C++/WinRT DeviceInformation No default Constructor exists 错误

Question

您好，我正在尝试从 C# 程序移植以下代码。



 public class DeviceListEntry
 {
     private DeviceInformation device;
     private String deviceSelector;

     public String InstanceId
     {
         get
         {
             return device.Properties[DeviceProperties.DeviceInstanceId] as String;
         }
     }

     public DeviceInformation DeviceInformation
     {
         get
         {
             return device;
         }
     }

     public String DeviceSelector
     {
         get
         {
             return deviceSelector;
         }
     }

     /// <summary>
     /// The class is mainly used as a DeviceInformation wrapper so that the UI can bind to a list of these.
     /// </summary>
     /// <param name="deviceInformation"></param>
     /// <param name="deviceSelector">The AQS used to find this device</param>
     public DeviceListEntry(Windows.Devices.Enumeration.DeviceInformation deviceInformation, String deviceSelector)
     {
         device = deviceInformation;
         this.deviceSelector = deviceSelector;
     }

 }
}

基本上，如果我尝试使用 deviceInformation 对象移植 DeviceListEntry 构造函数，它会错误地提示我没有 DeviceInformation 的默认构造函数 Class。

但是，如果我删除设备对象的相应代码，DevuceListEntry 构造函数不会 return 任何错误。

这是我的：

#include "pch.h"
#include "DeviceListEntry.h"
#include "Constants.h"
using namespace winrt::Windows::Devices::Enumeration;
using namespace winrt::Windows::Foundation::Collections;

namespace SerialArduino
{

    const winrt::hstring DeviceProperties::DeviceInstanceID = {L"System.Devices.DeviceInstanceId"};


    // having a DeviceInformation object as parameter as well as object causes no default constructor error
    DeviceListEntry::DeviceListEntry(winrt::Windows::Devices::Enumeration::DeviceInformation deviceInformation, winrt::hstring deviceSelector)
    {
        device = deviceInformation;
        this->deviceSelector = deviceSelector;
    }

    winrt::hstring DeviceListEntry::InstanceId()
    {

        return winrt::unbox_value<winrt::hstring>(device.Properties().Lookup(DeviceProperties::DeviceInstanceID));
    
    }

    winrt::Windows::Devices::Enumeration::DeviceInformation DeviceListEntry::DeviceInformation()
    {
        return device;
    }

    winrt::hstring DeviceListEntry::DeviceSelector()
    {
        return deviceSelector;
    }

}

错误：

Error (active)  E0291   no default constructor exists for class 
Error   C2512   'winrt::Windows::Devices::Enumeration::DeviceInformation': no appropriate default constructor available SerialArduino

任何帮助将不胜感激，因为我完全不知道自己做错了什么。提前致谢

Answer 1

假设您的 DeviceListEntry 声明如下：

namespace SerialArduino {

class DeviceListEntry {
public:
    //...

private:
    winrt::Windows::Devices::Enumeration::DeviceInformation device;
    winrt::hstring deviceSelector;
};

}

尝试像这样实现你的构造函数：

// having a DeviceInformation object as parameter as well as object causes no default constructor error
DeviceListEntry::DeviceListEntry(winrt::Windows::Devices::Enumeration::DeviceInformation deviceInformation, winrt::hstring deviceSelector_)
    : device(deviceInformation), deviceSelector(deviceSelector_)
{ }

这样，device 将从 deviceInformation 变为 copy-initialized。

否则，编译器会尝试default-constructdevice然后copy-assigndeviceInformation到它。

C++/WinRT DeviceInformation No default Constructor exists 错误

C++/WinRT DeviceInformation No default Constructor exists error

c++

c++17

windows-runtime

c++-winrt