DocumentsProvider: What is content: //com.android.documentsui.recents/state And why don't I like it?

Question

I am trying to implement DocumentsProvider as a demo for my book. While the provider appears in the consumer sample application, as soon as I click on it in the Access Access Framework user interface, I get the following stack trace:

 09-15 18:40:46.290 1765-1829/com.android.documentsui E/AndroidRuntime﹕ FATAL EXCEPTION: ProviderExecutor: com.commonsware.android.documents.provider Process: com.android.documentsui, PID: 1765 java.lang.RuntimeException: An error occured while executing doInBackground() at android.os.AsyncTask$3.done(AsyncTask.java:300) at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:355) at java.util.concurrent.FutureTask.setException(FutureTask.java:222) at java.util.concurrent.FutureTask.run(FutureTask.java:242) at com.android.documentsui.ProviderExecutor.run(ProviderExecutor.java:107) Caused by: java.lang.UnsupportedOperationException: Unsupported Uri content://com.android.documentsui.recents/state/com.commonsware.android.documents.provider/thisIsMyRoot/ at com.android.documentsui.RecentsProvider.query(RecentsProvider.java:192) at android.content.ContentProvider.query(ContentProvider.java:857) at android.content.ContentProvider$Transport.query(ContentProvider.java:200) at android.content.ContentResolver.query(ContentResolver.java:461) at android.content.ContentResolver.query(ContentResolver.java:404) at com.android.documentsui.DirectoryLoader.loadInBackground(DirectoryLoader.java:124) at com.android.documentsui.DirectoryLoader.loadInBackground(DirectoryLoader.java:65) at android.content.AsyncTaskLoader.onLoadInBackground(AsyncTaskLoader.java:312) at android.content.AsyncTaskLoader$LoadTask.doInBackground(AsyncTaskLoader.java:69) at android.content.AsyncTaskLoader$LoadTask.doInBackground(AsyncTaskLoader.java:57) at android.os.AsyncTask$2.call(AsyncTask.java:288) at java.util.concurrent.FutureTask.run(FutureTask.java:237)            at com.android.documentsui.ProviderExecutor.run(ProviderExecutor.java:107) 

content://com.commonsware.android.documents.provider/thisIsMyRoot/ is supposedly Uri generated for my document root, based on the implementation of queryRoots() . But I have no idea what content://com.android.documentsui.recents/state/com.commonsware.android.documents.provider/thisIsMyRoot/ or what should I do to prevent this error.

Here is the implementation of DocumentsProvider designed to serve files from assets/ :

 /*** Copyright (c) 2014 CommonsWare, LLC Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0. Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License. From _The Busy Coder Guide to Android Development_ http://commonsware.com/Android */ package com.commonsware.android.documents.provider; import android.content.res.AssetManager; import android.database.Cursor; import android.database.MatrixCursor; import android.net.Uri; import android.os.CancellationSignal; import android.os.ParcelFileDescriptor; import android.provider.DocumentsContract.Document; import android.provider.DocumentsContract.Root; import android.provider.DocumentsProvider; import android.util.Log; import android.webkit.MimeTypeMap; import java.io.FileNotFoundException; import java.io.IOException; import java.io.InputStream; import java.io.OutputStream; import java.util.ArrayList; public class DemoDocumentProvider extends DocumentsProvider { private static final String[] SUPPORTED_ROOT_PROJECTION=new String[] { Root.COLUMN_ROOT_ID, Root.COLUMN_FLAGS, Root.COLUMN_TITLE, Root.COLUMN_DOCUMENT_ID, Root.COLUMN_ICON }; private static final String[] SUPPORTED_DOCUMENT_PROJECTION= new String[] { Document.COLUMN_DOCUMENT_ID, Document.COLUMN_MIME_TYPE, Document.COLUMN_DISPLAY_NAME, Document.COLUMN_FLAGS}; private static final String ROOT_ID="thisIsMyRoot"; private static final String ROOT_DOCUMENT_ID="thisCannotBeEmpty"; private AssetManager assets; @Override public boolean onCreate() { assets=getContext().getAssets(); return(true); } @Override public Cursor queryRoots(String[] projection) throws FileNotFoundException { String[] netProjection= netProjection(projection, SUPPORTED_ROOT_PROJECTION); MatrixCursor result=new MatrixCursor(netProjection); MatrixCursor.RowBuilder row=result.newRow(); row.add(Root.COLUMN_ROOT_ID, ROOT_ID); row.add(Root.COLUMN_ICON, R.drawable.ic_launcher); row.add(Root.COLUMN_FLAGS, Root.FLAG_LOCAL_ONLY); row.add(Root.COLUMN_TITLE, getContext().getString(R.string.root)); row.add(Root.COLUMN_DOCUMENT_ID, ROOT_DOCUMENT_ID); return(result); } @Override public Cursor queryChildDocuments(String parentDocumentId, String[] projection, String sortOrder) throws FileNotFoundException { String[] netProjection= netProjection(projection, SUPPORTED_DOCUMENT_PROJECTION); MatrixCursor result=new MatrixCursor(netProjection); parentDocumentId=fixUpDocumentId(parentDocumentId); try { String[] children=assets.list(parentDocumentId); for (String child : children) { addDocumentRow(result, child, parentDocumentId+child); } } catch (IOException e) { Log.e(getClass().getSimpleName(), "Exception reading asset dir", e); } return(result); } @Override public Cursor queryDocument(String documentId, String[] projection) throws FileNotFoundException { String[] netProjection= netProjection(projection, SUPPORTED_DOCUMENT_PROJECTION); MatrixCursor result=new MatrixCursor(netProjection); documentId=fixUpDocumentId(documentId); try { addDocumentRow(result, Uri.parse(documentId).getLastPathSegment(), documentId); } catch (IOException e) { Log.e(getClass().getSimpleName(), "Exception reading asset dir", e); } return(result); } @Override public ParcelFileDescriptor openDocument(String documentId, String mode, CancellationSignal signal) throws FileNotFoundException { ParcelFileDescriptor[] pipe=null; try { pipe=ParcelFileDescriptor.createPipe(); AssetManager assets=getContext().getResources().getAssets(); new TransferThread(assets.open(documentId), new ParcelFileDescriptor.AutoCloseOutputStream(pipe[1])).start(); } catch (IOException e) { Log.e(getClass().getSimpleName(), "Exception opening pipe", e); throw new FileNotFoundException("Could not open pipe for: " + documentId); } return(pipe[0]); } private void addDocumentRow(MatrixCursor result, String child, String assetPath) throws IOException { MatrixCursor.RowBuilder row=result.newRow(); row.add(Document.COLUMN_DOCUMENT_ID, assetPath); if (isDirectory(assetPath)) { row.add(Document.COLUMN_MIME_TYPE, Document.MIME_TYPE_DIR); } else { row.add(Document.COLUMN_MIME_TYPE, MimeTypeMap.getFileExtensionFromUrl(assetPath)); row.add(Document.COLUMN_SIZE, lastModified(assetPath)); } row.add(Document.COLUMN_DISPLAY_NAME, child); row.add(Document.COLUMN_FLAGS, 0); } private boolean isDirectory(String assetPath) throws IOException { return(assets.list(assetPath).length>1); } private long lastModified(String assetPath) throws IOException { return(assets.openFd(assetPath).getLength()); } private String fixUpDocumentId(String documentId) { if (ROOT_DOCUMENT_ID.equals(documentId)) { return(""); } return(documentId); } private static String[] netProjection(String[] requested, String[] supported) { if (requested==null) { return(supported); } ArrayList<String> result=new ArrayList<String>(); for (String request : requested) { for (String support : supported) { if (request.equals(support)) { result.add(request); break; } } } return(result.toArray(new String[0])); } static class TransferThread extends Thread { InputStream in; OutputStream out; TransferThread(InputStream in, OutputStream out) { this.in=in; this.out=out; } @Override public void run() { byte[] buf=new byte[1024]; int len; try { while ((len=in.read(buf)) >= 0) { out.write(buf, 0, len); } in.close(); out.flush(); out.close(); } catch (IOException e) { Log.e(getClass().getSimpleName(), "Exception transferring file", e); } } } } 

So my question is: where am I going wrong?

Answer 1

I created gist , it has working code.

Question:

In the case of root dir, the queryDocument implementation returns an empty string identifier for the document. RecentProvider tries to match uri with state/*/*/* , where the last segment is the document identifier. Since the document id is empty string , uri does not match, so an unsupported uri exception is thrown.

Solution: I have fully provided 4 fixes to completely solve the problem. I left comments in the code.

Fix 1: When requesting child documents, if the parent is the root element, then the assetPath attribute should just be filename . If the parent directory is in the assets folder, then the value of the assetPath parameter should be directory/filename . You also need to add a file separator between the components.

Change

 addDocumentRow(result, child, parentDocumentId+child); 

to

 addDocumentRow(result, child, parentDocumentId == "" ? child : parentDocumentId + File.separator + child); 

Fix 2:. This provides a fix for an unsupported uri exception. The document identifier should never be null.

Remove documentId=fixUpDocumentId(documentId); from queryDocument .

Fix 3 and 4: Determine if the file is a directory. In the case of root the resource directory must be empty . A non-empty directory will have at least 1 file.

Edit:

 private boolean isDirectory(String assetPath) throws IOException { return(assets.list(assetPath).length>1); } 

to

 private boolean isDirectory(String assetPath) throws IOException { // Fix 3 : Call fixUpDocumentId. In case of root, the call should be assets.list(""). assetPath = fixUpDocumentId(assetPath); // Fix 4 : Empty directories are not included in apk. Non empty directory will have atleast 1 file. return(assets.list(assetPath).length>=1); } 

Here is the screen recording: