界面控件DevExpress WinForm - MVVM命令讲解（二）

2023-10-05 14:50:52

带参数的命令

DevExpress MVVM框架接受public void方法的一个参数作为参数化命令，您可以使用此参数在 View 和 ViewModel 之间传递数据。

//ViewModel
public class ViewModelWithParametrizedCommand {
public void DoSomething(object p) {
var msgBoxService = this.GetService<IMessageBoxService>();
msgBoxService.ShowMessage(string.Format("The parameter is {0}.", p));
}
}

//View
mvvmContext.ViewModelType = typeof(ViewModelWithParametrizedCommand);
var fluent = mvvmContext.OfType<ViewModelWithParametrizedCommand>();
object parameter = 5;
fluent.BindCommand(commandButton, x => x.DoSomething, x => parameter);

VB.NET

'ViewModel
Public Class ViewModelWithParametrizedCommand
Public Sub DoSomething(ByVal p As Object)
Dim msgBoxService = Me.GetService(Of IMessageBoxService)()
msgBoxService.ShowMessage(String.Format("The parameter is {0}.", p))
End Sub
End Class

'View
mvvmContext.ViewModelType = GetType(ViewModelWithParametrizedCommand)
Dim fluent = mvvmContext.OfType(Of ViewModelWithParametrizedCommand)()
Dim parameter As Object = 5
fluent.BindCommand(commandButton, Sub(x) x.DoSomething(Nothing), Function(x) parameter)

您还可以向 CanExecute 条件添加参数。

//ViewModel
public class ViewModelWithParametrizedConditionalCommand {
public void DoSomething(int p) {
var msgBoxService = this.GetService<IMessageBoxService>();
msgBoxService.ShowMessage(string.Format(
"The parameter is {0}.", p));
}
public bool CanDoSomething(int p) {
return (2 + 2) == p;
}
}

//View
mvvmContext.ViewModelType = typeof(ViewModelWithParametrizedConditionalCommand);
var fluent = mvvmContext.OfType<ViewModelWithParametrizedConditionalCommand>();
int parameter = 4;
fluent.BindCommand(commandButton, x => x.DoSomething, x => parameter);

VB.NET

'ViewModel
Public Class ViewModelWithParametrizedConditionalCommand
Public Sub DoSomething(ByVal p As Integer)
Dim msgBoxService = Me.GetService(Of IMessageBoxService)()
msgBoxService.ShowMessage(String.Format("The parameter is {0}.", p))
End Sub
Public Function CanDoSomething(ByVal p As Integer) As Boolean
Return (2 + 2) = p
End Function
End Class

'View
mvvmContext.ViewModelType = GetType(ViewModelWithParametrizedConditionalCommand)
Dim fluent = mvvmContext.OfType(Of ViewModelWithParametrizedConditionalCommand)()
Dim parameter As Integer = 4
fluent.BindCommand(commandButton, Sub(x) x.DoSomething(Nothing), Function(x) parameter)

异步命令

如果需要执行延迟或连续操作，请使用异步命令。要创建异步命令，请声明 System.Threading.Tasks.Task 类型的公共方法（您可以使用 async/await 语法），将 UI 元素绑定到命令的代码保持不变，框架在命令运行时禁用此元素。

//ViewModel
public class ViewModelWithAsyncCommand {
public async Task DoSomethingAsync() {
// do some work here
await Task.Delay(1000);
}
}

//View
mvvmContext.ViewModelType = typeof(ViewModelWithAsyncCommand);
var fluent = mvvmContext.OfType<ViewModelWithAsyncCommand>();
fluent.BindCommand(commandButton, x => x.DoSomethingAsync);

VB.NET

'ViewModel
Public Class ViewModelWithAsyncCommand
Public Async Sub DoSomethingAsync() As Task
' do some work here
Await Task.Delay(1000)
End Sub
End Class

'View
mvvmContext.ViewModelType = GetType(ViewModelWithAsyncCommand)
Dim fluent = mvvmContext.OfType(Of ViewModelWithAsyncCommand)()
fluent.BindCommand(commandButton, Sub(x) x.DoSomethingAsync(Nothing))

任务支持取消标记，允许您检查 IsCancellationRequested 属性并在此属性返回 true 时中止任务。如果将此代码添加到异步命令中，请使用 BindCancelCommand 方法创建停止正在进行的异步命令的 UI 元素。 DevExpress MVVM 框架锁定了这个取消按钮，并且只有在相关的异步命令正在运行时才启用它。

//ViewModel
public class ViewModelWithAsyncCommandAndCancellation {
public async Task DoSomethingAsynchronously() {
var dispatcher = this.GetService<IDispatcherService>();
var asyncCommand = this.GetAsyncCommand(x => x.DoSomethingAsynchronously());
for(int i = 0; i <= 100; i++) {
if(asyncCommand.IsCancellationRequested)
break;
// do some work here
await Task.Delay(25);
await UpdateProgressOnUIThread(dispatcher, i);
}
await UpdateProgressOnUIThread(dispatcher, 0);
}

public int Progress {
get;
private set;
}
//update the "Progress" property bound to the progress bar within a View
async Task UpdateProgressOnUIThread(IDispatcherService dispatcher, int progress) {
await dispatcher.BeginInvoke(() => {
Progress = progress;
this.RaisePropertyChanged(x => x.Progress);
});
}
}

//View
mvvmContext.ViewModelType = typeof(ViewModelWithAsyncCommandAndCancellation);
var fluent = mvvmContext.OfType<ViewModelWithAsyncCommandAndCancellation>();
fluent.BindCommand(commandButton, x => x.DoSomethingAsynchronously);
fluent.BindCancelCommand(cancelButton, x => x.DoSomethingAsynchronously);
fluent.SetBinding(progressBar, p => p.EditValue, x => x.Progress);

VB.NET

'ViewModel
Public Class ViewModelWithAsyncCommandAndCancellation
Public Async Sub DoSomethingAsynchronously() As Task
Dim dispatcher = Me.GetService(Of IDispatcherService)()
Dim asyncCommand = Me.GetAsyncCommand(Sub(x) x.DoSomethingAsynchronously())
For i As Integer = 0 To 100
If asyncCommand.IsCancellationRequested Then
Exit For
End If
' do some work here
Await Task.Delay(25)
Await UpdateProgressOnUIThread(dispatcher, i)
Next i
Await UpdateProgressOnUIThread(dispatcher, 0)
End Sub

Private privateProgress As Integer
Public Property Progress() As Integer
Get
Return privateProgress
End Get
Private Set(ByVal value As Integer)
privateProgress = value
End Set
End Property
'update the "Progress" property bound to the progress bar within a View
Private Async Sub UpdateProgressOnUIThread(ByVal dispatcher As IDispatcherService, ByVal progress As Integer) As Task
Await dispatcher.BeginInvoke(Sub()
Me.Progress = progress
Me.RaisePropertyChanged(Sub(x) x.Progress)
End Sub)
End Sub
End Class

'View
mvvmContext.ViewModelType = GetType(ViewModelWithAsyncCommandAndCancellation)
Dim fluent = mvvmContext.OfType(Of ViewModelWithAsyncCommandAndCancellation)()
fluent.BindCommand(commandButton, Sub(x) x.DoSomethingAsynchronously)
fluent.BindCancelCommand(cancelButton, Sub(x) x.DoSomethingAsynchronously)
fluent.SetBinding(progressBar, Sub(p) p.EditValue, Sub(x) x.Progress)

WithCommand Fluent API 方法还支持可取消的异步命令。

mvvmContext.ViewModelType = typeof(ViewModelWithAsyncCommandAndCancellation);
// Initialize the Fluent API
var fluent = mvvmContext.OfType<ViewModelWithAsyncCommandAndCancellation>();
// Binding for buttons
fluent.WithCommand(x => x.DoSomethingAsynchronously)
.Bind(commandButton)
.BindCancel(cancelButton);

VB.NET

mvvmContext.ViewModelType = GetType(ViewModelWithAsyncCommandAndCancellation)
' Initialize the Fluent API
Dim fluent = mvvmContext.OfType(Of ViewModelWithAsyncCommandAndCancellation)()
' Binding for buttons
fluent.WithCommand(Sub(x) x.DoSomethingAsynchronously).Bind(commandButton).BindCancel(cancelButton)

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带参数的命令

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