WPF中触发器Trigger、MultiTrigger、DataTrigger、MultiDataTrigger、EventTrigger几种

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

<span>  </span><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

<span>  </span><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="" 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=""  />
                                   </Storyboard>
                               </BeginStoryboard>
                           </EventTrigger.Actions>
                       </EventTrigger>
                       <EventTrigger RoutedEvent="Mouse.MouseLeave">
                           <EventTrigger.Actions>
                               <BeginStoryboard>
                                   <Storyboard>
                                       <DoubleAnimation
                                         Duration="0:0:0.2"
                                         Storyboard.TargetProperty="Width"
                                         To=""  />
                                   </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="" Height="">
            <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="" Background="Red"></Border>
                                    <Border x:Name="Border" CornerRadius="" BorderThickness=""  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="" BorderThickness="" VerticalAlignment="Stretch" Background="Transparent" ItemsSource="{Binding Children}" >
                <TreeView.ItemTemplate>
                    <HierarchicalDataTemplate ItemsSource="{Binding Children}">
                        <Border CornerRadius="" Margin=""  x:Name="back" MinWidth=""
                                Background="Transparent" DataContext="{Binding}" PreviewMouseMove="TreeItem_PreviewMouseMove">
                            <StackPanel Orientation="Horizontal" Margin="">
                                <Image x:Name="BGimage" Source="/Vdc3D.Coms.DModelEditor;component/Images/item.png" Height="" Width="" />
                                <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