uwp-xaml - C++ WinRT UWP XAML 数据绑定(bind) ItemsSource 和 SelectedIndex 到 IObservableVector 不起作用

Question

我正在使用 Visual Studio 2019 16.4.3、Microsoft.Windows.CppWinRT 2.0.200117.5、Windows 10 1809 Pro 和目标 10.0.17763.0。

我正在尝试将 C++/CX 应用程序移植到 C++ WinRT。我正在使用 ItemsSource 的数据绑定(bind), SelectedIndex和 SelectedItem组合框的属性，但我遇到了问题。

对于 ItemsSource我绑定(bind)到 IObservableVector<String> .该属性是使用 IObservableVector<hstring> 实现的并用 single_threaded_observable_vector(std::vector<hstring>({L"One", L"Two", L"Three"})) 初始化

启动应用程序时出现以下异常:

异常在 BlankCppWinRT.exe 中的 0x766B19B2 处抛出:Microsoft C++ 异常:内存位置 0x03AED210 处的 winrt::hresult_no_interface。发生

这应该有效吗？我如何数据绑定(bind) ItemsSource到一组字符串？这适用于 C# 和 C++/CX。 C++ WinRT 中的等效项是什么？

当我删除对 SelectedIndex 的双向绑定(bind)时应用程序启动并在组合框中显示三个字符串，并带有一个空的选定项。但是当我尝试通过 myComboBox().SelectedIndex(0); 在代码中设置选定的索引时(在构造函数中)我遇到了同样的异常。而同一行适用于 Loaded页面的处理程序。

详情如下。

有什么想法吗？

异常调用栈:

    KernelBase.dll!_RaiseException@16() Unknown
    vcruntime140d_app.dll!_CxxThrowException(void * pExceptionObject, const _s__ThrowInfo * pThrowInfo) Line 133    C++
>   BlankCppWinRT.exe!winrt::throw_hresult(const winrt::hresult result) Line 4623   C++
    BlankCppWinRT.exe!winrt::check_hresult(const winrt::hresult result) Line 4700   C++
    BlankCppWinRT.exe!winrt::impl::as<winrt::Windows::Foundation::IReference<winrt::hstring>,winrt::impl::abi<winrt::Windows::Foundation::IUnknown,void>::type>(winrt::impl::abi<winrt::Windows::Foundation::IUnknown,void>::type * ptr) Line 1941  C++
    BlankCppWinRT.exe!winrt::Windows::Foundation::IUnknown::as<winrt::Windows::Foundation::IReference<winrt::hstring>>() Line 2026  C++
    BlankCppWinRT.exe!winrt::unbox_value<winrt::hstring>(const winrt::Windows::Foundation::IInspectable & value) Line 2872  C++
    BlankCppWinRT.exe!winrt::impl::convertible_observable_vector<winrt::hstring,std::vector<winrt::hstring,std::allocator<winrt::hstring>>>::IndexOf(const winrt::Windows::Foundation::IInspectable & value, unsigned int & index) Line 2547    C++
    BlankCppWinRT.exe!winrt::impl::produce<winrt::impl::convertible_observable_vector<winrt::hstring,std::vector<winrt::hstring,std::allocator<winrt::hstring>>>,winrt::Windows::Foundation::Collections::IVector<winrt::Windows::Foundation::IInspectable>>::IndexOf(void * value, unsigned int * index, bool * winrt_impl_result) Line 566    C++
    Windows.UI.Xaml.dll!DirectUI::ItemCollection::IndexOf(IInspectable * value, unsigned int * index, unsigned char * found) Line 139   C++
    Windows.UI.Xaml.dll!DirectUI::ItemsControl::IsHostForItemContainer(Windows::UI::Xaml::IDependencyObject * pContainer, unsigned char * pIsHost) Line 1939    C++
    Windows.UI.Xaml.dll!DirectUI::ComboBox::IsHostForItemContainer(Windows::UI::Xaml::IDependencyObject * pContainer, unsigned char * pIsHost) Line 1239    C++
    Windows.UI.Xaml.dll!DirectUI::ItemContainerGenerator::ItemFromContainerImpl(Windows::UI::Xaml::IDependencyObject * container, IInspectable * * returnValue) Line 767    C++
    Windows.UI.Xaml.dll!DirectUI::ItemContainerGeneratorGenerated::ItemFromContainer(Windows::UI::Xaml::IDependencyObject * pContainer, IInspectable * * ppReturnValue) Line 222    C++

这是我的 XAML 代码:

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

    <StackPanel Orientation="Horizontal" HorizontalAlignment="Center" VerticalAlignment="Center">
        <Button Margin="8" Width="160" x:Name="myButton" Click="ClickHandler">Click Me</Button>
        <ComboBox Margin="8" Width="160" x:Name="myComboBox" ItemsSource="{x:Bind Path=BoxItems}" SelectedIndex="{x:Bind Path=SelectedBoxItemIndex, Mode=TwoWay}"/>
    </StackPanel>
</Page>

这是 .idl 文件:

namespace BlankCppWinRT
{
    [bindable]
    [default_interface]
    runtimeclass MainPage : Windows.UI.Xaml.Controls.Page, Windows.UI.Xaml.Data.INotifyPropertyChanged
    {
        MainPage();
        Windows.Foundation.Collections.IObservableVector<String> BoxItems{get;};
        Int32 SelectedBoxItemIndex;
        protected void RaisePropertyChanged(String propertyName);
    }
}

这个 MainPage.h:

#pragma once

#include "MainPage.g.h"

namespace winrt::BlankCppWinRT::implementation
{
    struct MainPage : MainPageT<MainPage>
    {
        MainPage();

        Windows::Foundation::Collections::IObservableVector<hstring> BoxItems();

        int32_t SelectedBoxItemIndex();
        void SelectedBoxItemIndex(int32_t value);

        void ClickHandler(Windows::Foundation::IInspectable const& sender, Windows::UI::Xaml::RoutedEventArgs const& args);

        void RaisePropertyChanged(hstring const& propertyName);
        winrt::event_token PropertyChanged(Windows::UI::Xaml::Data::PropertyChangedEventHandler const& handler);
        void PropertyChanged(winrt::event_token const& token) noexcept;

        void OnLoaded(winrt::Windows::Foundation::IInspectable const& sender, winrt::Windows::UI::Xaml::RoutedEventArgs const& e);

    protected:
        template<typename T>
        bool SetProperty(T& storage, const T& value, const hstring& propertyName)
        {
            if (storage == value)
                return false;
            storage = value;
            RaisePropertyChanged(propertyName);
            return true;
        }

    private:
        event<winrt::Windows::UI::Xaml::Data::PropertyChangedEventHandler> m_propertyChanged;

    private:
        Windows::Foundation::Collections::IObservableVector<hstring> m_boxItems;
        int m_selectedBoxItemIndex{};
    };
}

namespace winrt::BlankCppWinRT::factory_implementation
{
    struct MainPage : MainPageT<MainPage, implementation::MainPage>
    {
    };
}

这是 MainPage.cpp:

#include "pch.h"
#include "MainPage.h"
#include "MainPage.g.cpp"

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

namespace winrt::BlankCppWinRT::implementation
{
    MainPage::MainPage()
        : m_boxItems{single_threaded_observable_vector(std::vector<hstring>({L"One", L"Two", L"Three"}))}
    {
        InitializeComponent();
        //causes exception
        //myComboBox().SelectedIndex(0);
    }

    Windows::Foundation::Collections::IObservableVector<hstring> MainPage::BoxItems()
    {
        return m_boxItems;
    }

    int32_t MainPage::SelectedBoxItemIndex()
    {
        return m_selectedBoxItemIndex;
    }

    // data binding to SelectedBoxItemIndex causes exception

    void MainPage::SelectedBoxItemIndex(int32_t value)
    {
        SetProperty(m_selectedBoxItemIndex, value, L"SelectedBoxItemIndex");
    }

    void MainPage::ClickHandler(IInspectable const&, RoutedEventArgs const&)
    {
        myButton().Content(box_value(L"Clicked"));
        SelectedBoxItemIndex(2);
    }

    void MainPage::RaisePropertyChanged(hstring const& propertyName)
    {
        m_propertyChanged(*this, PropertyChangedEventArgs(propertyName));
    }

    winrt::event_token MainPage::PropertyChanged(Windows::UI::Xaml::Data::PropertyChangedEventHandler const& handler)
    {
        return m_propertyChanged.add(handler);
    }

    void MainPage::PropertyChanged(winrt::event_token const& token) noexcept
    {
        m_propertyChanged.remove(token);
    }

    void MainPage::OnLoaded(winrt::Windows::Foundation::IInspectable const& sender, winrt::Windows::UI::Xaml::RoutedEventArgs const& e)
    {
        // works
        myComboBox().SelectedIndex(0);
    }
}

Answer 1

作为权宜之计，您可以转到 Windows.Foundation.Collections.h 来覆盖 IndexOf() 方法。当 unbox_value 失败时，捕获 hresult_no_interface 异常并返回 false。更详细的可以引用这个thread .

bool IndexOf(Windows::Foundation::IInspectable const& value, uint32_t& index) const
{
    //return IndexOf(unbox_value<T>(value), index);
    try
    {
        return IndexOf(unbox_value<T>(value), index);
    }
    catch (hresult_no_interface const&)
    {
        return false; // unbox_value failed, "value" wasn't even a boxed T
    }
}