我有一个模拟水印文本框的用户控件。我需要允许在用户控件上放置文本文件。PreviewDragEnter 事件工作正常。这是我想验证被拖动的文件实际上是文本文件的事件。问题是 drop 事件永远不会触发。我想在用户释放鼠标按钮并决定将文件放入用户控件时捕获事件。我认为这与用户控件和层次结构中的多个控件有关。我真的不在乎哪个控件会触发 drop 事件，只要它实际触发即可。这是 xaml（我要针对放置事件的控件名称为 'txt'）
<UserControl x:Class="CrumbSearch.CustomControls.package_watermark"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
Height="45" Width="Auto"
FontFamily="B Yekan"
AllowDrop="true"
Grid.IsSharedSizeScope="True"
xmlns:wpfwatermarktextbox="clr-namespace:WPFWaterMarkTextBox;assembly=WPFWaterMarkTextBox">
<FrameworkElement.Resources>
<ResourceDictionary>
<FontFamily x:Key="simple_line_icon">/fonts/Simple-Line-Icons.ttf#simple-line-icons</FontFamily>
<Style x:Key="SimpleTextBox" TargetType="{x:Type TextBox}">
<Setter Property="AllowDrop" Value="True"/>
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type TextBox}">
<Border Name="border" BorderBrush="{TemplateBinding BorderBrush}"
BorderThickness="{TemplateBinding BorderThickness}" Background="{TemplateBinding Background}" SnapsToDevicePixels="True">
<ScrollViewer Name="PART_ContentHost" Focusable="False" Margin="2,10,0,0"
AllowDrop="True"
HorizontalScrollBarVisibility="Hidden" VerticalScrollBarVisibility="Hidden" />
</Border>
<ControlTemplate.Triggers>
<Trigger Property="UIElement.IsFocused" Value="True">
<Setter TargetName="border" Property="Border.BorderBrush" Value="Transparent" />
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
<Style x:Key="SimplePasswordBox" TargetType="{x:Type PasswordBox}">
<Setter Property="AllowDrop" Value="True"/>
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type PasswordBox}">
<Border Name="border" BorderBrush="{TemplateBinding BorderBrush}"
BorderThickness="{TemplateBinding BorderThickness}" Background="{TemplateBinding Background}"
SnapsToDevicePixels="True">
<ScrollViewer Name="PART_ContentHost"
Focusable="False" HorizontalScrollBarVisibility="Hidden" VerticalScrollBarVisibility="Hidden" />
</Border>
<ControlTemplate.Triggers>
<Trigger Property="UIElement.IsFocused" Value="True">
<Setter TargetName="border" Property="Border.BorderBrush" Value="#00000000" />
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
</ResourceDictionary>
</FrameworkElement.Resources>
<Border Name="border" BorderThickness="0.5" CornerRadius="4" MouseEnter="border_MouseEnter"
MouseLeave="border_MouseLeave">
<FrameworkElement.Style>
<Style TargetType="{x:Type Border}">
<Setter Property="BorderBrush" Value="White" />
<Setter Property="AllowDrop" Value="true" />
</Style>
</FrameworkElement.Style>
<Grid Name="MainGrid" PreviewMouseLeftButtonDown="MainGrid_PreviewMouseLeftButtonDown"
LostFocus="MainGrid_LostFocus">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="auto" />
<ColumnDefinition/>
</Grid.ColumnDefinitions>
<Label Name="lbl2" Padding="5,0" FontSize="10" Content="Name"
Margin="0,5,0,0"
HorizontalAlignment="Left" Foreground="White" FlowDirection="LeftToRight"
VerticalAlignment="Top" Height="13" Grid.IsSharedSizeScope="True"
Opacity="0" Grid.Column="1" Background="{x:Null}" />
<TextBlock Name="lbl" Text="WaterMark" HorizontalAlignment="Left"
Foreground="#0EE7EC" FontSize="12"
Padding="5,5,5,0" FlowDirection="LeftToRight" FontFamily="Andalus"
TextWrapping="WrapWithOverflow" FontStyle="Italic"
Opacity="0.7" Grid.Column="1"
VerticalAlignment="Center" Background="{x:Null}" />
<TextBox Name="txt" Style="{DynamicResource SimpleTextBox}" FlowDirection="LeftToRight"
AllowDrop="true" Background="{x:Null}"
PreviewDragEnter="txt_PreviewDragEnter"
PreviewDrop="txt_PreviewDrop" Drop="txt_Drop"
TextWrapping="NoWrap" VerticalContentAlignment="Center" FontSize="14"
VerticalScrollBarVisibility="Disabled" MaxLines="1" FontWeight="Medium" Grid.Column="1"
BorderBrush="{x:Null}" TextChanged="TextBox_TextChanged" Foreground="White"
PreviewGotKeyboardFocus="txt_PreviewGotKeyboardFocus"
PreviewLostKeyboardFocus="txt_PreviewLostKeyboardFocus" />
<PasswordBox Name="pass" Style="{DynamicResource SimplePasswordBox}" FontSize="14"
VerticalContentAlignment="Center"
ScrollViewer.VerticalScrollBarVisibility="Disabled" Grid.Column="1"
Visibility="Collapsed" BorderBrush="{x:Null}"
Background="{x:Null}" PasswordChanged="PasswordBox_PasswordChanged" />
<Label Name="LblIcon" Padding="0" FontFamily="{DynamicResource simple_line_icon}"
VerticalContentAlignment="Center" HorizontalContentAlignment="Center"
Foreground="#FF6A6A6A" FontSize="14" Background="{x:Null}" />
</Grid>
</Border>
</UserControl>