访问 getExternalStorageDirectory

Question

我正在尝试使用一些相当简单的Android代码按照以下逻辑访问文件夹：

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() );
    }
}

这里的subdir_x是由我的手机上的另一个应用程序创建的。

我可以使用文件管理器查看这些文件夹，但当我尝试使用file.listFiles()时，我的代码返回null。

我该如何访问这些文件？

- jason m

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https://dev59.com/J1wX5IYBdhLWcg3w-Thv#41221852 - Bipin Bharti

Answer 1

我在 Marshmallow (6.0) 上尝试了这个逻辑：

1. 确保您的清单文件中有以下内容：

<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.

- Gujarat Santana

Answer 2

在Marshmallow版本之前，请按照@Cory Charlton的答案操作。然而，他在Android Marshmallow（6.0）的回答将不起作用。

实际上，在Android 6.0（API级别23）中，我们不再拥有以下权限。

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

了解更多信息，请查看以下问题：

• Android Marshmallow权限模型在OS 4.0上READ_EXTERNAL_STORAGE权限始终未授予

顺便说一下，Environment e = new Environment();是无用的，请将其删除。

- frogatto

Answer 3

请确保您的 AndroidManifest.xml 文件具有适当的权限：

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

下一个可能的问题可能是您的文件名。 我在我的一个应用程序中使用以下内容，它可以正常工作（请注意末尾斜杠和缺少前导斜杠）：

directory = new File(Environment.getExternalStorageDirectory(), "Subdirectory/")
final File[] files = directory.listFiles();

下一个问题可能是路径Environment.getExternalStorageDirectory()提供给您的。较新的设备在内部存储器上有一个模拟SD卡的分区，Environment.getExternalStorageDirectory()可能会返回这个模拟SD卡而不是真实的SD卡。

- Cory Charlton