[英]QML can see my Q_GADGET but not Q_OBJECT
Why can my Q_GADGET
be read perfectly in QML (JS) but not my Q_OBJECT
? 为什么我的Q_GADGET
可以在QML(JS)中完美读取,但不能在我的Q_OBJECT
读取?
Running Qt 5.8.0 on Ubuntu 14.04. 在Ubuntu 14.04上运行Qt 5.8.0。
I'm attempting to return a list ( QVariantMap
) of objects to QML. 我正在尝试将对象列表( QVariantMap
)返回给QML。 I'm keeping it simple right now, no pointers, etc.. just copies of the objects. 我现在保持简单,没有指针等等。只是对象的副本。
struct Blob
{
Q_GADGET
Q_PROPERTY(QString uuid MEMBER uuid_ CONSTANT)
Q_PROPERTY(QVector3D centroid MEMBER centroid_)
// ...
Blob() {};
~Blob() = default;
Blob(const Blob& blob);
};
Q_DECLARE_METATYPE(Blob)
There are a bunch of QString
and QVector3D
members on Blob
. Blob
上有一堆QString
和QVector3D
成员。
In main.cpp, I also register the type: 在main.cpp中,我还注册了类型:
qmlRegisterType<Blob>("matt", 1, 0, "Blob");
Then my JS code is able to read all the properties (for loop iterating over them) on the object without issue. 然后我的JS代码能够在没有问题的情况下读取对象上的所有属性(用于循环遍历它们)。
But if I use a Q_OBJECT
但是如果我使用Q_OBJECT
struct Blob : public QObject
{
Q_OBJECT
Q_PROPERTY(QString uuid MEMBER uuid_ CONSTANT)
Q_PROPERTY(QVector3D centroid MEMBER centroid_)
// ...
explicit Blob(QObject parent = nullptr) : QObjecT(parent) {};
~Blob() = default;
Blob(const Blob& blob);
};
Q_DECLARE_METATYPE(Blob)
Then the JS receives an object where all the properies are the keys from the QVariantMap
, but whose values are empty objects. 然后JS接收一个对象,其中所有属性都是来自QVariantMap
的键,但其值是空对象。
Note, before sending it to the JS, I convert it to a QVariant and back again just to confirm that that works, eg 注意,在将它发送给JS之前,我将其转换为QVariant并再次返回以确认其有效,例如
Blob b;
qDebug() << "Created: " << b;
QVariant var = QVariant::fromValue(b);
qDebug() << " Converted back = " << var.value<Blob>().toQString();
I'd prefer to use a Q_OBJECT
such that I have slots/signals. 我更喜欢使用Q_OBJECT
,以便我有插槽/信号。
The reason I was seeing a difference between Q_OBJECT
and Q_GADGET
was that I was making copies of my object, which is allowed on a Q_GADGET
(a value ) object, but not on a Q_OBJECT
(an identity object.) See identities instead of values . 我之间看到Q_OBJECT
和Q_GADGET
之间差异的原因是我正在制作我的对象的副本,这在Q_GADGET
( 值 )对象上是允许的,但不在Q_OBJECT
( 标识对象)上。请参阅标识而不是值 。
The solution is to always work on Q_OBJECT
s with pointers. 解决方案是始终使用指针处理Q_OBJECT
。 This maintains their identity , and avoid copies. 这保持了他们的身份 ,并避免复制。
Also, my original intent was to use a smart pointer, but the reasons why that is a bad approach are explained in this answer . 此外,我最初的意图是使用智能指针,但在这个答案中解释了为什么这是一个糟糕的方法的原因。
The comment by @dtech also explained that Q_DECLARE_METATYPE
is redundant on a Q_OBJECT
. @dtech的评论还解释了Q_DECLARE_METATYPE
在Q_OBJECT
上是多余的。
Thus, my final declaration is: 因此,我的最后声明是:
ie 即
class Blob : public QObject
{
Q_OBJECT
Q_PROPERTY(QString uuid MEMBER uuid_ CONSTANT)
Q_PROPERTY(QVector3D centroid MEMBER centroid_)
// ...
explicit Blob(QObject parent = nullptr) : QObjecT(parent) {};
~Blob() = default;
Blob(const Blob& blob);
};
With this, I can easily put a raw pointer to these objects in a QVariantMap
, and they can be read on the QML/JS side. 有了这个,我可以轻松地将一个原始指针放在QVariantMap
这些对象上,并且可以在QML / JS端读取它们。
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