CredentialsSourcePrivate Sub New()End SubPrivate Shared credentials As System.Collections.HashtableShared Sub New()credentials = New System.Collections.Hashtable()credentials.Add("Guest", GetHash(Nothing))credentials.Add("John", GetHash("qwerty"))credentials.Add("Administrator", GetHash("admin"))credentials.Add("Mary", GetHash("12345"))End SubFriend Shared Function Check(ByVal login As String, ByVal pwd As String) As BooleanReturn Object.Equals(credentials(login), GetHash(pwd))End FunctionPrivate Shared Function GetHash(ByVal password As String) As ObjectReturn passwordEnd FunctionFriend Shared Iterator Function GetUserNames() As System.Collections.Generic.IEnumerable(Of String)For Each item As String In credentials.KeysYield itemNext itemEnd FunctionEnd Class

3. 对于本次登录View相关的ViewModel，可以使用Scaffolding Wizard生成或者手动实现，以下代码说明了最简单的 LoginViewModel 实现。

C#

using System.Collections.Generic;using DevExpress.Mvvm.POCO;using MVVMExpenses.Models;public class LoginViewModel {public IEnumerable<string> LookUpUsers {get { return CredentialsSource.GetUserNames(); }}public virtual User CurrentUser { get; set; }public bool IsCurrentUserCredentialsValid { get; private set; }//[DevExpress.Mvvm.DataAnnotations.Command(false)]public void Init() {this.CurrentUser = new User();}public void Update() {IsCurrentUserCredentialsValid = CredentialsSource.Check(CurrentUser.Login, CurrentUser.Password);}public static LoginViewModel Create() {return ViewModelSource.Create<LoginViewModel>();}}

VB.NET

Imports System.Collections.GenericImports DevExpress.Mvvm.POCOImports MVVMExpenses.ModelsPublic Class LoginViewModelPublic ReadOnly Property LookUpUsers() As IEnumerable(Of String)GetReturn CredentialsSource.GetUserNames()End GetEnd PropertyPublic Overridable Property CurrentUser() As UserPrivate privateIsCurrentUserCredentialsValid As BooleanPublic Property IsCurrentUserCredentialsValid() As BooleanGetReturn privateIsCurrentUserCredentialsValidEnd GetPrivate Set(ByVal value As Boolean)privateIsCurrentUserCredentialsValid = valueEnd SetEnd Property'<DevExpress.Mvvm.DataAnnotations.Command(False)>Public Sub Init()Me.CurrentUser = New User()End SubPublic Sub Update()IsCurrentUserCredentialsValid = CredentialsSource.Check(CurrentUser.Login, CurrentUser.Password)End SubPublic Shared Function Create() As LoginViewModelReturn ViewModelSource.Create(Of LoginViewModel)()End FunctionEnd Class

在此 ViewModel 中，定义了两个属性：存储当前登录用户的 CurrentUser 属性和指定输入凭据是否已通过验证的布尔值 IsCurrentUserCredentialsValid 属性。

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