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="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
