Question

在我的应用程序中，我有多个步进器以及相应的条目，以显示每个步进器的当前值。我正在尝试使用Xamarin.Essentials：Preferences保存该值，以便在重新打开该应用程序时供以后使用，但是“ Preferences”似乎没有保存步进值和/或在重新打开该应用程序时输入该值。

这是xaml的一个例子...

          <Grid x:Name="PurchasePriceGrid">
                <Grid.ColumnDefinitions>
                    <ColumnDefinition Width="*" />
                    <ColumnDefinition Width=".6*" />
                    <ColumnDefinition Width="*" />
                </Grid.ColumnDefinitions>
                <Grid.RowDefinitions>
                    <RowDefinition Height="40" />
                </Grid.RowDefinitions>
                <Label Text="Purchase Price" TextColor="Black" FontAttributes="Bold" Margin="0,0,25,0" Scale="1.2" TranslationX="15" 
                   Grid.Column="0" HorizontalTextAlignment="End" VerticalTextAlignment="Center" LineBreakMode="NoWrap" />
                <customentry:MyEntry x:Name="PurchasePriceEntry" Text="{Binding Source={x:Reference PurchasePriceStepper}, Path=Value, FallbackValue=0}"
                                 TextColor="DarkSlateGray" FontAttributes="Bold" BackgroundColor="Ivory" TranslationX="10"
                                 Grid.Column="1" HorizontalTextAlignment="Center" Keyboard="Numeric" VerticalOptions="End" MaxLength="5"
                                 TextChanged="PurchasePriceEntry_Completed" />
                <Stepper x:Name="PurchasePriceStepper" Grid.Column="2" HorizontalOptions="Center" VerticalOptions="Center"  Scale=".7" TranslationX="3"
                     Maximum="5" Minimum=".01" Increment=".01" Value="{Binding PurchasePriceStepperValue}" />
            </Grid>

这是C＃...

using Xamarin.Essentials;

...

    public double PurchasePriceStepperValue
    {
        get => Preferences.Get(nameof(PurchasePriceStepperValue), 1.75);
        set
        {
            Preferences.Set(nameof(PurchasePriceStepperValue), value);
            OnPropertyChanged(nameof(PurchasePriceStepperValue));
        }
    }

这是Android MainActivity.cs ...

using Xamarin.Essentials;

...

    protected override void OnCreate(Bundle bundle)
    {
        TabLayoutResource = Resource.Layout.Tabbar;
        ToolbarResource = Resource.Layout.Toolbar;

        base.OnCreate(bundle);
        global::Xamarin.Forms.Forms.Init(this, bundle);
        Xamarin.Essentials.Platform.Init(this, bundle);

        LoadApplication(new App());
    }

    public override void OnRequestPermissionsResult(int requestCode, string[] permissions, [GeneratedEnum] Permission[] grantResults)
    {
        Xamarin.Essentials.Platform.OnRequestPermissionsResult(requestCode, permissions, grantResults);

        base.OnRequestPermissionsResult(requestCode, permissions, grantResults);
    }

我是编程新手，并且花了多个小时尝试多种不同的方法，以弄清为什么Xamarin.Essentials：Preferences不会保存步进值并将其输入到条目中。我已经在所有项目中实现了NuGet包。如果有帮助，我可以尝试提供更多代码。

Answer 1

重新打开应用程序时的默认值为0.01 ，表示绑定无效。

我在Xaml和MainActivity.cs中使用与您相同的代码，并使用下面的代码，如下所示：

public partial class MainPage : ContentPage
{
    public MainPage()
    {
        InitializeComponent();

        PurchasePriceModel model = new PurchasePriceModel();

        BindingContext = model;
    }
}


class PurchasePriceModel : INotifyPropertyChanged
{

    public event PropertyChangedEventHandler PropertyChanged;


    public double PurchasePriceStepperValue
    {
        get => Preferences.Get(nameof(PurchasePriceStepperValue), 1.75);
        set
        {
            Preferences.Set(nameof(PurchasePriceStepperValue), value);
            PropertyChanged(this, new PropertyChangedEventArgs(nameof(PurchasePriceStepperValue)));
        }
    }

    public PurchasePriceModel()
    {

    }

}

它对我有用。请检查您的BindingContext和Model中的代码。

Xamarin.Essentials：首选项不存储步进值

1 个答案: