如何使用ViewModel实现单击以进行选择

3 回答

• 5

  根据日志语句，看起来property-changed-handler的取消订阅逻辑不能按预期工作 .

  使用 TextCellRenderer ，我们不需要显式订阅property-changed-event，因为有一个可在此上下文中重用的基本可覆盖方法 HandlePropertyChanged .

  更改渲染器代码以使用此方法（similar to this answer）应该有希望解决此问题：

  public class CustomTextCellRenderer : TextCellRenderer
  {
      public override UITableViewCell GetCell(Cell item, UITableViewCell reusableCell, UITableView tv)
      {
          var nativeCell = base.GetCell(item, reusableCell, tv);
  
          if (item is CustomTextCell formsCell)
          {
              SetCheckmark(nativeCell, formsCell);
              SetTap(nativeCell, formsCell);
          }
  
          return nativeCell;
      }
  
      protected override void HandlePropertyChanged(object sender, PropertyChangedEventArgs args)
      {
          base.HandlePropertyChanged(sender, args);
  
          System.Diagnostics.Debug.WriteLine($"HandlePropertyChanged {args.PropertyName}");
  
          var nativeCell = sender as CellTableViewCell;
          if (nativeCell?.Element is CustomTextCell formsCell)
          {
              if (args.PropertyName == CustomTextCell.IsCheckedProperty.PropertyName)
                  SetCheckmark(nativeCell, formsCell);
              else if (args.PropertyName == CustomTextCell.NoTapProperty.PropertyName)
                  SetTap(nativeCell, formsCell);
          }
      }
  
      void SetCheckmark(UITableViewCell nativeCell, CustomTextCell formsCell)
      {
          if (formsCell.IsChecked)
              nativeCell.Accessory = UITableViewCellAccessory.Checkmark;
          else
              nativeCell.Accessory = UITableViewCellAccessory.None;
      }
  
      void SetTap(UITableViewCell nativeCell, CustomTextCell formsCell)
      {
          if (formsCell.NoTap)
              _nativeCell.SelectionStyle = UITableViewCellSelectionStyle.None;
          else
              _nativeCell.SelectionStyle = UITableViewCellSelectionStyle.Default;
      }
  }
  

  回复于 2024-04-18T21:03:31+08:00
• 5

  我找不到导致该行为的错误，所以这是我对此的想法：

  您描述的行为听起来更像是 RadioButton . Since there are none in Xamarin.Forms您可以创建自己的，使用包或获得解决方法 .

  最简单的解决方法将在您的 cfsSelectValue 中 .

  您可以在可视树中搜索 local:CustomTextCells 的所有元素，并为每个 TextCell 设置 IsSelected 为false，这是 not 作为 sender 传递的_1291120_ .

  ---

  How I would do it:

  要尝试的事情：

  对于ViewModel，使用ObservableCollection而不是 Array

  private ObservableCollection<SSVViewModel> viewModels = new ObservableCollection<SSVViewModel>()
  {
      new SSVViewModel {Id = 0, Name=LANG.English.Text()},
      new SSVViewModel {Id = 1, Name=LANG.Romaji.Text()},
      new SSVViewModel {Id = 2, Name=LANG.Kana.Text()},
      new SSVViewModel {Id = 3, Name=LANG.Kanji.Text()},
      new SSVViewModel {Id = 4, Name=LANG.KanjiKana.Text()},
      new SSVViewModel {Id = 5, Name=LANG.KanaKanji.Text()},
  };
  

  从 INotifyPropertyChanged 而不是 ObservableProperty 派生ViewModel

  public class SSVViewModel : INotifyPropertyChanged
  {
      private int id;
      private string name;
      private bool isSelected = false; //Set the default here
  
      public int Id
      {
          get
          {
              return id;
          }
          set
          {
              if (value != id)
              {
                  id = value;
                  OnPropertyChanged();
              }
          }
      }
  
      public string Name
      {
          get
          {
              return name;
          }
          set
          {
              if (value != name)
              {
                  name = value;
                  OnPropertyChanged();
              }
          }
      }
  
      public bool IsSelected
      {
          get
          {
              return isSelected;
          }
          set
          {
              if (value != isSelected)
              {
                  isSelected = value;
                  OnPropertyChanged();
              }
          }
      }
  
  
      #region Implementation of INotifyPropertyChanged
  
      public event PropertyChangedEventHandler PropertyChanged;
  
      private void OnPropertyChanged([CallerMemberName] string propertyname = null)
      {
          if(PropertyChanged != null)
          {
              PropertyChanged.Invoke(this, new PropertyChangedEventArgs(propertyname));
          }
      }
  
      #endregion
  }
  

  将 cfsSelectValue 更改为：

  public void cfsSelectValue(object sender, EventArgs e)
  {
      //GetCurrentCell
      CustomTextCell cell = sender as CustomTextCell;
      if (cell == null)
      {
          return;
      }            
  
      foreach (SSVViewModel viewModel in CFS)
      {
          /*
          Since there is no Tag Property we gotta use something different
          you could use `CommandParameter` since it is of type object
  
          */
          if (viewModel.Name == cell.Text && viewModel.Id == int.Parse(cell.CommandParameter.ToString()))
          {
              viewModel.IsSelected = true;
          }
          else
          {
              viewModel.IsSelected = false;
          }                    
      }
  }
  

  回复于 2024-04-18T21:03:31+08:00
• 5

  代码看起来对我来说 - 我想象这种情况发生的唯一原因是字符串比较逻辑没有按预期工作 .

  也许基于参考的比较可能会解决问题 . 即将您的XAML更改为：

  <TableSection Title="Front Side" x:Name="cfsSection">
     <local:CustomTextCell BindingContext="{Binding [0]}" Text="{Binding Name}" IsChecked="{Binding IsSelected}" Tapped="cfsSelectValue"/>
     <local:CustomTextCell BindingContext="{Binding [1]}" Text="{Binding Name}" IsChecked="{Binding IsSelected}" Tapped="cfsSelectValue"/>
     <local:CustomTextCell BindingContext="{Binding [2]}" Text="{Binding Name}" IsChecked="{Binding IsSelected}" Tapped="cfsSelectValue"/>
     <local:CustomTextCell BindingContext="{Binding [3]}" Text="{Binding Name}" IsChecked="{Binding IsSelected}" Tapped="cfsSelectValue"/>
     <local:CustomTextCell BindingContext="{Binding [4]}" Text="{Binding Name}" IsChecked="{Binding IsSelected}" Tapped="cfsSelectValue"/>
     <local:CustomTextCell BindingContext="{Binding [5]}" Text="{Binding Name}" IsChecked="{Binding IsSelected}" Tapped="cfsSelectValue"/>
  </TableSection>
  

  并点击处理程序：

  void cfsSelectValue(object sender, EventArgs e)
  {
      var cell = sender as TextCell;
      if (cell == null)
          return;
  
      var selected = cell.BindingContext;
  
      foreach (var setting in CFS)
          setting.IsSelected = (setting == selected);
  
  }
  

  回复于 2024-04-18T21:03:31+08:00