使用Cordova在Android虚拟外部存储写入文件遇错误求助

Hey there! Let's figure out why you're hitting error codes 5 or 9 when trying to write files to BitWebServer's www directory (that virtual SD card location) with Cordova. I’ve tackled this exact scenario before, so let’s break down the fixes step by step:

• Error 5 (PERMISSION_DENIED): This means your app doesn’t have the right access permissions to write to that directory. It’s the most common culprit here.
• Error 9 (INVALID_PATH): Cordova can’t recognize the path you’re targeting—either it’s wrong, or the directory doesn’t exist (or isn’t accessible).

1. Fix Permission Configurations #

Cordova needs explicit storage permissions, especially on Android 10+ (API 29) where storage rules changed:

• Add these permissions to your config.xml to ensure they’re included in the Android manifest:

  <platform name="android">
      <config-file parent="/manifest" target="AndroidManifest.xml">
          <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
          <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
          <!-- For Android 13+, add these media-specific permissions too -->
          <uses-permission android:name="android.permission.READ_MEDIA_IMAGES" />
          <uses-permission android:name="android.permission.READ_MEDIA_VIDEO" />
          <uses-permission android:name="android.permission.READ_MEDIA_AUDIO" />
      </config-file>
  </platform>
  

• Don’t just rely on config—request permissions actively in your code before trying to write files:

  document.addEventListener("deviceready", onDeviceReady, false);
  function onDeviceReady() {
      // Request storage permissions first
      cordova.plugins.permissions.requestPermissions(
          [cordova.plugins.permissions.WRITE_EXTERNAL_STORAGE, cordova.plugins.permissions.READ_EXTERNAL_STORAGE],
          function(status) {
              if (status.hasPermission) {
                  // Permissions granted—proceed with file write
                  writeToBitWebServerDir();
              } else {
                  console.error("Storage permissions denied!");
              }
          },
          function(error) {
              console.error("Error requesting permissions: ", error);
          }
      );
  }
  

2. Verify the Target Path is Correct #

Error 9 almost always comes from a bad path. BitWebServer’s www directory is usually at /storage/emulated/0/bitwebserver/www/, but don’t hardcode it—use Cordova’s built-in path constants to avoid device-specific issues:

• Use cordova.file.externalRootDirectory to get the external storage root, then build the path dynamically:

  function writeToBitWebServerDir() {
      const externalRoot = cordova.file.externalRootDirectory;
      const targetDir = externalRoot + "bitwebserver/www/";
      const fileName = "test_file.txt";
      const fileContent = "Hello from Cordova!";
  
      // First check if the directory exists; create it if not
      window.resolveLocalFileSystemURL(targetDir, function(dir) {
          // Directory exists—create/write the file
          dir.getFile(fileName, {create: true, exclusive: false}, function(file) {
              file.createWriter(function(writer) {
                  writer.onwriteend = () => console.log("File written successfully!");
                  writer.onerror = (e) => console.error("Write failed: ", e);
                  const blob = new Blob([fileContent], {type: 'text/plain'});
                  writer.write(blob);
              }, err => console.error("Failed to create writer: ", err));
          }, err => console.error("Failed to access file: ", err));
      }, function() {
          // Directory doesn't exist—create it first
          window.requestFileSystem(LocalFileSystem.PERSISTENT, 0, function(fs) {
              fs.root.getDirectory(targetDir, {create: true, exclusive: false}, function(newDir) {
                  // Now create the file in the new directory
                  newDir.getFile(fileName, {create: true, exclusive: false}, function(file) {
                      // Repeat the write logic here
                      file.createWriter(function(writer) {
                          writer.onwriteend = () => console.log("File written after creating directory!");
                          writer.onerror = (e) => console.error("Write failed: ", e);
                          const blob = new Blob([fileContent], {type: 'text/plain'});
                          writer.write(blob);
                      }, err => console.error("Failed to create writer: ", err));
                  }, err => console.error("Failed to access file post-directory-creation: ", err));
              }, err => console.error("Failed to create directory: ", err));
          }, err => console.error("Failed to access file system: ", err));
      });
  }
  

3. Adapt to Android 10+ Scoped Storage #

Android 10 (API 29) introduced Scoped Storage, which restricts direct access to external storage by default. To get around this for BitWebServer’s directory:

• Add android:requestLegacyExternalStorage="true" to your AndroidManifest.xml under the <application> tag to use the old storage model (a quick fix for compatibility):

  <application
      android:requestLegacyExternalStorage="true"
      ...>
      <!-- Your other app config -->
  </application>
  

• Note: For Android 11+, you could use the MANAGE_EXTERNAL_STORAGE permission, but this requires users to manually enable it in settings and is heavily scrutinized by Google Play—only use it if your app is a file manager.

4. Check BitWebServer’s Directory Permissions #

BitWebServer might set restrictive permissions on its www directory, preventing other apps from writing to it:

• Use your Android file manager to navigate to /storage/emulated/0/bitwebserver/, long-press the www folder, and check its permissions—ensure "Write" access is enabled for other apps.
• Or use adb to verify permissions:

  adb shell ls -l /storage/emulated/0/bitwebserver/
  

  Look for permissions like drwxrwxrwx (read/write/execute for all users)—if it’s anything less, you’ll need to adjust the directory’s permissions (either via the file manager or adb).

1. Double-check that storage permissions are enabled for your app in Android’s Settings > Apps > [Your App] > Permissions.
2. Test with a simple text file first to rule out complex content issues.
3. Use console.log to print the full target path before writing—make sure it matches the actual location of BitWebServer’s www directory.

内容的提问来源于stack exchange，提问作者Disco Fever