wpf - 使用 gong-wpf 放入空集合

Question

我正在使用 wpf 组件 https://github.com/punker76/gong-wpf-dragdrop
为了进行拖放，但我似乎无法放入空集合。如果我用一个元素初始化集合，它就可以工作。

我还创建了自己的 drop 处理程序来查看会发生什么，但从未为空集合调用它。有什么方法可以删除空集合吗？

示例 xaml:

<UserControl.Resources>
    <wf:MyDefaultDropHandler x:Key="myDND" />                                 

    <HierarchicalDataTemplate ItemsSource="{Binding Instructions}" DataType="{x:Type wf:WhileBlock}">
        <TextBlock Text="While" />
    </HierarchicalDataTemplate>

    <DataTemplate DataType="{x:Type wf:InstructionsList}">
        <ItemsControl ItemsSource="{Binding}"
                      dd:DragDrop.IsDragSource="True"
                      dd:DragDrop.IsDropTarget="True"
                      dd:DragDrop.UseDefaultDragAdorner="True"
                      dd:DragDrop.DropHandler="{StaticResource myDND}" />
    </DataTemplate>

    <DataTemplate DataType="{x:Type wf:IfElseBlock}">
        <StackPanel>
            <TextBlock Text="If" />
            <ContentControl Content="{Binding IfInstructions}" />
            <TextBlock Text="Else" />
            <ContentControl Content="{Binding ElseInstructions}" />
        </StackPanel>
    </DataTemplate>
</UserControl.Resources>
<Grid>
    <Grid.ColumnDefinitions>
        <ColumnDefinition Width="100" />
        <ColumnDefinition />
    </Grid.ColumnDefinitions>

    <Border Grid.Column="0">
        <ContentControl Content="{Binding AvailableComponents}" />
    </Border>
    <Border Grid.Column="1"
            dd:DragDrop.IsDropTarget="True"
            dd:DragDrop.DropHandler="{StaticResource myDND}">
        <ContentControl Content="{Binding Instructions}" />
    </Border>
</Grid>

我的 View 模型。如果我取消注释该行//Instructions.Add(new IfElseBlock()); drop 按预期工作

public abstract class AInstruction
{
}

public abstract class ACondition
{
}

public class InstructionsList : ObservableCollection<AInstruction>
{

}

public class WhileBlock : AInstruction
{
    private readonly InstructionsList _instructions = new InstructionsList();

    public ACondition ExecuteIf { get; set; }
    public InstructionsList Instructions { get { return _instructions; } }
}

public class IfElseBlock : AInstruction
{
    private readonly InstructionsList _ifInstructions = new InstructionsList();
    private readonly InstructionsList _elseInstructions = new InstructionsList();

    public ACondition Condition { get; set; }

    public InstructionsList IfInstructions { get { return _ifInstructions; } }
    public InstructionsList ElseInstructions { get { return _elseInstructions; } }
}

public class Script
{
    private readonly InstructionsList _instructions = new InstructionsList();
    private readonly InstructionsList _availableComponents = new InstructionsList();

    public Script()
    {
        AvailableComponents.Add(new IfElseBlock());
        AvailableComponents.Add(new IfElseBlock());
        AvailableComponents.Add(new IfElseBlock());
        AvailableComponents.Add(new WhileBlock());
        AvailableComponents.Add(new WhileBlock());
        AvailableComponents.Add(new WhileBlock());

        //Instructions.Add(new IfElseBlock());
    }

    public InstructionsList Instructions { get { return _instructions; } }

    public InstructionsList AvailableComponents { get { return _availableComponents; } }
}

我的处理程序，只是为了做一些调试

public class MyDefaultDropHandler : DefaultDropHandler
{
    public override void DragOver(IDropInfo dropInfo)
    {
        Debug.WriteLine("DragOver " + dropInfo.TargetItem);
        base.DragOver(dropInfo);
    }

    public override void Drop(IDropInfo dropInfo)
    {
        Debug.WriteLine("Drop     " + dropInfo.TargetItem);
        base.Drop(dropInfo);
    }
}

Answer 1

由于透明背景和控件的大小，似乎没有命中目标。

我刚刚添加了 Padding="1" MinHeight="10" Background="White"到我的 ItemsControl，现在 drop 可用于空集合。

在我的示例 xaml 中，它看起来像这样:

<ItemsControl ItemsSource="{Binding}" Padding="1" BorderThickness="5,0,0,0"
                      MinHeight="10"
                      Background="White"
                      dd:DragDrop.IsDragSource="True"
                      dd:DragDrop.IsDropTarget="True"
                      dd:DragDrop.UseDefaultDragAdorner="True"
                      dd:DragDrop.DropHandler="{StaticResource myDND}" />