Accessing getExternalStorageDirectory

Question

Using some pretty simple android code I am trying to access a folder according to the following logic:

public void try_to_navigate_local_dir(){
    Environment e = new Environment();
    ArrayList<String> filesList = new ArrayList<String>();
    String sd_card = Environment.getExternalStorageDirectory().toString() + "/subdir_x";
    File file = new File( sd_card ) ;
    File list[] = file.listFiles();
    for( int i=0; i< list.length; i++) {
        filesList.add( list[i].getName() );
    }
}

Where subdir_x is created by another application on my phone.

I can view in those folders using file manager, yet my code returns null when I try to file.listFiles().

How may I access these files?

Answer 1

I have tried this logic in Marshmallow (6.0) :

1. make sure you have this in your manifest :

<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

2. when try to access external storage please check the permission before entering the logic to read directory :
   

   public void checkPermissionReadStorage(Activity activity){
            if (ContextCompat.checkSelfPermission(activity,      Manifest.permission.READ_EXTERNAL_STORAGE) !=     PackageManager.PERMISSION_GRANTED) {
   
           // Should we show an explanation?
           if (ActivityCompat.shouldShowRequestPermissionRationale(activity,
                   Manifest.permission.READ_EXTERNAL_STORAGE)) {
   
               // Show an expanation to the user *asynchronously* -- don't block
               // this thread waiting for the user's response! After the user
               // sees the explanation, try again to request the permission.
   
           } else {
   
               // No explanation needed, we can request the permission.
   
               ActivityCompat.requestPermissions(activity,
                       new String[]{Manifest.permission.READ_EXTERNAL_STORAGE},
                       MY_PERMISSIONS_REQUEST_READ_STORAGE);
   
               // MY_PERMISSIONS_REQUEST_READ_CONTACTS is an
               // app-defined int constant. The callback method gets the
               // result of the request.
           }
       }
   }
   

3. and then override this method in your activity :

   @Override
   public void onRequestPermissionsResult(int requestCode,
                                          String permissions[], int[] grantResults) {
       switch (requestCode) {
           case PermissionManager.MY_PERMISSIONS_REQUEST_READ_STORAGE: {
               //premission to read storage
               if (grantResults.length > 0
                       && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
   
                   // permission was granted, yay! Do the
                   // contacts-related task you need to do.
   
               } else {
   
                   // permission denied, boo! Disable the
                   // functionality that depends on this permission.
                   Toast.makeText(SnapSellAddActivity.this, "We Need permission Storage", Toast.LENGTH_SHORT).show();
               }
               return;
           }
   
           // other 'case' lines to check for other
           // permissions this app might request
       }
   }
   

4. after that you can finally read the external storage in android devices, I tried like this method to read directory in external storage :

   public File getPreviewTempExternalDirectory(Context context) {
       File previewDir = new File(context.getExternalFilesDir(null), PLACE YOUT DIR HERE);
       if (!previewDir.exists()) previewDir.mkdir();
       return previewDir;
   }
   

   and now you have the directory, you can list file or create file there. hope it helps.

Answer 2

Prior to Marshmallow, follow @Cory Charlton's answer. However his answer for Android Marshmallow (6.0) won't work.

Actually as of Android 6.0 (API level 23), we don't have the following permission anymore.

<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />

For more information, please this question:

• Android Marshmallow permission model on OS 4.0 READ_EXTERNAL_STORAGE permission always not granted

By the way, Environment e = new Environment(); is useless, remove it.