Considering the FileProvider problems, and also because I wanted to implement a max cache size for collected temp files, I went with a ContentProvider solution and it works a treat. Basically, you're allowed to use your internal cache without any problem but still provide third party apps with a URI they can use to reference your temporary files you want to share with them. Because you use your internal cache, there will be no unnecessary WRITE_EXTERNAL_STORAGE permission to ask for.
The added max cache size limit (that you can remove from the class by simply deleting everything from checkSize() to the end of the class, for instance, if you can make sure you delete all files directly after sharing, so they won't remain on the device) works by checking the cumulated max size upon each call and clearing up half the cache (deleting the oldest files) if necessary.
public class TemporaryFile extends ContentProvider {
private static final long MAX_SIZE = 512 * 1024;
// commented out on purpose so that you don't forget to rewrite it...
// public static final String AUTHORITY = "com.example.tempfile";
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 {
if (uriMatcher.match(uri) == 1) {
final String file = getContext().getCacheDir() + File.separator + uri.getLastPathSegment();
return ParcelFileDescriptor.open(new File(file), ParcelFileDescriptor.MODE_READ_ONLY);
}
else
throw new FileNotFoundException(uri.toString());
}
@Override
public int update (Uri uri, ContentValues values, String selection, String[] selectionArgs) {
return 0;
}
@Override
public int delete (Uri uri, String selection, String[] selectionArgs) {
return 0;
}
@Override
public Uri insert(Uri uri, ContentValues values) {
return null;
}
@Override
public String getType(Uri uri) {
return null;
}
@Override
public Cursor query (Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder) {
return null;
}
public static File getFile(Context context, String prefix, String extension) throws IOException {
checkSize(context);
File file = File.createTempFile(prefix, extension, context.getCacheDir());
file.setReadable(true);
file.deleteOnExit();
return file;
}
public static Uri getPublicUri(File file) {
return Uri.withAppendedPath(Uri.parse("content://" + AUTHORITY), file.getName());
}
public static void checkSize(Context context) throws IOException {
File dir = context.getCacheDir();
if (getDirSize(dir) > MAX_SIZE)
cleanDir(dir, MAX_SIZE / 2);
}
private static long getDirSize(File dir) {
long size = 0;
for (File file : dir.listFiles())
if (file.isFile())
size += file.length();
return size;
}
private static void cleanDir(File dir, long atLeast) {
long deleted = 0;
File[] files = dir.listFiles();
Arrays.sort(files, new Comparator<File>() {
public int compare(File f1, File f2) {
return Long.valueOf(f1.lastModified()).compareTo(f2.lastModified());
}
});
for (File file : files) {
deleted += file.length();
file.delete();
if (deleted >= atLeast)
break;
}
}
}
Using it couldn't be simpler, just call
File file = TemporaryFile.getFile(this, "prefix", ".extension");
whenever you want to create a new file and
TemporaryFile.getPublicUri(file)
whenever you want to get a public Uri to the file, eg. to pass it to an intent as data or Intent.EXTRA_STREAM.
Being a provider, don't forget to add the necessary manifest entry, either:
<provider
android:name=".TemporaryFile"
android:authorities="com.example.tempfile"
android:exported="true"
tools:ignore="ExportedContentProvider" >
</provider>
