Test app: Markdown Combiner

[LeonMatthesKDAB]

Markdown combiner using CXX-Qt.

I'm currently developing a simple Markdown combiner app (target: Linux + Android) using CXX-Qt.

The goal is to create an app that can work cross-platform to combine multiple markdown checklists into one.
In this discussion I'll list issues I've encountered and the reasoning to why I need them.

This can hopefully guide our future issue prioritization.

[LeonMatthesKDAB]

#55

I need to convert a QUrl, which is returned from a QtQuick FolderDialog to a local file name, which is certainly possible, though quite cumbersome to do in Rust atm.

[LeonMatthesKDAB]

Imagined API:

impl QUrl {
    pub fn to_local_file(&self) -> Option<QString>;
}

[ahayzen-kdab]

Right QUrl is missing loads of the methods that would be useful. This would just be bound to https://doc.qt.io/qt-6/qurl.html#toLocalFile QString QUrl::toLocalFile() const. If we don't do the Option and follow the Qt API it would be a straight CXX bridge definition with no wrapper methods.

[LeonMatthesKDAB]

#372

Caused a binding loop in my QML (See example in issue).

Current workaround:
Expose a #[qinvokable] update_value() that does the equality check (requires conversion to Rust atm.) and then calls the setter.

[LeonMatthesKDAB]

#373
Minor nuisance, can do use X; from within invokable to get around this.

[LeonMatthesKDAB]

#374
Not critical atm, but might come in handy in future.

[LeonMatthesKDAB]

#375
Not really pressing, just something I noticed.

[LeonMatthesKDAB]

#53
Especially the Debug impl would have been really nice!
Then just using #[derive(Debug)] would have been possible 🥳

[LeonMatthesKDAB]

#42
Especially the ability to define my own setters would have been very helpful.
Right now, I can't just assign the property from QML, as that will break things.
My current workaround is similar to #371 (comment) .
Define an invokable that does the actual value setting and updates all other related state.

[ahayzen-kdab]

Also for the workaround assume you have realised you could derive from the Rust class in C++ to add the property?

Eg have a read only field private to Rust, then an invokable to access it (could even have a signal to notify change)

#[cxx_qt::qobject]
pub struct MyObject {
  read_only_field: i32
}

impl qobject::MyObject {
   #[qinvokable] 
   pub fn read_only_field(&self) -> i32 { self.read_only_field() }
}

Then in C++

class MyObjectWithProp : public MyObject {
  Q_OBJECT
  Q_PROPERTY(::std::int32_t readOnlyField READ readOnlyField CONSTANT)
...
};

Then register and use MyObjectWithProp in QML with the readOnlyField :-)

The same process can be done to setup your own setters / signals etc.

[LeonMatthesKDAB]

Good point, I was trying to see what CXX-Qt can do without working around its restrictions too much...

[LeonMatthesKDAB]

#476

Associated constants are not allowed.