根據(jù)您綁定的屬性，存在以下三種可能的情況：
-
常規(guī)綁定 - ViewModel屬性綁定到任何不可編輯的View元素屬性。由于該元素不可編輯，因此您無(wú)需將更新通知發(fā)送回綁定屬性（單向綁定）。
-
數(shù)據(jù)綁定 - Model屬性（數(shù)據(jù)字段）綁定到編輯器屬性。如果用戶可以更改編輯器值，則需要更新綁定屬性（雙向綁定）。
-
屬性依賴 - 來(lái)自同一個(gè)ViewModel的兩個(gè)屬性被綁定。
獲取工具下載 - DevExpress WinForm v21.2
屬性依賴
屬性依賴是來(lái)自同一個(gè)ViewModel的兩個(gè)屬性之間的關(guān)系，當(dāng)一個(gè)屬性發(fā)生變化時(shí)，另一個(gè)屬性會(huì)更新其值。
在“MVVM 最佳實(shí)踐”演示中，多個(gè)模塊演示了以下設(shè)置：
-
兩個(gè)TextEdit控件綁定到ViewModel“Operand1”和“Operand2”屬性。
-
當(dāng)用戶更改 TextEdit 值時(shí)，操作數(shù)屬性會(huì)刷新其值。
-
當(dāng)操作數(shù)屬性更改時(shí)，它們會(huì)更新數(shù)字 “Result”屬性（依賴項(xiàng) #1）。
-
“Result”屬性更新字符串“ResultText”屬性（依賴項(xiàng)#2）。
對(duì)于使用示例 UI 的每個(gè)演示模塊，將 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(gè)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(dāng)相關(guān)屬性的值發(fā)生變化時(shí)，框架會(huì)調(diào)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(qǐng)使用 DevExpress.Mvvm.DataAnnotations.BindableProperty 屬性告訴框架它應(yīng)該在屬性值更改時(shí)調(diào)用此方法。 在下面的代碼示例中，DevExpress.Mvvm.POCO.RaisePropertyChanged 是一個(gè) DevExpress 擴(kuò)展方法，它將更新通知發(fā)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 屬性標(biāo)記依賴屬性。 請(qǐng)注意，與前面的示例不同，下面的代碼僅使用一個(gè)依賴項(xiàng)：“ResultText”取決于兩個(gè)“Operand”屬性，您不能使用此屬性創(chuàng)建鏈?zhǔn)揭蕾図?xiàng)。
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(chuàng)建自定義更新方法并使用單獨(dú)的元數(shù)據(jù)類將屬性與這些方法鏈接起來(lái)。 如果 BindableProperty 屬性按名稱引用更新方法，則 OnPropertyChangedCall 方法使用 lambda 表達(dá)式來(lái)檢索方法。 重命名自定義更新方法時(shí)，元數(shù)據(jù)類顯示編譯錯(cuò)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(shù)據(jù)源記錄填充多項(xiàng)目控件，請(qǐng)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)
-
Target - 您需要填充的目標(biāo) UI 元素。
-
Item Selector - 一個(gè)表達(dá)式，用于檢索應(yīng)從數(shù)據(jù)源填充的 UI 元素的項(xiàng)目集合。
-
Source Selector - 定位數(shù)據(jù)源的表達(dá)式，其項(xiàng)目應(yīng)用于填充目標(biāo)。
-
Match Expression -將數(shù)據(jù)源項(xiàng)與目標(biāo)子項(xiàng)進(jìn)行比較的表達(dá)式。 當(dāng)您更改或刪除數(shù)據(jù)源記錄時(shí)，框架會(huì)運(yùn)行此表達(dá)式以確定是否應(yīng)更新相應(yīng)的 Target 集合項(xiàng)。
-
Create Expression - 出現(xiàn)新數(shù)據(jù)源記錄時(shí)創(chuàng)建新目標(biāo)集合項(xiàng)的表達(dá)式。
-
Dispose Expression - 一個(gè)表達(dá)式，當(dāng)它的相關(guān)數(shù)據(jù)源記錄被刪除時(shí)處理一個(gè) Target 集合項(xiàng)。
-
Change Expression - 指定當(dāng)匹配表達(dá)式得出此項(xiàng)目與數(shù)據(jù)源記錄不同時(shí)如何更新目標(biāo)集合項(xiàng)目。
在 MVVM 最佳實(shí)踐演示中，以下代碼使用自定義實(shí)體類的對(duì)象填充列表框。 SetBinding 方法將編輯器的 SelectedItem 屬性與檢索相應(yīng)實(shí)體對(duì)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(fā)器
觸發(fā)器允許您在 ViewModel 屬性更改時(shí)修改 UI（視圖）。 在 DevExpress 演示中，復(fù)選框綁定到 ViewModel “IsActive”屬性。 當(dāng)此屬性的值更改時(shí)，觸發(fā)器會(huì)更改 UI 元素（標(biāo)簽）的背景顏色。
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)
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