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

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 upfluent.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 upfluent.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 = 5commandButton.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 = 4commandButton.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 CommandObjectPublic Sub Execute(ByVal parameter As Object)XtraMessageBox.Show("Hello!")End SubEnd 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 = 4commandButton.BindCommand(command, Sub() parameter)Public Class CommandObjectWithParameterPublic Sub Execute(ByVal parameter As Object)XtraMessageBox.Show(String.Format("The parameter is {0}.", parameter))End SubPublic Function CanExecute(ByVal parameter As Object) As BooleanReturn Object.Equals(2 + 2, parameter)End FunctionEnd Class

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