用户 select 如何在 Xamarin 中的单个标签上显示两个（或更多）字段中的 1 个

Question

我正在尝试使用单个标签在 Xamarin Forms 中交替显示两个数据字段之一。仅标签 1 显示绑定字段 (Contact_Name)，而我尝试使用变量“DisplayField”的第二个标签未显示 'Contact_Address' 或 'Contact_eMail'。之前发布的问题和另一位用户试图提供帮助，但没有成功！

型号Class

public class Contacts
{
  [PrimaryKey][Autoincrement]
  public int Contact_ID { get; set; }
  public string Contact_Name { get; set; }
  public string Contact_Address { get; set; }
  public string Contact_eMail { get; set; }
}

XAML 页

  <StackLayout>
    <Button Text="Display Address" FontSize="Large" HorizontalOptions="Center" VerticalOptions="Fill" Clicked="Display_Address" />
    <Button Text="Display Email" FontSize="Large" HorizontalOptions="Center" VerticalOptions="Fill" Clicked="Display_eMail" />
    <Entry HorizontalOptions="FillAndExpand" Text="{Binding DisplayField}" />
    <ListView x:Name="listView" HasUnevenRows="True" >
        <ListView.ItemTemplate>
            <DataTemplate>
                <ViewCell >
                    <StackLayout Orientation="Vertical" VerticalOptions="CenterAndExpand" >
                        <Frame >
                            <StackLayout Orientation="Vertical" VerticalOptions="Center">
                                <Label Text="{Binding Contact_Name}" FontSize="Medium" LineBreakMode="WordWrap" />
                                <Label Text="{Binding DisplayField}" LineBreakMode="WordWrap" />
                            </StackLayout>
                        </Frame>
                    </StackLayout>
                </ViewCell>
            </DataTemplate>
        </ListView.ItemTemplate>
    </ListView>
</StackLayout>

代码隐藏

 public partial class FieldSwap : ContentPage
 {
readonly FieldViewModel _fieldViewModel;
readonly SQLiteAsyncConnection _connection = DependencyService.Get<ISQLite>().GetConnection();
public ObservableCollection<Contacts> CList { get; set; }
public static string DisplayField { get; private set; }

public static int caseSwitch { get; private set; }

public FieldSwap()
{
    InitializeComponent();
    _fieldViewModel = new FieldViewModel();
    _fieldViewModel.Field = "Contact_Address";
    
    this.BindingContext = _fieldViewModel;
}

   public static void SelectField()
   {
    

       switch (caseSwitch)
       {
         case 1:
            DisplayField = "Contact_Address";
            break;

        case 2:
            DisplayField = "Contact_eMail";
            break;

        default:
            DisplayField = ("Contact_Address");
            break;
      }
   }

   private void Display_Address(object sender, EventArgs e)
   {
    caseSwitch = 1;
    SelectField();
    ReadData();
   }

   private void Display_eMail(object sender, EventArgs e)
   {
    caseSwitch = 2;
    SelectField();
    ReadData();
   }

   public void ReadData()
   {
     var list = _connection.Table<Contacts>().ToListAsync().Result;
     CList = new ObservableCollection<Contacts>(list);
     listView.ItemsSource = CList;
   }
}

查看模型Class

 public class FieldViewModel : INotifyPropertyChanged
 {
 public event PropertyChangedEventHandler PropertyChanged;

 String _field;

 public string Field
 {
    set
    {
        if (!value.Equals(_field, StringComparison.Ordinal))
        {
            _field = value;
            OnPropertyChanged("DisplayField");
        }
    }
    get
    {
        return _field;
    }
  }
  void OnPropertyChanged([CallerMemberName] string propertyName = null)
  {
    PropertyChanged?.Invoke(this, new 
    PropertyChangedEventArgs(propertyName));
  }
 }

Answer 1

你可以使用IsVisible 属性来实现，不需要只绑定一个标签。

因此，将Contact_Address和Contact_eMail与StackLayout中的两个标签绑定如下：

<StackLayout Orientation="Vertical" VerticalOptions="Center">
     <Label Text="{Binding Contact_Name}" FontSize="Medium" LineBreakMode="WordWrap" />
     <Label Text="{Binding Contact_Address}" IsVisible="{Binding AddressVisible}" LineBreakMode="WordWrap" />
     <Label Text="{Binding Contact_eMail}" IsVisible="{Binding EMailVisible}" LineBreakMode="WordWrap" />
</StackLayout>

然后在联系人中添加两个可见属性：

public class Contacts: INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;

    ...

    private bool addressVisible;
    public bool AddressVisible
    {
        set
        {
            if (addressVisible != value)
            {
                addressVisible = value;
                OnPropertyChanged("AddressVisible");
            }
        }
        get
        {
            return addressVisible;
        }
    }

    private bool eMailVisible;
    public bool EMailVisible
    {
        set
        {
            if (eMailVisible != value)
            {
                eMailVisible = value;
                OnPropertyChanged("EMailVisible");
            }
        }
        get
        {
            return eMailVisible;
        }
    }

    protected virtual void OnPropertyChanged(string propertyName)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }

}

现在在 Contentpage 中，您可以在单击按钮时修改可见的属性:

private void Display_Address(object sender, EventArgs e)
{
    foreach(var item in CList )
    {
        item.AddressVisible = true;
        item.EMailVisible = false;
    }
}

private void Display_eMail(object sender, EventArgs e)
{
    foreach (var item in CList )
    {
        item.AddressVisible = false;
        item.EMailVisible = true;
    }
}

效果如下：

用户 select 如何在 Xamarin 中的单个标签上显示两个（或更多）字段中的 1 个

How a user select to display 1 out of two (or more) fields on a single Label in Xamarin

data-binding

label

xamarin.forms.listview

型号Class

XAML 页

代码隐藏

查看模型Class