Qt/QML:将 QImage 从 C++ 发送到 QML 并在 GUI 上显示 QImage
我创建了一个 Publisher
类,它定期发出一个 QImage
对象.
但是,我很难将 QImage
绘制到 QML 元素.看起来 Image
和 Canvas
QML 组件需要 QUrl
而不是 QImage
,但我不需要确定如何将我的 QImage
转换为 QUrl
.Edit4:当我说 QUrl 时,并不是说我要尝试将图像转换为 URL.那是胡说八道.我的意思是我想生成对这个图像的引用,它不在磁盘上,而 QML 组件要求的数据类型是一个 URL.
我做了一些研究,发现 QQuickImageProvider
提供了一个解决方案,但我没有找到任何文档来解释如何将我的 QImage
信号转换为 QUrl
我可以用来绘图.任何示例代码或参考文档将不胜感激.
感谢您的帮助!
编辑 1:
我看过这里:http://qt-project.org/doc/qt-5.0/qtquick/qquickimageprovider.html 并且我不知道如何将 QImage 传递给快速图像提供程序并从中创建一个 QUrl.
编辑2.这是标题.实施应该不重要.
类发布者{Q_OBJECT民众:发布者(QObject* parent = 0);虚拟?发布者(无效);Q_信号:void newImage(const QImage& newImage);};
Edit 3. 这是我的 QML 代码,但我不知道如何绘制我的 QImage,所以这段代码没有意义.
我的 main.cpp 文件:
int main(int argc, char *argv[]){QGuiApplication app(argc, argv);qmlRegisterType("组件", 1, 0, "Publisher");QtQuick2ApplicationViewer 查看器;viewer.setMainQmlFile(QStringLiteral("qml/QQuickViewExample/main.qml"));查看器.showExpanded();返回 app.exec();}
我的 main.qml 文件:
导入QtQuick 2.0导入组件 1.0长方形 {id : testRect宽度:360高度:360图片{anchors.fill:父级编号:myImage出版商{编号:myPubonNewImage:{myImage.source = newImage;#我知道这行不通,它需要一个 QUrl 而不是 QImage}}}}
解决方案 换句话说,您有一个类发出携带 QImage 的信号,并想用该图像更新 QML 中的项目?有多种解决方案,其中没有一个涉及将 QImage 转换为 QUrl"(无论这意味着什么,您肯定不需要获取带有图像数据的 data
URL...)>
使用图像提供程序
这意味着您可以在 QML 文件中使用普通的 Image
项目.
- 创建一个
QQuickImageProvider
子类;给它一个QImage
成员(提供者的图像),覆盖requestImage
以提供该图像(实际请求的id
并不重要,请参阅下面),以及一个接收QImage
并更新成员的槽. - 将您的
Publisher
信号连接到您的提供商的插槽 - 通过
QQmlEngine::addImageProvider
将提供者安装到QML引擎中(见QQuickView::engine
);再次id
并不重要,只要使用一个合理的 在 QML 中,只需使用带有这样的源的普通
Image
元素图片{编号:myImage来源:图像://providerIdPassedToAddImageProvider/foobar"}
foobar
将传递给您的提供者,但同样,这并不重要.我们快到了,我们现在只需要一种方法将图像更新推送到 QML 世界(否则图像将永远不知道何时更新自己).请参阅我的回答,了解如何使用
Connections
元素和一点 JS.请注意,通常您不需要使
Publisher
成为 QML 类型,您只需要在 C++ 中创建 一个 实例并通过以下方式将其公开给 QML 世界QQmlContext::setContextProperty
.
使用自定义 Qt Quick 2 项目
QQuickPaintedItem
可能是最方便的工作,因为它提供了一个采用 QPainter
的 paint
方法.因此,大计划是
- 子类
QQuickPaintedItem
:子类存储要绘制的QImage
,并有一个槽位设置新的QImage.此外,它的paint
实现只是使用QPainter::drawImage
绘制图像. - 通过
qmlRegisterType
将子类暴露给 QML 世界(以便您可以在 QML 中使用它) 想办法将携带新图像的信号连接到物品的插槽.
这可能是棘手的部分.
要在 C++ 中执行连接,您需要一种方法来确定该项目已创建(并获得指向它的指针);通常通过将
objectName
属性分配给某个值,然后在根对象上使用findChild
(由QQuickView::rootObject()
) 以获取指向项目本身的指针.然后你就可以照常使用connect
.或者,可以改为在 QML 中执行连接,就像上面一样,通过向 QML 世界公开的发布者 C++ 对象上的
Connections
元素:MyItem {编号:我的项目}连接{目标: thePublisherObjectExposedFromC++onNewImage: myItem.setImage(image)}
无论您何时创建 MyItem 实例,这都有其优势;但我不能 100% 确定它会起作用,因为我不确定您是否可以处理 QML 中的
QImage
类型.
I created a class Publisher
which periodically emits a QImage
object.
However I'm having a tough time drawing the QImage
to a QML element. It appears that the Image
and Canvas
QML components require a QUrl
instead of a QImage
, but I'm not sure how to convert my QImage
to a QUrl
. Edit4: When I say QUrl, I don't mean I'm trying to convert an image to a URL. That's nonsense. I mean I want to generate a reference to this image, which is not on disk, and the data type that QML components are asking for is a URL.
I've done some research and found that QQuickImageProvider
provides a solution, but I haven't found any documentation explaining how to convert my QImage
signal to a QUrl
that I can use for drawing. Any example code or reference documentation would be appreciated.
Thanks for your help!
Edit1:
I've taken a look here: http://qt-project.org/doc/qt-5.0/qtquick/qquickimageprovider.html and I do not see how I pass a QImage to the quick image provider and from it create a QUrl.
Edit2. Here is the header. The implementation should not be important.
class Publisher
{
Q_OBJECT
public:
Publisher(QObject* parent = 0);
virtual ~Publisher(void);
Q_SIGNALS:
void newImage(const QImage& newImage);
};
Edit 3. Here is my QML code, but I don't know how to draw my QImage, so this code is kind of meaningless.
my main.cpp file:
int main(int argc, char *argv[])
{
QGuiApplication app(argc, argv);
qmlRegisterType<Publisher>("Components", 1, 0, "Publisher");
QtQuick2ApplicationViewer viewer;
viewer.setMainQmlFile(QStringLiteral("qml/QQuickViewExample/main.qml"));
viewer.showExpanded();
return app.exec();
}
my main.qml file:
import QtQuick 2.0
import Components 1.0
Rectangle {
id : testRect
width: 360
height: 360
Image{
anchors.fill: parent
id: myImage
Publisher {
id: myPub
onNewImage: {
myImage.source = newImage; #I know this doesnt work, it needs a QUrl and not a QImage
}
}
}
}
解决方案
In other words, you have a class emitting a signal carrying a QImage and want to update an item in QML with that image? There are various solutions, none of which involves "converting a QImage to a QUrl" (whatever that means, surely you don't need to get a data
URL carrying your image data...)
Use an image provider
This means you can use a plain Image
item in your QML files.
- Create a
QQuickImageProvider
subclass; give it aQImage
member (the image to provider), overriderequestImage
to provide that image (the actualid
requested does not really matter, see below), and a slot that receives aQImage
and updates the member. - Connect your
Publisher
signal to your provider's slot - Install the provider into the QML engine via
QQmlEngine::addImageProvider
(seeQQuickView::engine
); again theid
does not really matter, just use a sensible one In QML, just use a plain
Image
element with a source like thisImage { id: myImage source: "image://providerIdPassedToAddImageProvider/foobar" }
foobar
will be passed to your provider, but again, it doesn't really matter.We're almost there, we now only need a way to push the image updates to the QML world (otherwise Image will never know when to update itself). See my answer here for how to do that with a
Connections
element and a bit of JS.Note that in general you don't need to make
Publisher
a QML type, you just need to create one instance in C++ and expose it to the QML world viaQQmlContext::setContextProperty
.
Use a custom Qt Quick 2 Item
QQuickPaintedItem
is probably the most convenient for the job as it offers a paint
method taking a QPainter
. Hence the big plan is
- Subclass
QQuickPaintedItem
: the subclass stores theQImage
to be painted and has a slot that sets the new QImage. Also itspaint
implementation simply paints the image usingQPainter::drawImage
. - Expose the subclass to the QML world via
qmlRegisterType
(so that you can use it in QML) Figure out a way to connect the signal carrying the new image to the items' slot.
This might be the tricky part.
To perform the connection in C++ you need a way to figure out that the item has been created (and get a pointer to it); usually one does this by means of assigning the
objectName
property to some value, then usingfindChild
on the root object (as returned byQQuickView::rootObject()
) to get a pointer to the item itself. Then you can useconnect
as usual.Or, could instead perform the connection in QML, just like above, via a
Connections
element on the publisher C++ object exposed to the QML world:MyItem { id: myItem } Connections { target: thePublisherObjectExposedFromC++ onNewImage: myItem.setImage(image) }
This has the advantage of working no matter when you create the MyItem instance; but I'm not 100% sure it will work because I'm not sure you can handle the
QImage
type in QML.
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