c# - MVVM 灯 : Pass object from view to viewmodel

Question

我最近开始使用 MVVM light 来处理 WPF，并且我有以下(简单场景)。

1. MainWindow 包含一个元素列表框。

2. When one is selected and the button is clicked, I fire a command:

   ReservoirViewerCommand.Execute(null);
   

3. 在 viewmodel 类上，我实例化命令并使用所选对象发送消息:

   ReservoirViewerCommand = new RelayCommand(OpenReservoir);
   private void OpenReservoir()
   {
       Messenger.Default.Send(new LaunchShowReservoirMessage(){Reservoir=SelectedReservoir});          
   }
   

   哪里:

   class LaunchShowReservoirMessage:MessageBase
   {
       public Reservoir Reservoir { get; set; }
   }
   

4. 主视图注册消息并打开一个新的子窗口:

   private void RegisterMessages() 
   {
       Messenger.Default.Register<LaunchShowReservoirMessage>(this,OnLaunchShowReservoir);
   }
   
   public void OnLaunchShowReservoir(LaunchShowReservoirMessage msg) {
       var showReservoir = new ReservoirViewerView();
       showReservoir.Show(); 
   }
   

我需要的是新的 ViewModel (ReservoirViewerViewModel) 可以通过消息以某种方式获取传递的对象，以便我可以在子窗口上显示该对象的详细信息。

我进行了一些逐步调试，但似乎永远无法访问 ViewModel 构造函数。

Answer 1

"I did some step-by-step debugging and the ViewModel constructor seems never to be reached."

确保您实际使用以下方法之一将您的 View 绑定(bind)到您的 View 模型:

在代码隐藏

var showReservoir = new ReservoirViewerView();
showReservoir.DataContext = ViewModelLocator.ReservoirViewerViewModel; //static property
//OR showReservoir.DataContext = new ReservoirViewerViewModel();
showReservoir.Show();

在 Xaml View 中

<Window x:Class="Garmin.Cartography.AdminBucketTools.ChildWindowView"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"        
    DataContext="{Binding Path=ReservoirViewerViewModel, Source={StaticResource Locator}}">
    <!--Use the non-static property in your ViewModelLocator-->

    <Grid />
</Window>

在 Xaml 资源

<DataTemplate DataType="{x:Type viewmodels:ReservoirViewerViewModel}">
    <views:ReservoirViewerView/>
</DataTemplate>

"What I need is that the new ViewModel (ReservoirViewerViewModel) can somehow get hold of the passed object through the message so that I can then display the details of this object on the child window."

只需在您的 ReservoirViewerViewModel 类中注册相同的消息:

Messenger.Default.Register<LaunchShowReservoirMessage>(this, (msg) =>
{
    var reservoir = msg.Reservoir;
});

仅供引用，如果您从 GenericMessage<[content type]> 而不是 MessageBase 派生消息类，则可以使用 GenericMessage 类的已定义内容属性。例如:

public class LaunchShowReservoirMessage: GenericMessage<Reservoir>
{
    public LaunchShowReservoirMessage(Reservoir content) : base(content) { }
}

然后:

Messenger.Default.Register<LaunchShowReservoirMessage>(this, (msg) =>
{
    var reservoir = msg.Content;
});