c# - ReactiveUI命令退订

Question

我有2个 View 和2个ViewModel:

第一 View :

public partial class FirstView : Page
{
    FirstViewModel ViewModel;
    public FirstView()
    {
        ViewModel = new FirstViewModel();
        ViewModel.ShowSecondView.Subscribe(_ =>
        {              
            NavigationService.Navigate(new SecondView(ViewModel.ChildViewModel));
        });            

        this.DataContext = ViewModel;
        InitializeComponent();            
    }        
}

第一个ViewModel:

public class FirstViewModel
{
    SecondViewModel ChildViewModel;
    public ReactiveCommand<Unit, Unit> ShowSecondView { get; set; }
    public FirstViewModel()
    {
        ChildViewModel = new SecondViewModel();
        ShowSecondView = ReactiveCommand.Create(() => 
        {
             ChildViewModel.Reconfigure(...);  
        });          
    }        
}

第二种观点:

public partial class SecondView : Page
{
    SecondViewModel ViewModel;
    public SecondView(SecondViewModel viewModel)
    {
        ViewModel = viewModel;
        ViewModel.GoBack.Subscribe(_ => 
        {
            DoSomethingHard();
            if(NavigationService != null)  NavigationService.GoBack();
        });
        this.DataContext = ViewModel;
        InitializeComponent();            
    }        
}

第二个ViewModel:

public class SecondViewModel
{
    public ReactiveCommand<Unit, Unit> GoBack { get; set; }
    public FirstViewModel()
    {
        VeryLongInitialization();
        GoBack = ReactiveCommand.Create(() => { });          
    }        
    public void Reconfigure(...)
    { ... }
}

因此，当我多次运行FirstViewModel.ShowSecondView和多次运行SecondViewModel.GoBack时，DoSomethingHard()在每个创建的SecondView上也执行了多次。

为什么我要一次在ChildViewModel中创建FilstViewModel？因为创建SecondViewModel需要很长时间。而且我不会每次都重新创建SecondViewModel，而只是重新配置它。

我的问题是如何取消订阅ViewModel.GoBack.Subscribe中的SecondView？

附言也许我不应该在SecondView中重新创建FirstView，而要像SecondViewModel一样重新配置它？

更新1 (感谢Julien Mialon)

我添加IDisposable goBackSubscr，它可以工作!我执行它正确吗？

public partial class SecondView : Page
{
    SecondViewModel ViewModel;
    IDisposable goBackSubscr;
    public SecondView(SecondViewModel viewModel)
    {
        ViewModel = viewModel;
        goBackSubscr = ViewModel.GoBack.Subscribe(_ => 
        {
            DoSomethingHard();
            if(NavigationService != null)  NavigationService.GoBack();
            goBackSubscr.Dispose();
        });
        this.DataContext = ViewModel;
        InitializeComponent();            
    }        
}

Answer 1

在您的 View 上使用WhenAcitvated:
在页面的构造函数中(必须为IViewFor):

 this.WhenActivated(
     disposables =>
     {
         ViewModel.Command.Subscribe(...).(disposables);
     });