DevExpress WinForm控件入门指南：WinForms MVVM - 数据和属性绑定（Part 3）-控件新闻-慧都网

DevExpress WinForm控件入门指南：WinForms MVVM - 数据和属性绑定（Part 3）

翻译|使用教程|编辑：龚雪|2021-11-15 10:03:21.883|阅读 213 次

概述：DevExpress WinForm创建的应用程序可利用MVVM设计模式，本文主要为大家介绍这其中的第三种属性依赖，欢迎下载最新版体验！

# 慧都年终大促·界面/图表报表/文档/IDE等千款热门软控件火热促销中 >>

属性依赖

属性依赖是来自同一个ViewModel的两个属性之间的关系，当一个属性发生变化时，另一个属性会更新其值。

在“MVVM 最佳实践”演示中，多个模块演示了以下设置：

两个TextEdit控件绑定到ViewModel“Operand1”和“Operand2”属性。
当用户更改 TextEdit 值时，操作数属性会刷新其值。
当操作数属性更改时，它们会更新数字 “Result”属性（依赖项 #1）。
“Result”属性更新字符串“ResultText”属性（依赖项#2）。

DevExpress WinForm控件入门指南：WinForms MVVM - 数据和属性绑定（Part 3）

对于使用示例 UI 的每个演示模块，将 View 元素绑定到 ViewModel 属性的代码都是相同的。

mvvmContext.ViewModelType = typeof(MultViewModel);
var fluentAPI = mvvmContext.OfType<MultViewModel>();
fluentAPI.SetBinding(editor1, e => e.EditValue, x => x.Operand1);
fluentAPI.SetBinding(editor2, e => e.EditValue, x => x.Operand2);
fluentAPI.SetBinding(resultLabel, l => l.Text, x => x.ResultText);

VB.NET

mvvmContext.ViewModelType = GetType(MultViewModel)
Dim fluentAPI = mvvmContext.OfType(Of MultViewModel)()
fluentAPI.SetBinding(editor1, Sub(e) e.EditValue, Sub(x) x.Operand1)
fluentAPI.SetBinding(editor2, Sub(e) e.EditValue, Sub(x) x.Operand2)
fluentAPI.SetBinding(resultLabel, Sub(l) l.Text, Sub(x) x.ResultText)

然而，属性依赖在每个模块中的声明都不同。

OnPropertyChanged 方法

在POCO ViewModels中，您可以声明OnXChanged方法，其中 X 是属性名称。当相关属性的值发生变化时，框架会调用这些方法。

public class MultViewModel {
public virtual int Operand1 { get; set; }
public virtual int Operand2 { get; set; }
public virtual int Result { get; set; }
public virtual string ResultText { get; set; }

protected void OnOperand1Changed() {
UpdateResult();
}
protected void OnOperand2Changed() {
UpdateResult();
}
protected void OnResultChanged() {
UpdateResultText();
}
void UpdateResult() {
Result = Operand1 * Operand2;
}
void UpdateResultText() {
ResultText = string.Format("The result is: {0:n0}", Result);
}
}

VB.NET

Public Class MultViewModel
Public Overridable Property Operand1() As Integer
Public Overridable Property Operand2() As Integer
Public Overridable Property Result() As Integer
Public Overridable Property ResultText() As String

Protected Sub OnOperand1Changed()
UpdateResult()
End Sub
Protected Sub OnOperand2Changed()
UpdateResult()
End Sub
Protected Sub OnResultChanged()
UpdateResultText()
End Sub
Private Sub UpdateResult()
Result = Operand1 * Operand2
End Sub
Private Sub UpdateResultText()
ResultText = String.Format("The result is: {0:n0}", Result)
End Sub
End Class

自定义更新方法

如果您的更新方法未被称为“On...Changed”，请使用 DevExpress.Mvvm.DataAnnotations.BindableProperty 属性告诉框架它应该在属性值更改时调用此方法。在下面的代码示例中，DevExpress.Mvvm.POCO.RaisePropertyChanged 是一个 DevExpress 扩展方法，它将更新通知发送到依赖属性。

public class SumViewModel {
[BindableProperty(OnPropertyChangedMethodName = "NotifyResultAndResultTextChanged")]
public virtual int Operand1 { get; set; }
[BindableProperty(OnPropertyChangedMethodName = "NotifyResultAndResultTextChanged")]
public virtual int Operand2 { get; set; }
public int Result {
get { return Operand1 + Operand2; }
}
public string ResultText {
get { return string.Format("The result is: {0:n0}", Result); }
}
protected void NotifyResultAndResultTextChanged() {
this.RaisePropertyChanged(x => x.Result);
this.RaisePropertyChanged(x => x.ResultText);
}
}

VB.NET

Public Class SumViewModel
<BindableProperty(OnPropertyChangedMethodName := "NotifyResultAndResultTextChanged")>
Public Overridable Property Operand1() As Integer
<BindableProperty(OnPropertyChangedMethodName := "NotifyResultAndResultTextChanged")>
Public Overridable Property Operand2() As Integer
Public ReadOnly Property Result() As Integer
Get
Return Operand1 + Operand2
End Get
End Property
Public ReadOnly Property ResultText() As String
Get
Return String.Format("The result is: {0:n0}", Result)
End Get
End Property
Protected Sub NotifyResultAndResultTextChanged()
Me.RaisePropertyChanged(Function(x) x.Result)
Me.RaisePropertyChanged(Function(x) x.ResultText)
End Sub
End Class

依赖属性

使用 DevExpress.Mvvm.DataAnnotations.DependsOnProperties 属性标记依赖属性。请注意，与前面的示例不同，下面的代码仅使用一个依赖项：“ResultText”取决于两个“Operand”属性，您不能使用此属性创建链式依赖项。

public class MultViewModelEx {
public virtual int Operand1 { get; set; }
public virtual int Operand2 { get; set; }

[DependsOnProperties("Operand1", "Operand2")]
public string ResultText {
get { return string.Format("The result is: {0:n0}", Operand1 * Operand2); }
}
}

VB.NET

Public Class MultViewModelEx
Public Overridable Property Operand1() As Integer
Public Overridable Property Operand2() As Integer

<DependsOnProperties("Operand1", "Operand2")>
Public ReadOnly Property ResultText() As String
Get
Return String.Format("The result is: {0:n0}", Operand1 * Operand2)
End Get
End Property
End Class

Metadata类

在这种方法中，您创建自定义更新方法并使用单独的元数据类将属性与这些方法链接起来。如果 BindableProperty 属性按名称引用更新方法，则 OnPropertyChangedCall 方法使用 lambda 表达式来检索方法。重命名自定义更新方法时，元数据类显示编译错误。

//View Model code
[System.ComponentModel.DataAnnotations.MetadataType(typeof(Metadata))]
public class SumViewModel_MetaPOCO {
public virtual int Operand1 { get; set; }
public virtual int Operand2 { get; set; }
public virtual int Result { get; set; }
public string ResultText {
get { return string.Format("The result is: {0:n0}", Result); }
}
protected void NotifyResultAndResultTextChanged() {
Result = Operand1 + Operand2;
this.RaisePropertyChanged(x => x.Result);
this.RaisePropertyChanged(x => x.ResultText);
}
//Metadata class
public class Metadata : IMetadataProvider<SumViewModel_MetaPOCO> {
void IMetadataProvider<SumViewModel_MetaPOCO>.BuildMetadata(MetadataBuilder<SumViewModel_MetaPOCO> builder) {
builder.Property(x => x.Result)
.DoNotMakeBindable();
builder.Property(x => x.Operand1).
OnPropertyChangedCall(x => x.NotifyResultAndResultTextChanged());
builder.Property(x => x.Operand2).
OnPropertyChangedCall(x => x.NotifyResultAndResultTextChanged());
}
}
}

VB.NET

<System.ComponentModel.DataAnnotations.MetadataType(GetType(Metadata))>
Public Class SumViewModel_MetaPOCO
Public Overridable Property Operand1() As Integer
Public Overridable Property Operand2() As Integer
Public Overridable Property Result() As Integer
Public ReadOnly Property ResultText() As String
Get
Return String.Format("The result is: {0:n0}", Result)
End Get
End Property
Protected Sub NotifyResultAndResultTextChanged()
Result = Operand1 + Operand2
Me.RaisePropertyChanged(Function(x) x.Result)
Me.RaisePropertyChanged(Function(x) x.ResultText)
End Sub
'Metadata class
Public Class Metadata
Implements IMetadataProvider(Of SumViewModel_MetaPOCO)

Private Sub IMetadataProviderGeneric_BuildMetadata(ByVal builder As MetadataBuilder(Of SumViewModel_MetaPOCO)) Implements IMetadataProvider(Of SumViewModel_MetaPOCO).BuildMetadata
builder.Property(Function(x) x.Result).DoNotMakeBindable()
builder.Property(Function(x) x.Operand1).OnPropertyChangedCall(Function(x) x.NotifyResultAndResultTextChanged())
builder.Property(Function(x) x.Operand2).OnPropertyChangedCall(Function(x) x.NotifyResultAndResultTextChanged())
End Sub
End Class
End Class

集合绑定

要使用数据源记录填充多项目控件，请使用 SetItemsSourceBinding 方法。

var fluentApi = mvvmContext1.OfType<ViewModelClass>();
fluentApi.SetItemsSourceBinding(
Target
ItemSelector,
SourceSelector,
MatchExpression,
CreateExpression,
DisposeExpression,
ChangeExpression
);

VB.NET

Dim fluentApi = mvvmContext1.OfType(Of ViewModelClass)()
fluentApi.SetItemsSourceBinding(Target ItemSelector, SourceSelector, MatchExpression, CreateExpression, DisposeExpression, ChangeExpression)

Target - 您需要填充的目标 UI 元素。
Item Selector - 一个表达式，用于检索应从数据源填充的 UI 元素的项目集合。
Source Selector - 定位数据源的表达式，其项目应用于填充目标。
Match Expression -将数据源项与目标子项进行比较的表达式。当您更改或删除数据源记录时，框架会运行此表达式以确定是否应更新相应的 Target 集合项。
Create Expression - 出现新数据源记录时创建新目标集合项的表达式。
Dispose Expression - 一个表达式，当它的相关数据源记录被删除时处理一个 Target 集合项。
Change Expression - 指定当匹配表达式得出此项目与数据源记录不同时如何更新目标集合项目。

在 MVVM 最佳实践演示中，以下代码使用自定义实体类的对象填充列表框。 SetBinding 方法将编辑器的 SelectedItem 属性与检索相应实体对象的 ViewModel SelectedEntity 属性绑定。

//View code
mvvmContext.ViewModelType = typeof(ViewModel);
var fluentApi = mvvmContext.OfType<ViewModel>();
fluentApi.SetItemsSourceBinding(
listBox,
lb => lb.Items,
x => x.Entities,
(item, entity) => object.Equals(item.Value, entity),
entity => new ImageListBoxItem(entity),
null,
(item, entity) => {
((ImageListBoxItem)item).Description = entity.Text;
}
);
fluentApi.SetBinding(listBox, lb => lb.SelectedValue, x => x.SelectedEntity);

//ViewModel code
public class ViewModel {
public virtual Entity SelectedEntity { get; set; }
public virtual ObservableCollection<Entity> Entities { get; set;}
protected void OnSelectedEntityChanged() {
//"Remove" is a custom ViewModel method that deletes a selected entity
this.RaiseCanExecuteChanged(x => x.Remove());
}
protected void OnEntitiesChanged() {
SelectedEntity = Entities.FirstOrDefault();
}
}

//Model code
public class Entity {
public Entity(int id) {
this.ID = id;
this.Text = "Entity " + id.ToString();
}
public int ID { get; private set; }
public string Text { get; set; }
}

VB.NET

'View code
mvvmContext.ViewModelType = GetType(ViewModel)
Dim fluentApi = mvvmContext.OfType(Of ViewModel)()
fluentApi.SetItemsSourceBinding(
listBox,
Function(lb) lb.Items,
Function(x) x.Entities,
Function(item, entity) Object.Equals(item.Value, entity),
Function(entity) New ImageListBoxItem(entity),
Nothing,
Function(item, entity) CType(item, ImageListBoxItem).Description = entity.Text
)
fluentApi.SetBinding(listBox, Function(lb) lb.SelectedValue, Function(x) x.SelectedEntity)

'ViewModel code
Public Class ViewModel
Public Overridable Property SelectedEntity() As Entity
Public Overridable Property Entities() As ObservableCollection(Of Entity)
Protected Sub OnSelectedEntityChanged()
'"Remove" is a custom ViewModel method that deletes a selected entity
Me.RaiseCanExecuteChanged(Function(x) x.Remove())
End Sub
Protected Sub OnEntitiesChanged()
SelectedEntity = Entities.FirstOrDefault()
End Sub
End Class

'Model code
Public Class Entity
Public Sub New(ByVal id As Integer)
Me.ID = id
Me.Text = "Entity " & id.ToString()
End Sub
Private privateID As Integer
Public Property ID() As Integer
Get
Return privateID
End Get
Private Set(ByVal value As Integer)
privateID = value
End Set
End Property
Public Property Text() As String
End Class

触发器

触发器允许您在 ViewModel 属性更改时修改 UI（视图）。在 DevExpress 演示中，复选框绑定到 ViewModel “IsActive”属性。当此属性的值更改时，触发器会更改 UI 元素（标签）的背景颜色。

//ViewModel code
public class ViewModel {
public virtual bool IsActive { get; set; }
}

//ViewModel code
var fluent = mvvmContext.OfType<ViewModel>();
fluent.SetBinding(checkEdit, c => c.Checked, x => x.IsActive);
fluent.SetTrigger(x => x.IsActive, (active) => {
if(active)
label.Appearance.BackColor = Color.LightPink;
else
label.Appearance.BackColor = Color.Empty;
});

VB.NET

'ViewModel code
Public Class ViewModel
Public Overridable Property IsActive() As Boolean
End Class

'ViewModel code
Private fluent = mvvmContext.OfType(Of ViewModel)()
fluent.SetBinding(checkEdit, Function(c) c.Checked, Function(x) x.IsActive)
fluent.SetTrigger(Function(x) x.IsActive, Sub(active)
If active Then
label.Appearance.BackColor = Color.LightPink
Else
label.Appearance.BackColor = Color.Empty
End If
End Sub)

DevExpress WinForm | 下载试用

DevExpress WinForm拥有180+组件和UI库，能为Windows Forms平台创建具有影响力的业务解决方案。DevExpress WinForms能完美构建流畅、美观且易于使用的应用程序，无论是Office风格的界面，还是分析处理大批量的业务数据，它都能轻松胜任！

更多产品正版授权详情及优惠，欢迎咨询

DevExpress技术交流群5：742234706 欢迎一起进群讨论