[英]MVVM Binding To Property == Null
I want to show some elements when a property is not null. 我想在属性不为null时显示一些元素。 What is the best way of achieving this?
实现此目标的最佳方法是什么?
The following is my ViewModel: 以下是我的ViewModel:
class ViewModel : ViewModelBase
{
public Trade Trade
{
get { return _trade; }
set { SetField(ref _trade, value, () => Trade); }
} private Trade _trade;
}
ViewModelBase inherits INotifyPropertyChanged and contains SetField() ViewModelBase继承INotifyPropertyChanged并包含SetField()
The Following is the Trade class: 以下是贸易类:
public class Trade : INotifyPropertyChaged
{
public virtual Company Company
{
get { return _company; }
set { SetField(ref _company, value, () => Company); }
} private Company _company;
......
}
This is part of my View.xaml 这是我的View.xaml的一部分
<GroupBox Visibility="{Binding Path=Trade.Company,
Converter={StaticResource boolToVisConverter}}" />
I would like this groupbox to show only if Trade.Company is not null (so when a user selects a company). 我希望仅当Trade.Company不为null时才显示此组框(因此,当用户选择公司时)。 Would I need to create a custom converter to check for null and return the correct visibility or is there one in .NET?
我是否需要创建一个自定义转换器来检查null并返回正确的可见性,或者.NET中是否存在此可见性?
Rather than using a BooleanToVisibilityConverter
, you'll need to use a different converter (one you'll have to write) that will return the appropriate visibility value if the bound value is null. 除了使用
BooleanToVisibilityConverter
,您需要使用其他转换器(必须编写一个转换器),如果绑定值为null,它将返回适当的可见性值。
Something like this: 像这样:
public class NullValueToVisibilityConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter,
CultureInfo culture)
{
return (value != null ? Visibility.Visible : Visibility.Collapsed);
}
public object ConvertBack(object value, Type targetType, object parameter,
CultureInfo culture)
{
return null; // this shouldn't ever happen, since
// you'll need to ensure one-way binding
}
}
You'll need to add Mode = OneWay
to your binding, since you won't be able to make a round-trip conversion. 您将需要在绑定中添加
Mode = OneWay
,因为您将无法进行往返转换。
You can also use DataTriggers to do pretty much the same thing without the converter... 您也可以使用DataTriggers在没有转换器的情况下做几乎相同的事情...
<GroupBox DataContext="{Binding Path=Trade.Company}">
<GroupBox.Style TargetType="GroupBox">
<Style.Triggers>
<DataTrigger Binding="{Binding Path=.}" Value="{x:Null}">
<Setter Property="Visibility" Value="Collapsed"/>
</DataTrigger>
</Style.Triggers>
</GroupBoxStyle>
</GroupBox>
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