使用Flutter下载器插件，下载应用程序关闭后

Question

**我使用Flutter下载器包在完成下载一些文件后，我的应用程序会自动关闭并断开与Android Studio的连接。任何人都可以帮我找到溶剂。

    final status = await Permission.storage.request();
            if (status.isGranted) {
              await downloadPDF();
            } 

downloadPDF() async {
    final externalDir = await getExternalStorageDirectory();
    taskId = await FlutterDownloader.enqueue(
      url: pdfURL,
      savedDir: externalDir.path,
      fileName: "Flamingo Order Details",
      showNotification: true,
      openFileFromNotification: true,
    );
  }

以下是我的控制台错误:

I/flutter (15913): Fatal: could not find callback
F/libc    (15913): Fatal signal 11 (SIGSEGV), code 1 (SEGV_MAPERR), fault addr 0x0 in tid 15956 (1.raster), pid 15913 (le.order_system)
*** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ***
Build fingerprint: 'motorola/chef/chef_sprout:10/QPTS30.61-18-16-8/03acd:user/release-keys'
Revision: 'pvt'
ABI: 'arm64'
Timestamp: 2021-04-23 16:39:38+0530
pid: 15913, tid: 15956, name: 1.raster  >>> com.example.order_system <<<
uid: 10870
signal 11 (SIGSEGV), code 1 (SEGV_MAPERR), fault addr 0x0
Cause: null pointer dereference
    x0  000000741e5a6478  x1  00000074841cfa00  x2  0000000000000001  x3  0000000000000000
    x4  0000000000000000  x5  00000000ffffffff  x6  00000000ffffffff  x7  0000000b96c6a75c
    x8  0000000080000081  x9  658adf78f7e836ee  x10 0000000000000000  x11 0000000000000000
    x12 0000000000000001  x13 000000747b19fe80  x14 0000007489a0a280  x15 0000000000000000
    x16 000000747b19b050  x17 0000007515c9787c  x18 000000741d05e000  x19 000000741e5a6478
    x20 00000074841cfa00  x21 0000000000000001  x22 0000000000000000  x23 00000074843db380
    x24 000000741e5a7020  x25 000000741e5a7020  x26 0000000000000000  x27 0000000000000001
    x28 0000000000000043  x29 000000741e5a6450
    sp  000000741e5a6420  lr  000000747b013f84  pc  000000747b01c378
backtrace:
      #00 pc 00000000001d8378  /vendor/lib64/egl/libGLESv2_adreno.so (BuildId: 22cc95e0051ae85072c405eeeeeb312d)
      #01 pc 00000000001cff80  /vendor/lib64/egl/libGLESv2_adreno.so (BuildId: 22cc95e0051ae85072c405eeeeeb312d)
      #02 pc 00000000000207b0  /system/lib64/libEGL.so (android::eglSwapBuffersWithDamageKHRImpl(void*, void*, int*, int)+316) (BuildId: 248ba7f2d80e7bb9952a20e1c3493c86)
      #03 pc 000000000001d0a8  /system/lib64/libEGL.so (eglSwapBuffers+80) (BuildId: 248ba7f2d80e7bb9952a20e1c3493c86)
      #04 pc 00000000012ec528  /data/app/com.example.order_system-8XYsushVsEZPOltQ3k8npA==/lib/arm64/libflutter.so (BuildId: e14966237eb013b063fed6484195268f7398b594)
Lost connection to device.

Answer 1

也许已经很晚了，但它可能会帮助别人。最近我遇到了这个错误，我解决了它。您的 UI 在 Main 隔离中呈现，您的下载事件来自后台隔离。由于回调中的代码是在后台隔离运行的，因此您必须处理两个隔离之间的通信。通常，需要进行通信以在主UI中显示下载进度。实现以下代码来处理通信：

import 'dart:isolate';
import 'dart:ui'; // You need to import these 2 libraries besides another libraries to work with this code

final 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]);
  }


void _download(String url) async {
    final status = await Permission.storage.request();

    if(status.isGranted) {
      final externalDir = await getExternalStorageDirectory();

      final id = await FlutterDownloader.enqueue(
          url: url,
          savedDir: externalDir!.path,
        showNotification: true,
        openFileFromNotification: true,
      );
    } else {
      print('Permission Denied');
    }
  }

调用按钮中的_download（url）函数，即可开始使用。

名词（noun的缩写）b:我在我的应用程序中使用了健全的空安全，因此我在这行代码中使用了空感知运算符:

final SendPort send = IsolateNameServer.lookupPortByName('downloader_send_port')!;