wpf 如何让 DataTemplate.DataTrigger 检查大于或小于？

How to get DataTemplate.DataTrigger to check for greater than or less than?

提问by Edward Tanguay

The following DataTemplate.DataTriggermakes the age display red if it is equal to30.

DataTemplate.DataTrigger如果年龄等于30 ，则以下使年龄显示为红色。

How do I make the age display red if it is greater than30?

如果年龄大于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>

回答by Mikko Rantanen

You could create an IValueConverter, which converts an integer to a boolean based on the CutOff. Then use DataTrigger.Valueof True(or False, depending on what you are returning).

您可以创建一个IValueConverter，它根据 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）。

WPF DataTriggers are strictly equality comparers if I remember correctly.

DataTrigger如果我没记错的话，WPF是严格相等的比较器。

So something similar to:

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; }
}

Then use the following XAML.

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>

回答by Drew McGhie

I'd recommend using an IValueConverterto bind to the Foregroundelement of the Age TextBlockand isolating the coloring logic there.

我建议使用 anIValueConverter来绑定到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}}" />

Then in the Code:

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);
   }
}

回答by ΩmegaMan

I believe there is a simpler way of acheiving the goal by using the powers of MVVM and INotifyPropertyChanged.

我相信有一种更简单的方法可以通过使用 MVVM 和INotifyPropertyChanged.

---

---

With the Ageproperty create another property which will be a boolean called IsAgeValid. The IsAgeValidwill simply be an on demandcheck which does not technicallyneed an the OnNotifycall. How?

使用该Age属性创建另一个属性，该属性将是一个名为IsAgeValid. 这IsAgeValid将只是一个按需检查，技术上不需要OnNotify呼叫。如何？

To get changes pushed to the Xaml, place the OnNotifyPropertyChangedevent to be fired for IsAgeValidwithinthe Agesetter instead.

要将更改推送到 Xaml，请将OnNotifyPropertyChanged要触发的事件IsAgeValid放置在Agesetter 中。

Any binding to IsAgeValidwill alsohave a notify message sent on any Agechange subscriptions; which is what really is being looked at...

任何结合IsAgeValid将还具有通知上的任何发送的消息Age的变化订阅; 这才是真正被关注的......

---

---

Once setup, of course bind the style trigger for false and true accordingly to the IsAgeValidresult.

设置后，当然会根据IsAgeValid结果将样式触发器绑定为 false 和 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.
   } 
 }

回答by Mark

If possible, you could add a property to your model, that's the easiest way. Eg.

如果可能，您可以向模型添加属性，这是最简单的方法。例如。

public int AgeBoundry
{
    get
    {
        if (Age < 30)
            return 0;
        else if (Age == 30)
            return 1;
        else
            return 2;
    }
}

then you can check on the value of the integer.

然后你可以检查整数的值。

<DataTemplate.Triggers>
    <DataTrigger Binding="{Binding Path=Age}">
        <DataTrigger.Value>0</DataTrigger.Value>
        <Setter TargetName="Age" Property="Foreground" Value="Green"/> 
    </DataTrigger>
    <DataTrigger Binding="{Binding Path=Age}">
        <DataTrigger.Value>1</DataTrigger.Value>
        <Setter TargetName="Age" Property="Foreground" Value="Orange"/> 
    </DataTrigger>
    <DataTrigger Binding="{Binding Path=Age}">
        <DataTrigger.Value>2</DataTrigger.Value>
        <Setter TargetName="Age" Property="Foreground" Value="Red"/> 
    </DataTrigger>
</DataTemplate.Triggers>