Android PDF加载时间

Question

• The requirements: ensure that the PDF document is deleted from the device after the user has left the PDF viewing screen

  • The problem: on certain devices (Samsung 4.4.2 and Samsung 4.1.2 for sure, but not Asus 4.2.1) only the first time that the PDF is requested after restarting the application an error message is displayed stating "This document cannot be opened". Thereafter the PDF will load normally. I'm thinking this is a timing issue due to processes that need to be started the first time, but are running after the first attempted load.

  • The code: note that createFile() is called first, then startActivityForIntentResult()

     private File file; private ArrayList<Uri> uriList = new ArrayList<Uri>(); private void createFile() { int fileNameLength = pdfFileName[0].length(); String fileName = pdfFileName[0].substring(0, fileNameLength - 4) + DateTime.now(); String fileExtension = pdfFileName[0].substring(fileNameLength - 4, fileNameLength); byte[] content = Base64.decodeBase64(pdfData[0].getBytes()); BufferedOutputStream outputStream = null; try { File path = new File(getExternalFilesDir(null).getAbsolutePath(), "temp"); if (!path.exists()) { path.mkdirs(); } file = new File(path, fileName + fileExtension); outputStream = new BufferedOutputStream(new FileOutputStream(file)); outputStream.write(content); file.deleteOnExit(); uriList.add(Uri.fromFile(file)); } catch (FileNotFoundException ex) { ex.printStackTrace(); } catch (IOException ex) { ex.printStackTrace(); } finally { try { if (outputStream != null) { outputStream.flush(); outputStream.close(); } } catch (IOException ex) { ex.printStackTrace(); } } } private static int REQUEST_CODE = 1; private Intent intent; private void startActivityForIntentResult() { if (file.exists()) { Uri targetUri = uriList.get(0); intent = new Intent(Intent.ACTION_VIEW); intent.setDataAndType(targetUri, "application/pdf"); intent.setFlags(Intent.FLAG_ACTIVITY_NO_HISTORY); try { startActivityForResult(intent, REQUEST_CODE); } catch (ActivityNotFoundException e) { toastTitle = "Error Displaying PDF"; toastMessage = "Please make sure you have an application for viewing PDFs installed on your device and try again."; toast = new GenericCustomToast(); toast.show(toastTitle, toastMessage, QueryForPDF.this); } } } @Override protected void onActivityResult(int requestCode, int resultCode, Intent intent) { if (resultCode == RESULT_CANCELED && requestCode == REQUEST_CODE) { if(!file.delete()) { file.delete(); } } searchAgain(); } @Override public void onBackPressed() { super.onBackPressed(); if(!file.delete()) { file.delete(); } searchAgain(); } @Override public void onStop() { super.onStop(); if(!file.delete()) { file.delete(); } } @Override public void onDestroy() { super.onDestroy(); if(!file.delete()) { file.delete(); } } 

EDIT: I have also tried implementing a callback to be absolutely certain that createFile() has finished it's work. I even tried adding delays (of different time increments) as well as adding (the completely unnecessary) flags for Intent.FLAG_GRANT_READ_URI_PERMISSION , Intent.FLAG_GRANT_WRITE_URI_PERMISSION , and Intent.FLAG_GRANT_PERSISTABLE_URI_PERMISSION .

Answer 1

I still don't know why this works, but here's the solution in case anyone else runs into this issue: It's the directory where the file is created. For some reason on the two Samsung devices there was something different in how the files were either accessed or created versus the Asus device. So File path = new File(getExternalFilesDir(null).getAbsolutePath(), "temp"); becomes File path = new File(getExternalCacheDir().getAbsolutePath()); and the problem goes away.