POCO(Plain Old CLR Objects)視圖模型簡化并加快了開發過程。

POCO 視圖模型允許您：

• 將可綁定屬性定義為簡單的自動實現的屬性。
• 創建在運行時用作命令的方法。
• 使屬性和方法實現特定于 MVVM 的接口。

這允許您創建干凈、簡單、可維護和可測試的 MVVM 代碼，POCO 視圖模型與任何 WPF 控件完全兼容。

您可以使用在編譯時生成的視圖模型在編譯時為您的視圖模型生成樣板代碼。

DevExpress WPF v21.2正式版下載

Services

 DevExpress MVVM框架包括Services機制，下面的代碼示例演示了如何訪問 Message Box 服務。

C#

using DevExpress.Mvvm.POCO;
...
public class LoginViewModel {
public IMessageBoxService MessageBoxService { get { return this.GetService<IMessageBoxService>(); } }
}

依賴注入

要將視圖綁定到視圖模型，請創建解析正確 ViewModel 類型的 MarkupExtension：

C#

public class DISource : MarkupExtension {
public static Func<Type, object, string, object> Resolver { get; set; }

public Type Type { get; set; }
public object Key { get; set; }
public string Name { get; set; }

public override object ProvideValue(IServiceProvider serviceProvider) => Resolver?.Invoke(Type, Key, Name);
}

在應用程序啟動時注冊解析器：

C#

protected override void OnStartup(StartupEventArgs e) {
base.OnStartup(e);
DISource.Resolver = Resolve;
}
object Resolve(Type type, object key, string name) {
if(type == null)
return null;
if(key != null)
return Container.ResolveKeyed(key, type);
if(name != null)
return Container.ResolveNamed(name, type);
return Container.Resolve(type);
}

通過以下方式在 XAML 中指定 DataContext：

XAML

DataContext="{common:DISource Type=common:MainViewModel}"

要在依賴注入容器中使用 POCO 視圖模型，請利用 ViewModelSource.GetPOCOType 方法注冊在運行時生成的 POCO 類型：

C#

container.RegisterType(typeof(IMainViewModel),
ViewModelSource.GetPOCOType(typeof(MainViewModel)));

查看模型父子關系

POCO 視圖模型可以通過父子關系相互關聯。 這是通過 ISupportParentViewModel 接口實現的，該接口在您使用 ViewModelSource 類創建 POCO 對象時自動實現。 通過這個接口，子視圖模型可以訪問在主視圖模型中注冊的服務。

自動 IDataErrorInfo 實現

接口是 WPF 中數據驗證的標準機制，您可以使用此接口為每個單獨的屬性或整個對象定義驗證規則。 POCO 機制允許您基于定義的屬性或 Fluent API 自動實現接口。

要啟用此功能，請為您的視圖模型應用 POCOViewModel 屬性并將 POCOViewModel.ImplementIDataErrorInfo 參數設置為 True。

C#

//Attribute-based approach
[POCOViewModel(ImplementIDataErrorInfo = true)]
public class LoginViewModel {
[Required(ErrorMessage = "Please enter the user name.")]
public virtual string UserName { get; set; }
}

//Fluent API
[POCOViewModel(ImplementIDataErrorInfo = true)]
[MetadataType(typeof(LoginViewModel.Metadata))]
public class LoginViewModel {
public class Metadata : IMetadataProvider<LoginViewModel> {
void IMetadataProvider<LoginViewModel>.BuildMetadata(MetadataBuilder<LoginViewModel> builder) {
builder.Property(x => x.UserName).
Required(() => "Please enter the user name.");
}
}
public virtual string UserName { get; set; }
}

當 ViewModelSource 生成 View Model 的后代時，它會實現 IDataErrorInfo 接口，如下所示：

C#

public class LoginViewModel : IDataErrorInfo {
...
string IDataErrorInfo.Error {
get { return string.Empty; }
}
string IDataErrorInfo.this[string columnName] {
get { return IDataErrorInfoHelper.GetErrorText(this, columnName); }
}
}

類允許您根據指定的 屬性或 Fluent API 獲取錯誤。

下面的代碼示例演示了如何使用 POCO 機制來實現 IDataErrorInfo 接口。

MainView.xaml

<UserControl x:Class="Example.View.MainView"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:dx="http://schemas.devexpress.com/winfx/2008/xaml/core"
xmlns:dxe="http://schemas.devexpress.com/winfx/2008/xaml/editors"
xmlns:dxmvvm="http://schemas.devexpress.com/winfx/2008/xaml/mvvm"
xmlns:ViewModel="clr-namespace:Example.ViewModel"
mc:Ignorable="d" d:DesignHeight="400" d:DesignWidth="400"
DataContext="{dxmvvm:ViewModelSource Type=ViewModel:MainViewModel}">
<UserControl.Resources>
<dxmvvm:BooleanNegationConverter x:Key="BooleanNegationConverter"/>
</UserControl.Resources>

<Grid>
<StackPanel Orientation="Vertical" Margin="10" dxe:ValidationService.IsValidationContainer="True" x:Name="validationContainer">
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="*"/>
<ColumnDefinition Width="*"/>
</Grid.ColumnDefinitions>
<StackPanel Orientation="Vertical" Margin="0,0,4,6">
<TextBlock Text="Name" Margin="6,2,0,2"/>
<dxe:TextEdit NullText="First" EditValue="{Binding FirstName, ValidatesOnDataErrors=True, UpdateSourceTrigger=PropertyChanged}"/>
</StackPanel>
<StackPanel Orientation="Vertical" Margin="4,0,0,6" Grid.Column="1">
<TextBlock Text=" " Margin="6,2,0,2"/>
<dxe:TextEdit NullText="Last" EditValue="{Binding LastName, ValidatesOnDataErrors=True, UpdateSourceTrigger=PropertyChanged}"/>
</StackPanel>
</Grid>
<StackPanel Orientation="Vertical" Margin="0,0,0,6">
<TextBlock Text="Email" Margin="6,2,0,2"/>
<dxe:TextEdit EditValue="{Binding Email, ValidatesOnDataErrors=True, UpdateSourceTrigger=PropertyChanged}"/>
</StackPanel>
<StackPanel Orientation="Vertical" Margin="0,0,0,6">
<TextBlock Text="Password" Margin="6,2,0,2"/>
<dxe:PasswordBoxEdit EditValue="{Binding Password, ValidatesOnDataErrors=True, UpdateSourceTrigger=PropertyChanged}"/>
</StackPanel>
<StackPanel Orientation="Vertical" Margin="0,0,0,6">
<TextBlock Text="Confirm Password" Margin="6,2,0,2"/>
<dxe:PasswordBoxEdit EditValue="{Binding ConfirmPassword, ValidatesOnDataErrors=True, UpdateSourceTrigger=PropertyChanged}"/>
</StackPanel>

<Button VerticalAlignment="Top" Content="Sign Up" Width="150" HorizontalAlignment="Right" Margin="0,10"
IsEnabled="{Binding Path=(dxe:ValidationService.HasValidationError), ElementName=validationContainer, Converter={StaticResource BooleanNegationConverter}}"/>
</StackPanel>
</Grid>
</UserControl>

MainViewModel.cs

using DevExpress.Mvvm;
using DevExpress.Mvvm.DataAnnotations;
using System.Windows.Media;

namespace Example.ViewModel {
[POCOViewModel(ImplementIDataErrorInfo = true)]
public class MainViewModel : ViewModelBase {
static PropertyMetadataBuilder<MainViewModel, string> AddPasswordCheck(PropertyMetadataBuilder<MainViewModel, string> builder) {
return builder.MatchesInstanceRule((name, vm) => vm.Password == vm.ConfirmPassword, () => "The passwords don't match.")
.MinLength(8, () => "The password must be at least 8 characters long.")
.MaxLength(20, () => "The password must not exceed the length of 20.");
}
public static void BuildMetadata(MetadataBuilder<MainViewModel> builder) {
builder.Property(x => x.FirstName)
.Required(() => "Please enter the first name.");
builder.Property(x => x.LastName)
.Required(() => "Please enter the last name.");
builder.Property(x => x.Email)
.EmailAddressDataType(() => "Please enter a correct email address.");
AddPasswordCheck(builder.Property(x => x.Password))
.Required(() => "Please enter the password.");
AddPasswordCheck(builder.Property(x => x.ConfirmPassword))
.Required(() => "Please confirm the password.");
}
public virtual string FirstName { get; set; }
public virtual string LastName { get; set; }
public virtual string Email { get; set; }
public virtual string Password { get; set; }
public virtual string ConfirmPassword { get; set; }
public void OnPasswordChanged() {
this.RaisePropertyChanged(() => ConfirmPassword);
}
public void OnConfirmPasswordChanged() {
this.RaisePropertyChanged(() => Password);
}
}
}

MainViewModel.vb

Imports DevExpress.Mvvm
Imports DevExpress.Mvvm.DataAnnotations
Imports System.Windows.Media

Namespace Example.ViewModel
<POCOViewModel(ImplementIDataErrorInfo := True)> _
Public Class MainViewModel
Inherits ViewModelBase

Private Shared Function AddPasswordCheck(ByVal builder As PropertyMetadataBuilder(Of MainViewModel, String)) As PropertyMetadataBuilder(Of MainViewModel, String)
Return builder.MatchesInstanceRule(Function(name, vm) vm.Password = vm.ConfirmPassword, Function() "The passwords don't match.").MinLength(8, Function() "The password must be at least 8 characters long.").MaxLength(20, Function() "The password must not exceed the length of 20.")
End Function
Public Shared Sub BuildMetadata(ByVal builder As MetadataBuilder(Of MainViewModel))
builder.Property(Function(x) x.FirstName).Required(Function() "Please enter the first name.")
builder.Property(Function(x) x.LastName).Required(Function() "Please enter the last name.")
builder.Property(Function(x) x.Email).EmailAddressDataType(Function() "Please enter a correct email address.")
AddPasswordCheck(builder.Property(Function(x) x.Password)).Required(Function() "Please enter the password.")
AddPasswordCheck(builder.Property(Function(x) x.ConfirmPassword)).Required(Function() "Please confirm the password.")
End Sub
Public Overridable Property FirstName() As String
Public Overridable Property LastName() As String
Public Overridable Property Email() As String
Public Overridable Property Password() As String
Public Overridable Property ConfirmPassword() As String
Public Sub OnPasswordChanged()
Me.RaisePropertyChanged(Function() ConfirmPassword)
End Sub
Public Sub OnConfirmPasswordChanged()
Me.RaisePropertyChanged(Function() Password)
End Sub
End Class
End Namespace

DevExpress WPF | 下載試用

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