android - 访问 getExternalStorageDirectory

Question

使用一些非常简单的 android 代码，我试图根据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() );
    }
}

其中 subdir_x 是由我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，但是当我尝试 file.listFiles() 时，我的代码返回 null。

我如何访问这些文件？

Answer 1

我在 Marshmallow (6.0) 中尝试过这种逻辑:

1. 确保你的 list 中有这个:

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

1. 当尝试访问外部存储时，请在进入读取目录的逻辑之前检查权限:
   

   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.
           }
       }
   }
   

2. 然后在您的 Activity 中覆盖此方法:

   @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
       }
   }
   

3. 之后你终于可以读取android设备中的外部存储，我试过这样的方法来读取外部存储中的目录:

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

   现在您有了目录，您可以在那里列出文件或创建文件。希望对您有所帮助。