WPF触发器(Trigger) – DataTrigger

官方文档中对DataTrigger的介绍

Represents a trigger that applies property values or performs actions when the bound data meets a specified condition.

某词典的翻译:

当绑定的数据满足指定的条件时,应用(指定的)属性或执行操作的触发器

下面我演示一遍官方文档中的示例,根据官网的描述,建立实体类,然后编写前台代码

先来张效果图

通过DataTrigger,将省份为江苏省的Item项的文字颜色设置成了红色;
然后又通过MultoDataTrigger,将省份为江西省市为南昌的Item设置的背景设置成浅蓝色

关键部分代码:

<Page.Resources>
    <dataTrigger:Places x:Key="Places"/>
    <Style TargetType="ListBoxItem">
        <Style.Triggers>
            <DataTrigger Binding="{Binding Path=Province}" Value="江苏省">
                <Setter Property="Foreground"  Value="Red"/>
            </DataTrigger>
            <MultiDataTrigger>
                <MultiDataTrigger.Conditions>
                    <Condition Binding="{Binding Path=Province}" Value="江西省"/>
                    <Condition Binding="{Binding Path=Name}" Value="南昌"/>
                </MultiDataTrigger.Conditions>
                <Setter Property="Background" Value="Cyan"/>
            </MultiDataTrigger>
        </Style.Triggers>
    </Style>
    <DataTemplate x:Key="PlaceTemplate" DataType="{x:Type dataTrigger:Place}">
        <StackPanel Orientation="Horizontal">
            <TextBlock Text="{Binding Province,Mode=OneWay,StringFormat={}{0}- -   }"/>
            <TextBlock Text="{Binding Name,Mode=OneWay}"/>
        </StackPanel>
    </DataTemplate>
</Page.Resources>
<Grid>
    <ListBox Margin="20 30"
             MaxWidth="300" MaxHeight="250"
             ItemsSource="{StaticResource Places}"
             ItemTemplate="{StaticResource PlaceTemplate}">
    </ListBox>
</Grid>

新建一个测试项目:

添加两个类:

Place

Places

namespace Demo.DataTrigger
{
    public class Place
    {
        public string Name { get; set; }
        public string Province { get; set; }    public Place(string name,string province)
    {
        Name = name;
        Province = province;
    }
}

}
using System.Collections.ObjectModel;
namespace Demo.DataTrigger
{
public class Places:ObservableCollection<Place>
{
public Places()
{
Add(new Place("南京", "江苏省"));
Add(new Place("宁波", "浙江省"));
Add(new Place("苏州", "江苏省"));
Add(new Place("南通", "江苏省"));
Add(new Place("深圳", "广州省"));
Add(new Place("芜湖", "安徽省"));
Add(new Place("东菀", "广东省"));
Add(new Place("无锡", "江苏省"));
Add(new Place("南昌", "江西省"));
}
}
}

xaml代码

<Page.Resources>
    <dataTrigger:Places x:Key="Places"/>
    <Style TargetType="ListBoxItem">
        <Style.Triggers>
            <DataTrigger Binding="{Binding Path=Province}" Value="江苏省">
                <Setter Property="Foreground"  Value="Red"/>
            </DataTrigger>
            <MultiDataTrigger>
                <MultiDataTrigger.Conditions>
                    <Condition Binding="{Binding Path=Province}" Value="江西省"/>
                    <Condition Binding="{Binding Path=Name}" Value="南昌"/>
                </MultiDataTrigger.Conditions>
                <Setter Property="Background" Value="Cyan"/>
            </MultiDataTrigger>
        </Style.Triggers>
    </Style>&lt;DataTemplate x:Key=&quot;PlaceTemplate&quot; DataType=&quot;{x:Type dataTrigger:Place}&quot;&gt;
    &lt;StackPanel Orientation=&quot;Horizontal&quot;&gt;
        &lt;TextBlock Text=&quot;{Binding Province,Mode=OneWay,StringFormat={}{0}- - &amp;#160;&amp;#160;}&quot;/&gt;
        &lt;TextBlock Text=&quot;{Binding Name,Mode=OneWay}&quot;/&gt;
    &lt;/StackPanel&gt;
&lt;/DataTemplate&gt;

</Page.Resources>
<ListBox Margin="20 30"
MaxWidth="300" MaxHeight="250"
ItemsSource="{StaticResource Places}"
ItemTemplate="{StaticResource PlaceTemplate}">
</ListBox>

下面的一个例子是我在项目中遇到的

Image控件的Source属性通过数据绑定到后台属性的一个图片的路径,当后台属性为null时,默认一个路径提供给Image控件,恰巧这两天看到一个DataTrigger,就想着用它来实现,结果经历了一番周折,最终通过一个Converter值转化器和DataTrigger配合实现了,下面演示代码;

先看前台xaml代码:

<StackPanel Orientation="Horizontal">
    <StackPanel.Resources>
        <dataTrigger:PathValidateConverter x:Key="Converter"></dataTrigger:PathValidateConverter>
    </StackPanel.Resources>
    <Image>
        <Image.Style>
            <Style TargetType="Image">
                <Style.Triggers>
                    <DataTrigger Binding="{Binding Path=ThumbnailPath,Mode=OneWay,Converter={StaticResource Converter}}"
                                    Value="False">
                        <Setter Property="Source" Value="/Resources/Images/icons8-thumbnails-80.png"/>
                    </DataTrigger>
                    <DataTrigger Binding="{Binding Path=ThumbnailPath,Mode=OneWay,Converter={StaticResource Converter}}"
                                    Value="True">
                        <Setter Property="Source" Value="E:\\Media\\Images\\Src\\s.png"/>
                    </DataTrigger>
                </Style.Triggers>
            </Style>
        </Image.Style>
    </Image>
    <CheckBox Content="设置ThumbnailPath为有效的路径值"
                Checked="CheckBox_Checked" Unchecked="CheckBox_Unchecked"/>
</StackPanel>

然后看一下那个简单的值转换器,就是通过File.Exists()方法来判断文件路径是否合法,不合法则返回false:

PathValidatorConverter

using System;
using System.Globalization;
using System.IO;
using System.Windows.Data;namespace Demo.DataTrigger

{

class PathValidateConverter:IValueConverter

{

public object Convert(object value, Type targetType, object parameter, CultureInfo culture)

{

if (value == null) return false;

if (value.GetType() != typeof(string)) throw new ArgumentOutOfRangeException(nameof(value));        return File.Exists((string) value);
    }    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}

}

由于这个项目我只是用来演示的,所以就懒得去建立ViewModel,直接把代码xaml的隐藏类作为DataContext,后台代码中定义一个依赖属性来表示图片路径:

public string ThumbnailPath
{
    get => (string)GetValue(MyPropertyProperty);
    set => SetValue(MyPropertyProperty, value);
}// Using a DependencyProperty as the backing store for MyProperty.  This enables animation, styling, binding, etc...

public static readonly DependencyProperty MyPropertyProperty =

DependencyProperty.Register(nameof(ThumbnailPath), typeof(string), typeof(Demo),

new FrameworkPropertyMetadata(null));

还有两个函数处理前台CheckBox的Checked和UnChecked事件:

        private void CheckBox_Checked(object sender, RoutedEventArgs e)
        {
            ThumbnailPath = @"E:\\Media\\Images\\Src\\s.png";
        }        private void CheckBox_Unchecked(object sender, RoutedEventArgs e)
        {
            ThumbnailPath = null;
        }

当CheckedBox被选中时,或将ThumbnailPath设置成一个图片的绝对路径,而没被选中时,ThumbnailPath则被置为null

最终效果如下: