所以，我检查了以下问题，这些问题似乎与我现有的问题最相似：
QML: Using cpp signal in QML always results in "Cannot assign to non-existent property"
不幸的是，这没有帮助。 （我也没有在stackoverflow / google / qt论坛上找到任何其他解决方案等）
我一直收到以下两个错误：
qrc：/view.qml：30：9：QML连接：无法分配给不存在的属性“onNewFrameReceived”qrc：/view.qml：31：ReferenceError：imageProvide未定义
这是我的代码（编辑成为“最小工作示例”）。
唯一重要的文件应该是：
我包含了imagesource类，只是为了完整，以防有人想要自己编译它。
Q1。所以，我不明白为什么即使在main.cpp中设置了context属性之后，也会出现以下错误。
qrc：/view.qml：31：ReferenceError：未定义imageProvide
有趣的是，intellisense / autocomplete似乎完全正确地检测到imageProvide。
Q2。即使在我的imageprovider.h中，我添加了应该在qml文件中看到的属性（newimage）和信号（newFrameReceived），但仍然会出现以下错误。此外，Qt智能感知/自动完成无法在此显示我定义的信号（onNewFrameReceived）。
qrc：/view.qml：30：9：QML连接：无法分配给不存在的属性“onNewFrameReceived”
main.cpp中
#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QQmlContext>
#include "imageprovidervm.h"
#include "imagesource.h"
int main(int argc, char *argv[])
{
QGuiApplication app(argc, argv);
QQmlApplicationEngine engine;
QQmlContext *context = new QQmlContext(engine.rootContext());
auto model = std::make_shared<ImageSource>();
auto vm = new ImageProviderVM(model);
engine.addImageProvider(QLatin1String("imageProvider"), vm);
context->setContextProperty("imageProvide", vm );
model->generateImages();
engine.load(QUrl(QStringLiteral("qrc:/view.qml")));
return app.exec();
}
view.qml
import QtQuick 2.5
import QtQuick.Controls 1.4
import QtQml.Models 2.2
import QtQuick.Dialogs 1.2
import QtQuick.Window 2.0
ApplicationWindow {
visible: true
width: 640
height: 480
title: qsTr("Hello World")
menuBar: MenuBar {
Menu {
title: qsTr("File")
MenuItem {
text: qsTr("&Open")
onTriggered: console.log("Open action triggered");
}
MenuItem {
text: qsTr("Exit")
onTriggered: Qt.quit();
}
}
}
Rectangle {
Connections {
target: imageProvide
onNewFrameReceived: image.reload();
}
anchors.fill: parent
Column {
Image {
id: image
source: "image://imageProvider/images.jpeg?id=" + Math.random()
cache: false
asynchronous: true
function reload() {
var oldSource = source;
source = "";
source = oldSource;
}
}
}
}
Label {
text: qsTr("Hello World")
anchors.centerIn: parent
}
}
imageprovidervm.h
#ifndef IMAGEPROVIDERVM_H
#define IMAGEPROVIDERVM_H
#include <QQuickImageProvider>
#include <QObject>
#include "imagesource.h"
class ImageProviderVM : public QObject, public QQuickImageProvider
{
Q_OBJECT
public:
ImageProviderVM(std::shared_ptr<ImageSource> model);
~ImageProviderVM();
virtual QPixmap requestPixmap(const QString &id, QSize *size, const QSize &requestedSize) override;
virtual QImage requestImage(const QString & id, QSize * size, const QSize & requestedSize) override;
// Properties
Q_PROPERTY(QImage newimage READ getNewImage NOTIFY newFrameReceived)
// Signals
signals:
void newFrameReceived();
private:
QImage getNewImage() const;
QPixmap m_pixmap;
QImage m_image;
std::shared_ptr<ImageSource> m_model;
};
#endif // IMAGEPROVIDERVM_H
imageprovidervm.cpp
#include "imageprovidervm.h"
#include <functional>
#include <QPixmap>
#include <QDebug>
ImageProviderVM::ImageProviderVM()
: QQuickImageProvider(QQuickImageProvider::Image)
{
}
ImageProviderVM::ImageProviderVM(std::shared_ptr<ImageSource> model)
: QQuickImageProvider (QQuickImageProvider::Image)
, m_pixmap()
, m_model(model)
{
m_model->subscribeNewPixMap([this](QPixmap pixmap) {
qDebug() << "setting m_pixmap";
if (pixmap.size().isValid()) {
m_pixmap = pixmap;
}
else
qDebug() << "is it NULL ??? " << pixmap.isNull();
});
m_model->subscribeNewImage([this](QImage image) {
qDebug() << "setting m_image";
if (image.size().isValid()) {
m_image = image;
emit newFrameReceived();
}
else
qDebug() << "is it NULL ??? " << image.isNull();
});
qDebug() << "imageproviderVM constructed";
}
ImageProviderVM::~ImageProviderVM()
{
}
QPixmap ImageProviderVM::requestPixmap(const QString &id, QSize *size, const QSize &requestedSize)
{
// look into the parameters id, size and requestedSize once the rest of the structure is there
return m_pixmap;
}
QImage ImageProviderVM::requestImage(const QString & id, QSize * size, const QSize & requestedSize)
{
return m_image;
}
QQuickTextureFactory * ImageProviderVM::requestTexture(const QString & id, QSize * size, const QSize & requestedSize)
{
// return QQuickTextureFactory::createTexture();
}
QImage ImageProviderVM::getNewImage() const
{
return m_image;
}
imagesource.h
#ifndef IMAGESOURCE_H
#define IMAGESOURCE_H
#include <QImage>
#include <boost/signals2.hpp>
class ImageSource
{
public:
ImageSource();
void generateImages();
void generatePixmaps(const QString &id, QSize *size, const QSize &requestedSize);
typedef boost::signals2::signal<void (QPixmap)> NewPixMapDelegate;
boost::signals2::connection subscribeNewPixMap(NewPixMapDelegate::slot_function_type f);
typedef boost::signals2::signal<void (QImage)> NewImageDelegate;
boost::signals2::connection subscribeNewImage(NewImageDelegate::slot_function_type f);
private:
NewPixMapDelegate m_newPixMap;
NewImageDelegate m_newImage;
};
#endif // IMAGESOURCE_H
imagesource.cpp
#include "imagesource.h"
#include <QPixmap>
#include <QPainter>
#include <thread>
ImageSource::ImageSource()
{
}
boost::signals2::connection ImageSource::subscribeNewImage(NewImageDelegate::slot_function_type f)
{
return m_newImage.connect(f);
}
void ImageSource::generateImages()
{
std::thread t([this]() {
auto image = QImage("/home/junaid/testing_ground/fourthtime/images.jpeg");
m_newImage(image);
/// useless wait. just simulating that another image comes after sometime and so on onwards.
int random_wait = 2; //sec
sleep(random_wait);
image = QImage("/home/junaid/Downloads/pnggrad16rgb.png");
m_newImage(image);
});
t.detach();
}
boost::signals2::connection ImageSource::subscribeNewPixMap(NewPixMapDelegate::slot_function_type f)
{
return m_newPixMap.connect(f);
}
void ImageSource::generatePixmaps(const QString &id, QSize *size, const QSize &requestedSize)
{
int width = 100;
int height = 50;
if (size) {
*size = QSize(width, height);
}
QPixmap pixmap(requestedSize.width() > 0 ? requestedSize.width() : width,
requestedSize.height() > 0 ? requestedSize.height() : height);
pixmap.fill(QColor(id).rgba());
// write the color name
QPainter painter(&pixmap);
QFont f = painter.font();
f.setPixelSize(20);
painter.setFont(f);
painter.setPen(Qt::black);
if (requestedSize.isValid())
painter.scale(requestedSize.width() / width, requestedSize.height() / height);
painter.drawText(QRectF(0, 0, width, height), Qt::AlignCenter, id);
m_newPixMap(pixmap);
}
这是CMake文件：
cmake_minimum_required(VERSION 2.8.12)
project(non_existent_property LANGUAGES CXX)
set(CMAKE_INCLUDE_CURRENT_DIR ON)
set(CMAKE_AUTOMOC ON)
set(CMAKE_AUTORCC ON)
find_package(Qt5 COMPONENTS Core Quick REQUIRED)
file( GLOB SRCS *.cpp *.h )
add_executable(${PROJECT_NAME} "qml.qrc" ${SRCS})
target_link_libraries(${PROJECT_NAME} Qt5::Core Qt5::Quick "pthread")
那么，这是工作main.cpp的外观。我被我正在创建的QmlContext误导，并且在@ GrecKo和jpnurmi的评论的帮助下，我明白我必须为根上下文设置属性。
#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QQmlContext>
#include "imageprovidervm.h"
#include "imagesource.h"
int main(int argc, char *argv[])
{
QGuiApplication app(argc, argv);
QQmlApplicationEngine engine;
// QQmlContext *context = new QQmlContext(engine.rootContext());
auto model = std::make_shared<ImageSource>();
auto vm = new ImageProviderVM(model);
engine.addImageProvider(QLatin1String("imageProvider"), vm);
engine.rootContext()->setContextProperty("imageProvide", vm );
model->generateImages();
engine.load(QUrl(QStringLiteral("qrc:/view.qml")));
return app.exec();
}