How to access MainPage.xaml controls from another page

Question

i have an image element in the MainPage.xaml and a flyout in SettingsContract1.xaml, when the flyout item is clicked the filepicker is
opened and i want to set them image source of the image in the Mainpage with the file picked from the filepicker. How can i access the image from SettingsContract1.xaml
image in MainPage.xaml
<Image x:Name="img" HorizontalAlignment="Left" Height="332" VerticalAlignment="Top" Width="778" Margin="349,406,0,0"/>
menuflyout sub in SettingsContract1.xaml.vb
Private Sub chooseFile_Click(sender As Object, e As RoutedEventArgs) Handles chooseFile.Click
Dim filePicker As FileOpenPicker
filePicker = New FileOpenPicker()
filePicker.ViewMode = PickerViewMode.Thumbnail
filePicker.SuggestedStartLocation = PickerLocationId.PicturesLibrary
filePicker.FileTypeFilter.Add(".png")
Dim file As StorageFile = Await filePicker.PickSingleFileAsync()
Using filestream As Streams.IRandomAccessStream = Await file.OpenAsync(FileAccessMode.Read)
Dim bitmapImage As Windows.UI.Xaml.Media.Imaging.BitmapImage = New BitmapImage
bitmapImage.SetSource(filestream)
img.Source = bitmapImage 'gives an error
End Using
End Sub

Answer 1

Found the answer from stackoverflow
Private Async Sub chooseFile_Click(sender As Object, e As RoutedEventArgs) Handles chooseFile.Click
Dim mapImage As Frame = Window.Current.Content
Dim mainPage As MainPage = mapImage.Content
Dim filePicker As FileOpenPicker
filePicker = New FileOpenPicker()
filePicker.ViewMode = PickerViewMode.Thumbnail
filePicker.SuggestedStartLocation = PickerLocationId.PicturesLibrary
filePicker.FileTypeFilter.Add(".png")
Dim file As StorageFile = Await filePicker.PickSingleFileAsync()
Using filestream As Streams.IRandomAccessStream = Await file.OpenAsync(FileAccessMode.Read)
Dim bitmapImage As Windows.UI.Xaml.Media.Imaging.BitmapImage = New BitmapImage
bitmapImage.SetSource(filestream)
mainPage.img.Source = bitmapImage
End Using
End Sub