C# 如何替换Activity use viewmodel中的片段

我对Android使用Xamarin C#和MVVM Cross有问题。 程序创建主活动，但在使用ShowViewModel（TripsViewModel）时给出异常。在trips.xml中，我使用Mvx.MvxListView，因为这是一个动态列表视图。我不知道我有什么不好：（我看了好几页/教程，仍然有问题。也许我没有写什么东西

错误很少。如果我修复了一个，它将显示下一个：/

TripsViewModel.cs

public class TripsViewModel : MvxViewModel
{
    private readonly IUserRepository _userRepository;
    private readonly ITripsRepository _tripsRepostitory;

    public TripsViewModel()
    {

    }

    private MvxObservableCollection<Trip> _searchTripsList;
    public MvxObservableCollection<Trip> SearchTripsList
    {
        get { return _searchTripsList; }
        set
        {
            _searchTripsList = value;
            RaisePropertyChanged(() => SearchTripsList);
        }
    }

    private Trip _selectedTrip;
    public Trip SelectedTrip
    {
        get { return _selectedTrip; }
        set
        {
            _selectedTrip = value;
            RaisePropertyChanged(() => SelectedTrip);
        }
    }

    public TripsViewModel(IUserRepository userRepository)
    {
        _userRepository = userRepository;
    }

    #endregion

    #region VM LifeCycle
    public void Init()
    {

    }

    public override void Start()
    {
        base.Start();
    }

    public void ReloadState(SavedState savedState)
    {

    }

    public SavedState SaveState()
    {
        return new SavedState() { };
    }

    public class SavedState{
        //add save state class
    }
    #endregion

}

public class MainViewModel : MvxViewModel
{
    private readonly Lazy<TripsViewModel> _tripsViewModel;
    public TripsViewModel TripsViewModel => _tripsViewModel.Value;

    public MainViewModel()
    {
        _tripsViewModel = new Lazy<TripsViewModel>(Mvx.IocConstruct<TripsViewModel>);
    }


    public void ShowMenu()
    {
        ShowViewModel<MenuViewModel>();
    }

    public void ShowTripsList()
    {
        ShowViewModel<TripsViewModel>();
    }

}

[MvxFragmentPresentationAttribute(typeof(MainViewModel), Resource.Id.content_frame, true)]
[Register("GTMS.MobileNative.Droid.Views.TripsListFragment")]
public class TripsListFragment : MvxFragment<TripsViewModel>
{

    public TripsListFragment()
    {

    }

    public override View OnCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
    {
        base.OnCreateView(inflater, container, savedInstanceState);
        return this.BindingInflate(Resource.Layout.trips, container);
    }
}

[Activity(Label = "MainActivity", MainLauncher = true)]
public class MainActivity : MvxAppCompatActivity<MainViewModel>
{
    private BottomNavigationView bottomNavigation;
    private DrawerLayout _drawerLayout;
    internal DrawerLayout DrawerLayout { get { return _drawerLayout; } }

    private FragmentManager _fragmentManager;
    static MainActivity instance = new MainActivity();
    public static MainActivity CurrentActivity => instance;

    public new MainViewModel ViewModel
    {
        get { return (MainViewModel)base.ViewModel; }
        set { base.ViewModel = value; }
    }

    protected override void OnCreate(Bundle savedInstanceState)
    {
        base.OnCreate(savedInstanceState);
        SetContentView(Resource.Layout.main);
        _fragmentManager = FragmentManager;

        bottomNavigation = FindViewById<BottomNavigationView>(Resource.Id.bottom_navigation);
        bottomNavigation.NavigationItemSelected += NavigationItemSelected;


        /*zmiana pomiedzy fragmentami*/
        ViewModel.ShowTripsList();
        //ViewModel.NavigateToFragment(0);
        // Create your application here
    }

    private void NavigationItemSelected(object sender, BottomNavigationView.NavigationItemSelectedEventArgs e)
    {
        Android.Support.V4.App.Fragment fragment = null;
        switch (e.Item.ItemId)
        {
            case Resource.Id.menu_home:
                ViewModel.ShowTripsList();
                break;
            case Resource.Id.menu_audio:
                //fragment = Fragment2.NewInstance();
                break;
            case Resource.Id.menu_video:
               // fragment = Fragment3.NewInstance();
                break;
        }

        if (fragment == null)
            return;


    }

公共类TripsViewModel:MvxViewModel
{
专用只读IUserRepository\u userRepository；
专用只读ITripsRepository\u TripsReplicatory；
公共TripsViewModel（）
{
}
私有MvxObservableCollection\u searchTripsList；
公共MvxObservableCollection SearchTripList
{
获取{return\u searchTripsList；}
设置
{
_searchTripsList=值；
RaisePropertyChanged（（）=>SearchTripList）；
}
}
私人旅行_选择Trip；
公共交通选择Trip
{
获取{return\u selectedTrip；}
设置
{
_selectedTrip=值；
RaisePropertyChanged（（）=>SelectedTrip）；
}
}
公共TripsViewModel（IUserRepository userRepository）
{
_userRepository=userRepository；
}
#端区
#区域虚拟机生命周期
公共void Init（）
{
}
公共覆盖无效开始（）
{
base.Start（）；
}
公共void重载状态（SavedState SavedState）
{
}
公共SavedState SaveState（）
{
返回新的SavedState（）{}；
}
公共类存储状态{
//添加保存状态类
}
#端区
}

MainViewModel.cs

public class TripsViewModel : MvxViewModel
{
    private readonly IUserRepository _userRepository;
    private readonly ITripsRepository _tripsRepostitory;

    public TripsViewModel()
    {

    }

    private MvxObservableCollection<Trip> _searchTripsList;
    public MvxObservableCollection<Trip> SearchTripsList
    {
        get { return _searchTripsList; }
        set
        {
            _searchTripsList = value;
            RaisePropertyChanged(() => SearchTripsList);
        }
    }

    private Trip _selectedTrip;
    public Trip SelectedTrip
    {
        get { return _selectedTrip; }
        set
        {
            _selectedTrip = value;
            RaisePropertyChanged(() => SelectedTrip);
        }
    }

    public TripsViewModel(IUserRepository userRepository)
    {
        _userRepository = userRepository;
    }

    #endregion

    #region VM LifeCycle
    public void Init()
    {

    }

    public override void Start()
    {
        base.Start();
    }

    public void ReloadState(SavedState savedState)
    {

    }

    public SavedState SaveState()
    {
        return new SavedState() { };
    }

    public class SavedState{
        //add save state class
    }
    #endregion

}

public class MainViewModel : MvxViewModel
{
    private readonly Lazy<TripsViewModel> _tripsViewModel;
    public TripsViewModel TripsViewModel => _tripsViewModel.Value;

    public MainViewModel()
    {
        _tripsViewModel = new Lazy<TripsViewModel>(Mvx.IocConstruct<TripsViewModel>);
    }


    public void ShowMenu()
    {
        ShowViewModel<MenuViewModel>();
    }

    public void ShowTripsList()
    {
        ShowViewModel<TripsViewModel>();
    }

}

[MvxFragmentPresentationAttribute(typeof(MainViewModel), Resource.Id.content_frame, true)]
[Register("GTMS.MobileNative.Droid.Views.TripsListFragment")]
public class TripsListFragment : MvxFragment<TripsViewModel>
{

    public TripsListFragment()
    {

    }

    public override View OnCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
    {
        base.OnCreateView(inflater, container, savedInstanceState);
        return this.BindingInflate(Resource.Layout.trips, container);
    }
}

[Activity(Label = "MainActivity", MainLauncher = true)]
public class MainActivity : MvxAppCompatActivity<MainViewModel>
{
    private BottomNavigationView bottomNavigation;
    private DrawerLayout _drawerLayout;
    internal DrawerLayout DrawerLayout { get { return _drawerLayout; } }

    private FragmentManager _fragmentManager;
    static MainActivity instance = new MainActivity();
    public static MainActivity CurrentActivity => instance;

    public new MainViewModel ViewModel
    {
        get { return (MainViewModel)base.ViewModel; }
        set { base.ViewModel = value; }
    }

    protected override void OnCreate(Bundle savedInstanceState)
    {
        base.OnCreate(savedInstanceState);
        SetContentView(Resource.Layout.main);
        _fragmentManager = FragmentManager;

        bottomNavigation = FindViewById<BottomNavigationView>(Resource.Id.bottom_navigation);
        bottomNavigation.NavigationItemSelected += NavigationItemSelected;


        /*zmiana pomiedzy fragmentami*/
        ViewModel.ShowTripsList();
        //ViewModel.NavigateToFragment(0);
        // Create your application here
    }

    private void NavigationItemSelected(object sender, BottomNavigationView.NavigationItemSelectedEventArgs e)
    {
        Android.Support.V4.App.Fragment fragment = null;
        switch (e.Item.ItemId)
        {
            case Resource.Id.menu_home:
                ViewModel.ShowTripsList();
                break;
            case Resource.Id.menu_audio:
                //fragment = Fragment2.NewInstance();
                break;
            case Resource.Id.menu_video:
               // fragment = Fragment3.NewInstance();
                break;
        }

        if (fragment == null)
            return;


    }

public类主视图模型：MvxViewModel
{
私有只读Lazy_tripsViewModel；
public TripsViewModel TripsViewModel=>\u TripsViewModel.Value；
公共主视图模型（）
{
_tripsViewModel=新的惰性（Mvx.IocConstruct）；
}
公共void ShowMenu（）
{
ShowViewModel（）；
}
公开作废ShowTripsList（）
{
ShowViewModel（）；
}
}

TripListFragment.cs

public class TripsViewModel : MvxViewModel
{
    private readonly IUserRepository _userRepository;
    private readonly ITripsRepository _tripsRepostitory;

    public TripsViewModel()
    {

    }

    private MvxObservableCollection<Trip> _searchTripsList;
    public MvxObservableCollection<Trip> SearchTripsList
    {
        get { return _searchTripsList; }
        set
        {
            _searchTripsList = value;
            RaisePropertyChanged(() => SearchTripsList);
        }
    }

    private Trip _selectedTrip;
    public Trip SelectedTrip
    {
        get { return _selectedTrip; }
        set
        {
            _selectedTrip = value;
            RaisePropertyChanged(() => SelectedTrip);
        }
    }

    public TripsViewModel(IUserRepository userRepository)
    {
        _userRepository = userRepository;
    }

    #endregion

    #region VM LifeCycle
    public void Init()
    {

    }

    public override void Start()
    {
        base.Start();
    }

    public void ReloadState(SavedState savedState)
    {

    }

    public SavedState SaveState()
    {
        return new SavedState() { };
    }

    public class SavedState{
        //add save state class
    }
    #endregion

}

public class MainViewModel : MvxViewModel
{
    private readonly Lazy<TripsViewModel> _tripsViewModel;
    public TripsViewModel TripsViewModel => _tripsViewModel.Value;

    public MainViewModel()
    {
        _tripsViewModel = new Lazy<TripsViewModel>(Mvx.IocConstruct<TripsViewModel>);
    }


    public void ShowMenu()
    {
        ShowViewModel<MenuViewModel>();
    }

    public void ShowTripsList()
    {
        ShowViewModel<TripsViewModel>();
    }

}

[MvxFragmentPresentationAttribute(typeof(MainViewModel), Resource.Id.content_frame, true)]
[Register("GTMS.MobileNative.Droid.Views.TripsListFragment")]
public class TripsListFragment : MvxFragment<TripsViewModel>
{

    public TripsListFragment()
    {

    }

    public override View OnCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
    {
        base.OnCreateView(inflater, container, savedInstanceState);
        return this.BindingInflate(Resource.Layout.trips, container);
    }
}

[Activity(Label = "MainActivity", MainLauncher = true)]
public class MainActivity : MvxAppCompatActivity<MainViewModel>
{
    private BottomNavigationView bottomNavigation;
    private DrawerLayout _drawerLayout;
    internal DrawerLayout DrawerLayout { get { return _drawerLayout; } }

    private FragmentManager _fragmentManager;
    static MainActivity instance = new MainActivity();
    public static MainActivity CurrentActivity => instance;

    public new MainViewModel ViewModel
    {
        get { return (MainViewModel)base.ViewModel; }
        set { base.ViewModel = value; }
    }

    protected override void OnCreate(Bundle savedInstanceState)
    {
        base.OnCreate(savedInstanceState);
        SetContentView(Resource.Layout.main);
        _fragmentManager = FragmentManager;

        bottomNavigation = FindViewById<BottomNavigationView>(Resource.Id.bottom_navigation);
        bottomNavigation.NavigationItemSelected += NavigationItemSelected;


        /*zmiana pomiedzy fragmentami*/
        ViewModel.ShowTripsList();
        //ViewModel.NavigateToFragment(0);
        // Create your application here
    }

    private void NavigationItemSelected(object sender, BottomNavigationView.NavigationItemSelectedEventArgs e)
    {
        Android.Support.V4.App.Fragment fragment = null;
        switch (e.Item.ItemId)
        {
            case Resource.Id.menu_home:
                ViewModel.ShowTripsList();
                break;
            case Resource.Id.menu_audio:
                //fragment = Fragment2.NewInstance();
                break;
            case Resource.Id.menu_video:
               // fragment = Fragment3.NewInstance();
                break;
        }

        if (fragment == null)
            return;


    }

[MvxFragmentPresentationAttribute（typeof（MainViewModel），Resource.Id.content\u frame，true）]
[注册表（“GTMS.mobilenactive.Droid.Views.TripsListFragment”）]
公共类TripsListFragment:MvxFragment
{
公共TripsListFragment（）
{
}
创建视图上的公共覆盖视图（布局、充气机、视图组容器、捆绑包保存状态）
{
base.OnCreateView（充气机、容器、保存状态）；
返回此.BindingInflate（Resource.Layout.trips，container）；
}
}

MainActivity.cs

public class TripsViewModel : MvxViewModel
{
    private readonly IUserRepository _userRepository;
    private readonly ITripsRepository _tripsRepostitory;

    public TripsViewModel()
    {

    }

    private MvxObservableCollection<Trip> _searchTripsList;
    public MvxObservableCollection<Trip> SearchTripsList
    {
        get { return _searchTripsList; }
        set
        {
            _searchTripsList = value;
            RaisePropertyChanged(() => SearchTripsList);
        }
    }

    private Trip _selectedTrip;
    public Trip SelectedTrip
    {
        get { return _selectedTrip; }
        set
        {
            _selectedTrip = value;
            RaisePropertyChanged(() => SelectedTrip);
        }
    }

    public TripsViewModel(IUserRepository userRepository)
    {
        _userRepository = userRepository;
    }

    #endregion

    #region VM LifeCycle
    public void Init()
    {

    }

    public override void Start()
    {
        base.Start();
    }

    public void ReloadState(SavedState savedState)
    {

    }

    public SavedState SaveState()
    {
        return new SavedState() { };
    }

    public class SavedState{
        //add save state class
    }
    #endregion

}

public class MainViewModel : MvxViewModel
{
    private readonly Lazy<TripsViewModel> _tripsViewModel;
    public TripsViewModel TripsViewModel => _tripsViewModel.Value;

    public MainViewModel()
    {
        _tripsViewModel = new Lazy<TripsViewModel>(Mvx.IocConstruct<TripsViewModel>);
    }


    public void ShowMenu()
    {
        ShowViewModel<MenuViewModel>();
    }

    public void ShowTripsList()
    {
        ShowViewModel<TripsViewModel>();
    }

}

[MvxFragmentPresentationAttribute(typeof(MainViewModel), Resource.Id.content_frame, true)]
[Register("GTMS.MobileNative.Droid.Views.TripsListFragment")]
public class TripsListFragment : MvxFragment<TripsViewModel>
{

    public TripsListFragment()
    {

    }

    public override View OnCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
    {
        base.OnCreateView(inflater, container, savedInstanceState);
        return this.BindingInflate(Resource.Layout.trips, container);
    }
}

[Activity(Label = "MainActivity", MainLauncher = true)]
public class MainActivity : MvxAppCompatActivity<MainViewModel>
{
    private BottomNavigationView bottomNavigation;
    private DrawerLayout _drawerLayout;
    internal DrawerLayout DrawerLayout { get { return _drawerLayout; } }

    private FragmentManager _fragmentManager;
    static MainActivity instance = new MainActivity();
    public static MainActivity CurrentActivity => instance;

    public new MainViewModel ViewModel
    {
        get { return (MainViewModel)base.ViewModel; }
        set { base.ViewModel = value; }
    }

    protected override void OnCreate(Bundle savedInstanceState)
    {
        base.OnCreate(savedInstanceState);
        SetContentView(Resource.Layout.main);
        _fragmentManager = FragmentManager;

        bottomNavigation = FindViewById<BottomNavigationView>(Resource.Id.bottom_navigation);
        bottomNavigation.NavigationItemSelected += NavigationItemSelected;


        /*zmiana pomiedzy fragmentami*/
        ViewModel.ShowTripsList();
        //ViewModel.NavigateToFragment(0);
        // Create your application here
    }

    private void NavigationItemSelected(object sender, BottomNavigationView.NavigationItemSelectedEventArgs e)
    {
        Android.Support.V4.App.Fragment fragment = null;
        switch (e.Item.ItemId)
        {
            case Resource.Id.menu_home:
                ViewModel.ShowTripsList();
                break;
            case Resource.Id.menu_audio:
                //fragment = Fragment2.NewInstance();
                break;
            case Resource.Id.menu_video:
               // fragment = Fragment3.NewInstance();
                break;
        }

        if (fragment == null)
            return;


    }

[活动（Label=“MainActivity”，MainLauncher=true）]
公共类MainActivity:MvxAppCompatActivity
{
私有底部导航查看底部导航；
私人抽屉布局_抽屉布局；
内部抽屉布局抽屉布局{get{return}
私人碎片管理器\u碎片管理器；
静态MainActivity实例=新的MainActivity（）；
公共静态MainActivity CurrentActivity=>instance；
公共新主视图模型视图模型
{
获取{return（MainViewModel）base.ViewModel；}
设置{base.ViewModel=value；}
}
创建时受保护的覆盖无效（Bundle savedInstanceState）
{
base.OnCreate（savedInstanceState）；
SetContentView（Resource.Layout.main）；
_fragmentManager=fragmentManager；
bottomNavigation=findviewbyd（Resource.Id.bottom\u navigation）；
bottomNavigation.NavigationItemSelected+=NavigationItemSelected；
/*波米耶兹碎片*/
ViewModel.ShowTripsList（）；
//ViewModel.NavigateToFragment（0）；
//在此处创建应用程序
}
private void NavigationItemSelected（对象发送方，底部导航视图。导航项SelectedEventArgs e）
{
Android.Support.V4.App.Fragment Fragment=null；
开关（例如Item.ItemId）
{
案例资源.Id.menu\u主页：
ViewModel.ShowTripsList（）；
打破
案例资源.Id.menu\u音频：
//fragment=Fragment2.NewInstance（）；
打破
案例资源.Id.menu\u视频：
//fragment=Fragment3.NewInstance（）；
打破
}
if（片段==null）
返回；
}