View Model to view model comunication

Question

Hello

I am making a note-taking application I already have all my notes, and notebook listed, But now I am facing this problem.

I am using the MVVM pattern, and to communicate with the other VM, I am using the messaging center, so I have zero code-behind.

Look at this VM

   public NotesVM() {

            CreateNewNoteCommand = new Command(async () => {
                var note = await CreateNote(RecivedNotebook);
                await GetNotes(RecivedNotebook);
            });

            SelectedNoteCommand = new Command(async () => {
                await Application.Current.MainPage.Navigation.PushAsync(new EditorPage());
                MessagingCenter.Send(this, "note", SelectedNote);
            });

I want to navigate to the EditorPage, when the user creates a new note or when the user selects a note, the big problem is that in both scenarios I need information from the note such as the ID

I tried to subscribe to both scenarios in my EditoVM, which works, but is very messy, and have to duplicate my subscribing for both scenarios, and when debugging I get duplicates messages.

Everybody tells me to use an MVVM framework but if xamarin is MVVM out of the box, I don't see the point

Answer 1

Hello,
Welcome to our Microsoft Q&A platform!

I noticed that you display a dialog to create a new note and give it a title. If you want to navigate to the EditorPage when you create or select a note, you can pass value(ID,model) like following code:

UpDate

NotesVM

 CreateNewNoteCommand = new Command(async () => {  

                //you can use action to pass Id             
                EditorPage editorPage = new EditorPage();  
                await Application.Current.MainPage.Navigation.PushAsync(editorPage);  
                EditorVM Editor = (EditorVM)editorPage.BindingContext;  
                Editor.reciviceBookIdAction(RecivedNotebook.Id);  
                /*  
                //you can also use MessagingCenter to pass Id  
                await Application.Current.MainPage.Navigation.PushAsync(new EditorPage());  
                MessagingCenter.Send(this, "RecivedNotebookId", RecivedNotebook.Id);  
                */  
            });  
            SelectedNoteCommand = new Command(async () => {  
                //you can use action to pass SelectedNote  
                EditorPage editorPage = new EditorPage();  
                await Application.Current.MainPage.Navigation.PushAsync(editorPage);  
                EditorVM Editor = (EditorVM)editorPage.BindingContext;  
                Editor.RecivedNoteAction(SelectedNote);  
                /*  
                //you can also use MessagingCenter to pass SelectedNote  
                await Application.Current.MainPage.Navigation.PushAsync(new EditorPage());  
                MessagingCenter.Send(this, "SelectedNote", SelectedNote);  
                */  
            });  

EditorPage(none)

    /*  
public EditorPage(String NotebookId)  
    {  
    InitializeComponent();  
    EditorVM Editor = (EditorVM)BindingContext;  
    Editor.CreateNote(NotebookId);  
    Console.WriteLine("{0}", NotebookId);  
    }  
    public EditorPage(Model.Note note)  
    {  
    InitializeComponent();  
    EditorVM Editor = (EditorVM)BindingContext;  
    Editor.RecivedNote = note;  
    Console.WriteLine("{0}", note.Id);  
    }  
*/  

EditorVM

        public Action<string> reciviceBookIdAction; //use action  
        public Action<Note> RecivedNoteAction;   
        public EditorVM() {  

            SaveContent = new Command(() => { UpdateNote(); });  

            //use action(reciviceBookId)  

            reciviceBookIdAction = (reciviceBookId) =>  
            {  
                Console.WriteLine("reciviceBookId-----{0}", reciviceBookId);  
                //CreateNote(reciviceBookId);  
            };  

            /*  
            //use MessagingCenter(reciviceBookId)  
            MessagingCenter.Subscribe<NotesVM, string>(this, "RecivedNotebookId", (obj, item) => {  
                Console.WriteLine("reciviceBookId-----{0}", item);  
            });  
            */  

            //use action(note)  
            RecivedNoteAction = (note) =>  
            {  
                RecivedNote = note;  
                Title = RecivedNote.Title;  
                Console.WriteLine("RecivedNote.id-----{0}", RecivedNote.Id);  
            };  
            /*  
            //use MessagingCenter(note)  
            MessagingCenter.Subscribe<NotesVM, Note>(this, "SelectedNote", (obj, item) => {  
                RecivedNote = item;  
                Title = RecivedNote.Title;  
                Console.WriteLine("RecivedNote.id-----{0}", item.Id);  
            });  
            */  
        }  

Best Regards,
Wenyan Zhang

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