flutter - Flutter：无法在 dart Isolate 中执行数据库 CRUD
问题描述
我正在尝试在单独的 dart 隔离/计算中从服务器同步数据，并且还需要使用 SQFlite 将下载的数据转储到数据库，但我收到错误，我无法弄清楚出了什么问题。
这是代码
import "dart:isolate";
import "package:flutter/foundation.dart";
import "package:flutter/widgets.dart";
//import 'package:path_provider/path_provider.dart';
import "package:sqflite/sqflite.dart";
Future<Database> getDB() async{
//var dir= await getExternalStorageDirectory();
//var dbPath= "${dir.path}youtility.db";
var dbPath= "/storage/emulated/0/Android/data/com.example.sampleapp/files/test.db";
var database= await openDatabase(
dbPath,
version: 1,
onCreate: (db, version) {
return db.execute(
"CREATE TABLE typeassist ("
"taid INTEGER PRIMARY KEY,"
"tacode TEXT,"
"taname TEXT"
");"
);
}
);
return database;
}
Future<int> upsert() async {
print("upsert() -");
Database db= await getDB();
var taMapList= [
{ "taid": 1, "tacode": "ASSET", "taname": "ASSET" },
{ "taid": 2, "tacode": "SMARTPLACE", "taname": "SMARTPLACE" },
{ "taid": 3, "tacode": "CHECKPOINT", "taname": "CHECKPOINT" },
];
for(var i= 0; i < taMapList.length; i++) {
print("upsert() taMapList[$i] ${taMapList[i]}");
await db.insert("typeassist", taMapList[i], conflictAlgorithm: ConflictAlgorithm.replace);
}
await db.close();
print("upsert() db closed");
db= null;
print("upsert() +");
return 0;
}
Future<int> fetch(String name) async {
print("fetch(name $name) -");
Database db= await getDB();
var list= await db.rawQuery("select * from typeassist");
for(var i= 0; i < list.length; i++) {
print("fetch() [$i] ${list[i]}");
}
await db.close();
print("fetch() db closed");
db= null;
print("fetch() +");
return 0;
}
// NORMAL
Future<int> dbNormal() async {
print("dbNormal() -");
await upsert();
await fetch("normal");
print("dbNormal() +");
return 0;
}
// COMPUTE
Future<int> dbCompute() async{
print("dbCompute() -");
await upsert();
compute(fetch, "compute");
print("dbCompute() +");
return 0;
}
// ISOLATE
Isolate isolate;
Future<int> start() async {
print("start() -");
ReceivePort receivePort= new ReceivePort();
isolate= await Isolate.spawn(fetchData, receivePort.sendPort);
receivePort.listen((data) {
print("start() RECEIVE: $data");
});
print("start() +");
return 0;
}
int stop() {
print("stop() -");
if(isolate != null) {
isolate.kill(priority: Isolate.immediate);
isolate= null;
}
print("stop() +");
return 0;
}
int fetchData(SendPort sendPort) {
print("fetchDB(sendPort $sendPort) -");
var f= fetch("isolate");
f.then((rc) {
print("fetchDB() SEND: 0");
sendPort.send(0);
});
print("fetchDB() +");
return 0;
}
Future<int> dbIsolate() async {
print("dbIsolate() -");
start();
print("dbIsolate() +");
return 0;
}
Future<int> main() async {
print("main() -");
WidgetsFlutterBinding.ensureInitialized();
print("main() normal execution -");
var n= dbNormal();
n.then((rc){
print("main() normal execution +");
});
await Future.delayed(new Duration(seconds: 1));
/*print("main() compute execution -");
var c= dbCompute();
c.then((rc){
print("main() compute execution +");
});*/
print("main() isolate execution -");
var i= dbIsolate();
i.then((rc){
print("main() isolate execution +");
});
print("main() +");
return 0;
}
这是错误日志
Performing hot restart...
Syncing files to device XT1706...
Restarted application in 1,801ms.
I/flutter (15820): main() -
I/flutter (15820): main() normal execution -
I/flutter (15820): dbNormal() -
I/flutter (15820): upsert() -
I/flutter (15820): upsert() taMapList[0] {taid: 1, tacode: ASSET, taname: ASSET}
I/flutter (15820): upsert() taMapList[1] {taid: 2, tacode: SMARTPLACE, taname: SMARTPLACE}
I/flutter (15820): upsert() taMapList[2] {taid: 3, tacode: CHECKPOINT, taname: CHECKPOINT}
I/flutter (15820): upsert() db closed
I/flutter (15820): upsert() +
I/flutter (15820): fetch(name normal) -
I/flutter (15820): fetch() [0] {taid: 1, tacode: ASSET, taname: ASSET}
I/flutter (15820): fetch() [1] {taid: 2, tacode: SMARTPLACE, taname: SMARTPLACE}
I/flutter (15820): fetch() [2] {taid: 3, tacode: CHECKPOINT, taname: CHECKPOINT}
I/flutter (15820): fetch() db closed
I/flutter (15820): fetch() +
I/flutter (15820): dbNormal() +
I/flutter (15820): main() normal execution +
I/flutter (15820): main() isolate execution -
I/flutter (15820): dbIsolate() -
I/flutter (15820): start() -
I/flutter (15820): dbIsolate() +
I/flutter (15820): main() +
I/flutter (15820): main() isolate execution +
I/flutter (15820): fetchDB(sendPort SendPort) -
I/flutter (15820): start() +
I/flutter (15820): fetch(name isolate) -
I/flutter (15820): fetchDB() +
E/flutter (15820): [ERROR:flutter/runtime/dart_isolate.cc(915)] Unhandled exception:
E/flutter (15820): ServicesBinding.defaultBinaryMessenger was accessed before the binding was initialized.
E/flutter (15820): If you're running an application and need to access the binary messenger before `runApp()` has been called (for example, during plugin initialization), then you need to explicitly call the `WidgetsFlutterBinding.ensureInitialized()` first.
E/flutter (15820): If you're running a test, you can call the `TestWidgetsFlutterBinding.ensureInitialized()` as the first line in your test's `main()` method to initialize the binding.
E/flutter (15820): #0 defaultBinaryMessenger.<anonymous closure> (package:flutter/src/services/binary_messenger.dart:76:7)
E/flutter (15820): #1 defaultBinaryMessenger (package:flutter/src/services/binary_messenger.dart:89:4)
E/flutter (15820): #2 MethodChannel.binaryMessenger (package:flutter/src/services/platform_channel.dart:140:62)
E/flutter (15820): #3 MethodChannel.invokeMethod (package:flutter/src/services/platform_channel.dart:314:35)
E/flutter (15820): #4 invokeMethod (package:sqflite/src/sqflite_impl.dart:17:13)
E/flutter (15820): #5 SqfliteDatabaseFactoryImpl.invokeMethod (package:sqflite/src/factory_impl.dart:82:7)
E/flutter (15820): #6 SqfliteDatabaseMixin.invokeMethod (package:sqflite_common/src/database_mixin.dart:287:15)
E/flutter (15820): #7 SqfliteDatabaseMixin.safeInvokeMethod.<anonymous closure> (package:sqflite_common/src/database_mixin.dart:208:43)
E/flutter (15820): #8 wrapDatabaseException (package:sqflite/src/exception_impl.dart:7:32)
E/flutter (15820): #9 SqfliteDatabaseFactoryImpl.wrapDatabaseException (package:sqflite/src/factory_impl.dart:78:7)
E/flutter (15820): #10 SqfliteDatabaseMixin.safeInvokeMethod (package:sqflite_common/src/database_mixin.dart:208:15)
E/flutter (15820): #11 SqfliteDatabaseMixin.openDatabase (package:sqflite_common/src/database_mixin.dart:542:15)
E/flutter (15820): #12 SqfliteDatabaseMixin.doOpen (package:sqflite_common/src/database_mixin.dart:635:28)
E/flutter (15820): #13 SqfliteDatabaseOpenHelper.openDatabase (package:sqflite_common/src/database.dart:46:22)
E/flutter (15820): #14 SqfliteDatabaseFactoryMixin.openDatabase.<anonymous closure> (package:sqflite_common/src/factory_mixin.dart:104:43)
E/flutter (15820): <asynchronous suspension>
E/flutter (15820): #15 ReentrantLock.synchronized.<anonymous closure>.<anonymous closure> (package:synchronized/src/reentrant_lock.dart:35:24)
E/flutter (15820): #16 _rootRun (dart:async/zone.dart:1126:13)
E/flutter (15820): #17 _CustomZone.run (dart:async/zone.dart:1023:19)
E/flutter (15820): #18 _runZoned (dart:async/zone.dart:1518:10)
E/flutter (15820): #19 runZoned (dart:async/zone.dart:1465:12)
E/flutter (15820): #20 ReentrantLock.synchronized.<anonymous closure> (package:synchronized/src/reentrant_lock.dart:34:24)
E/flutter (15820): #21 BasicLock.synchronized (package:synchronized/src/basic_lock.dart:32:26)
E/flutter (15820): #22 ReentrantLock.synchronized (package:synchronized/src/reentrant_lock.dart:30:17)
E/flutter (15820): #23 SqfliteDatabaseFactoryMixin.openDatabase (package:sqflite_common/src/factory_mixin.dart:71:17)
E/flutter (15820): #24 openDatabase (package:sqflite/sqflite.dart:152:26)
E/flutter (15820): #25 getDB (package:sampleapp/main.dart:11:23)
E/flutter (15820): #26 fetch (package:sampleapp/main.dart:48:22)
E/flutter (15820): #27 fetchData (package:sampleapp/main.dart:103:10)
E/flutter (15820): #28 _startIsolate.<anonymous closure> (dart:isolate-patch/isolate_patch.dart:310:17)
E/flutter (15820): #29 _RawReceivePortImpl._handleMessage (dart:isolate-patch/isolate_patch.dart:174:12)
我被这个问题困住了，寻找所有可能的解决方案，也尝试了很多方法，但我仍然不明白出了什么问题。请帮忙