WPF触发器(Trigger)

WPF触发器(Trigger、DataTrigger、EventTrigger)

WPF中有种叫做触发器的东西(记住不是数据库的trigger哦)。它的主要作用是根据trigger的不同条件来自动更改外观属性，或者执行动画等操作。

　　WPFtrigger的主要类型有：Trigger、MultiTrigger、DataTrigger、MultiDataTrigger、EventTrigger几种。从字面意思上我们想大家已经知道个大概，接下来我将还会用实例代码逐一进行介绍。trigger主要运用的场景在Style、ControlTemplate、DataTemplate三个地方。在这些地方可以使用trigger，具体视情况而定。

　　1.在Style中使用各种trigger

　　在style中使用的trigger主要是属性的触发器，当属性的值发生改变是将会引发触发器。

　　a.普通属性trigger 当鼠标滑过时字体变成红色

<CheckBox Content="Style Trigger MouseOver Red">             <CheckBox.Resources>                 <Style TargetType="{x:Type CheckBox}">                     <Setter Property="Foreground" Value="SkyBlue"/>                     <Style.Triggers>                         <!--鼠标滑过时字体为红色-->                         <Trigger Property="IsMouseOver" Value="True">                             <Setter Property="Foreground" Value="Red"/>                         </Trigger>                     </Style.Triggers>                 </Style>             </CheckBox.Resources>         </CheckBox>

　　b.普通属性MultiTrigger 当checkbox勾选并且鼠标滑过时字体变成绿色

<CheckBox Content="Style MultiTrigger Checked and MouseOver Green ">             <CheckBox.Resources>                 <Style TargetType="{x:Type CheckBox}">                     <Setter Property="Foreground" Value="SkyBlue"/>                     <Style.Triggers>                         <MultiTrigger>                             <MultiTrigger.Conditions>                                 <Condition Property="IsChecked" Value="True" />                                 <Condition Property="IsMouseOver" Value="True" />                             </MultiTrigger.Conditions>                             <Setter Property="Foreground" Value="Green"/>                         </MultiTrigger>                     </Style.Triggers>                 </Style>             </CheckBox.Resources>         </CheckBox>

　　c.EventTrigger 鼠标划入长度变长 鼠标移出 长度变短

 <CheckBox Content="Style EventTrigger " Width="70" HorizontalAlignment="Left">             <CheckBox.Resources>                 <Style TargetType="{x:Type CheckBox}">                     <Setter Property="Foreground" Value="SkyBlue"/>                     <Style.Triggers>                         <EventTrigger RoutedEvent="Mouse.MouseEnter">                             <EventTrigger.Actions>                                 <BeginStoryboard>                                     <Storyboard>                                         <DoubleAnimation                                           Duration="0:0:0.2"                                           Storyboard.TargetProperty="Width"                                           To="150"  />                                     </Storyboard>                                 </BeginStoryboard>                             </EventTrigger.Actions>                         </EventTrigger>                         <EventTrigger RoutedEvent="Mouse.MouseLeave">                             <EventTrigger.Actions>                                 <BeginStoryboard>                                     <Storyboard>                                         <DoubleAnimation                                           Duration="0:0:0.2"                                           Storyboard.TargetProperty="Width"                                           To="70"  />                                     </Storyboard>                                 </BeginStoryboard>                             </EventTrigger.Actions>                         </EventTrigger>                     </Style.Triggers>                 </Style>             </CheckBox.Resources>         </CheckBox>

　　2.在ControlTemplate中使用trigger

　　在ControlTemplate中使用的trigger主要是在controltemplate中的元素的触发器，当属性的值发生改变是将会引发触发器。

　　属性为“Border” 的鼠标滑过时背景变色，其他的trigger同上面的style一样 这里就不多举例了

<Button Content="ControlTemplate" Width="120" Height="30">             <Button.Resources>                 <Style TargetType="{x:Type Button}">                     <Setter Property="Background" Value="Gray"/>                     <Setter Property="BorderBrush" Value="Black"/>                     <Setter Property="Cursor" Value="Hand"/>                     <Setter Property="Template">                         <Setter.Value>                             <ControlTemplate TargetType="{x:Type Button}">                                 <StackPanel>                                     <Border Height="10" Background="Red"></Border>                                     <Border x:Name="Border" CornerRadius="0" BorderThickness="1"  Background="{TemplateBinding Background}" BorderBrush="{TemplateBinding BorderBrush}">                                         <ContentPresenter VerticalAlignment="Center" HorizontalAlignment="Center"/>                                     </Border>                                 </StackPanel>                                                                  <ControlTemplate.Triggers>                                     <Trigger Property="IsMouseOver" Value="True">                                         <Setter TargetName="Border" Property="Background" Value="#FFC2E0FF"/>                                         <Setter TargetName="Border" Property="BorderBrush" Value="#FF3399FF"/>                                     </Trigger>                                 </ControlTemplate.Triggers>                             </ControlTemplate>                         </Setter.Value>                     </Setter>                 </Style>             </Button.Resources>         </Button>

　　3.在DataTemplate中使用trigger

　　在DataTemplate中使用trigger可以根据绑定的数据不同显示不同的内容。

<TreeView Name="_tree" Margin="0" BorderThickness="0" VerticalAlignment="Stretch" Background="Transparent" ItemsSource="{Binding Children}" >                 <TreeView.ItemTemplate>                     <HierarchicalDataTemplate ItemsSource="{Binding Children}">                         <Border CornerRadius="0" Margin="1"  x:Name="back" MinWidth="70"                                 Background="Transparent" DataContext="{Binding}" PreviewMouseMove="TreeItem_PreviewMouseMove">                             <StackPanel Orientation="Horizontal" Margin="2">                                 <Image x:Name="BGimage" Source="/Vdc3D.Coms.DModelEditor;component/Images/item.png" Height="15" Width="15" />                                 <TextBlock Text="{Binding ShowText}" Margin="2 0"/>                             </StackPanel>                             <Border.ContextMenu>                                 <ContextMenu x:Name="menu" >                                     <MenuItem Header="Add Directory" x:Name="menu_addDir" Click="AddDir_Click" DataContext="{Binding}"/>                                     <MenuItem Header="Add Property" x:Name="menu_addChild"  Click="AddChild_Click" DataContext="{Binding}"/>                                     <MenuItem Header="Edit" Click="Modify_Click" DataContext="{Binding}"/>                                     <MenuItem Header="Delete" Click="Delete_Click" DataContext="{Binding}"/>                                 </ContextMenu>                             </Border.ContextMenu>                         </Border>                         <HierarchicalDataTemplate.Triggers>                             <MultiDataTrigger>                                 <MultiDataTrigger.Conditions>                                     <Condition Binding="{Binding RelativeSource={RelativeSource Mode=FindAncestor,AncestorType={x:Type TreeViewItem}},Path=IsExpanded}"  Value="False"/>                                     <Condition Binding="{Binding IsDir}" Value="True"/>                                 </MultiDataTrigger.Conditions>                                 <MultiDataTrigger.Setters>                                     <Setter TargetName="BGimage" Property="Source" Value="/Vdc3D.Coms.DModelEditor;component/Images/dir.png" />                                 </MultiDataTrigger.Setters>                             </MultiDataTrigger>                             <MultiDataTrigger>                                 <MultiDataTrigger.Conditions>                                     <Condition Binding="{Binding RelativeSource={RelativeSource Mode=FindAncestor,AncestorType={x:Type TreeViewItem}},Path=IsExpanded}"  Value="True"/>                                     <Condition Binding="{Binding IsDir}" Value="True"/>                                 </MultiDataTrigger.Conditions>                                 <MultiDataTrigger.Setters>                                     <Setter TargetName="BGimage" Property="Source" Value="/Vdc3D.Coms.DModelEditor;component/Images/dir_open.png" />                                 </MultiDataTrigger.Setters>                             </MultiDataTrigger>                             <DataTrigger Binding="{Binding IsDir}" Value="True">                                 <Setter TargetName="menu_addDir"  Property="Visibility" Value="Visible"/>                                 <Setter TargetName="menu_addChild"  Property="Visibility" Value="Visible"/>                             </DataTrigger>                             <DataTrigger Binding="{Binding IsDir}" Value="False">                                 <Setter TargetName="menu_addDir"  Property="Visibility" Value="Collapsed"/>                                 <Setter TargetName="menu_addChild"  Property="Visibility" Value="Collapsed"/>                             </DataTrigger>                         </HierarchicalDataTemplate.Triggers>                     </HierarchicalDataTemplate>                 </TreeView.ItemTemplate>             </TreeView>

　　这是一个treeview控件 根据绑定的isdir值不同 可以显示icon是一个目录(文件夹)或者是一个文件，看是不是很简单呢

　　以上只是简单的介绍了trigger的一些用法，具体的功能大家可以自由发挥，这也是wpf的强大之处

　　本文来自lhx527099095的博客，原文地址：http://blog.csdn.net/lhx527099095/article/details/8029207

WPF快速指导6：触发器     本文摘要：     1：属性触发器；     2：数据触发器；     3：事件触发器；

    Style、ControlTemplate 和 DataTemplate 都有触发器集合。     属性触发器只检查WPF从属属性，而数据触发器则可检查任何一种可绑定的属性。属性触发器一般用来检查WPF可视元素的属性，而数据触发器则通常用来检查不可视对象的属性。     属性触发器：通过此机制，一个属性的更改会在另一个属性中触发即时或动态更改。     数据触发器：通过此机制，事件会在属性中触发动态更改。     数据触发器：EventTrigger，它根据事件的引发来启动一组操作，但这类操作仅限于动画。

一：属性触发器     查看代码片段1：

   <Style TargetType="ListBoxItem">
      <Setter Property="Opacity" Value="0.5" />
      <Setter Property="MaxHeight" Value="75" />
      <Style.Triggers>
        <Trigger Property="IsSelected" Value="True">
          <Trigger.Setters>
            <Setter Property="Opacity" Value="1.0" />
          </Trigger.Setters>
        </Trigger>
      </Style.Triggers>
    </Style>

    表示在ListBoxItem的IsSelected属性变为True的时候，其另外一个属性Opacity的值变为1.0。 1.1单个触发器     代码片段1就是单个触发器。 1.2多个触发器     可以为ListBoxItem设置多个触发器。 1.3多条件属性触发器     多条件触发器就是说，同时满足几个条件的时候才触发行为。     如代码片段2： 

               <MultiTrigger>
                    <MultiTrigger.Conditions>
                        <Condition Property="IsFocused" Value="True"></Condition>
                        <Condition Property="Content" Value="{x:Null}"></Condition>
                    </MultiTrigger.Conditions>
                    <Setter Property="ToolTip" Value="content is null!"></Setter>
                </MultiTrigger>

二：数据触发器     使用 DataTrigger，可以在数据对象的属性值与指定的 Value 匹配时设置属性值。例如，在显示 Employee 对象列表时，可能希望前景色根据每个 Employee 的当前出勤情况而变化。（例如，用紫色前景色显示当前正在休假的 Employee。）     查看代码片段3

       <Window.Resources>
            <c:Places x:Key="PlacesData"/>

            <Style TargetType="ListBoxItem">
                <Style.Triggers>
                    <DataTrigger Binding="{Binding Path=State}" Value="WA">
                        <Setter Property="Foreground" Value="Red" />
                    </DataTrigger>
                    <MultiDataTrigger>
                        <MultiDataTrigger.Conditions>
                            <Condition Binding="{Binding Path=Name}" Value="Portland" />
                            <Condition Binding="{Binding Path=State}" Value="OR" />
                        </MultiDataTrigger.Conditions>
                        <Setter Property="Background" Value="Cyan" />
                    </MultiDataTrigger>
                </Style.Triggers>
            </Style>

            <DataTemplate DataType="{x:Type c:Place}">
                <Canvas Width="160" Height="20">
                    <TextBlock FontSize="12"
             Width="130" Canvas.Left="0" Text="{Binding Path=Name}"/>
                    <TextBlock FontSize="12" Width="30"
                 Canvas.Left="130" Text="{Binding Path=State}"/>
                </Canvas>
            </DataTemplate>
        </Window.Resources>

        <StackPanel>
            <TextBlock FontSize="18" Margin="5" FontWeight="Bold"
    HorizontalAlignment="Center">Data Trigger Sample</TextBlock>
            <ListBox Width="180" HorizontalAlignment="Center" Background="Honeydew"
    ItemsSource="{Binding Source={StaticResource PlacesData}}"/>
        </StackPanel>

2.1单条件触发     以上的DataTrigger就是一个单条件触发器。 2.2多条件触发     以上的MultiDataTrigger就是一个多条件触发器。

三：事件触发器     属性触发器用来检查从属属性的值，数据触发器用来检查CLR属性的值，而事件触发器用来监视事件。当一个事件发生的时候，事件触发器就会通过引发相关的动画事件来响应。     如代码片段4:

    <Style TargetType="ListBoxItem">
      <Setter Property="Opacity" Value="0.5" />
      <Setter Property="MaxHeight" Value="75" />
      <Style.Triggers>
        <Trigger Property="IsSelected" Value="True">
          <Trigger.Setters>
            <Setter Property="Opacity" Value="1.0" />
          </Trigger.Setters>
        </Trigger>
        <EventTrigger RoutedEvent="Mouse.MouseEnter">
          <EventTrigger.Actions>
            <BeginStoryboard>
              <Storyboard>
                <DoubleAnimation
                  Duration="0:0:0.2"
                  Storyboard.TargetProperty="MaxHeight"
                  To="90"  />
              </Storyboard>
            </BeginStoryboard>
          </EventTrigger.Actions>
        </EventTrigger>
        <EventTrigger RoutedEvent="Mouse.MouseLeave">
          <EventTrigger.Actions>
            <BeginStoryboard>
              <Storyboard>
                <DoubleAnimation
                  Duration="0:0:1"
                  Storyboard.TargetProperty="MaxHeight"  />
              </Storyboard>
            </BeginStoryboard>
          </EventTrigger.Actions>
        </EventTrigger>
      </Style.Triggers>
    </Style>