Question

我正在尝试将文件拖放到文本框中，以便使用文件路径（第二个DataTemplate）设置文本框的内容。所以我在我的textBox上添加了事件DragOver。但我得到一个Null引用异常。我尝试了很多其他事件并得到了同样的错误。在第一个dataTemplate中，事件正常工作。

这可能是因为我的文本框位于嵌套列表中。但我不确定。

有什么想法吗？

    <ListBox ItemsSource="{Binding Model.Attributes, Mode=TwoWay}" HorizontalContentAlignment="Stretch" VerticalAlignment="Stretch" Background="{x:Null}" BorderBrush="{x:Null}" Margin="0" BorderThickness="0" VerticalContentAlignment="Stretch" PreviewKeyDown="ListBox_PreviewKeyDown">
    <ListBox.Resources>
        <DataTemplate DataType="{x:Type local:TransformModel}">
            <Expander Header="Transform" VerticalAlignment="Top" d:LayoutOverrides="Width" FontSize="10.667" HorizontalAlignment="Stretch" IsExpanded="{Binding DataContext.Model.TransformIsExpanded, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type UserControl}}}">
                <StackPanel HorizontalAlignment="Stretch">
                    <Grid HorizontalAlignment="Stretch">
                        <Grid.ColumnDefinitions>
                            <ColumnDefinition Width="14"/>
                            <ColumnDefinition Width="0.333*"/>
                            <ColumnDefinition Width="14"/>
                            <ColumnDefinition Width="0.333*"/>
                            <ColumnDefinition Width="14"/>
                            <ColumnDefinition Width="0.333*"/>
                        </Grid.ColumnDefinitions>
                        <Grid.RowDefinitions>
                            <RowDefinition Height="0.215*"/>
                            <RowDefinition Height="0.785*"/>
                        </Grid.RowDefinitions>
                        <TextBlock Margin="4,0" TextWrapping="Wrap" Text="Position" d:LayoutOverrides="Width, Height" Grid.ColumnSpan="6" FontSize="10.667"/>   
                        <TextBlock TextWrapping="Wrap" Text="X" Grid.Row="1" VerticalAlignment="Top" Margin="4,0,0,0" d:LayoutOverrides="Width"/>
                        <TextBox Grid.Column="1" Grid.Row="1" TextWrapping="Wrap" Text="{Binding Position.X, Mode=TwoWay}" VerticalAlignment="Top" FontSize="8" Margin="0,0,-0.001,0" d:LayoutOverrides="Width" GotFocus="TextGotFocus" PreviewMouseLeftButtonDown="SelectivelyIgnoreMouseButton" />
                        <TextBlock TextWrapping="Wrap" Text="Y" Grid.Row="1" VerticalAlignment="Top" Margin="3.998,0,4.562,0" Grid.Column="2" d:LayoutOverrides="Width"/>
                        <TextBox Grid.Column="3" Grid.Row="1" TextWrapping="Wrap" Text="{Binding Position.Y, Mode=TwoWay}" VerticalAlignment="Top" FontSize="8" Margin="0" GotFocus="TextGotFocus" PreviewMouseLeftButtonDown="SelectivelyIgnoreMouseButton"/>
                        <TextBlock TextWrapping="Wrap" Text="Z" Grid.Row="1" VerticalAlignment="Top" Margin="3.999,0,4.344,0" Grid.Column="4" d:LayoutOverrides="Width"/>
                        <TextBox Grid.Column="5" Grid.Row="1" TextWrapping="Wrap" Text="{Binding Position.Z, Mode=TwoWay}" VerticalAlignment="Top" FontSize="8" Margin="0,0,4,0" GotFocus="TextGotFocus" PreviewMouseLeftButtonDown="SelectivelyIgnoreMouseButton"/>
                    </Grid>
                    <Grid HorizontalAlignment="Stretch">
                        <Grid.ColumnDefinitions>
                        <ColumnDefinition Width="14"/>
                            <ColumnDefinition Width="0.333*"/>
                            <ColumnDefinition Width="14"/>
                            <ColumnDefinition Width="0.333*"/>
                            <ColumnDefinition Width="14"/>
                            <ColumnDefinition Width="0.333*"/>
                        </Grid.ColumnDefinitions>
                        <Grid.RowDefinitions>
                            <RowDefinition Height="0.215*"/>
                            <RowDefinition Height="0.785*"/>
                        </Grid.RowDefinitions>
                        <TextBlock Margin="4,0" TextWrapping="Wrap" Text="Size" d:LayoutOverrides="Width, Height" Grid.ColumnSpan="6" FontSize="10.667"/>
                        <TextBlock TextWrapping="Wrap" Text="X" Grid.Row="1" VerticalAlignment="Top" Margin="4,0,0,0" d:LayoutOverrides="Width"/>
                        <TextBox Grid.Column="1" Grid.Row="1" TextWrapping="Wrap" Text="{Binding Size.X, Mode=TwoWay}" VerticalAlignment="Top" FontSize="8" Margin="0,0,-0.001,0" d:LayoutOverrides="Width"  GotFocus="TextGotFocus" PreviewMouseLeftButtonDown="SelectivelyIgnoreMouseButton"/>
                        <TextBlock TextWrapping="Wrap" Text="Y" Grid.Row="1" VerticalAlignment="Top" Margin="3.998,0,4.562,0" Grid.Column="2" d:LayoutOverrides="Width"/>
                        <TextBox Grid.Column="3" Grid.Row="1" TextWrapping="Wrap" Text="{Binding Size.Y, Mode=TwoWay}" VerticalAlignment="Top" FontSize="8" Margin="0" GotFocus="TextGotFocus" PreviewMouseLeftButtonDown="SelectivelyIgnoreMouseButton"/>
                        <TextBlock TextWrapping="Wrap" Text="Z" Grid.Row="1" VerticalAlignment="Top" Margin="3.999,0,4.344,0" Grid.Column="4" d:LayoutOverrides="Width"/>
                        <TextBox Grid.Column="5" Grid.Row="1" TextWrapping="Wrap" Text="{Binding Size.Z, Mode=TwoWay}" VerticalAlignment="Top" FontSize="8" Margin="0,0,4,0" GotFocus="TextGotFocus" PreviewMouseLeftButtonDown="SelectivelyIgnoreMouseButton"/>
                    </Grid>
                    <Separator Height="1" Margin="5,2,5,0"/>
                </StackPanel>
            </Expander>
        </DataTemplate>
        <DataTemplate DataType="{x:Type local:UnknownModel}">
            <Expander Header="Miscellaneous" VerticalAlignment="Top" d:LayoutOverrides="Width" FontSize="10.667" HorizontalAlignment="Stretch" IsExpanded="{Binding DataContext.Model.TransformIsExpanded, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type UserControl}}}">
                <StackPanel HorizontalAlignment="Stretch">
                    <ListBox Grid.Row="1" VerticalAlignment="Top" ItemsSource="{Binding Attributs}" HorizontalContentAlignment="Stretch" VerticalContentAlignment="Stretch" Background="{x:Null}" BorderBrush="{x:Null}" Margin="0" BorderThickness="0">
                        <ListBox.Resources>
                            <DataTemplate DataType="{x:Type local:PropertiesAssetsModel}">
                                <Grid d:DesignWidth="682.4" Margin="0,0,0,4" d:DesignHeight="144">
                                    <Grid.ColumnDefinitions>
                                        <ColumnDefinition Width="0.163*"/>
                                        <ColumnDefinition Width="0.837*"/>
                                     </Grid.ColumnDefinitions>
                                     <TextBlock TextWrapping="Wrap" VerticalAlignment="Center" d:LayoutOverrides="Width" Text="Assets" Margin="0,0,-0.003,0"/>
                                     <TextBox Grid.Column="1" Grid.Row="1" TextWrapping="Wrap" Text="{Binding Value, Mode=TwoWay}" VerticalAlignment="Top" FontSize="8" Margin="0,0,-0.001,0" d:LayoutOverrides="Width" AllowDrop="True" DragOver="AssetPathDragOvers"/>
                                </Grid>                           
                            </DataTemplate>
                        </ListBox.Resources>
                    </ListBox>
                    <Separator Height="1" Margin="5,2,5,0"/>
                </StackPanel>
            </Expander>
        </DataTemplate>
    </ListBox.Resources>
</ListBox>

Answer 1

我刚遇到同样的问题（我的问题是comboBox和LostFocus event）。我可以通过将Event handling位移动到我视图ResourceDictionary中的样式来解决它。

尝试这样的事情：

    <ResourceDictionary>
        <Style x:Key="TextBoxStyle" TargetType="{x:Type TextBox}">
            <EventSetter Event="DragOver" Handler="AssetPathDragOvers"/>
        </Style>
    </ResourceDictionary>

    <TextBox Style="{StaticResource ComboBoxStyle}" ...

Answer 2

谢谢，

嵌套数据模板在.NET 4.0中无法正常运行

您可以阅读有关此错误的更多信息： Official bug report

我的解决方法：

创建我自己的数据模板选择器：

public class TemplateSelector : DataTemplateSelector
{
    public DataTemplate UnknownTemplate { get; set; }

    public override DataTemplate SelectTemplate(object item,
               DependencyObject container)
    {
        if (item is PropertiesUnkownModel)
        {
            return UnknownTemplate;
        }
        return UnknownTemplate;
    }
}

xaml中的模板选择器：

<view:TemplateSelector x:Key="templateSelector" UnknownTemplate="{StaticResource PropertiesUnkownModel}"/>

以及我如何使用它：

<ListBox Grid.Row="1" VerticalAlignment="Top" ItemsSource="{Binding Attributs}" ItemTemplateSelector="{DynamicResource templateSelector}"/>

Answer 3

有hotfix可用来修复此错误。

嵌套列表中的Wpf设置事件会抛出空引用异常

3 个答案: