xamarin - 如何使 ViewCell 的 Tapped 事件将参数发送到通用函数，然后为该 ViewCell 元素打开一个选择器？

Question

更新:只是提醒一下，如果有人可以告诉我如何在不使用手势的情况下实现此功能，则有 500 分奖励>

我正在使用 ViewCell 和手势识别器使用以下代码打开选择器。 ViewCell 在左侧有一个标签，在右侧有一个标签区域，最初在应用程序启动时填充，然后在单击 ViewCell 时使用选取器填充。

XAML

<ViewCell x:Name="ati" Tapped="OpenPickerCommand">
   <Grid VerticalOptions="CenterAndExpand" Padding="20, 0">
      <Grid.GestureRecognizers>
         <TapGestureRecognizer 
             Command="{Binding OpenPickerCommand}" 
             CommandParameter="{x:Reference atiPicker}" NumberOfTapsRequired="1" />
      </Grid.GestureRecognizers>
      <local:LabelBodyRendererClass Text="Answer Time Interval" HorizontalOptions="StartAndExpand" />
      <Picker x:Name="atiPicker" IsVisible="false" HorizontalOptions="End" SelectedIndexChanged="atiPickerSelectedIndexChanged" ItemsSource="{Binding Times}"></Picker>
      <local:LabelBodyRendererClass x:Name="atiLabel" HorizontalOptions="End"/>
   </Grid>
</ViewCell>

<ViewCell x:Name="pti" Tapped="OpenPickerCommand">
   <Grid VerticalOptions="CenterAndExpand" Padding="20, 0">
      <Grid.GestureRecognizers>
         <TapGestureRecognizer 
             Command="{Binding OpenPickerCommand}" 
             CommandParameter="{x:Reference ptiPicker}" NumberOfTapsRequired="1" />
      </Grid.GestureRecognizers>
      <local:LabelBodyRendererClass Text="Phrase Time Interval" HorizontalOptions="StartAndExpand" />
      <Picker x:Name="ptiPicker" IsVisible="false" HorizontalOptions="End" SelectedIndexChanged="ptiPickerSelectedIndexChanged" ItemsSource="{Binding Times}"></Picker>
      <local:LabelBodyRendererClass x:Name="ptiLabel" HorizontalOptions="End"/>
   </Grid>
</ViewCell>

C# 这适用于具有 CommandParameter 的不同选择器(ati、bti、pti 等)

public SettingsPage()
{
   InitializeComponent();
   BindingContext = new CommandViewModel();
}

void atiPickerSelectedIndexChanged(object sender, EventArgs e)
    {
        var picker = (Picker)sender;
        int selectedIndex = picker.SelectedIndex;
        if (selectedIndex != -1)
        {
            App.DB.UpdateIntSetting(Settings.Ati, selectedIndex);
            atiLabel.Text = AS.ati.Text();
        }
    }

void ptiPickerSelectedIndexChanged(object sender, EventArgs e)
    {
        var picker = (Picker)sender;
        int selectedIndex = picker.SelectedIndex;
        if (selectedIndex != -1)
        {
            App.DB.UpdateIntSetting(Settings.Pti, selectedIndex);
            ptiLabel.Text = AS.pti.Text();
        }
    }


public class CommandViewModel: ObservableProperty
{
    public ICommand openPickerCommand;

    public CommandViewModel()
    {
        openPickerCommand = new Command<Picker>(PickerFocus);
        //openPickerCommand = new Command(tapped);
    }

    public ICommand OpenPickerCommand
    {
        get { return openPickerCommand; }
    }

    void PickerFocus(Picker param)
    {
        param.Focus();
    }
}

我想删除 TapGestureRecognizers 的使用，但我仍然想保留功能和布局。

有人向我建议，如果我像这样使用 ViewCell 的 Tapped 事件会更好:

 Tapped="OnTapped"

有人可以详细解释一下我如何在 C# 中连接它。我最好在 CommandViewModel 和 C# 支持代码中编写一些代码。 View 模型也可以有一种方法来接受参数，以便它可以用来打开不同的选择器吗？

非常感谢我如何做到这一点的一个例子。请注意，如果有一种方法可以通过仅在 .cs 支持代码中进行编码来做到这一点，我就不需要特别使用 CommandViewModel。

Answer 1

您可以使用附加属性解决此问题。只需为添加命令/参数属性的 ViewCell 定义一个“行为”类。

public static class TappedCommandViewCell
{
    private const string TappedCommand = "TappedCommand";
    private const string TappedCommandParameter = "TappedCommandParameter";

    public static readonly BindableProperty TappedCommandProperty =
        BindableProperty.CreateAttached(
            TappedCommand,
            typeof(ICommand),
            typeof(TappedCommandViewCell),
            default(ICommand),
            BindingMode.OneWay,
            null,
            PropertyChanged);

    public static readonly BindableProperty TappedCommandParameterProperty =
        BindableProperty.CreateAttached(
            TappedCommandParameter,
            typeof(object),
            typeof(TappedCommandViewCell),
            default(object),
            BindingMode.OneWay,
            null);

    private static void PropertyChanged(BindableObject bindable, object oldValue, object newValue)
    {
        if (bindable is ViewCell cell)
        {
            cell.Tapped -= ViewCellOnTapped;
            cell.Tapped += ViewCellOnTapped;
        }
    }

    private static void ViewCellOnTapped(object sender, EventArgs e)
    {
        if (sender is ViewCell cell && cell.IsEnabled)
        {
            var command = GetTappedCommand(cell);
            var parameter = GetTappedCommandParameter(cell);

            if (command != null && command.CanExecute(parameter))
            {
                command.Execute(parameter);
            }
        }
    }

    public static ICommand GetTappedCommand(BindableObject bindableObject) =>
        (ICommand)bindableObject.GetValue(TappedCommandProperty);

    public static void SetTappedCommand(BindableObject bindableObject, object value) =>
        bindableObject.SetValue(TappedCommandProperty, value);

    public static object GetTappedCommandParameter(BindableObject bindableObject) =>
        bindableObject.GetValue(TappedCommandParameterProperty);

    public static void SetTappedCommandParameter(BindableObject bindableObject, object value) =>
        bindableObject.SetValue(TappedCommandParameterProperty, value);
}

之后在 XAML 中引用您的行为命名空间并使用完全限定名称指定属性值:

<ViewCell StyleId="disclosure-indicator"
          behaviors:TappedCommandViewCell.TappedCommand="{Binding BrowseCommand}"
          behaviors:TappedCommandViewCell.TappedCommandParameter="https://www.google.com">
    <StackLayout Orientation="Horizontal">
        <Label Text="Recipient"
               VerticalOptions="Center"
               Margin="20,0"/>
        <Label Text="{Binding LedgerRecord.Recipient}"
               HorizontalOptions="EndAndExpand"
               VerticalOptions="Center"
               Margin="0,0,20,0"/>
        </Label>
    </StackLayout>
</ViewCell>

以上将允许您使用 MVVM 并且没有点击手势识别器。