使用事件聚合器在用户控件之间导航

Question

我有一个 MainWindow，我通过单击菜单在 UserControls 之间导航，它工作正常。

我正在使用以下模式：

https://rachel53461.wordpress.com/2011/05/08/simplemvvmexample/

在其中一个用户控件中有一个按钮。通过单击此按钮，我想导航到另一个用户控件。

我该怎么做？

主视图

<UserControl.Resources>
    <DataTemplate DataType="{x:Type cvm:FirstViewModel}">
        <cv:FirstView/>
    </DataTemplate>
    <DataTemplate DataType="{x:Type cvm:SecondViewModel}">
        <cv:SecondView/>
    </DataTemplate>
    <cvm:MainViewModel x:Key="main"/>
</UserControl.Resources>

<Grid DataContext="{Binding Source={StaticResource main}}">
    <Border Grid.Row="0">
        <Menu Height="58">
             <ItemsControl ItemsSource="{Binding PageViewModels}" Width="289" Height="58">
                 <ItemsControl.ItemTemplate>
                     <DataTemplate>
                         <TextBlock>
                             <Hyperlink Command="{Binding ChangePageCommand, Mode=OneWay, Source={StaticResource main}}" CommandParameter="{Binding}" TextDecorations="{x:Null}">
                                 <InlineUIContainer>
                                     <TextBlock Text="{Binding Name}"/>
                                 </InlineUIContainer>
                             </Hyperlink>    
                         </TextBlock>
                      </DataTemplate>
                 </ItemsControl.ItemTemplate>
             </ItemsControl>
        </Menu>
    </Border>       
    <Border Grid.Row="1" >
        <ContentControl Content="{Binding CurrentUserControl}"/>
    </Border>
</Grid>

MainViewModel

public class MainViewModel : ViewModelBase
{
        public MainViewModel()
        {
            PageViewModels.Add(new FirstViewModel());
            PageViewModels.Add(new SecondViewModel());

            // Set starting page
            CurrentUserControl = PageViewModels[0];
        }

        #region Fields

        private List<IUserContentViewModel> _pageViewModels;
        public List<IUserContentViewModel> PageViewModels
        {
            get
            {
                if (_pageViewModels == null)
                    _pageViewModels = new List<IUserContentViewModel>();

                return _pageViewModels;
            }
        }

        private IUserContentViewModel _currentUserControl;
        public IUserContentViewModel CurrentUserControl
        {
            get { return _currentUserControl; }
            set
            {
                if (value != _currentUserControl)
                {
                    _currentUserControl = value;
                    OnPropertyChanged("CurrentUserControl");
                }
            }
        }

        #region Methods

        private void ChangeViewModel(IUserContentViewModel viewModel)
        {
            if (!PageViewModels.Contains(viewModel))
                PageViewModels.Add(viewModel);

            CurrentUserControl = PageViewModels
                .FirstOrDefault(vm => vm == viewModel);


        }

        #endregion

        private ICommand _changePageCommand;
        #endregion
        public ICommand ChangePageCommand
        {
            get
            {
                if (_changePageCommand == null)
                {
                    _changePageCommand = new RelayCommand(
                        p => ChangeViewModel((IUserContentViewModel)p),
                        p => p is IUserContentViewModel);
                }

                return _changePageCommand;
            }
        }
    }

第二视图

<Grid Background="Blue">
    <Button /> <!-- Going to ThirdView?????????-->
</Grid>

Answer 1

您必须通过按钮拨打ChangePageCommand：

<Button DataContext="{Binding Source={StaticResource main}}"
        Command="{Binding ChangePageCommand"} 
        CommandParameter="{Binding PageViewModels[2]}">

我假设您的FirstViewModel 存储在PageViewModels[0]，您的SecondViewModel 存储在PageViewModels[1]。

您还必须创建一个指向您的ThirdViewModel 的ThirdView 链接，作为您的其他两个视图/视图模型：

<UserControl.Resources>
    ...
    <DataTemplate DataType="{x:Type cvm:ThirdViewModel}">
        <cv:ThirdView/>
    </DataTemplate>
</UserControl.Resources>

作为建议，您可以在代码开头设置 UserControl DataContext，而不是在任何 UIElement（在您的情况下为按钮和网格）中使用它，如下所示：

<UserControl.DataContext>
    <cvm:MainViewModel />
</UserControl.DataContext>

编辑>>>>

忘了说您还必须将您的 ThirdViewModel 添加到您的 PageViewModels 集合中：

PageViewModels.Add(new ThirdViewModel());

Answer 2

我终于有了解决办法。

我在 Prism 6 中使用事件聚合器。

首先我创建一个单例。

internal sealed class ApplicationService
    {
        private ApplicationService() { }

        private static readonly ApplicationService _instance = new ApplicationService();

        internal static ApplicationService Instance { get { return _instance; } }

        private IEventAggregator _eventAggregator;
        internal IEventAggregator EventAggregator
        {
            get
            {
                if (_eventAggregator == null)
                    _eventAggregator = new EventAggregator();

                return _eventAggregator;
            }
        }
    }

然后public class GoToThird : PubSubEvent<TEvent> { }

在MainViewModel 我订阅了活动并添加了我的ThirdViewModel()。

public class MainViewModel : ViewModelBase
{
        protected readonly IEventAggregator _eventAggregator;

        public MainViewModel(IEventAggregator eventAggregator)
        {
            PageViewModels.Add(new FirstViewModel());
            PageViewModels.Add(new SecondViewModel(ApplicationService.Instance.EventAggregator)));

            PageViewModels.Add(new ThirdViewModel());

            // Set starting page
            CurrentUserControl = PageViewModels[0];

            this._eventAggregator = eventAggregator;
        }

        private void GoToThird()
        {
            CurrentUserControl = PageViewModels[2];
        } 
}

最后我将活动发布到SecondViewModel()

public class SecondViewModel
    {

        protected readonly IEventAggregator _eventAggregator;

        public SecondViewModel(IEventAggregator eventAggregator)
        {
            this._eventAggregator = eventAggregator;

        }



        private void Go()
        {
            _eventAggregator.GetEvent<GoToThird>().Publish();
        }


        private ICommand goToThirdCommand;

        public ICommand GoToThirdCommand
        {
            get
            {
                return goToThirdCommand ?? (goToThirdCommand = new RelayCommand(p => this.Go(), p => this.CanGo()));
            }
        }

        private bool CanGo()
        {
            return true;
        }
}

非常感谢 Rachel 和 Kirenenko