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Question

I am using AsyncTask (for the first time) to display a progress bar while a file is being encrypted. My encryption worked before I tried adding the progress bar but seems to crash the app now. I know the onPreExecute() works from testing so I think the problem lies in doInBackground(). Any help would be really appreciated.

public class EncryptAsync extends AsyncTask<Void, Void, Void> {
    //ProgressDialog progressDialog;

    //declare other objects as per your need
    @Override
    protected void onPreExecute() {
        //   progressDialog = ProgressDialog.show(EncryptFile.this, "Progress Dialog Title Text", "Process Description Text", true);


        if (password.getText().toString().equals(confirmPassword.getText().toString())) {

            correctPassword = password.getText().toString();
            //Toast.makeText(this,correctPassword,Toast.LENGTH_LONG).show();

            //copies Plain Text to String
            fileEditText.setInputType(InputType.TYPE_CLASS_TEXT);
            returnFile = fileEditText.getText().toString();
            Toast.makeText(EncryptFile.this, returnFile, Toast.LENGTH_LONG).show();
        } else {
            Toast.makeText(EncryptFile.this, "Passwords do not match", Toast.LENGTH_LONG).show();

        }

    }



    @Override
    protected Void doInBackground(Void... params) {


        if (spinnerValue.equals("AES")) {
            Toast.makeText(EncryptFile.this, returnFile, Toast.LENGTH_LONG).show();

            try {
                // Here you read the cleartext.
                FileInputStream fis = new FileInputStream(returnFile);
                // This stream write the encrypted text. This stream will be wrapped by another stream.
                FileOutputStream fos = new FileOutputStream(returnFile + ".aes");

                // hash password with SHA-256 and crop the output to 128-bit for key
                MessageDigest digest = MessageDigest.getInstance("SHA-256");
                digest.update(correctPassword.getBytes());

                // copys hashed password to key
                System.arraycopy(digest.digest(), 0, key, 0, key.length);


                SecretKeySpec sks = new SecretKeySpec(key, "AES");
                // Create cipher
                Cipher cipher = Cipher.getInstance("AES");
                cipher.init(Cipher.ENCRYPT_MODE, sks);
                // Wrap the output stream
                CipherOutputStream cos = new CipherOutputStream(fos, cipher);
                // Write bytes
                int b;
                byte[] d = new byte[8];
                while ((b = fis.read(d)) != -1) {
                    cos.write(d, 0, b);
                }
                // Flush and close streams.
                cos.flush();
                cos.close();
                fis.close();
            } catch (Exception ex) {
                Toast.makeText(EncryptFile.this, "Error with Exception", Toast.LENGTH_LONG).show();
            } catch(Throwable t){
                Toast.makeText(EncryptFile.this, "Error with throwable", Toast.LENGTH_LONG).show();
            }

        } else if (spinnerValue.equals("Blowfish")) {
//code for blowfish
        }



         return null;
    }
@Override
    protected void onPostExecute(Void result) {
        Toast.makeText(EncryptFile.this, "Finished Encryption", Toast.LENGTH_LONG).show();
        // super.onPostExecute(result);
        // progressDialog.dismiss();
    }

This is called by clicking this button

public void EncryptButton(View view) {

    EncryptAsync task = new EncryptAsync();
    task.execute();

}

Answer 1

The exception you're getting will most likely be something like NetworkOnMainThreadException.

In an AsyncTask, you are not allowed to do any modifications to the view in the doInBackground method. This should all be moved to either the onPreExecute, onPostExecute or onUpdate.

At least this line is in violation of that:

Toast.makeText(EncryptFile.this, returnFile, Toast.LENGTH_LONG).show();