C# 如何使用带有null参数的x:Bind函数绑定?
我试图格式化一个对象的几个属性,并使用C# 如何使用带有null参数的x:Bind函数绑定?,c#,xaml,data-binding,uwp,xbind,C#,Xaml,Data Binding,Uwp,Xbind,我试图格式化一个对象的几个属性,并使用x:bind函数绑定将结果绑定到TextBlock。绑定如下所示: <TextBlock Text="{x:Bind local:MainViewModel.FormatWidget(ViewModel.SelectedItem), Mode=OneWay}" /> MainPage.xaml.cs using Windows.UI.Xaml.Controls; namespace NullFunctionBindingParameter {
x:bind
函数绑定将结果绑定到TextBlock
。绑定如下所示:
<TextBlock Text="{x:Bind local:MainViewModel.FormatWidget(ViewModel.SelectedItem), Mode=OneWay}" />
MainPage.xaml.cs
using Windows.UI.Xaml.Controls;
namespace NullFunctionBindingParameter
{
public sealed partial class MainPage : Page
{
public MainPage()
{
InitializeComponent();
}
public MainViewModel ViewModel { get; } = new MainViewModel();
}
}
using System;
using System.Collections.ObjectModel;
using System.ComponentModel;
namespace NullFunctionBindingParameter
{
public class MainViewModel : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
private Widget _selectedItem;
public Widget SelectedItem
{
get => _selectedItem;
set
{
if (_selectedItem != value)
{
_selectedItem = value;
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(SelectedItem)));
}
}
}
public ObservableCollection<Widget> Widgets { get; } = new ObservableCollection<Widget>()
{
new Widget
{
Id = Guid.NewGuid(),
Name = "Regular Widget",
Model = "WX2020-01",
Description = "Your typical everyday widget."
},
new Widget
{
Id = Guid.NewGuid(),
Name = "Super Widget",
Model = "WX2020-02",
Description = "An extra special upgraded widget."
},
new Widget
{
Id = Guid.NewGuid(),
Name = "Broken Widget",
Model = "WX2020-03",
Description = "A widget that has been used and abused."
},
new Widget
{
Id = Guid.NewGuid(),
Name = "Fake Widget",
Model = "WX2020-04",
Description = "It's not really a widget at all!"
},
new Widget
{
Id = Guid.NewGuid(),
Name = "Surprise Widget",
Model = "WX2020-05",
Description = "What kind of widget will it be?"
},
new Widget
{
Id = Guid.NewGuid(),
Name = "Invisible Widget",
Model = "WX2020-06",
Description = "Our most inexpensive widget."
},
new Widget
{
Id = Guid.NewGuid(),
Name = "Backwards Widget",
Model = "WX2020-07",
Description = "Really more of a tegdiw, come to think of it."
}
};
public static string FormatWidget(Widget widget)
{
if (widget == null)
return "No widget selected";
else
return $"{widget.Name} [{widget.Model}] {widget.Description}";
}
public string GetFormattedWidget()
{
return FormatWidget(SelectedItem);
}
}
}
using System;
using System.ComponentModel;
namespace NullFunctionBindingParameter
{
public class Widget : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
private Guid _id;
private string _name;
private string _model;
private string _description;
public Guid Id
{
get => _id;
set
{
if (_id != value)
{
_id = value;
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(Id)));
}
}
}
public string Name
{
get => _name;
set
{
if (_name != value)
{
_name = value;
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(Name)));
}
}
}
public string Model
{
get => _model;
set
{
if (_model != value)
{
_model = value;
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(Model)));
}
}
}
public string Description
{
get => _description;
set
{
if (_description != value)
{
_description = value;
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(Description)));
}
}
}
}
}
MainViewModel.cs
using Windows.UI.Xaml.Controls;
namespace NullFunctionBindingParameter
{
public sealed partial class MainPage : Page
{
public MainPage()
{
InitializeComponent();
}
public MainViewModel ViewModel { get; } = new MainViewModel();
}
}
using System;
using System.Collections.ObjectModel;
using System.ComponentModel;
namespace NullFunctionBindingParameter
{
public class MainViewModel : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
private Widget _selectedItem;
public Widget SelectedItem
{
get => _selectedItem;
set
{
if (_selectedItem != value)
{
_selectedItem = value;
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(SelectedItem)));
}
}
}
public ObservableCollection<Widget> Widgets { get; } = new ObservableCollection<Widget>()
{
new Widget
{
Id = Guid.NewGuid(),
Name = "Regular Widget",
Model = "WX2020-01",
Description = "Your typical everyday widget."
},
new Widget
{
Id = Guid.NewGuid(),
Name = "Super Widget",
Model = "WX2020-02",
Description = "An extra special upgraded widget."
},
new Widget
{
Id = Guid.NewGuid(),
Name = "Broken Widget",
Model = "WX2020-03",
Description = "A widget that has been used and abused."
},
new Widget
{
Id = Guid.NewGuid(),
Name = "Fake Widget",
Model = "WX2020-04",
Description = "It's not really a widget at all!"
},
new Widget
{
Id = Guid.NewGuid(),
Name = "Surprise Widget",
Model = "WX2020-05",
Description = "What kind of widget will it be?"
},
new Widget
{
Id = Guid.NewGuid(),
Name = "Invisible Widget",
Model = "WX2020-06",
Description = "Our most inexpensive widget."
},
new Widget
{
Id = Guid.NewGuid(),
Name = "Backwards Widget",
Model = "WX2020-07",
Description = "Really more of a tegdiw, come to think of it."
}
};
public static string FormatWidget(Widget widget)
{
if (widget == null)
return "No widget selected";
else
return $"{widget.Name} [{widget.Model}] {widget.Description}";
}
public string GetFormattedWidget()
{
return FormatWidget(SelectedItem);
}
}
}
using System;
using System.ComponentModel;
namespace NullFunctionBindingParameter
{
public class Widget : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
private Guid _id;
private string _name;
private string _model;
private string _description;
public Guid Id
{
get => _id;
set
{
if (_id != value)
{
_id = value;
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(Id)));
}
}
}
public string Name
{
get => _name;
set
{
if (_name != value)
{
_name = value;
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(Name)));
}
}
}
public string Model
{
get => _model;
set
{
if (_model != value)
{
_model = value;
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(Model)));
}
}
}
public string Description
{
get => _description;
set
{
if (_description != value)
{
_description = value;
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(Description)));
}
}
}
}
}
在这种情况下,我建议您使用
Converter
,而不是直接在binding语句中使用静态方法
WidgetConverter
公共类WidgetConverter:IValueConverter
{
公共对象转换(对象值、类型targetType、对象参数、字符串语言)
{
var widget=作为widget的值;
返回MainViewModel.FormatWidget(小部件);
}
公共对象转换回(对象值、类型targetType、对象参数、字符串语言)
{
抛出新的NotImplementedException();
}
}
用法
...
...
致意。谢谢你的建议。当然,这将是获得相同产出的有效途径;然而,我真的很喜欢的简易性和可读性,并希望有一个解决方案,不需要回到转换器。目前没有好的解决方案。函数绑定中可能有一种拦截机制,防止在计算中使用null。转换器没有这种问题,建议使用method@RichardZhangMSFT根据,鼓励使用函数格式化和转换值:“提示您可以使用x:Bind中的函数来实现与WPF中的转换器和多绑定支持的场景相同的场景。”并说,“{x:Bind}”使绑定路径中的最后一步成为函数。这可用于执行转换,以及执行依赖于多个属性的绑定。“您好,这可能是对绑定设计的疏忽
Converter
可以用作解决问题的临时解决方案。这是作为GitHub上的一个组件添加的。