qml qt6: use ZXing-based camera

[SomberNight]

This builds on top of spesmilo#8545, to use the old ZXing-based camera code for QR code scanning on Android, instead of QtMultimedia, as the latter seems buggy in Qt6.4.

The p4a branch needs this commit:
SomberNight/python-for-android@f2741f0

TODO:

• make scanner_layout.xml look reasonable
• how to avoid hardcoding testnet/mainnet in SimpleScannerActivity.java in the imports?
• test all scanning code paths

[SomberNight]

Hmm, opened PR against your repo instead of spesmilo sort of accidentally. But anyway, at least the diff is clearer this way.

[SomberNight]

(temporary)

[SomberNight]

Any idea how to avoid hardcoding the package name here?
This is annoying because of https://github.com/spesmilo/electrum/blob/ac177577a62134763547ac416d1098b8bf5f87e1/contrib/android/make_apk.sh#L48

[SomberNight]

Do we need an explicit destroy somewhere to avoid a memleak?
I see most dialogs have onClosed: destroy(), but not sure how to mimic that.
Also see main.qml::scanDialog (line 393).

[accumulator]

onClosed is a signal handler for Popup. Since you use a bare QObject as the base for QEQRScanner, you don't have the plumbing provided by Popup, and you need to detect when the activity is closed and emit a signal, which can then be used to destroy the instance from QML.

However, you don't really need to wrap the scanner in a Qt object and manage the lifecycle. Since there's at most 1 scanner active, you can basically also spawn the Activity from a @pyqtSlot decorated method in e.g. AppController, and just emit signals from AppController depending on the result. I think the Activity will be auto-deleted by the JVM when it's closed, and you don't need to manage any lifecycle on the QML side.

[accumulator]

The last part would be something like this:

Button {
    onClicked: AppController.showQRScanner()
}

Connections {
    target: AppController
    function onQRScanned(data) {
        // handle data
    }
}

[SomberNight]

you can basically also spawn the Activity from a @pyqtSlot decorated method in e.g. AppController, and just emit signals from AppController depending on the result

Yes I already had something like that a refactor prior, e.g. see
SomberNight@bc5f596
I've changed to QEQRScanner(QObject) instead as this way I can easily replace both the ScanDialog and the SendDialog use cases. In particular, QEQRScanner now has an API that is a drop-in replacement for the main.qml::scanDialog usages. The AppController signal approach worked nicely for the SendDialog, but I found it not easy to adapt to the ScanDialog usages.

you don't have the plumbing provided by Popup, and you need to detect when the activity is closed and emit a signal, which can then be used to destroy the instance from QML.
However, you don't really need to wrap the scanner in a Qt object and manage the lifecycle

But just to confirm, if we do use this QEQRScanner(QObject) approach, do we need to explicitly call destroy for the object? (/manually manage the lifecycle)
I guess I could just call destroy wherever the code on master calls close/closeDialog.

[accumulator]

I've merged this branch, but changed the zxing qr scan method to android-only, keeping the qt6 way for desktop/testing use, so we don't have to resurrect this when trying if things have improved in qt6.6+