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DevExpress WinForm控件入门指南:WinForms MVVM - 命令(三)

来源:   发布时间:2021-12-16   浏览:310次

获取工具下载 - DevExpress WinForm v21.2

命令触发器

Triggers允许您执行与命令关联的其他查看操作,根据触发Triggers的条件,共有三种触发器类型。

  • “Before”触发器 - 允许您在目标命令执行之前执行操作。

C#

mvvmContext.ViewModelType = typeof(ViewModelWithSimpleCommand);
var fluent = mvvmContext.OfType<ViewModelWithSimpleCommand>();
fluent.BindCommand(commandButton, x => x.DoSomething);
fluent.WithCommand(x => x.DoSomething)
.Before(() => XtraMessageBox.Show("The target command is about to be executed"));

VB.NET

mvvmContext.ViewModelType = GetType(ViewModelWithSimpleCommand)
Dim fluent = mvvmContext.OfType(Of ViewModelWithSimpleCommand)()
fluent.BindCommand(commandButton, Function(x) x.DoSomething)
fluent.WithCommand(Sub(x) x.DoSomething)
.Before(Function() XtraMessageBox.Show("The target command is about to be executed"))
  • “After”触发器 - 允许您在目标命令完成后执行操作。

C#

mvvmContext.ViewModelType = typeof(ViewModelWithSimpleCommand);
var fluent = mvvmContext.OfType<ViewModelWithSimpleCommand>();
fluent.BindCommand(commandButton, x => x.DoSomething);
fluent.WithCommand(x => x.DoSomething)
.After(() => XtraMessageBox.Show("The target command has been executed"));

VB.NET

mvvmContext.ViewModelType = GetType(ViewModelWithSimpleCommand)
Dim fluent = mvvmContext.OfType(Of ViewModelWithSimpleCommand)()
fluent.BindCommand(commandButton, Function(x) x.DoSomething)
fluent.WithCommand(Function(x) x.DoSomething).After(Function() XtraMessageBox.Show("The target command has been executed"))
  • “CanExecute”条件触发器 - 允许您在目标命令的 CanExecute 条件更改时执行操作。

C#

var fluent = mvvmContext.OfType<ViewModelWithSimpleCommandAndCanExecute>();
fluent.BindCommand(commandButton, x => x.DoSomething);
// When the CanExecute condition changes, the message shows up
fluent.WithCommand(x => x.DoSomething)
.OnCanExecuteChanged(() => XtraMessageBox.Show("The CanExecute condition has changed"));

VB.NET

Dim fluent = mvvmContext.OfType(Of ViewModelWithSimpleCommandAndCanExecute)()
fluent.BindCommand(commandButton, Function(x) x.DoSomething)
' When the CanExecute condition changes, the message shows up
fluent.WithCommand(Function(x) x.DoSomething)
.OnCanExecuteChanged(Function() XtraMessageBox.Show("The CanExecute condition has changed"))

请注意,触发器为绑定到目标命令的每个 UI 元素执行。 单击任何按钮时,下面的代码示例会显示一个消息框。

C#

mvvmContext1.OfType<BulkEditViewModel>()
.WithCommand(vm => vm.RemoveFields())
.Bind(button1)
.Bind(button2)
.After(() => MessageBox.Show("Test"));

VB.NET

mvvmContext1.OfType(Of BulkEditViewModel)()
.WithCommand(Function(vm) vm.RemoveFields())
.Bind(button1)
.Bind(button2)
.After(Function() MessageBox.Show("Test"))
非 POCO 命令

上面描述的 POCO 类命令允许您使用最直接和无故障的语法,DevExpress MVVM 框架还支持其他命令类型 - 以确保旧项目的轻松迁移。

DevExpress 委托命令对象

委托命令是 System.Windows.Input.ICommand 接口的实现。

运行demo: Simple Commands

C#

DelegateCommand command = new DelegateCommand(() => {
XtraMessageBox.Show("Hello!");
});
commandButton.BindCommand(command);

VB.NET

Dim command As New DelegateCommand(Sub() XtraMessageBox.Show("Hello!"))
commandButton.BindCommand(command)

运行demo:Commands with CanExecute Conditions

C#

Func<bool> canExecute = () => (2 + 2 == 4);
DelegateCommand command = new DelegateCommand(() => {
XtraMessageBox.Show("Hello!");
}, canExecute);
commandButton.BindCommand(command);

VB.NET

Dim canExecute As Func(Of Boolean) = Function() (2 + 2 = 4)
Dim command As New DelegateCommand(Sub() XtraMessageBox.Show("Hello!"), canExecute)
commandButton.BindCommand(command)

运行demo:Commands with Parameters

C#

DelegateCommand<object> command = new DelegateCommand<object>((v) => {
XtraMessageBox.Show(string.Format("The parameter is {0}.", v));
});
object parameter = 5;
commandButton.BindCommand(command, () => parameter);

VB.NET

Dim command As New DelegateCommand(Of Object)(Sub(v) XtraMessageBox.Show(String.Format("The parameter is {0}.", v)))
Dim parameter As Object = 5
commandButton.BindCommand(command, Function() parameter)

运行demo:Commands with Parameterized CanExecute Conditions

C#

Func<int, bool> canExecute = (p) => (2 + 2 == p);
DelegateCommand<int> command = new DelegateCommand<int>((v) => {
XtraMessageBox.Show(string.Format("The parameter is {0}.", v));
}, canExecute);
int parameter = 4;
commandButton.BindCommand(command, () => parameter);

VB.NET

Dim canExecute As Func(Of Integer, Boolean) = Function(p) (2 + 2 = p)
Dim command As New DelegateCommand(Of Integer)(Sub(v) XtraMessageBox.Show(String.Format("The parameter is {0}.", v)), canExecute)
Dim parameter As Integer = 4
commandButton.BindCommand(command, Function() parameter)

自定义命令类

这些是具有至少一个 Execute 方法的任何自定义类型的对象。 如果需要,您可以添加 CanExecute 方法和 CanExecuteChanged 事件。

运行demo:Simple Commands

C#

CommandObject command = new CommandObject();
commandButton.BindCommand(command);

public class CommandObject {
public void Execute(object parameter) {
XtraMessageBox.Show("Hello!");
}
}

VB.NET

Private command As New CommandObject()
commandButton.BindCommand(command)

Public Class CommandObject
Public Sub Execute(ByVal parameter As Object)
XtraMessageBox.Show("Hello!")
End Sub
End Class

运行demo:Commands with Parameters

C#

CommandObjectWithParameter command = new CommandObjectWithParameter();
int parameter = 4;
commandButton.BindCommand(command, () => parameter);

public class CommandObjectWithParameter {
public void Execute(object parameter) {
XtraMessageBox.Show(string.Format(
"The parameter is {0}.", parameter));
}
public bool CanExecute(object parameter) {
return object.Equals(2 + 2, parameter);
}
}

VB.NET

Dim command As New CommandObjectWithParameter()
Dim parameter As Integer = 4
commandButton.BindCommand(command, Sub() parameter)

Public Class CommandObjectWithParameter
Public Sub Execute(ByVal parameter As Object)
XtraMessageBox.Show(String.Format("The parameter is {0}.", parameter))
End Sub
Public Function CanExecute(ByVal parameter As Object) As Boolean
Return Object.Equals(2 + 2, parameter)
End Function
End Class

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