Issue
I tried to use ovprogresshud (https://pub.dev/packages/ovprogresshud) to show download progress. I used flutter_downloader (https://pub.dev/packages/flutter_downloader) for download.
I try to update progress via an Isolate, but receive errors.
(If I call Progresshud.showWithStatusdirectly in my code, say before download, it works)
My code:
ReceivePort _port = ReceivePort();
...
IsolateNameServer.registerPortWithName(
_port.sendPort, 'downloader_send_port');
_port.listen(
(dynamic data) {
String id = data[0];
DownloadTaskStatus status = data[1];
int progress = data[2];
if (status == DownloadTaskStatus.complete) {
} else if (status == DownloadTaskStatus.running) {
Progresshud.showWithStatus("%$progress Downloaded");
}
},
onDone: () {
checkIfDictionaryUnzipped(DBFilePath);
},
onError: (error) {},
);
The error I receive:
Unhandled Exception: PlatformException(error, Attempt to invoke virtual method 'android.view.ViewParent android.view.ViewGroup.getParent()' on a null object reference, null)
E/flutter (29114): #0 StandardMethodCodec.decodeEnvelope (package:flutter/src/services/message_codecs.dart:569:7)
E/flutter (29114): #1 MethodChannel.invokeMethod (package:flutter/src/services/platform_channel.dart:321:33)
E/flutter (29114): <asynchronous suspension>
E/flutter (29114): #2 Progresshud.showWithStatus (package:ovprogresshud/progresshud.dart:18:27)
E/flutter (29114): <asynchronous suspension>
....
Solution
check important note here
Important note: your UI is rendered in the main isolate, while download events come from a background isolate (in other words, codes in callback are run in the background isolate), so you have to handle the communication between two isolates.
Check Example,
ReceivePort _port = ReceivePort();
@override
void initState() {
super.initState();
IsolateNameServer.registerPortWithName(_port.sendPort, 'downloader_send_port');
_port.listen((dynamic data) {
String id = data[0];
DownloadTaskStatus status = data[1];
int progress = data[2];
setState((){ });
});
FlutterDownloader.registerCallback(downloadCallback);
}
@override
void dispose() {
IsolateNameServer.removePortNameMapping('downloader_send_port');
super.dispose();
}
static void downloadCallback(String id, DownloadTaskStatus status, int progress) {
final SendPort send = IsolateNameServer.lookupPortByName('downloader_send_port');
send.send([id, status, progress]);
}
Answered By – Abhay Koradiya
Answer Checked By – Pedro (FlutterFixes Volunteer)