Topics

C#•11mo ago

✅ Need help understanding parent and child views

So basically, spent the past four hours learning thoroughly about the MVVM design pattern because there was a problem with my application. Although i did get some insight into it, i was not able to overcome the hurdle i have. Hence i'd like someone to help me through my situation. I saw a lot scenarios gluing views and models using view models. But did not particulary come across the problem i had. So basically, i have a main view and a child view. The child view does not inherit from the main view nor does it get any data from the main view model. The parameters in both views although are triggered by a button on the main view. I was able to contain the variables that each view needed to their respective viewmodels. I have a problem with linking the both dataupdate method calls to the button click event. But before that problem, I have problems properly displaying the data made in the child view model on the application. I'm sure it has to do with the way i'm binding the view to the main view but i am not experienced enough to determine the fault in that. Please i require some assistance :pepecry:

34 Replies

KingdawanageOP•11mo ago

https://paste.mod.gg/bxhhutrtlepf/1

BlazeBin - bxhhutrtlepf

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KingdawanageOP•11mo ago

It has both the mainviewmodel and the homeview model the home view model is the nested view Just to add, the home view is bound to a content control by binding the content to currentview as shown here

public MainViewModel()
{
    HomeVM = new HomeViewModel();
    CurrentView = HomeVM;
}

public MainViewModel()
{
    HomeVM = new HomeViewModel();
    CurrentView = HomeVM;
}

nohopestage•11mo ago

The task doesn't run because it's not awaited. Use AsyncRelayCommand instead

AsyncRelayCommand - Community Toolkits for .NET

An asynchronous command whose sole purpose is to relay its functionality to other objects by invoking delegates

KingdawanageOP•11mo ago

Whaat task are you refering to I'm pretty sure all the variables for the binding are being populated at runtime and after the button push event

nohopestage•11mo ago

Both You just assign the async task to a discarded task variable, so basically your command does nothing

KingdawanageOP•11mo ago

public void SearchButtonPressed(HomeViewModel homeVM)
{
    //Task _ = UpdateCurrentData();
    Task _ = homeVM.UpdateWeeklyData(this);
}

public void SearchButtonPressed(HomeViewModel homeVM)
{
    //Task _ = UpdateCurrentData();
    Task _ = homeVM.UpdateWeeklyData(this);
}

you mean this? i get errors doing this. I was just trying stuff out

nohopestage•11mo ago

Yes

KingdawanageOP•11mo ago

but the commented line actually displays the contents to my application

KingdawanageOP•11mo ago

Like this, the info on the right side shows up

No description

KingdawanageOP•11mo ago

I dont know how to trigger the other method from the home view model

nohopestage•11mo ago

Just use the command type I shared above Is it a synchronous task?

KingdawanageOP•11mo ago

Yah Wait, can i bind more than one command to the button?

nohopestage•11mo ago

Guess that's why it works, but then it's no different than a regular void-returning method

KingdawanageOP•11mo ago

Wait non, its async

nohopestage•11mo ago

No, I don't think so Hmm, then I probably don't know enough about how tasks work

KingdawanageOP•11mo ago

If i could bind more than one command to a button it might be a bit easir to solve this problem

nohopestage•11mo ago

Either way, if you need async commands, use the appropriate type (AsyncRelayCommand)

KingdawanageOP•11mo ago

The command itself is not async. It just calls an async method But if you have any idea on how to call the second method from the homeview model, i'd like to hear it

nohopestage•11mo ago

I mean if you need a command to run async code, use AsyncRelayCommand

KingdawanageOP•11mo ago

I guess if that's the properway i'll change mine

nohopestage•11mo ago

You mean the UpdateWeeklyData one?

KingdawanageOP•11mo ago

Yah

nohopestage•11mo ago

What errors are you having with it?

KingdawanageOP•11mo ago

it was a null reference exception The homeVM reference passed in was empty here did i have to make a new instance of homeVM in the HomeViewModel before passing it as a reference here

nohopestage•11mo ago

It's supposed to be a parameter you assign in xaml. The property is CommandParameter

KingdawanageOP•11mo ago

First I've heard of, can you elaborate

nohopestage•11mo ago

Buttons have a Command property that you already seem to be using, and a CommandParameter that you can use to pass some data every time the bound command is executed So because you didn't set CommandParameter in xaml, you get a NullReferenceException

KingdawanageOP•11mo ago

Currently looking into it @nohopestage IT ACTUALLY WORKED LETS FUCKING GOOOO"

KingdawanageOP•11mo ago

No description

nohopestage•11mo ago

Glad to hear! What did you do to fix it?

KingdawanageOP•11mo ago

basically made new async relay command and passed into it a method that contained my dataupdate methods That's all i needed to do basically this

        public MainViewModel()
        {
            HomeVM = new HomeViewModel();
            CurrentView = HomeVM;
            UpdateCommand = new AsyncRelayCommand(SearchButtonPressed);
        }

        public MainViewModel()
        {
            HomeVM = new HomeViewModel();
            CurrentView = HomeVM;
            UpdateCommand = new AsyncRelayCommand(SearchButtonPressed);
        }

        [RelayCommand]
        public async Task SearchButtonPressed()
        {
            
            await UpdateCurrentData();
            await HomeVM.UpdateWeeklyData(SearchBoxText);
        }

        [RelayCommand]
        public async Task SearchButtonPressed()
        {
            
            await UpdateCurrentData();
            await HomeVM.UpdateWeeklyData(SearchBoxText);
        }

nohopestage•11mo ago

You can also remove the attribute now

KingdawanageOP•11mo ago

Oh ya, lol Thanks man Been having this problem for a while now and because of you i have a better understanding of mvvm

nohopestage•11mo ago

Glad I could help!

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