UWP - Saving Settings does not work all the time - xaml

Question

I've got the following code just copied from here. I want to bind a double value to a xaml slider, get this value from the localsetting every time I navigate to the SettingsPage and everytime the slidervalue gets changed by the user I want it to be saved to localsettings. Here is my code so far:
SettingsPage.xaml.cpp:
Windows::Storage::ApplicationDataContainer^ localSettings = Windows::Storage::ApplicationData::Current->LocalSettings;
SettingsPage::SettingsPage()
{
InitializeComponent();
this->viewModel = ref new SettingsViewModel();
this->DataContext = this->viewModel;
}
void SettingsPage::QSlider_ValueChanged(Platform::Object^ sender, Windows::UI::Xaml::Controls::Primitives::RangeBaseValueChangedEventArgs^ e)
{
Windows::Storage::ApplicationDataCompositeValue^ composite =ref new Windows::Storage::ApplicationDataCompositeValue();
bool a = composite->Insert(SETTINGS_TAG_SLIDER_Q, dynamic_cast<PropertyValue^>(PropertyValue::CreateDouble((double)sldQ->Value)));
auto values = localSettings->Values;
bool b = values->Insert(SETTINGS_TAG_SETTINGS_PAGE, composite);
}
SettingsPage.xaml:
<Slider x:Name="sldQ" Margin="15,5,15,0" Value="{Binding SliderQValue}" ValueChanged="Slider_ValueChanged" MaxWidth="300" HorizontalContentAlignment="Left" ></Slider>
SettingsViewModel.cpp:
double SettingsViewModel::SliderQValue::get()
{
Windows::Storage::ApplicationDataContainer^ localSettings = Windows::Storage::ApplicationData::Current->LocalSettings;
ApplicationDataCompositeValue^ composite = safe_cast<ApplicationDataCompositeValue^>(localSettings->Values->Lookup(SETTINGS_TAG_SETTINGS_PAGE));
if (composite != nullptr)
{
if (composite->HasKey(SETTINGS_TAG_SLIDER_Q)) {
double value = safe_cast<IPropertyValue^>(composite->Lookup(SETTINGS_TAG_SLIDER_Q))->GetDouble();
return value;
}
}
return 99;
}
My Problem is that this works exactly once! If I navigate from other pages to SettingsPage, I get slidervalue=99. Then I set it by dragging to e.g. 50. Then I navigat back to other page. From the other page I navigate again to SettingsPage and get slidervalue=50. But doing it once again I get 99 again. So it only works for 1 page navigation-cycle but it should work even if the app is rebooted. What is the problem in my code? Am I understanding something wrong?

Answer 1

I actually solved the problem with the help of this. In my code above I was initializing a new 'ApplicationDateCompositeValue' each time I wanted to write/read it. So with the new method it works like it was planned to do:
OnValueChanged:
Windows::Storage::ApplicationDataContainer^ localSettings = Windows::Storage::ApplicationData::Current->LocalSettings;
auto values = localSettings->Values;
values->Insert(TAG_SLIDER, dynamic_cast<PropertyValue^>(PropertyValue::CreateDouble((double)sldQuality->Value)));
Property::get():
ApplicationDataContainer^ localSettings = ApplicationData::Current->LocalSettings;
auto values = localSettings->Values;
if (localSettings->Values->HasKey(TAG_SLIDER)) {
double value = safe_cast<double>(localSettings->Values->Lookup(TAG_SLIDER));
return value;
}
else
return default_value;