绑定属性何时获得输入？

Question

Currently im learning to build windows apps with mvvm with the Template Studio. I added a SettingsPage what contains some elements like:

<StackPanel x:Name="ContentArea">
        <CommandBar Background="Transparent" OverflowButtonVisibility="Collapsed">
            <AppBarButton Click="BtnSave_Click" Icon="Save" />          
        </CommandBar>
        <Pivot>
            <PivotItem x:Uid="Settings_Personal">
                <StackPanel Margin="{StaticResource XSmallTopMargin}">
                    <TextBlock x:Uid="Settings_Personal_Firstname" />
                    <TextBox x:Uid="Settings_Personal_FirstnameBox" Text="{x:Bind ViewModel.Firstname, Mode=TwoWay}" />                        
                </StackPanel>
            </PivotItem>
        <Pivot>
</StackPanel>

My SettingsPage.xaml.cs:

public sealed partial class SettingsPage : Page
{
      public SettingsViewModel ViewModel { get; }

      public SettingsPage()
      {
         ViewModel = App.GetService<SettingsViewModel>();
         InitializeComponent();
      }

      public void BtnSave_Click(object sender, RoutedEventArgs routedEventArgs)
      {
         ViewModel.SetSetting();
      }
}

And my Viewmodel:

public class SettingsViewModel : ObservableRecipient
{
private string _firstname;

public string Firstname
{
    get => _firstname;
    set => SetProperty(ref _firstname, value);
}

public SettingsViewModel(ILocalSettingsService localSettingsService)
{
    _localSettingsService = localSettingsService;
}

public async Task SetSetting()
{
    string test = Firstname;  // < My Breakpoint
    await _localSettingsService.SaveSettingAsync("Firstname", Firstname);
}

}

At debug time, i'm filling the box with my firstname and set a brakpoint to the SetSettings Task. After clicking on the "Save" Button i can see, that Firstname is null. Do i have to add some more code for gettings the information from the box?

Answer 1

由于{x:Bind}具有OneTime的默认模式，因此您应该将绑定的Mode设置为TwoWay ，以便您的源属性按预期设置：

Text="{x:Bind ViewModel.Firstname, Mode=TwoWay}"