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Pigeon: add lifecycle / ability to close down pigeon channels #66994
Description
This is a mix of feature request and a question for pigeon:
Let's say I have a screen in Flutter that requires some data from native code. Data comes over time, so I'm using @FlutterApi. When screen opens, I create Pigeon instance in Flutter and start receiving data.
However, what happens when user closes said screen? From what I can see, Pigeon instances are singletons that never die, potentially causing memory leaks since they reference the UI classes that are not displayed anymore.
Ideally, there would be a way for me to close/dispose the pigeon instance after screen closes. Or is there another pattern that is supposed to be used?
Thanks.
Activity
gaaclarke commentedon Sep 30, 2020
I think what you are looking for is
Api.setup(binaryMessenger, null);, right?matejdro commentedon Oct 2, 2020
Would this work? From what I can see, new message channel is created every time
setupis called. Do those channels share single message handler?matejdro commentedon Oct 2, 2020
Also, from what I see, this does not work on the dart side. Setup method does not check for the null value anywhere.
dispose dart callbacks when activity is closed.preserve_connection_state
dispose dart callbacks when activity is closed
gaaclarke commentedon Oct 2, 2020
Yea, they are confusing. Channels aren't the things that store the connections. It's all saved on the binary messenger. That's why it is a parameter to creating channels and setting up pigeon.
This would clear things out:
{ Channel channel = Channel(binaryMessenger, "foobar"); channel.setHandler(() { print('hello'); }); } { Channel channel = Channel(binaryMessenger, "foobar"); channel.setHandler(null); }matejdro commentedon Oct 2, 2020
Thanks for the explanation. However, from what I see, pigeons generated on the dart side do not handle null well (they call the listener even it if it null, spewing errors into the console).
gaaclarke commentedon Oct 2, 2020
Thanks @matejdro, it would be helpful if you can supply some code where you are seeing the problem. The code using Pigeon and the code generated by Pigeon is helpful. That will make it easier for me to get started when looking into it. I appreciate your help.
matejdro commentedon Oct 2, 2020
Here is an example:
ScanCallbacksinterface (https://github.com/pebble-dev/mobile-app/blob/42c81f4e559d777cd2c9367839add86ae65f9d2d/pigeons/pigeons.dart#L18) generates into this:https://github.com/pebble-dev/mobile-app/blob/42c81f4e559d777cd2c9367839add86ae65f9d2d/lib/infrastructure/pigeons/pigeons.dart#L142
Note that nullability of the
apivariable is never checked, methods are just called blindly. So I can't putnullthere.Keep Pebble connected at all times (#12)
[pigeon] add null handling to FlutterApi.setup()
github-actions commentedon Aug 11, 2021
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