C++ 当 //用户正在执行拖动操作。 e、 AcceptedOperation（Windows:：ApplicationModel:：DataTransfer:：DataPackageOperation:：Copy）； } void MainPage:：OnListViewDrop（Windows:：Foundation:：IInspectable常量和目标，Windows:：UI:：Xaml:：DragEventArgs常量和e） { //使用从中拖动的数据更新目标ListView //源列表视图。 auto p=target。请按（）进行尝试； auto x=e.DataView（）.GetTextAsync（）；//**此行在删除时触发异常。 } }

在开始拖动之前，在源

列表视图

中选择项目的应用程序屏幕截图如下所示。源

ListView

控件位于左侧，目标

ListView

控件位于右侧。

附录：参考和文件

---

其中包含指向此示例项目的链接，该示例项目似乎正在使用C++/CX，其中包含一个有用的示例。

出现异常的原因是由于误用了

GetTextAsync（）

方法，该方法是一种异步方法，需要使用线程、任务、协同程序或其他一些并发功能

我找到了示例源代码，它提供了关于我做错了什么的提示。另见

为纠正问题所做更改概述

我决定与

GetTextAsync（）

一起使用协同程序，因为我使用的是Visual Studio 2017社区版的最新版本。为此，需要将方法返回类型从

void

更改为

winrt:：Windows:：Foundation:：iasyncation

，同时对解决方案属性进行一些更改，并添加一些include文件，以允许正确编译和运行协程更改

请参阅有关几种不同并发方法的答案和注释，以及Visual Studio 2017解决方案属性更改，以使用协同路由和

co_wait

操作符

在MainPage.cpp的顶部，我添加了以下两个include指令：

#include <experimental\resumable>
#include <pplawait.h>

最后，我重写了方法

OnListViewDrop（）

，以如下方式使用协同程序（还要求更改类声明中声明的返回类型以与新的返回类型一致）：

winrt:：Windows:：Foundation:：IAsyncAction主页：：OnListViewDrop（Windows:：Foundation:：IInspectable const&target，Windows:：UI:：Xaml:：DragEventArgs const&e）
{
//使用从中拖动的数据更新目标ListView
//源ListView。方法GetTextAsync（）是一个异步方法，因此
//我们正在使用协程来获得操作的结果。
//在执行co_wait之前，我们需要捕获目标ListView
//在局部变量中，以便我们知道要更新哪个ListView。
auto p=target。请按（）进行尝试；
//执行GetTextAsync（）并使用协同例程获得结果。
auto ss=co_wait e.DataView（）.GetTextAsync（）；
//更新最初触发此处理程序的ListView控件。
p、 Items（）.追加（框_值（ss））；
}

auto x = e.DataView().GetTextAsync();

{m_handle={m_value=0x05550330 L"DataPackage does not contain the specified format. Verify its presence using DataPackageView.Contains or DataPackageView.AvailableFormats." } }

App::App()
{
    InitializeComponent();
    DataSource::InitializeDataBase();
    Suspending({ this, &App::OnSuspending });
    //  … other code

#include "winrt/Windows.ApplicationModel.DataTransfer.h"    // ADD_TO:  need to add to allow use of drag and drop in MainPage.cpp

 <Page
    x:Class="TouchExperiment_01.MainPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="using:TouchExperiment_01"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d">

    <StackPanel Orientation="Horizontal" HorizontalAlignment="Center" VerticalAlignment="Center" Width="1130" Margin="0,0,0,0">
        <ListView x:Name="myList" HorizontalAlignment="Left" Height="100" VerticalAlignment="Top" Width="300" SelectionChanged="OnSelectionChanged"
                  CanDragItems="True" DragItemsStarting="OnListViewDragItemsStarting" BorderBrush="AliceBlue" BorderThickness="3">
        </ListView>
        <TextBlock x:Name="myTextBlock" Height="200" Width="200" Text="this is temp text to replace." TextWrapping="WrapWholeWords" Margin="5"/>
        <ListView x:Name="myList2" HorizontalAlignment="Right" Height="100" VerticalAlignment="Top" Width="300" SelectionChanged="OnSelectionChanged" AllowDrop="True"
                  DragOver="OnListViewDragOver" Drop="OnListViewDrop"  BorderBrush="DarkGreen" BorderThickness="5">
        </ListView>
    </StackPanel>
</Page>

#pragma once
class DataSource
{
public:
    DataSource();
    ~DataSource();

    static int InitializeDataBase();

    struct DataSourceType
    {
        std::wstring  name;
        std::wstring  description;
    };

    static std::vector<DataSourceType> myDataBase;

}

;

int DataSource::InitializeDataBase()
{
    myDataBase.clear();

    for (int i = 0; i < 50; i++) {
        DataSourceType x;
        wchar_t  buffer[256] = { 0 };

        swprintf_s(buffer, 255, L"Name for %d Item", i);
        x.name = buffer;
        swprintf_s(buffer, 255, L"Description %d. Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam.", i);
        x.description = buffer;
        myDataBase.push_back(x);
    }

    return 0;
}

#include "pch.h"
#include "MainPage.h"
#include "DataSource.h"

using namespace winrt;
using namespace Windows::UI::Xaml;


namespace winrt::TouchExperiment_01::implementation
{
    MainPage::MainPage()
    {
        InitializeComponent();

        // load up the source ListView with the name field from out
        // in memory database.
        auto p = myList().Items();
        for (auto a : DataSource::myDataBase) {
            p.Append(box_value(a.name));
        }

        // add a single ListViewItem to the destination ListView so that we
        // know where it is.
        p = myList2().Items();
        p.Append(box_value(L"list"));
    }

    int32_t MainPage::MyProperty()
    {
        throw hresult_not_implemented();
    }

    void MainPage::MyProperty(int32_t /* value */)
    {
        throw hresult_not_implemented();
    }

    void MainPage::OnSelectionChanged(Windows::Foundation::IInspectable const & target, Windows::UI::Xaml::RoutedEventArgs const & )
    {
        // the user has selected a different item in the source ListView so we want to display
        // the associated description information for the selected ListViewItem.
        winrt::Windows::UI::Xaml::Controls::ListView p = target.try_as<winrt::Windows::UI::Xaml::Controls::ListView>();
        if (p) {
            int iIndex = p.SelectedIndex();
            myTextBlock().Text(DataSource::myDataBase[iIndex].description);
        }
    }

    void MainPage::OnListViewDragItemsStarting(Windows::Foundation::IInspectable const & target, Windows::UI::Xaml::Controls::DragItemsStartingEventArgs  const & e)
    {
        // provide the data that we have in the ListView which the user has selected
        // to drag to the other ListView. this is the data that will be copied from
        // the source ListView to the destination ListView.
        auto p = target.try_as<winrt::Windows::UI::Xaml::Controls::ListView>();
        if (p) {
            int iIndex = p.SelectedIndex();
            e.Items().SetAt(0, box_value(iIndex));
        }
    }

    void MainPage::OnListViewDragOver(Windows::Foundation::IInspectable const & target, Windows::UI::Xaml::DragEventArgs  const & e)
    {
        // indicate that we are Copy of data from one ListView to another rather than one of the other
        // operations such as Move. This provides the operation type informative user indicator when the
        // user is doing the drag operation.
        e.AcceptedOperation(Windows::ApplicationModel::DataTransfer::DataPackageOperation::Copy);
    }

    void MainPage::OnListViewDrop(Windows::Foundation::IInspectable const & target, Windows::UI::Xaml::DragEventArgs const & e)
    {
        // update the destination ListView with the data that was dragged from the
        // source ListView.
        auto p = target.try_as<winrt::Windows::UI::Xaml::Controls::ListView>();

        auto x = e.DataView().GetTextAsync();  // ** this line triggers exception on drop.
    }

}

    // We need to take a Deferral as we won't be able to confirm the end
    // of the operation synchronously
    auto def = e->GetDeferral();
    create_task(e->DataView->GetTextAsync()).then([def, this, e](String^ s)
    {
        // Parse the string to add items corresponding to each line
        auto wsText = s->Data();
        while (wsText) {
            auto wsNext = wcschr(wsText, L'\n');
            if (wsNext == nullptr)
            {
                // No more separator
                _selection->Append(ref new String(wsText));
                wsText = wsNext;
            }
            else
            {
                _selection->Append(ref new String(wsText, wsNext - wsText));
                wsText = wsNext + 1;
            }
        }

        e->AcceptedOperation = DataPackageOperation::Copy;
        def->Complete();
    });

#include <experimental\resumable>
#include <pplawait.h>

void MainPage::OnListViewDragItemsStarting(Windows::Foundation::IInspectable const & target, Windows::UI::Xaml::Controls::DragItemsStartingEventArgs  const & e)
{
    // provide the data that we have in the ListView which the user has selected
    // to drag to the other ListView. this is the data that will be copied from
    // the source ListView to the destination ListView.
    auto p = target.try_as<winrt::Windows::UI::Xaml::Controls::ListView>();
    unsigned int n = e.Items().Size();
    if (p) {
        int iIndex = p.SelectedIndex();
        e.Data().Properties().Title(hstring (L"my Title"));
        e.Data().SetText(DataSource::myDataBase[iIndex].name.c_str());
        e.Data().RequestedOperation(winrt::Windows::ApplicationModel::DataTransfer::DataPackageOperation::Copy);
    }
}

winrt::Windows::Foundation::IAsyncAction MainPage::OnListViewDrop(Windows::Foundation::IInspectable const & target, Windows::UI::Xaml::DragEventArgs const & e)
{
    // update the destination ListView with the data that was dragged from the
    // source ListView. the method GetTextAsync() is an asynch method so
    // we are using coroutines to get the result of the operation.

    // we need to capture the target ListView before doing the co_await
    // in a local variable so that we will know which ListView we are to update.
    auto p = target.try_as<winrt::Windows::UI::Xaml::Controls::ListView>();

    // do the GetTextAsync() and get the result by using coroutines.
    auto ss = co_await e.DataView().GetTextAsync();

    // update the ListView control that originally triggered this handler.
    p.Items().Append(box_value(ss));
}