Flutter在Android平板使用image_picker选取相机视频出现0字节问题

问题排查与修复方案 #

1. 解决相机文件写入延迟 #

平板相机拍完视频后，可能还没把内容写完就返回了文件路径，这时候读取自然是空文件。加个几百毫秒的延迟再读取试试：

final result = await picker.pickVideo(source: ImageSource.camera);
// 等500ms让相机完成文件写入
await Future.delayed(const Duration(milliseconds: 500));
Uint8List datList = await result.readAsBytes();
log("file length ${datList.length}");

2. 针对content:// URI的正确读取方式 #

当返回的路径是content://开头的URI时，直接用readAsBytes()可能有权限或读取逻辑问题，推荐两种处理方式：

方法一：转成真实文件路径读取

先在Flutter中调用原生方法转换URI：

import 'package:flutter/services.dart';

// 定义获取真实路径的方法，渠道名替换为你的项目标识
Future<String> getRealPath(String contentUri) async {
  const channel = MethodChannel('com.your.app.media');
  return await channel.invokeMethod('getRealPath', {'uri': contentUri});
}

// 使用示例
final result = await picker.pickVideo(source: ImageSource.camera);
if (result != null) {
  String realPath;
  if (result.path.startsWith('content://')) {
    realPath = await getRealPath(result.path);
  } else {
    realPath = result.path;
  }
  final file = File(realPath);
  Uint8List datList = await file.readAsBytes();
  log("file length ${datList.length}");
}

然后在Android的MainActivity中添加对应的原生代码：

import android.content.ContentUris;
import android.content.Context;
import android.database.Cursor;
import android.net.Uri;
import android.os.Build;
import android.os.Environment;
import android.provider.DocumentsContract;
import android.provider.MediaStore;

import androidx.annotation.NonNull;

import io.flutter.embedding.android.FlutterActivity;
import io.flutter.embedding.engine.FlutterEngine;
import io.flutter.plugin.common.MethodChannel;

public class MainActivity extends FlutterActivity {
    private static final String CHANNEL = "com.your.app.media"; // 和Flutter渠道名保持一致

    @Override
    public void configureFlutterEngine(@NonNull FlutterEngine flutterEngine) {
        super.configureFlutterEngine(flutterEngine);
        new MethodChannel(flutterEngine.getDartExecutor().getBinaryMessenger(), CHANNEL)
                .setMethodCallHandler((call, result) -> {
                    if (call.method.equals("getRealPath")) {
                        String uriStr = call.argument("uri");
                        Uri uri = Uri.parse(uriStr);
                        String realPath = getRealPathFromUri(getApplicationContext(), uri);
                        result.success(realPath);
                    } else {
                        result.notImplemented();
                    }
                });
    }

    // 核心方法：将content URI转换为真实文件路径
    private String getRealPathFromUri(Context context, Uri uri) {
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.KITKAT && DocumentsContract.isDocumentUri(context, uri)) {
            if ("com.android.externalstorage.documents".equals(uri.getAuthority())) {
                String docId = DocumentsContract.getDocumentId(uri);
                String[] split = docId.split(":");
                String type = split[0];
                if ("primary".equalsIgnoreCase(type)) {
                    return Environment.getExternalStorageDirectory() + "/" + split[1];
                }
            } else if ("com.android.providers.media.documents".equals(uri.getAuthority())) {
                String docId = DocumentsContract.getDocumentId(uri);
                String[] split = docId.split(":");
                String type = split[0];
                Uri contentUri = null;
                if ("video".equals(type)) {
                    contentUri = MediaStore.Video.Media.EXTERNAL_CONTENT_URI;
                }
                String selection = "_id=?";
                String[] selectionArgs = {split[1]};
                return getDataColumn(context, contentUri, selection, selectionArgs);
            }
        } else if ("content".equalsIgnoreCase(uri.getScheme())) {
            return getDataColumn(context, uri, null, null);
        } else if ("file".equalsIgnoreCase(uri.getScheme())) {
            return uri.getPath();
        }
        return null;
    }

    private String getDataColumn(Context context, Uri uri, String selection, String[] selectionArgs) {
        Cursor cursor = null;
        final String column = "_data";
        final String[] projection = {column};
        try {
            cursor = context.getContentResolver().query(uri, projection, selection, selectionArgs, null);
            if (cursor != null && cursor.moveToFirst()) {
                int index = cursor.getColumnIndexOrThrow(column);
                return cursor.getString(index);
            }
        } finally {
            if (cursor != null) cursor.close();
        }
        return null;
    }
}

3. 检查权限配置 #

确保AndroidManifest.xml中添加了必要权限：

<uses-permission android:name="android.permission.CAMERA" />
<!-- Android 13及以下需要的存储权限 -->
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" android:maxSdkVersion="32" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" android:maxSdkVersion="32" />
<!-- Android 13+ 需要的视频读取权限 -->
<uses-permission android:name="android.permission.READ_MEDIA_VIDEO" />

同时在代码中动态申请权限：

import 'package:permission_handler/permission_handler.dart';
import 'dart:io';

// 提前申请必要权限
await Permission.camera.request();
if (Platform.isAndroid) {
  if (await Permission.storage.isDenied) {
    await Permission.storage.request();
  }
  if (await Permission.readMediaVideo.isDenied) {
    await Permission.readMediaVideo.request();
  }
}

4. 升级image_picker版本 #

旧版本的image_picker可能存在平板适配bug，前往pub.dev查看最新稳定版，更新pubspec.yaml：

dependencies:
  image_picker: ^最新版本号 # 替换为实际最新版本，比如0.8.11+3

内容的提问来源于stack exchange，提问作者Hamza Ch