为什么第二次导航到ViewModel时未调用Init（）方法？

Question

I develop Win 8.1 application using MvvmCross 3.5.1. The user sequentially goes through the some views and returns to the first view from the last view. Everything works perfect during first iteration of the workflow. But when the user starts the workflow again - Init() methods in viewmodels are not called.

For example, interaction between FirstViewModel and SecondViewModel looks like below.

FirstViewModel:

ShowViewModel<SecondViewModel>(
    new
    {
        code = ItemCode,
        descr = ItemDescription
    });

SecondViewModel:

public void Init(string code, string descr)
{
    ...
}

So simple but works only one time :(

What reasons may entail such behavior?

---

As workaround I tried to load viewmodel "manually":

var d = new Dictionary<string, string>
{
    {"code", ItemCode},
    {"descr", ItemDescription}
};

var b = new MvxBundle(d);

var r = new MvxViewModelRequest<SecondViewModel>(b, null, null);

var m = Mvx.Resolve<IMvxViewModelLoader>().LoadViewModel(r, null);

It solved the problem with Init() methods calling. But I don't know how to show the viewmodel using the m variable. Anyone knows?

---

Apologies for my poor english and thanks in advance!

Answer 1

Init() is only being called once, because Windows 8.1 apps cache pages. Hence, the ViewModel for that page is not ever destroyed and hence the Init() method is not called again.

You can make your own BasePage which overrides this behavior by overriding OnNavigatedTo:

protected override void OnNavigatedTo(NavigationEventArgs e)
{
    if (e.NavigationMode == NavigationMode.New)
        ViewModel = null;

    base.OnNavigatedTo(e);
}