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:

• 不选中CheckBox时:
  
  
• 选中时:
  
  

总结,DataTrigger可以在某些数据发生改变时设置一些UI的样式,应该还有不少应用,WPF里的东西感觉比较多,有些东西用完不记录东西,容易遗忘,所以多记录以下总是好的.另外,各位大虾,你们如果有啥思路实现上面第二个例子的效果,欢迎指教....我暂时就先这么用了

  </div>