Android Scoped Storage: 如何读取外部存储特定文件夹的文件

import android.app.Activity; import android.content.Context; import android.content.Intent; import android.net.Uri; import android.os.storage.StorageManager; import android.util.Log;  public class Check {     Context context;     private String TAG="SOMNATH";      public Check(Context context) {         this.context = context;     }      public boolean  ch(){         if (android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.Q) {             StorageManager sm = (StorageManager) context.getSystemService(Context.STORAGE_SERVICE);              Intent intent = sm.getPrimaryStorageVolume().createOpenDocumentTreeIntent();             //String startDir = "Android";             //String startDir = "Download"; // Not choosable on an Android 11 device             //String startDir = "DCIM";             //String startDir = "DCIM/Camera";  // replace "/", "%2F"             //String startDir = "DCIM%2FCamera";             String startDir = "Documents";              Uri uri = intent.getParcelableExtra("android.provider.extra.INITIAL_URI");              String scheme = uri.toString();              Log.d(TAG, "INITIAL_URI scheme: " + scheme);              scheme = scheme.replace("/root/", "/document/");              scheme += "%3A" + startDir;              uri = Uri.parse(scheme);              intent.putExtra("android.provider.extra.INITIAL_URI", uri);              Log.d(TAG, "uri: " + uri.toString());              ((Activity) context).startActivityForResult(intent, 12123);              return true;         }         else{             return false;         }     }    }

package com.axanor.saf_sample  import android.app.Activity import android.content.Intent import android.net.Uri import android.provider.DocumentsContract import android.util.Log import android.widget.Toast import androidx.appcompat.app.AppCompatActivity import androidx.documentfile.provider.DocumentFile import java.io.FileNotFoundException import java.io.FileOutputStream import java.io.IOException  class StorageAccess {     val activity:Activity;     val LOGTAG = "SOMNATH"     val REQUEST_CODE = 12123     constructor(activity: Activity) {         this.activity = activity     }         public fun openDocumentTree() {         val check = Check(activity)         val uriString = SpUtil.getString(SpUtil.FOLDER_URI, "")         when {             uriString == "" -> {                 Log.w(LOGTAG, "uri not stored")                   if (!check.ch()){                     askPermission()                 }              }             arePermissionsGranted(uriString) -> {                 makeDoc(Uri.parse(uriString))             }             else -> {                 Log.w(LOGTAG, "uri permission not stored")                 if (!check.ch()){                     askPermission()                 }             }         }     }      // this will present the user with folder browser to select a folder for our data     public fun askPermission() {         val intent = Intent(Intent.ACTION_OPEN_DOCUMENT_TREE)         activity.startActivityForResult(intent, REQUEST_CODE)     }        public fun makeDoc(dirUri: Uri) {         val dir = DocumentFile.fromTreeUri(activity, dirUri)         if (dir == null || !dir.exists()) {             //the folder was probably deleted             Log.e(LOGTAG, "no Dir")             //according to Commonsware blog, the number of persisted uri permissions is limited             //so we should release those we cannot use anymore             //https://commonsware.com/blog/2020/06/13/count-your-saf-uri-permission-grants.html             releasePermissions(dirUri)             //ask user to choose another folder             Toast.makeText(activity,"Folder deleted, please choose another!", Toast.LENGTH_SHORT).show()             openDocumentTree()         } else {             val file = dir.createFile("*/txt", "test.txt")             if (file != null && file.canWrite()) {                 Log.d(LOGTAG, "file.uri = ${file.uri.toString()}")                 alterDocument(file.uri)             } else {                 Log.d(LOGTAG, "no file or cannot write")                 //consider showing some more appropriate error message                 Toast.makeText(activity,"Write error!", Toast.LENGTH_SHORT).show()              }         }     }       public fun releasePermissions(uri: Uri) {         val flags: Int = Intent.FLAG_GRANT_READ_URI_PERMISSION or                 Intent.FLAG_GRANT_WRITE_URI_PERMISSION         activity.contentResolver.releasePersistableUriPermission(uri,flags)         //we should remove this uri from our shared prefs, so we can start over again next time         SpUtil.storeString(SpUtil.FOLDER_URI, "")     }       //Just a test function to write something into a file, from https://developer.android.com     //Please note, that all file IO MUST be done on a background thread. It is not so in this     //sample - for the sake of brevity.     public fun alterDocument(uri: Uri) {         try {              activity.contentResolver.openFileDescriptor(uri, "w")?.use { parcelFileDescriptor ->                 FileOutputStream(parcelFileDescriptor.fileDescriptor).use {                     it.write(                         ("String written at ${System.currentTimeMillis()}n")                             .toByteArray()                     )                     Toast.makeText(activity,"File Write OK!", Toast.LENGTH_SHORT).show()                       val intent = Intent(Intent.ACTION_OPEN_DOCUMENT)                     intent.addCategory(Intent.CATEGORY_OPENABLE)                     intent.type = "application/pdf"                      // Optionally, specify a URI for the file that should appear in the                     // system file picker when it loads.                      // Optionally, specify a URI for the file that should appear in the                     // system file picker when it loads.                     intent.putExtra(DocumentsContract.EXTRA_INITIAL_URI, uri)                      activity.startActivityForResult(intent, 2)                    }             }         } catch (e: FileNotFoundException) {             e.printStackTrace()         } catch (e: IOException) {             e.printStackTrace()         }     }       public fun arePermissionsGranted(uriString: String): Boolean {         // list of all persisted permissions for our app         val list = activity.contentResolver.persistedUriPermissions         for (i in list.indices) {             val persistedUriString = list[i].uri.toString()             //Log.d(LOGTAG, "comparing $persistedUriString and $uriString")             if (persistedUriString == uriString && list[i].isWritePermission && list[i].isReadPermission) {                 //Log.d(LOGTAG, "permission ok")                 return true             }         }         return false     }        }

StorageAccess access = new StorageAccess(this); access.openDocumentTree();

    public fun makeDoc(dirUri: Uri) {         val dir = DocumentFile.fromTreeUri(activity, dirUri)         if (dir == null || !dir.exists()) {             //the folder was probably deleted             Log.e(LOGTAG, "no Dir")             //according to Commonsware blog, the number of persisted uri permissions is limited             //so we should release those we cannot use anymore             //https://commonsware.com/blog/2020/06/13/count-your-saf-uri-permission-grants.html             releasePermissions(dirUri)             //ask user to choose another folder             Toast.makeText(activity,"Folder deleted, please choose another!", Toast.LENGTH_SHORT).show()             openDocumentTree()         } else {             val file = dir.createFile("*/txt", "test.txt")             if (file != null && file.canWrite()) {                 Log.d(LOGTAG, "file.uri = ${file.uri.toString()}")                 alterDocument(file.uri)             } else {                 Log.d(LOGTAG, "no file or cannot write")                 //consider showing some more appropriate error message                 Toast.makeText(activity,"Write error!", Toast.LENGTH_SHORT).show()              }         }     }

    public fun arePermissionsGranted(uriString: String): Boolean {         // list of all persisted permissions for our app         val list = activity.contentResolver.persistedUriPermissions         for (i in list.indices) {             val persistedUriString = list[i].uri.toString()             //Log.d(LOGTAG, "comparing $persistedUriString and $uriString")             if (persistedUriString == uriString && list[i].isWritePermission && list[i].isReadPermission) {                 //Log.d(LOGTAG, "permission ok")                 return true             }         }         return false     }