未定义值错误和QML文本字段不更新，尽管在Qt Quick C++项目中正确的qvod输出

xu3bshqb  于 2024-01-09  发布在  其他
关注(0)|答案(1)|浏览(151)

下面是我写的一个函数，它旨在使用COM和JavaScript返回用户PC存储的名称：

  1. Q_INVOKABLE QString systeminfo::getDiskInfo() {
  2.     // Disk info
  3.     HRESULT hres;
  4.     IWbemLocator* pLoc = NULL;
  5.     IWbemServices* pSvc = NULL;
  7.     initializeCOM(hres, pLoc, pSvc);
  9.     IEnumWbemClassObject* pEnumerator = NULL;
  10.     hres = pSvc->ExecQuery(
  11.         ConvertStringToBSTR("WQL"),
  12.         ConvertStringToBSTR("SELECT * FROM Win32_DiskDrive"),
  13.         WBEM_FLAG_FORWARD_ONLY | WBEM_FLAG_RETURN_IMMEDIATELY,
  14.         NULL,
  15.         &pEnumerator);
  17.     if (FAILED(hres))
  18.     {
  19.         std::cout << "Error code = 0x" << std::hex << hres << std::endl;
  20.         pSvc->Release();
  21.         pLoc->Release();
  22.         CoUninitialize();
  23.         return QString(); // Returns an empty string in case of an error
  24.     }
  26.     // Getting data
  27.     QString storageModel;
  28.     while (pEnumerator)
  29.     {
  30.         IWbemClassObject* pclsObj = NULL;
  31.         ULONG uReturn = 0;
  32.         HRESULT hr = pEnumerator->Next(WBEM_INFINITE, 1, &pclsObj, &uReturn);
  34.         if (0 == uReturn)
  35.         {
  36.             break;
  37.         }
  39.         VARIANT vtProp;
  41.         hr = pclsObj->Get(L"Model", 0, &vtProp, 0, 0);
  42.         storageModel = QString::fromWCharArray(vtProp.bstrVal);
  43.         qDebug() << "Storage: " << storageModel;
  44.         VariantClear(&vtProp);
  46.         pclsObj->Release();
  47.     }
  49.     // Cleanup
  50.     pSvc->Release();
  51.     pLoc->Release();
  52.     pEnumerator->Release();
  53.     CoUninitialize();
  54.     return storageModel;
  55. }

字符串
在App.qml中，我将值赋给了一个文本字段：

  1. Component.onCompleted: {
  2.         mainScreen.gpuInfoField.text = sysInfo.getGpuInfo();
  3.         mainScreen.diskInfoField.text = sysInfo.getDiskInfo();
  4.     }

型
在构建项目时，qDebug()触发的控制台输出显示了预期的值，即磁盘的名称。但随后它抛出了此错误，文本字段的值没有更改：
qrc:/qt/qml/content/App.qml:20: TypeError: Value is undefined and could not be converted to an object个
类似编写的getGpuInfo（）;函数工作正常。
要重现此问题，请在Qt Creator中创建一个Qt Quick项目，并添加一个带有getData Info（）函数的类“systeminfo.cpp”，不要忘记初始化COM并包含Wbemidl. h和comdef. h。在Qt Design Studio中添加一个文本字段，并尝试在App. qml中分配值。这很明显，但请注意，除了Windows之外的任何操作系统都无法工作，因为Windows Management Instrumentation API是Windows特定的。
我花了整整一天的时间试图弄清楚到底是什么问题，添加了很多错误处理程序和qDebugs，然后完全删除了该函数，并编写了一个类似的函数getRamInfo（），具有完全相同的问题和完全相同的错误。qDebugs（）将预期值输出到控制台，但是仍然有一个错误，指出该值是未定义的。getGpuInfo（）功能正常，它几乎是一样的。我最初认为这个错误是特定于getGpuInfo（），但同样的问题，在新编写的函数暗示相反.不知道是什么问题，因为函数本身似乎工作正常，并打印磁盘的名称.如果你需要更多的信息，试图找到解决这个问题，随时写在评论.我真的需要帮助.
任何帮助，任何想法，在这一点上的任何东西都将受到高度赞赏。

Minimal Reproducible ExampleSide Note：* 有趣的是，当我创建这个示例并构建它时，没有一个函数可以工作。甚至getGpuInfo（）;函数也不再按预期工作，而当控制台中显示预期值时，有一个TypeError。我肯定错过了一些东西。*

在新创建的Qt Quick项目中创建一个systeminfo类。.cpp代码必须包含COM初始化函数，getGpuInfo（）和getGpuInfo（），如下所示：

  1. #define _WIN32_DCOM
  2. #include <iostream>
  3. #include <comdef.h>
  4. #include <Wbemidl.h>
  5. #include "systeminfo.h"
  7. #include <QDebug>
  9. #pragma comment(lib, "wbemuuid.lib")
  11. systeminfo::systeminfo(QObject *parent) : QObject(parent) {
  12.     HRESULT hres;
  13.     IWbemLocator* pLoc = nullptr;
  14.     IWbemServices* pSvc = nullptr;
  15.     initializeCOM(hres, pLoc, pSvc);
  16. }
  18. // Function for converting char* to BSTR.
  19. BSTR ConvertStringToBSTR(const char *pSrc)
  20. {
  21.     const size_t cSize = strlen(pSrc)+1;
  22.     wchar_t* wc = new wchar_t[cSize];
  23.     mbstowcs (wc, pSrc, cSize);
  25.     BSTR bstr = SysAllocString(wc);
  26.     delete [] wc;
  27.     return bstr;
  28. }
  30. void systeminfo::initializeCOM(HRESULT& hres, IWbemLocator*& pLoc, IWbemServices*& pSvc) {
  31.     // Initializing COM.
  32.     hres = CoInitializeEx(nullptr, COINIT_MULTITHREADED);
  33.     if (FAILED(hres) && hres != RPC_E_CHANGED_MODE)
  34.     {
  35.         std::cout << "There was an error initializing COM. Error code = 0x" << std::hex << hres << std::endl;
  36.         return;
  37.     }
  39.     // Configuring COM security level.
  40.     hres = CoInitializeSecurity(
  41.         NULL,
  42.         -1,
  43.         NULL,
  44.         NULL,
  45.         RPC_C_AUTHN_LEVEL_DEFAULT,
  46.         RPC_C_IMP_LEVEL_IMPERSONATE,
  47.         NULL,
  48.         EOAC_NONE,
  49.         NULL);
  51.     if(hres == RPC_E_TOO_LATE)
  52.         hres = S_OK;
  53.     else if (FAILED(hres))
  54.     {
  55.         std::cout << "There was an error configuring COM security level. Error code = 0x" << std::hex << hres << std::endl;
  56.         CoUninitialize();
  57.         return;
  58.     }
  60.     // Getting a pointer to the WMI service.
  61.     hres = CoCreateInstance(
  62.         CLSID_WbemLocator,
  63.         0,
  64.         CLSCTX_INPROC_SERVER,
  65.         IID_IWbemLocator, (LPVOID*)&pLoc);
  67.     if (FAILED(hres))
  68.     {
  69.         std::cout << "Error creating IWbemLocator instance. Error code = 0x" << std::hex << hres << std::endl;
  70.         CoUninitialize();
  71.         return;
  72.     }
  74.     // Connecting to WMI namespace.
  76.     hres = pLoc->ConnectServer(
  77.         ConvertStringToBSTR("ROOT\\CIMV2"),
  78.         nullptr,
  79.         nullptr,
  80.         0,
  81.         0,
  82.         0,
  83.         0,
  84.         &pSvc);
  86.     if (FAILED(hres))
  87.     {
  88.         std::cout << "There was an error connecting to WMI namespace. Error code = 0x" << std::hex << hres << std::endl;
  89.         pLoc->Release();
  90.         CoUninitialize();
  91.         return;
  92.     }
  94.     // Setting the security level for WMI proxy.
  95.     hres = CoSetProxyBlanket(
  96.         pSvc,
  97.         RPC_C_AUTHN_WINNT,
  98.         RPC_C_AUTHZ_NONE,
  99.         NULL,
  100.         RPC_C_AUTHN_LEVEL_CALL,
  101.         RPC_C_IMP_LEVEL_IMPERSONATE,
  102.         NULL,
  103.         EOAC_NONE);
  105.     if (FAILED(hres))
  106.     {
  107.         std::cout << "Error setting security level. Error code = 0x" << std::hex << hres << std::endl;
  108.         pSvc->Release();
  109.         pLoc->Release();
  110.         CoUninitialize();
  111.         return;
  112.     }
  113. }
  115. Q_INVOKABLE QString systeminfo::getGpuInfo() {
  116.     HRESULT hres;
  117.     IWbemLocator* pLoc = NULL;
  118.     IWbemServices* pSvc = NULL;
  119.     initializeCOM(hres, pLoc, pSvc);
  120.     // Using WMI to retrieve information about the video controller.
  121.     IEnumWbemClassObject* pEnumerator = NULL;
  122.     hres = pSvc->ExecQuery(
  123.         ConvertStringToBSTR("WQL"),
  124.         ConvertStringToBSTR("SELECT * FROM Win32_VideoController"),
  125.         WBEM_FLAG_FORWARD_ONLY | WBEM_FLAG_RETURN_IMMEDIATELY,
  126.         NULL,
  127.         &pEnumerator);
  128.     if (FAILED(hres))
  129.     {
  130.         std::cout << "Query execution failed. Error code = 0x" << std::hex << hres << std::endl;
  131.         pSvc->Release();
  132.         pLoc->Release();
  133.         CoUninitialize();
  134.         return QString(); // Returns an empty string in case of an error.
  135.     }
  137.     IWbemClassObject* pclsObj = NULL;
  138.     ULONG uReturn = 0;
  139.     QString gpuInfo;
  140.     while (pEnumerator)
  141.     {
  142.         HRESULT hr = pEnumerator->Next(WBEM_INFINITE, 1, &pclsObj, &uReturn);
  143.         if (0 == uReturn)
  144.         {
  145.             break;
  146.         }
  147.         VARIANT vtProp;
  148.         // Getting the name of the GPU.
  149.         hr = pclsObj->Get(L"Name", 0, &vtProp, 0, 0);
  150.         gpuInfo = QString::fromWCharArray(vtProp.bstrVal);
  151.         qDebug() << "GPU: " << gpuInfo;
  152.         VariantClear(&vtProp);
  153.         pclsObj->Release();
  154.     }
  155.     // Cleanup.
  156.     pSvc->Release();
  157.     pLoc->Release();
  158.     pEnumerator->Release();
  159.     CoUninitialize();
  160.     return gpuInfo;
  161. }
  163. Q_INVOKABLE QString systeminfo::getDiskInfo() {
  164.     // Using WMI to get retrieve information about the storage.
  165.     HRESULT hres;
  166.     IWbemLocator* pLoc = NULL;
  167.     IWbemServices* pSvc = NULL;
  169.     initializeCOM(hres, pLoc, pSvc);
  171.     IEnumWbemClassObject* pEnumerator = NULL;
  172.     hres = pSvc->ExecQuery(
  173.         ConvertStringToBSTR("WQL"),
  174.         ConvertStringToBSTR("SELECT * FROM Win32_DiskDrive"),
  175.         WBEM_FLAG_FORWARD_ONLY | WBEM_FLAG_RETURN_IMMEDIATELY,
  176.         NULL,
  177.         &pEnumerator);
  179.     if (FAILED(hres))
  180.     {
  181.         std::cout << "Query execution failed. Error code = 0x" << std::hex << hres << std::endl;
  182.         pSvc->Release();
  183.         pLoc->Release();
  184.         CoUninitialize();
  185.         return QString(); // Returns an empty string in case of an error.
  186.     }
  188.     QString storageModel;
  189.     while (pEnumerator)
  190.     {
  191.         IWbemClassObject* pclsObj = NULL;
  192.         ULONG uReturn = 0;
  193.         HRESULT hr = pEnumerator->Next(WBEM_INFINITE, 1, &pclsObj, &uReturn);
  195.         if (0 == uReturn)
  196.         {
  197.             break;
  198.         }
  200.         VARIANT vtProp;
  202.         // Getting the name of the disk.
  203.         hr = pclsObj->Get(L"Model", 0, &vtProp, 0, 0);
  204.         storageModel = QString::fromWCharArray(vtProp.bstrVal);
  205.         qDebug() << "Storage: " << storageModel;
  206.         VariantClear(&vtProp);
  208.         pclsObj->Release();
  209.     }
  211.     // Cleanup.
  212.     pSvc->Release();
  213.     pLoc->Release();
  214.     pEnumerator->Release();
  215.     CoUninitialize();
  216.     return storageModel;
  217. }

型
在头文件（systeminfo. h）中定义systeminfo类

  1. #ifndef SYSTEMINFO_H
  2. #define SYSTEMINFO_H
  4. #include <QObject>
  5. #include <comdef.h>
  6. #include <Wbemidl.h>
  8. interface IWbemLocator;
  9. interface IWbemServices;
  11. class systeminfo : public QObject
  12. {
  13.     Q_OBJECT
  14. public:
  15.     explicit systeminfo(QObject *parent = nullptr);
  16.     Q_INVOKABLE QString getGpuInfo();
  17.     Q_INVOKABLE QString getDiskInfo();
  19. private:
  20.     void initializeCOM(HRESULT& hres, IWbemLocator*& pLoc, IWbemServices*& pSvc);
  21. };
  23. #endif // SYSTEMINFO_H

型
在你的main.cpp文件中定义一个sysInfo对象，并使它对QML可用，包括QQmlContext和systeminfo.h：

  1. #include <QGuiApplication>
  2. #include <QQmlApplicationEngine>
  3. #include <QQmlContext> // Add this line
  5. #include "app_environment.h"
  6. #include "import_qml_components_plugins.h"
  7. #include "import_qml_plugins.h"
  9. #include "../systeminfo.h" // And this
  11. int main(int argc, char *argv[])
  12. {
  13.     set_qt_environment();
  15.     QGuiApplication app(argc, argv);
  17.     QQmlApplicationEngine engine;
  19.     // Add these two lines below:
  20.     systeminfo sysInfo;
  21.     engine.rootContext()->setContextProperty("sysInfo", &sysInfo);
  23.     const QUrl url(u"qrc:/qt/qml/Main/main.qml"_qs);
  24.     QObject::connect(
  25.         &engine,
  26.         &QQmlApplicationEngine::objectCreated,
  27.         &app,
  28.         [url](QObject *obj, const QUrl &objUrl) {
  29.             if (!obj && url == objUrl)
  30.                 QCoreApplication::exit(-1);
  31.         },
  32.         Qt::QueuedConnection);
  34.     engine.addImportPath(QCoreApplication::applicationDirPath() + "/qml");
  35.     engine.addImportPath(":/");
  37.     engine.load(url);
  39.     if (engine.rootObjects().isEmpty()) {
  40.         return -1;
  41.     }
  43.     return app.exec();
  44. }

型
请注意，我的代码中的#include ".../systeminfo.h"假设该文件位于项目的根目录中。如果您在其他地方创建了一个systeminfo类，则需要指定该路径-显然。
在Screen01.ui.qml中创建两个ID为gpuInfoField和diskInfoField的文本区域，并禁用它们：

  1. import QtQuick 6.2
  2. import QtQuick.Controls 6.2
  3. import nameofyourproject
  5. Rectangle {
  6.     id: rectangle
  7.     width: Constants.width
  8.     height: Constants.height
  10.     color: Constants.backgroundColor
  12.     TextArea {
  13.         id: gpuInfoField
  14.         x: 511
  15.         y: 267
  16.         width: 714
  17.         height: 136
  18.         enabled: false
  19.         placeholderText: qsTr("Text Area")
  20.     }
  22.     TextArea {
  23.         id: diskInfoField
  24.         x: 511
  25.         y: 453
  26.         width: 714
  27.         height: 136
  28.         enabled: false
  29.         placeholderText: qsTr("Text Area")
  30.     }
  31. }

型
将值分配给App.qml中的文本区域：

  1. Component.onCompleted: {
  2.             mainScreen.gpuInfoField.text = sysInfo.getGpuInfo();
  3.             mainScreen.diskInfoField.text = sysInfo.getDiskInfo();
  4.         }

型
最后，确保在CMakeLists.txt中链接wbemuuid库：

  1. target_link_libraries(MREApp PRIVATE
  2.     Qt6::Core
  3.     Qt6::Gui
  4.     Qt6::Qml
  5.     Qt6::Quick
  6.     wbemuuid #Add this library
  7. )

型
在我的例子中，文本区域的值没有改变，控制台输出如下所示：

  1. GPU:  "NVIDIA GeForce RTX 3080 Ti"
  2. qrc:/qt/qml/content/App.qml:19: TypeError: Value is undefined and could not be converted to an object

型

c++

1条答案

按热度按时间
sxissh06

sxissh061#

你的问题与你正在阅读的C++对象无关。这是你试图向其分配文本的TextArea对象的问题。你不能访问对象的子对象的ID。相反，你需要通过属性公开对象。在我上面的评论中，我应该建议使用属性别名而不仅仅是属性，但它们在这种情况下都应该工作。
MainScreen.qml

  1. Rectangle {
  2.     // Expose objects that are accessed from outside
  3.     property alias gpuInfoField: gpuInfoField
  4.     property alias diskInfoField: diskInfoField
  6.     TextArea {
  7.         id: gpuInfoField
  8.     }
  10.     TextArea {
  11.         id: diskInfoField
  12.     }
  13. }

字符串
App.qml

  1. Window {
  2.     MainScreen {
  3.         id: mainScreen
  4.     }
  6.     Component.onCompleted: {
  7.         mainScreen.gpuInfoField.text = sysInfo.getGpuInfo();
  8.         mainScreen.diskInfoField.text = sysInfo.getDiskInfo();
  9.     }
  10. }

型
也就是说，你通常不需要访问整个对象。通常最好是简单地将需要的子对象的属性暴露在类之外：
MainScreen.qml

  1. Rectangle {
  2.     // Just expose the text properties, not the whole object
  3.     property alias gpuText: gpuInfoField.text
  4.     property alias diskText: diskInfoField.text
  6.     TextArea {
  7.         id: gpuInfoField
  8.     }
  10.     TextArea {
  11.         id: diskInfoField
  12.     }
  13. }

型
App.qml

  1. Window {
  2.     MainScreen {
  3.         id: mainScreen
  4.     }
  6.     Component.onCompleted: {
  7.         mainScreen.gpuText = sysInfo.getGpuInfo();
  8.         mainScreen.diskText = sysInfo.getDiskInfo();
  9.     }
  10. }

型

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