WPF MVVM导航来自同一层次级别的视图

Question

I am trying to make a small program mainly to learn MVVM. Its a small Book Library.

I have 4 views(and 4 viewmodels). MainWindow is the parent view, where i display the other 3 view in a content control.

The other 3 child views are HomeView, BookManagingView, ReaderManagingView.

In HomeView, i display 2 ListViews(one with readers, one with books), and in the other 2 views i edit/add books or readers.

In my HomeView i also have 2 buttons. When i click the buttons i want to switch from the HomeView, to BookManagingView or ReaderManagingView.

If i am trying to switch to any of the Views from the MainWindow, it works.

What i am trying to do is to switch from the HomeView, to BookManagingView or ReaderManagingView. How can i achieve that?

MainWindow:

    <Grid>
    <ContentControl Content="{Binding CurrentView}" Height="340" Width="500" />
    <Button x:Name="btnHomeView" Content="Home" Command="{Binding ChangeViewToHomeView, UpdateSourceTrigger=PropertyChanged}" HorizontalAlignment="Left" Margin="16,70,0,0" VerticalAlignment="Top" Width="75"/>
    <Button x:Name="btnBookManagingView" Content="Reader Options" Command="{Binding ChangeViewToReaderManagView,UpdateSourceTrigger=PropertyChanged}" HorizontalAlignment="Left" Margin="96,70,0,0" VerticalAlignment="Top" Width="92"/>
    <Button x:Name="btnReaderManagingView" Content="Books Options" Command="{Binding ChangeViewToBookManagView,UpdateSourceTrigger=PropertyChanged}" HorizontalAlignment="Left" Margin="193,70,0,0" VerticalAlignment="Top" Width="92"/>
</Grid>

MainWindowVM:

    public class MainWindowViewModel : ViewModelBase
{
    private object currentView;
    private HomeViewModel homeVM;
    private ReaderManagingViewModel readerManagingVM;
    private BookManagingViewModel bookManagingVM;


    public MainWindowViewModel()
    {
        homeVM = new HomeViewModel();
        readerManagingVM = new ReaderManagingViewModel();
        bookManagingVM = new BookManagingViewModel();
        CurrentView = homeVM;

        ChangeViewToHomeView = new DefCommand(DisplayHomeView);
        ChangeViewToReaderManagView = new DefCommand(DisplayReaderManagingView);
        ChangeViewToBookManagView = new DefCommand(DisplayBookManagingView);
    }

    public DefCommand ChangeViewToHomeView { get; private  set; }
    public DefCommand ChangeViewToReaderManagView { get; private set; }
    public DefCommand ChangeViewToBookManagView { get; private set; }


    public object CurrentView
    {
        get { return currentView; }
        set { currentView = value; RaisePropertyChanged(); }
    }

    public void DisplayHomeView()
    {
        CurrentView = homeVM;
    }

    public void DisplayReaderManagingView()
    {
        CurrentView = readerManagingVM;
    }

    public void DisplayBookManagingView()
    {
        CurrentView = bookManagingVM;
    }

HomeView:

<Grid>
    <ListView x:Name="listviewReaders" ItemsSource="{Binding ReadersList}" SelectedItem="{Binding SelectedReader, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" Width="160" Margin="25,23,315,40">

...

    <ListView x:Name="listviewBooks" ItemsSource="{Binding BookList, Mode=OneWay}" SelectedItem="{Binding SelectedBook, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" Width="160" Margin="316,50,24,117">

...

    <Button x:Name="btnEditReader" Command="{Binding EditReaderSwitch, UpdateSourceTrigger=PropertyChanged}" Content="EditR" HorizontalAlignment="Left" Margin="316,305,0,0" VerticalAlignment="Top" Width="74"/>
    <Button x:Name="btnEditBook" Command="{Binding EditBookSwitch, UpdateSourceTrigger=PropertyChanged}" Content="EditB" HorizontalAlignment="Left" Margin="402,305,0,0" VerticalAlignment="Top" Width="74"/>
</Grid>

HomeVM:

 private Reader selectedReader;
    private Book selectedBook;
    private BookListFilter selectedFilter;

    private ObservableCollection<Book> bookList;
    private ObservableCollection<Reader> readerList;
    private IEnumerable<BookListFilter> bookLstItemSrc;

    public HomeViewModel()
    {
        SelectedReader = new Reader();
        SelectedBook = new Book();
        SelectedFilter = BookListFilter.AllBooks;

        BookDBDataContext rdb = new BookDBDataContext();

        ReadersList = new ObservableCollection<Reader>(rdb.Readers);
        GetBookList();

        EditReaderSwitch = new DefCommand(EditReaderInfo);
        EditBookSwitch = new DefCommand(EditBookInfo);
    }

    public DefCommand EditReaderSwitch { get; private set; }
    public DefCommand EditBookSwitch { get; private set; }
 private void EditBookInfo()
    {
        var tmpBook = new BookManagingViewModel(this);
        var tmpMwvm = new MainWindowViewModel();
        tmpMwvm.DisplayBookManagingView();
    }

    private void EditReaderInfo()
    {
        var tmpReader = new ReaderManagingViewModel(this);
        var tmpMwvm = new MainWindowViewModel();
        tmpMwvm.DisplayReaderManagingView();
    }

Book & Reader ManagingViews have a bunch of textboxes and buttons for adding, deleting to/from database.

Book & Reader ManagingVM have methods for adding/deleting to/from database(right now they are empty and i will finish them if i manage to solve this problem first)

I have tried to navigate from HomeView to Book/ReaderManagingView with the EditBook/ReaderSwitch commands and EditBook/ReaderInfo() methods, but it doesnt work.

What am i doing wrong, and what should i do to fix it?

Sorry for the long post.

Answer 1

You need to set the CurrentView property of the existing MainWindowViewModel instance. Right now you are creating a new instance of the class.

You could inject the HomeViewModel with a MainWindowViewModel :

private readonly MainWindowViewModel _x;
public HomeViewModel(MainWindowViewModel x)
{
    _x = x;
    SelectedReader = new Reader();
    ...
}

private void EditBookInfo()
{
    _x.DisplayBookManagingView();
}

MainWindowViewModel:

public MainWindowViewModel()
{
    homeVM = new HomeViewModel(this);
}