根據您綁定的屬性，存在以下三種可能的情況：
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屬性依賴屬性依賴是來自同一個ViewModel的兩個屬性之間的關系，當一個屬性發生變化時，另一個屬性會更新其值。
在“MVVM 最佳實踐”演示中，多個模塊演示了以下設置：
對于使用示例 UI 的每個演示模塊，将 View 元素綁定到 ViewModel 屬性的代碼都是相同的。
C#
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，屬性依賴在每個模塊中的聲明都不同。
OnPropertyChanged 方法
在POCO ViewModels中，您可以聲明OnXChanged方法，其中 X 是屬性名稱。 當相關屬性的值發生變化時，框架會調用這些方法。
C#
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
自定義更新方法
如果您的更新方法未被稱為“On...Changed”，請使用 DevExpress.Mvvm.DataAnnotations.BindableProperty 屬性告訴框架它應該在屬性值更改時調用此方法。 在下面的代碼示例中，DevExpress.Mvvm.POCO.RaisePropertyChanged 是一個 DevExpress 擴展方法，它将更新通知發送到依賴屬性。
C#
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
依賴屬性
使用 DevExpress.Mvvm.DataAnnotations.DependsOnProperties 屬性标記依賴屬性。 請注意，與前面的示例不同，下面的代碼僅使用一個依賴項：“ResultText”取決于兩個“Operand”屬性，您不能使用此屬性創建鍊式依賴項。
C#
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類
在這種方法中，您創建自定義更新方法并使用單獨的元數據類将屬性與這些方法鍊接起來。 如果 BindableProperty 屬性按名稱引用更新方法，則 OnPropertyChangedCall 方法使用 lambda 表達式來檢索方法。 重命名自定義更新方法時，元數據類顯示編譯錯誤。
C#
//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
集合綁定
要使用數據源記錄填充多項目控件，請使用 SetItemsSourceBinding 方法。
C#
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)
在 MVVM 最佳實踐演示中，以下代碼使用自定義實體類的對象填充列表框。 SetBinding 方法将編輯器的 SelectedItem 屬性與檢索相應實體對象的 ViewModel SelectedEntity 屬性綁定。
C#
//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
觸發器
觸發器允許您在 ViewModel 屬性更改時修改 UI（視圖）。 在 DevExpress 演示中，複選框綁定到 ViewModel “IsActive”屬性。 當此屬性的值更改時，觸發器會更改 UI 元素（标簽）的背景顔色。
C#
//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
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