Hey there, I’ve dealt with this exact problem using barteksc’s Android PDF Viewer before—let me break down why your pages(0) trick isn’t working, and how to implement true progressive page loading for large PDFs.

Why pages(0) doesn’t help #

The core issue here is how the library handles PDF loading: even if you specify to only show page 0, it still needs to parse the entire PDF’s structure (like the cross-reference table that maps page locations) first. That means it has to load the full file into memory/local storage before it can render any single page—so your pages(0) call only controls what’s displayed, not what’s loaded in the background.

Solutions to fix progressive loading #

1. Optimize file loading (quick win)

Your current code reads the entire PDF stream into memory via BufferedInputStream, which is slow and memory-heavy for large files. Instead, download the PDF to a temporary local file first, then use fromFile() instead of fromStream(). This lets the underlying Pdfium library use random file access to parse pages faster, without loading everything into memory at once.

Here’s how to adjust your RetrievePDFStream AsyncTask:

class RetrievePDFStream extends AsyncTask<String, Void, File> {
    @Override
    protected File doInBackground(String... strings) {
        try {
            URL url = new URL(strings[0]);
            HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
            
            // Create a temporary file in cache (gets deleted when app exits)
            File tempPdf = File.createTempFile("store_flyer", ".pdf", getCacheDir());
            tempPdf.deleteOnExit();
            
            // Download directly to file (no in-memory buffering of the full file)
            try (InputStream in = new BufferedInputStream(urlConnection.getInputStream());
                 OutputStream out = new FileOutputStream(tempPdf)) {
                byte[] buffer = new byte[4096];
                int bytesRead;
                while ((bytesRead = in.read(buffer)) != -1) {
                    out.write(buffer, 0, bytesRead);
                }
            }
            return tempPdf;
        } catch (IOException e) {
            e.printStackTrace();
            return null;
        }
    }

    @Override
    protected void onPostExecute(File tempPdf) {
        ProgressBar progressBar = findViewById(R.id.progressBar2);
        progressBar.setVisibility(View.GONE);
        
        if (tempPdf == null) {
            // Handle download failure here
            return;
        }

        // First, load ONLY the first page to show it immediately
        mPDFview.fromFile(tempPdf)
                .pages(0)
                .enableSwipe(false) // Disable swiping until full load is done
                .onLoadComplete(() -> {
                    // Once first page is visible, load the full PDF in the background
                    // This will let users swipe through pages once ready
                    new Handler(Looper.getMainLooper()).post(() -> {
                        mPDFview.fromFile(tempPdf)
                                .enableSwipe(true)
                                .load();
                    });
                })
                .load();
    }
}

2. Upgrade the library (best long-term fix)

Your 2.8.2 version is pretty old—later versions (3.x+) of barteksc’s PDF Viewer have major optimizations for large files, including better memory management and native progressive loading. After upgrading your dependency to the latest stable version:

// Replace your old dependency with this
implementation 'com.github.barteksc:android-pdf-viewer:3.2.0-beta.1'

You can simplify your code to let the library handle progressive loading automatically:

mPDFview.fromFile(tempPdf)
        .enableAntialiasing(true)
        .swipeHorizontal(false)
        .onFirstPageLoaded(() -> {
            // Hide progress bar as soon as the first page is visible
            progressBar.setVisibility(View.GONE);
        })
        .load();

The library will now render the first page as soon as it’s parsed, while continuing to load the rest of the PDF in the background.

3. Bonus: True partial download (advanced)

If you want to go all-in and load only the first page without downloading the full PDF, you’ll need to use HTTP Range requests to download only the initial bytes of the file (enough to parse the first page). This is more complex because you have to parse the PDF’s internal structure to know how many bytes to download, but it’s doable with some PDF spec knowledge. For most apps though, the first two solutions will be more than sufficient.

Extra quick fixes #

• Replace addValueEventListener with addListenerForSingleValueEvent in your Firebase call—you don’t need to listen for repeated data changes, just get the PDF URL once.
• Consider using OkHttp instead of HttpURLConnection for faster, more reliable downloads.

内容的提问来源于stack exchange，提问作者user9091408