我之前的问题(Is it possible to share an image on Android via a data URL?)与这个问题有关。我已经想出如何在没有将文件写入外部存储的权限的情况下将图像从我的应用程序共享到另一个应用程序。但是，我仍然遇到一些问题行为:

1. 当我尝试从我的手机 (Android 2.2.2) 共享图像时，接收应用程序出现 fatal error ，它们根本无法提供图像。 (这可能是我的应用程序中的某些操作在 Android 2.2.2 上不受支持的结果吗？或者这会导致我的应用程序而不是目标应用程序出错？)
2. 当我尝试将图片分享到 Evernote 时，一切正常，但有时保存笔记几秒钟后，我的应用屏幕底部会收到一条消息(来自 Evernote App): "java.lang.SecurityException: Permission Denial: opening provider com.enigmadream.picturecode.PictureContentProvider from ProcessRecord{413db6d0 1872:com.evernote/u0a10105} (pid=1872, uid=10105) 未从 uid 10104 导出"
3. 当我尝试将图片分享到 Facebook 时，图片有一个矩形，但里面没有图片。

下面是我的 ContentProvider 代码。必须有一种更简单和/或更合适的方法来实现基于文件的 ContentProvider(尤其是查询功能)。我预计很多问题都来自查询实现。有趣的是，在我的 Nexus 7 上访问 GMail 时，这确实工作得很好。它还会为附件选择正确的显示名称和大小。

public class PictureContentProvider extends ContentProvider implements AutoAnimate {
    public static final Uri CONTENT_URI = Uri.parse("content://com.enigmadream.picturecode.snapshot/picture.png");
    private static String[] mimeTypes = {"image/png"};
    private Uri generatedUri;

    @Override
    public int delete(Uri uri, String selection, String[] selectionArgs) {
       throw new RuntimeException("PictureContentProvider.delete not supported");
    }

    @Override
    public String getType(Uri uri) {
       return "image/png";
    }

    @Override
    public Uri insert(Uri uri, ContentValues values) {
       throw new RuntimeException("PictureContentProvider.insert not supported");
    }

    @Override
    public boolean onCreate() {
       generatedUri = Uri.EMPTY;
       return true;
    }

    @Override
    public Cursor query(Uri uri, String[] projection, String selection,
          String[] selectionArgs, String sortOrder) {
       long fileSize = 0;
       MatrixCursor result = new MatrixCursor(projection);
       File tempFile;
       try {
          tempFile = generatePictureFile(uri);
          fileSize = tempFile.length();
       } catch (FileNotFoundException ex) {
          return result;
       }
       Object[] row = new Object[projection.length];
       for (int i = 0; i < projection.length; i++) {

          if (projection[i].compareToIgnoreCase(MediaStore.MediaColumns.DISPLAY_NAME) == 0) {
             row[i] = getContext().getString(R.string.snapshot_displaystring);
          } else if (projection[i].compareToIgnoreCase(MediaStore.MediaColumns.SIZE) == 0) {
             row[i] = fileSize;
          } else if (projection[i].compareToIgnoreCase(MediaStore.MediaColumns.DATA) == 0) {
             row[i] = tempFile;
          } else if (projection[i].compareToIgnoreCase(MediaStore.MediaColumns.MIME_TYPE)==0) {
             row[i] = "image/png";
          }
       }

       result.addRow(row);
       return result;
    }

    @Override
    public int update(Uri uri, ContentValues values, String selection,
          String[] selectionArgs) {
       throw new RuntimeException("PictureContentProvider.update not supported");
    }

    @Override
    public String[] getStreamTypes(Uri uri, String mimeTypeFilter) {
       return mimeTypes;
    }

    private File generatePictureFile(Uri uri) throws FileNotFoundException {
       if (generatedUri.compareTo(uri)==0)
          return new File(getContext().getFilesDir(), "picture.png");;
          Context context = getContext();
          String query = uri.getQuery();
          String[] queryParts = query.split("&");
          String pictureCode = "016OA";
          int resolution = 36;
          int frame = 0;
          int padding = 0;
          for (String param : queryParts) {
             if (param.length() < 2)
                continue;
             if (param.substring(0,2).compareToIgnoreCase("p=") == 0) {             
                pictureCode = param.substring(2);
             } else if (param.substring(0,2).compareToIgnoreCase("r=") == 0) {
                resolution = Integer.parseInt(param.substring(2));              
             } else if (param.substring(0, 2).compareToIgnoreCase("f=") == 0) {
                frame = Integer.parseInt(param.substring(2));
             } else if (param.substring(0, 2).compareToIgnoreCase("a=") == 0) {
                padding = Integer.parseInt(param.substring(2));
             }
          }
          Bitmap picture = RenderPictureCode(pictureCode, resolution, frame, padding);
          File tempFile = new File(context.getFilesDir(), "picture.png");       
          FileOutputStream stream;
          stream = new FileOutputStream(tempFile);
          picture.compress(CompressFormat.PNG, 90, stream);
          try {
             stream.flush();
             stream.close();
          } catch (IOException e) {
             e.printStackTrace();
             throw new Error(e);
          }
          picture.recycle();
          generatedUri = uri;
          return tempFile;
    }

    @Override
    public ParcelFileDescriptor openFile(Uri uri, String mode) throws FileNotFoundException {
       File tempFile = generatePictureFile(uri);
       return ParcelFileDescriptor.open(tempFile, ParcelFileDescriptor.MODE_READ_ONLY);
    }
...
}

我在 AndroidManifest.xml 文件中也有这个作为 <activity> 的兄弟文件元素:

    <provider 
        android:name="PictureContentProvider"
        android:authorities="com.enigmadream.picturecode.snapshot"
        android:grantUriPermissions="true"
        android:readPermission="com.enigmadream.picturecode.snapshot"
        tools:ignore="ExportedContentProvider">
        <grant-uri-permission android:path="/picture.png" />
    </provider>

创建 Intent 的代码如下所示:

        resolution = mPicView.getWidth();
        if (mPicView.getHeight() > resolution)
            resolution = mPicView.getHeight();
        String paddingText = mPadding.getEditableText().toString();
        int padding;
        try {
            padding = Integer.parseInt(paddingText);
        } catch (NumberFormatException ex) {
            padding = 0;
        }
        Uri uri = Uri.parse(PictureContentProvider.CONTENT_URI 
            + "?p=" + Uri.encode(mPicView.getPictureCode()) + "&r=" + Integer.toString(resolution) 
            + "&f=" + Integer.toString(mPicView.getFrame()) + "&a=" + Integer.toString(padding));
        Intent share = new Intent(Intent.ACTION_SEND);
        share.setType("image/png");
        share.putExtra(Intent.EXTRA_STREAM, uri);
        share.putExtra(Intent.EXTRA_SUBJECT, getString(R.string.share_subject_made));
        share.addFlags(Intent.FLAG_GRANT_READ_URI_PERMISSION);
        startActivity(Intent.createChooser(share, getString(R.id.menu_share)));

编辑 这是我手机上发生错误时堆栈跟踪的前两行:

04-07 13:56:24.423: E/DatabaseUtils(19431): java.lang.SecurityException: Permission Denial: reading com.enigmadream.picturecode.PictureContentProvider uri content://com.enigmadream.picturecode.snapshot/picture.png?p=01v131&r=36&f=0&a=0 from pid=19025, uid=10062 requires com.enigmadream.picturecode.snapshot

04-07 13:56:24.423: E/DatabaseUtils(19431): at android.content.ContentProvider$Transport.enforceReadPermission(ContentProvider.java:271)

最佳答案

由于 query 方法，我在与某些电子邮件和消息传递客户端共享时遇到了问题。一些收件人应用为 projection 参数发送 null。发生这种情况时，您的代码将抛出一个 NullPointerException。 NPE很容易解决。但是，发送 null 的应用程序仍然需要返回一些信息。我仍然无法分享到 Facebook，但我可以分享到我测试过的所有其他应用:

编辑 我也无法让它与 Google Hangout 一起使用。有了这个，至少，我得到了一个提示 You can't send this file on Hangouts 的提示。尝试使用图片。 另见这个问题:Picture got deleted after send via Google hangout .我认为这是因为我使用的是私有(private)内容，而 Hangouts 出于某种原因不能/不会接受它。

@Override
public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs,
        String sortOrder) {
    if (projection == null) {
        projection = new String[] {
                MediaStore.MediaColumns.DISPLAY_NAME,
                MediaStore.MediaColumns.SIZE,
                MediaStore.MediaColumns._ID,
                MediaStore.MediaColumns.MIME_TYPE
        };
    }

    final long time = System.currentTimeMillis();
    MatrixCursor result = new MatrixCursor(projection);
    final File tempFile = generatePictureFile(uri);

    Object[] row = new Object[projection.length];
    for (int i = 0; i < projection.length; i++) {

       if (projection[i].compareToIgnoreCase(MediaStore.MediaColumns.DISPLAY_NAME) == 0) {
          row[i] = uri.getLastPathSegment();
       } else if (projection[i].compareToIgnoreCase(MediaStore.MediaColumns.SIZE) == 0) {
          row[i] = tempFile.length();
       } else if (projection[i].compareToIgnoreCase(MediaStore.MediaColumns.DATA) == 0) {
          row[i] = tempFile;
       } else if (projection[i].compareToIgnoreCase(MediaStore.MediaColumns.MIME_TYPE)==0) {
          row[i] = _mimeType;
       } else if (projection[i].compareToIgnoreCase(MediaStore.MediaColumns.DATE_ADDED)==0 ||
               projection[i].compareToIgnoreCase(MediaStore.MediaColumns.DATE_MODIFIED)==0 ||
               projection[i].compareToIgnoreCase("datetaken")==0) {
           row[i] = time;
       } else if (projection[i].compareToIgnoreCase(MediaStore.MediaColumns._ID)==0) {
           row[i] = 0;
       } else if (projection[i].compareToIgnoreCase("orientation")==0) {
           row[i] = "vertical";
       }
    }

    result.addRow(row);
    return result;
}

关于java - 如何实现 ContentProvider 以向 Gmail、Facebook、Evernote 等提供图像，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/15865979/