Flutter：HTTP Get 返回未来的实例而不是图像导致异常

Question

My objective: Download Image from a URL, save it in a directory and then using carousel_slider.dart package, create a slider. Everything runs fine then after the for loop is executed I get a runtime error saying Exception: Could not instantiate image codec. After using a print statement I get an Instance of 'response'.

Based on this error message what I can guess is my code is trying to decode image before it's downloaded.

Console:

Performing hot restart...
Syncing files to device sdk google atv x86...
Restarted application in 3,046ms.
I/flutter ( 3664): ::Data connection is available.
I/flutter ( 3664): ::Mosquitto client connecting....
I/flutter ( 3664): ::Subscription confirmed -> topic -> topic/registered
I/flutter ( 3664): ::Change notification:: topic -> <topic/registered>, payload ->  <1> 
I/flutter ( 3664): Payload: 1
I/flutter ( 3664): ::Subscription confirmed -> topic -> topic/control_instruction
I/flutter ( 3664): Instance of 'Response'
I/flutter ( 3664): Instance of 'Response'
I/flutter ( 3664): Instance of 'Response'
I/flutter ( 3664): [/data/user/0/com.stellar.dnb/app_flutter/Notice/1583231584.jpg, /data/user/0/com.stellar.dnb/app_flutter/Notice/1583237477.jpg, /data/user/0/com.stellar.dnb/app_flutter/Notice/1583237505.jpg]
I/flutter ( 3664): ::Mosquitto client connected

════════ Exception caught by image resource service ════════════════════════════════════════════════
The following _Exception was thrown resolving an image codec:
Exception: Could not instantiate image codec.

When the exception was thrown, this was the stack: 
#0      _futurize (dart:ui/painting.dart:4304:5)
#1      instantiateImageCodec (dart:ui/painting.dart:1682:10)
#2      PaintingBinding.instantiateImageCodec (package:flutter/src/painting/binding.dart:88:12)
#3      FileImage._loadAsync (package:flutter/src/painting/image_provider.dart:653:24)
<asynchronous suspension>
...
Path: /data/user/0/com.stellar.dnb/app_flutter/Notice/1583231584.jpg
════════════════════════════════════════════════════════════════════════════════════════════════════

════════ (2) Exception caught by image resource service ════════════════════════════════════════════
Exception: Could not instantiate image codec.
════════════════════════════════════════════════════════════════════════════════════════════════════

════════ (3) Exception caught by image resource service ════════════════════════════════════════════
Exception: Could not instantiate image codec.
════════════════════════════════════════════════════════════════════════════════════════════════════

My code snippet:

getAssetList() async {
    response =
        await http.post(_noticeURL, body: parseJson.convertToJson(deviceID));
    if (response.statusCode == 200) {
      parseJson.decodeJson(response.body.toString());
      await downloadAsset(addNoticeToList());
    } else
      print('HTTP Response StatusCode: ${response.statusCode}');
  }

  addNoticeToList() {
    List _assetList = [];
    if (parseJson.responseJsonDecoded.isNotEmpty) {
      for (dynamic value in parseJson.responseJsonDecoded.values) {
        for (dynamic notice in value) {
          _assetList.add(notice);
        }
      }
      return _assetList;
    }
  }

  downloadAsset(List assetList) async {
    //imgList.clear();
    String _dirPath = await dirManager.createFolderInAppDocDir('Notice');
    for (String _asset in assetList) {
      var assetResponse = await http.get(_noticeDownloadURL + _asset);
      var _filePathAndName = (p.join(_dirPath, _asset));
      imgList.add(_filePathAndName);
      File imageFile = File(_filePathAndName);
      print(assetResponse);
      imageFile.writeAsBytesSync(assetResponse.bodyBytes);
    }
    print('$imgList');
  }

Answer 1

Okay the issue is resolved. The url was incorrect, hence the error.