轉載於(https://social.msdn.microsoft.com/Forums/windowsapps/zh-CN/af3161ce-f020-4b0b-9b84-95ae597e53fd/resourcedictionary-xclass-xaml-mouseleftbuttondown-xclass?forum=wpfzhchs)

在資源字典中設置listboxItem的鼠標左擊的事件樣式。

打出這段代碼提示“ResourceDictionary”根元素需要 x:Class 特性來支持 XAML 文件中的事件處理程序。請移除 MouseLeftButtonDown 事件的事件處理程序，或將 x:Class 特性添加到根元素。 ”錯誤，

這句話是什麽意思？難道EventSetter 不能在資源字典中寫？

<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
 

                    xmlns:local="clr-namespace:WpfApplication1">
    <Style x:Key="remenber" TargetType="{x:Type ListBoxItem}"  >
        <Setter Property="Margin" Value="1"></Setter>

<EventSetter Event="MouseLeftButtonDown"  Handler="ProjectMouseLeftButtonDown"/>
        <Style
 
.Triggers>
            <Trigger Property="IsMouseOver" Value="True">
                <Setter Property="Background" Value="#FF569BEE"></Setter>
            </Trigger>
        </Style.Triggers>

    </Style>
</ResourceDictionary>

解決思路:

1.首先，EventSetter 是可以在資源字典中寫的。那句提示意思是需要在ResourceDictionary標簽內加上x:Class特性。
你可以寫成這樣：

ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
                    xmlns:local="clr-namespace:WpfApplication1"                    
                    x:Class="命名空間.資源字典的名稱" >
</ResourceDictionary>

命名空間：以你的代碼為例，此處應為”WpfApplication1”
資源字典的名稱：如果資源字典文件是”Dictionary1.xaml”，這裏就是”Dictionary1”
完整寫法就是 x:Class=”WpfApplication1. Dictionary1”

2.下面的Demo供你參考：

Dictionary1.xaml：

<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
                    xmlns:local="clr-namespace:WriteEventInResourceDictionary"
                    x:Class="WriteEventInResourceDictionary.Dictionary1">

    <Style  TargetType="{x:Type ListBoxItem}" BasedOn="{StaticResource {x:Type ListBoxItem}}">
        <EventSetter Event="PreviewMouseLeftButtonDown" Handler="MyCustomMouseEvent"/>
    </Style>

</ResourceDictionary>

Dictionary1.xaml.cs:

namespace WriteEventInResourceDictionary
{
    public partial class Dictionary1
    {
        private void MyCustomMouseEvent(object sender, RoutedEventArgs e)
        {
            MessageBox.Show("Hello");
        }
    }
}

MainWindow.xaml:

<ListBox>                       
      <ListBoxItem>Item 1</ListBoxItem>                        
      <ListBoxItem>Item 2</ListBoxItem>                        
      <ListBoxItem>Item 3</ListBoxItem>                
</ListBox>

App.xaml:

<Application x:Class="WriteEventInResourceDictionary.App"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:local="clr-namespace:WriteEventInResourceDictionary"
             StartupUri="MainWindow.xaml">
    <Application.Resources>
        <ResourceDictionary>
            <ResourceDictionary.MergedDictionaries>
                <ResourceDictionary Source="Dictionary1.xaml" />
            </ResourceDictionary.MergedDictionaries>
        </ResourceDictionary>
    </Application.Resources>
</Application>

錯誤:“ResourceDictionary”根元素需要 x:Class 特性來支持 XAML 文件中的事件處理程序。請移除 MouseLeftButtonDown 事件的事件處理程序.