如何让DataTemplate.DataTrigger检查大于或小于？

Question

以下DataTemplate.DataTrigger使年龄显示为红色,如果它等于 30.

如果年龄显示大于 30,如何使年龄显示为红色？

<DataTemplate DataType="{x:Type local:Customer}">
    <Grid x:Name="MainGrid" Style="{StaticResource customerGridMainStyle}">
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="100"/>
            <ColumnDefinition Width="150"/>
        </Grid.ColumnDefinitions>
        <Grid.RowDefinitions>
            <RowDefinition/>
            <RowDefinition/>
            <RowDefinition/>
        </Grid.RowDefinitions>
        <TextBlock Grid.Column="0" Grid.Row="0" Text="First Name" Margin="5"/>
        <TextBlock Grid.Column="1" Grid.Row="0" Text="{Binding FirstName}" Margin="5"/>
        <TextBlock Grid.Column="0" Grid.Row="1" Text="Last Name" Margin="5"/>
        <TextBlock Grid.Column="1" Grid.Row="1" Text="{Binding LastName}" Margin="5"/>
        <TextBlock Grid.Column="0" Grid.Row="2" Text="Age" Margin="5"/>
        <TextBlock x:Name="Age" Grid.Column="1" Grid.Row="2" Text="{Binding Age}" Margin="5"/>
    </Grid>

    <DataTemplate.Triggers>
        <DataTrigger Binding="{Binding Path=Age}">
            <DataTrigger.Value>30</DataTrigger.Value>
            <Setter TargetName="Age" Property="Foreground" Value="Red"/> 
        </DataTrigger>
    </DataTemplate.Triggers>

</DataTemplate>

Answer 1

你可以创建一个IValueConverter,它根据整数将整数转换为布尔值CutOff.然后使用DataTrigger.Value的True(或者False,这取决于你正在返回什么).

DataTrigger如果我没记错的话,WPF 是严格的相等比较器.

所以类似于:

public class CutoffConverter : IValueConverter {
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture) {
        return ((int)value) > Cutoff;
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture) {
        throw new NotImplementedException();
    }

    public int Cutoff { get; set; }
}

然后使用以下XAML.

<Window.Resources>
    <myNamespace:CutoffConverter x:Key="AgeConverter" Cutoff="30" />
</Window.Resources>

<DataTemplate.Triggers>
    <DataTrigger Binding="{Binding Path=Age,
                                   Converter={StaticResource AgeConverter}}">
        <DataTrigger.Value>true</DataTrigger.Value>
        <Setter TargetName="Age" Property="Foreground" Value="Red"/> 
    </DataTrigger>
</DataTemplate.Triggers>

Answer 2

我建议使用一个IValueConverter绑定到ForegroundAge 的元素TextBlock并在那里隔离着色逻辑.

<TextBlock x:Name="Age"  
           Text="{Binding Age}" 
           Foreground="{Binding Path=Age, Converter={StaticResource AgeToColorConverter}}" />

然后在代码中:

[ValueConversion(typeof(int), typeof(Brush))]
public class AgeToColorConverter : IValueConverter
{
   public object Convert(object value, Type target)
   {
      int age;
      Int32.TryParse(value.ToString(), age);
      return (age >= 30 ? Brushes.Red : Brushes.Black);
   }
}

Answer 3

我相信有一种更简单的方法可以通过使用MVVM和MV的功能来实现目标INotifyPropertyChanged.

使用该Age属性创建另一个属性,该属性将被称为布尔值IsAgeValid.这IsAgeValid只是一个按需检查,在技术上不需要OnNotify通话.怎么样？

要将更改推送到Xaml,请将OnNotifyPropertyChangedfor IsAgeValid放在Agesetter中.

任何绑定都IsAgeValid将在任何Age更改上发送通知消息,这实际上是正在查看的内容.

一旦设置,当然将样式触发器绑定为false,并相应地IsAgeValid结果为true .

public bool IsAgeValid{ get { return Age > 30; } }

public int Age
{ 
  get { return _Age; }

  set
  {
   _Age=value;
   OnPropertyChanged("Age");   
   OnPropertyChanged("IsAgeValid"); // When age changes, so does the
                                    // question *is age valid* changes. So 
                                    // update the controls dependent on it.
   } 
 }