The way open PDF in android.

Without considering the use of webView：

1. Use intent to open an app that can use pdf

   private void openPdfFile(String url) {
        Intent intent = new Intent("android.intent.action.VIEW");
        intent.addCategory("android.intent.category.DEFAULT");
        intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
        Uri uri = Uri.parse(url);
        intent.setDataAndType(uri, "application/pdf");
        startActivity(Intent.createChooser(intent, "開啟PDF檔案"));
    }
   

2. google drive URL (if the file is too large, it cannot be previewed)

   public void setDocumentPath(final String url) {
   WebView webView = (WebView) findViewById(R.id.webview);
   webView.getSettings().setJavaScriptEnabled(true);
   webView.getSettings().setPluginsEnabled(true);
   webView.loadUrl("https://docs.google.com/viewer?url="+url);
   }
   

3. third-party package
   There are many similar projects on github, choose the one that is used by the most people
   I choose this android pdf viewer

Step 1. Add two classes

• RetrivePDFfromUrl is AsyncTask.
• TaskCancel is responsible for deleting tasks after seconds to avoid excessive loading.

class RetrivePDFfromUrl extends AsyncTask<String, Void, InputStream> {
        @Override
        protected InputStream doInBackground(String... strings) {
            InputStream inputStream = null;
            try {
                URL url = new URL(strings[0]);
                HttpURLConnection urlConnection = (HttpsURLConnection) url.openConnection();
                if (urlConnection.getResponseCode() == 200) {
                    inputStream = new BufferedInputStream(urlConnection.getInputStream());
                }

            } catch (IOException e) {
                e.printStackTrace();
                return null;
            }
            return inputStream;
        }

        @Override
        protected void onPostExecute(InputStream inputStream) {

            pdfView.fromStream(inputStream).onLoad(new OnLoadCompleteListener() {
                @Override
                public void loadComplete(int nbPages) {
                    mProgressBar.setVisibility(View.GONE);
                }
            }).load();
        }
    }
class TaskCanceler implements Runnable {
        private AsyncTask task;
        public TaskCanceler(AsyncTask task) {
            this.task = task;
        }
        @Override
        public void run() {
            if (task.getStatus() == AsyncTask.Status.RUNNING) {
                task.cancel(true);
                pdfView.setVisibility(View.GONE);
                mProgressBar.setVisibility(View.GONE);
                Toast.makeText(getContext(), getResources().getText(R.string.error_message_timeout), Toast.LENGTH_LONG).show();
            }
        }
    }

Step 2. This function is used in fragment onCreate().

private void fetchStoreFileUrl() {
        mProgressBar.setVisibility(View.VISIBLE);
        final PushMailAPI api = DataProvider.getInstance().getStoreFile();
        if (api == null) {
            return;
        }
        final String accessToken = AccountProvider.getInstance().getToken();
        api.getStoreFileUrl(accessToken, new Callback<StoreFile>() {

            @Override
            public void success(StoreFile storeFile, Response response) {
                String url = storeFile.getStoreUrl();
                pdfView.setVisibility(View.VISIBLE);
                handler = new Handler();
                RetrivePDFfromUrl task = new RetrivePDFfromUrl();
                taskCanceler = new TaskCanceler(task);
                handler.postDelayed(taskCanceler, Constants.LOADING_TIME_LIMIT );
                task.execute(url);
            }

            @Override
            public void failure(RetrofitError error) {
                mProgressBar.setVisibility(View.GONE);
                new ErrorHandler(getActivity(), TAG) {

                    @Override
                    protected void onUnknownError(String code, String message, String description) {
                        super.onUnknownError(code, message, description);
                    }

                }.handle(error);
            }
        });
    }

Step 3.
Finally, add and delete taskCanceler in onDestroyView().
To prevent the task from continuing after the Fragment is destroyed.

@Override
    public void onDestroyView() {
        super.onDestroyView();
        unbinder.unbind();
        if (taskCanceler != null && handler != null)
            handler.removeCallbacks(taskCanceler);
    }