[Bug] RefreshView refreshes multiple times when a page uses a shared binding context

[haavamoa]

Description

Hi, and thank you for the awesome work with RefreshView. This issue is more of a question regarding RefreshView that keeps it's bindings when you have a page that gets navigated to.

Here is a project that has:

• Two pages: MainPage and SecondPage
  • MainPage has a button that navigates to SecondPage
  • SecondPage has a RefreshView with a ScrollView, which means that I can pull to refresh.
• SecondPage get's newed up and navigated to when you click the button in MainPage.
• SecondPage binding context get's set to a global view model, which means that the binding context instance lives even if the page get's navigated out of.
• The binding context has a RefreshCommand and a IsRefreshing.

The first time I navigate to SecondPage and pull to refresh the command gets run. Great.
When I navigate back and forth and do the same thing, the commands gets run twice.
When I navigate back and forth and do the same thing, the commands gets run three times.
This keeps going on.

Is this an intentional behavior?

We are doing this in an production app because we want the MainPage to bind to properties of the binding context of the SecondPage. We also want to pre-load the second pages binding context data when the MainPage loads. So thats why that binding context is shared and not newed up with every page.

I respect it if it is intentional, I just want to hear from the Xamarin.Forms team if it is so. If it is, I can change my architecture to bypass the problem.

Expected Behavior

The RefreshView's command to run once every time.

Actual Behavior

The RefreshView's command to run's x amount of times I've navigated to the page.

Basic Information

• Version with issue: 4.5.0.617
• Last known good version: not sure
• IDE: Visual Studio for Windows

Reproduction Link

https://github.com/haavamoa/GithubIssues/tree/master/src/RefreshViewSharedBindingContext

Workaround

Change the architecture to always new up a view model and have a new viewmodel in between the pages.

[jsuarezruiz]

@haavamoa Interesting question. The current behavior is intentional, although what you need in your App has made me think about it in ways that we could cover both cases (have a new view model in between the pages or reuse it).

[haavamoa]

Interesting indeed. Not entirely sure if you need more information from me or not.

Our solution was to keep one view model for each page, but to have a viewmodel globally in the first page that gets sent to the second viewmodel when the second page is created. That way we have a sort of scoped singleton that has pre-loaded data and can be used by the pull to refresh to get data.

[zoli13]

We use MVVMCross, where ViewModels are not re-created, so every time we switch views, we get "one extra" refresh when Pull-To-Refresh is called on the RefreshView. It does not look possible to prevent this, VMs lifescycle is handled by MVVMCross.
Any idea? (I can have a bool flag to prevent command body running multiple times - but still it will be called more and more times)