Email from internal storage

I think you may have found a bug (or at least unnecessary limitation) in the android Gmail client. I was able to work around it, but it strikes me as too implementation specific, and would need a little more work to be portable:

First CommonsWare is very much correct about needing to make the file world readable:

fos = openFileOutput(xmlFilename, MODE_WORLD_READABLE);

Next, we need to work around Gmail's insistence on the /mnt/sdcard (or implementation specific equivalent?) path:

Uri uri = Uri.fromFile(new File("/mnt/sdcard/../.."+getFilesDir()+"/"+xmlFilename));

At least on my modified Gingerbread device, this is letting me Gmail an attachment from private storage to myself, and see the contents using the preview button when I receive it. But I don't feel very "good" about having to do this to make it work, and who knows what would happen with another version of Gmail or another email client or a phone which mounts the external storage elsewhere.

I have been struggling with this issue lately and I would like to share the solution I found, using FileProvider, from the support library. its an extension of Content Provider that solve this problem well without work-around, and its not too-much work.

As explained in the link, to activate the content provider: in your manifest, write:

<application
    ....
    <provider
        android:name="android.support.v4.content.FileProvider"
        android:authorities="com.youdomain.yourapp.fileprovider"
        android:exported="false"
        android:grantUriPermissions="true">
        <meta-data
            android:name="android.support.FILE_PROVIDER_PATHS"
            android:resource="@xml/file_paths" />
    </provider>
    ...

the meta data should indicate an xml file in res/xml folder (I named it file_paths.xml):

<?xml version="1.0" encoding="utf-8"?>
<paths xmlns:android="http://schemas.android.com/apk/res/android">
    <files-path path="" name="document"/>
</paths>

the path is empty when you use the internal files folder, but if for more general location (we are now talking about the internal storage path) you should use other paths. the name you write will be used for the url that the content provider with give to the file.

and now, you can generate a new, world readable url simply by using:

Uri contentUri = FileProvider.getUriForFile(context, "com.yourdomain.yourapp.fileprovider", file);

on any file from a path in the res/xml/file_paths.xml metadata.

and now just use:

    Intent mailIntent = new Intent(Intent.ACTION_SEND);
    mailIntent.setType("message/rfc822");
    mailIntent.putExtra(Intent.EXTRA_EMAIL, recipients);

    mailIntent.putExtra(Intent.EXTRA_SUBJECT, subject);
    mailIntent.putExtra(Intent.EXTRA_TEXT, body);
    mailIntent.putExtra(Intent.EXTRA_STREAM, contentUri);

    try {
        startActivity(Intent.createChooser(mailIntent, "Send email.."));
    } catch (android.content.ActivityNotFoundException ex) {
        Toast.makeText(this, R.string.Message_No_Email_Service, Toast.LENGTH_SHORT).show();
    }

you don't need to give a permission, you do it automatically when you attach the url to the file.

and you don't need to make your file MODE_WORLD_READABLE, this mode is now deprecated, make it MODE_PRIVATE, the content provider creates new url for the same file which is accessible by other applications.

I should note that I only tested it on an emulator with Gmail.

Chris Stratton proposed good workaround. However it fails on a lot of devices. You should not hardcode /mnt/sdcard path. You better compute it:

String sdCard = Environment.getExternalStorageDirectory().getAbsolutePath();
Uri uri = Uri.fromFile(new File(sdCard + 
          new String(new char[sdCard.replaceAll("[^/]", "").length()])
                    .replace("\0", "/..") + getFilesDir() + "/" + xmlFilename));

Taking into account recommendations from here: http://developer.android.com/reference/android/content/Context.html#MODE_WORLD_READABLE, since API 17 we're encouraged to use ContentProviders etc. Thanks to that guy and his post http://stephendnicholas.com/archives/974 we have a solution:

public class CachedFileProvider extends ContentProvider {
public static final String AUTHORITY = "com.yourpackage.gmailattach.provider";
private UriMatcher uriMatcher;
@Override
public boolean onCreate() {
    uriMatcher = new UriMatcher(UriMatcher.NO_MATCH);
    uriMatcher.addURI(AUTHORITY, "*", 1);
    return true;
}
@Override
public ParcelFileDescriptor openFile(Uri uri, String mode) throws FileNotFoundException {
    switch (uriMatcher.match(uri)) {
        case 1:// If it returns 1 - then it matches the Uri defined in onCreate
            String fileLocation = AppCore.context().getCacheDir() + File.separator +     uri.getLastPathSegment();
            ParcelFileDescriptor pfd = ParcelFileDescriptor.open(new File(fileLocation),     ParcelFileDescriptor.MODE_READ_ONLY);
            return pfd;
        default:// Otherwise unrecognised Uri
            throw new FileNotFoundException("Unsupported uri: " + uri.toString());
    }
}
@Override public int update(Uri uri, ContentValues contentvalues, String s, String[] as) { return     0; }
@Override public int delete(Uri uri, String s, String[] as) { return 0; }
@Override public Uri insert(Uri uri, ContentValues contentvalues) { return null; }
@Override public String getType(Uri uri) { return null; }
@Override public Cursor query(Uri uri, String[] projection, String s, String[] as1, String s1) {     return null; }
}

Than create file in Internal cache:

    File tempDir = getContext().getCacheDir();
    File tempFile = File.createTempFile("your_file", ".txt", tempDir);
    fout = new FileOutputStream(tempFile);
    fout.write(bytes);
    fout.close();

Setup Intent:

...
emailIntent.putExtra(Intent.EXTRA_STREAM, Uri.parse("content://" + CachedFileProvider.AUTHORITY + "/" + tempFile.getName()));

And register Content provider in AndroidManifest file:

<provider android:name="CachedFileProvider" android:authorities="com.yourpackage.gmailattach.provider"></provider>