我正在尝试实现一个 DocumentsProvider 作为我的书的演示。当提供者出现在消费者示例应用程序中时，只要我在存储访问框架的 UI 中单击它，我就会得到以下堆栈跟踪:

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/ 大概是根据 queryRoots( ) 实现。但我不知道什么 content://com.android.documentsui.recents/state/com.commonsware.android.documents.provider/thisIsMyRoot/ 或者我应该做什么来防止这个错误.

这是 DocumentsProvider 实现，旨在为来自 assets/ 的文件提供服务:

/***
  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's 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);
      }
    }
  }
}

那么，我的问题是:我哪里出错了？

最佳答案

我创建了一个 gist , 它有工作代码。

问题:

在 root 目录的情况下，queryDocument 实现返回空字符串 文档 ID。 RecentProvider 尝试将 uri 与 state/*/*/* 进行匹配，其中最后一段是文档 ID。由于文档id是空字符串，uri匹配失败，因此抛出不支持的uri异常。

解决方案: 我总共提供了 4 个修复程序来使解决方案完全起作用。我在代码中留下了注释。

修复 1: 在查询子文档时，如果父文档是根文档，则 assetPath 应该只是 文件名。如果父级是 Assets 文件夹中的目录，则 Assets 路径应为 directory/filename。您还需要在组件之间添加文件分隔符。

改变

addDocumentRow(result, child, parentDocumentId+child);

到

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

修复 2: 这为不受支持的 uri 异常提供了修复。文档 ID 绝不能为空。

从 queryDocument 中删除 documentId=fixUpDocumentId(documentId);。

修复 3 和 4: 确定文件是否为目录。在 root 的情况下， Assets 目录应该是 空 字符串。非空目录将至少有 1 个文件。

改变:

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

到

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);
}

录屏如下:

关于android - DocumentsProvider : What Is content://com. android.documentsui.recents/state 为什么它不喜欢我？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/25858032/