How to use things derived from QAbstractListModel as field/property?

[araraloren]

Hi, I know we can create a type derived from QAbstractListModel, such as

    extern "RustQt" {

        #[qobject]
        #[base = "QAbstractListModel"]
        #[qml_element]
        type CustomBaseClass = super::CustomBaseClassRS;
    }

    unsafe extern "RustQt" {
        #[qobject]
        #[qml_element]
        #[qproperty(CustomBaseClass, files_model)]
        type FileServer = super::FileServerRS;
    }

Could someone tell me how can I use CustomBaseClass in the filed, so I can access it in qml file?

{
...
FileServer {
 id: fileServer
}

...
model: fileServer.filesModel
...
}

Thanks

[ahayzen-kdab]

Hey,

So QML will be wanting a raw pointer in C++, eg CustomBaseClass*. We can use Rust raw pointers for this, if we look at the nested_qobjects example this is similar.

This says that there is a Q_PROPERTY which is a pointer under the field inner.

cxx-qt/examples/qml_features/rust/src/nested_qobjects.rs

Lines 32 to 35 in f82ab4e

	#[qobject]
	#[qml_element]
	#[qproperty(*mut InnerObject, inner)]
	type OuterObject = super::OuterObjectRust;

Then we store a raw pointer to the QObject as a field in the struct

cxx-qt/examples/qml_features/rust/src/nested_qobjects.rs

Lines 67 to 78 in f82ab4e

	/// The outer QObject which has a Q_PROPERTY pointing to the inner QObject
	pub struct OuterObjectRust {
	inner: *mut qobject::InnerObject,
	}
	impl Default for OuterObjectRust {
	fn default() -> Self {
	Self {
	inner: std::ptr::null_mut(),
	}
	}
	}

This will need to go into your FileServerRS.

Note this example also shows how to use the pointer with methods and shows how to get from a raw pointer back to a pinned mutable reference (so that you can reach methods on the pointer object.

Note that you might need a C++ method to create the raw pointer of the CustomBaseClass if you are doing this in Rust rather than QML. (we have an issue somewhere about generating helpers for this automatically somewhere i think).

Feel free to ask more questions as this area is a little tricky :-)

[araraloren]

Thanks for your reply!

[realroot2185]

https://doc.qt.io/qt-6/qabstractlistmodel.html

When subclassing QAbstractListModel, you must provide implementations of the rowCount() and data() functions. Well behaved models also provide a headerData() implementation.

Is there an example to how use a type derived from QAbstractListModel for a QML ListView where you can add/remove elements and save/load the list?

I cannot call the function from the type instance in QML:
main.qml:109: TypeError: Property 'do_something' of object MyType(0x5dbb2a6c9810) is not a function

[ahayzen-kdab]

This example has a QAbstractListModel implemented in Rust and has various add methods that are called from QML.

https://github.com/KDAB/cxx-qt/blob/main/examples/qml_features/rust/src/custom_base_class.rs

https://github.com/KDAB/cxx-qt/blob/main/examples/qml_features/qml/pages/CustomBaseClassPage.qml

[realroot2185]

Any suggestion to how save/load models in the ListView from a file?

So that when you open it there are already models from the last time.
And initially it loads the default models from a file.

[ahayzen-kdab]

So you'll want to use the Initialize trait to run code in the constructor of the QObject https://docs.rs/cxx-qt/latest/cxx_qt/trait.Initialize.html this could then be used to load things. Then probably the Drop trait on the struct might be enough to write values in the fields to a file.

[LeonMatthesKDAB]

Also, take a look at this example: https://github.com/KDAB/cxx-qt/blob/main/examples/qml_features/rust/src/serialisation.rs

Which shows how to serialize/deserialize data stored in a QObject.

@ahayzen-kdab By the way, I think we should be able to simplify this example, a lot.
I don't think we need the separate data struct anymore with our current API 🤔
We can just derive Serialize and Deserialize on the inner struct itself.