Passing Parameter From Main to Detail in MVVMCross

Question

I am trying to pass the selected item from the list to the detail view, but myitem is null in the DetailViewmodel even though it is not in the MyViewModel.

MyViewModel.cs

    public virtual ICommand ItemSelected
    {
        get
        {
            return new MvxCommand<MyViewModel>(item =>{SelectedItem = item;});
        }
     }

    public MyViewModel SelectedItem
    {
        get { return _selectedItem; }
        set
        {
            _selectedItem = value;
            // myItem is NOT null here!!!
            ShowViewModel<MyDetailViewModel>(new { date = Date, myItem = _selectedItem });
            RaisePropertyChanged(() => SelectedItem);
        }
    }

MyDetailViewModel.cs

public class  MyDetailViewModel: MvxViewModel
{
    private MyViewModel _myItem;

    public void Init(DateTime date, MyViewModel myItem = null)
    {
        // myItem is NULL here!!!
        _myItem = myItem;
    }
}

score 4 · Accepted Answer · edited May 23 '17 at 12:07

4

You can use a parameter object, because you can only pass one parameter. I usually crate a nested class Parameter for this.

public class  MyDetailViewModel: MvxViewModel
{
    private MyViewModel _myItem;

    public class Parameter
    {
        public DateTime Date {get; set; }
        public string Name {get; set;}
    }

    public void Init(Parameter param)
    {
        Name = param.Name;
    }
}

and show the viewmodel like:

ShowViewModel<MyDetailViewModel>(new MyDetailViewModel.Parameter { Date = Date, Name = _selectedItem.Name });

But be aware!

The paramters cannot be complex due certain platform issues. You might have to pass only the Id of your Item within the Parameter object and then load MyItem in your Init function. Or you pass only a string and use serialization: https://stackoverflow.com/a/19059938/1489968

edited May 23 '17 at 12:07

Community

1
1

answered Apr 19 '16 at 21:43

Sven-Michael Stübe

14,560
4
52
103

But I have another place where I do not have second parameter to pass. How should I handle that? – casillas Apr 19 '16 at 21:49
just don't set it in the parameter class when you call `ShowViewModel`. In your `Init` function you can then write `if(param.Item != null)` for example. – Sven-Michael Stübe Apr 19 '16 at 21:50
I am still getting null! `param.Item` is null. Date is not null, but Item is null. – casillas Apr 19 '16 at 22:02
see the 'Be aware' part :) So it depends on your Item class how the real solution would look like. – Sven-Michael Stübe Apr 19 '16 at 22:03
`MyItem` is just a small object contains Age, Gender, etc. – casillas Apr 19 '16 at 22:08
So you could copy every property of `myItem` into `Parameter` or add date to `Item` and pass item directly without wrapping it into Parameter. – Sven-Michael Stübe Apr 19 '16 at 22:12
You mean rather than sending the object itself, break the object and pass each property? – casillas Apr 19 '16 at 22:13
Let us [continue this discussion in chat](http://chat.stackoverflow.com/rooms/109602/discussion-between-sven-michael-stube-and-hotspring). – Sven-Michael Stübe Apr 19 '16 at 22:14

score 1 · Answer 2 · edited Jun 20 '20 at 09:12

myItem is null because if you pass typed parameter to Init it should be the only parameter you pass. According to MvvmCross ViewModel Creation documentation:

Init() can come in several flavors:.

individual simply-Typed parameters

a single Typed parameter object with simply-Typed properties

as InitFromBundle() with an IMvxBundle parameter - this last flavor is always supported via the IMvxViewModel interface.

Passing Parameter From Main to Detail in MVVMCross

2 Answers2

But be aware!

Linked