Question

I found this code snippet in latest Android notepad tutorial link which is using contentprovider and implementing PipeDataWriter.

The interface has its method writeDataToPipe which they implemented like this:

@Override
public void writeDataToPipe(ParcelFileDescriptor output, Uri uri, String mimeType, Bundle opts, Cursor c) {
    // We currently only support conversion-to-text from a single note entry,
    // so no need for cursor data type checking here.
    FileOutputStream fout = new FileOutputStream(output.getFileDescriptor());
    PrintWriter pw = null;
    try {
        pw = new PrintWriter(new OutputStreamWriter(fout, "UTF-8"));
        pw.println(c.getString(READ_NOTE_TITLE_INDEX));
        pw.println("");
        pw.println(c.getString(READ_NOTE_NOTE_INDEX));
    } catch (UnsupportedEncodingException e) {
        Log.w(TAG, "Ooops", e);
    } finally {
        c.close();
        if (pw != null) {
            pw.flush();
        }
        try {
            fout.close();
        } catch (IOException e) {
        }
    }
}

My doubt is that why specifically they are using PipeDataWriter?

Is that some kind of design pattern?

I found no other source where it has been used. Why so?

Answer 1

why specifically they are using PipeDataWriter?

They are using openPipeHelper() in their implementation of openTypedAssetFile(). openPipeHelper() takes a PipeDataWriter as a parameter. In their case, they implemented PipeDataWriter on the NotePadProvider itself, and therefore need to implement openPipeHelper() to fulfill the contract required by the PipeDataWriter interface.

PipeDataWriter and openPipeHelper() are new to API Level 11. Previously, you had to roll your own solution for forking a thread to return the contents of a file.