UWP

Question

我刚刚从 here 复制了以下代码。我想将一个双精度值绑定到一个 xaml 滑块，每次我导航到 SettingsPage 时从 localsetting 获取这个值，每次用户更改 slidervalue 时我希望它保存到 localsettings。到目前为止，这是我的代码：

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;
}

我的问题是这只能工作一次！如果我从其他页面导航到 SettingsPage，我会得到 slidervalue=99。然后我通过拖动来设置它，例如50. 然后我导航回其他页面。从另一个页面我再次导航到 SettingsPage 并获得 slidervalue=50。但是再做一次，我又得到了 99。所以它只适用于 1 页导航周期，但即使应用程序重新启动它也应该工作。我的代码有什么问题？我理解错了吗？

Answer 1

其实我是在this的帮助下解决了这个问题。在我上面的代码中，每次我想要 write/read 时，我都会初始化一个新的 'ApplicationDateCompositeValue'。因此，使用新方法，它的工作方式与计划的一样：

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)));

属性::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;

UWP - 保存设置并不总是有效

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