Stupid Experiments

Sometimes I just get to wondering and it leads me to Stupid Experiments.

Stupid Experiment One: Activity Constructor

Wondering: If I wrote a no-parameter Activity constructor, would it be called and, if so, would it be called on every call to onCreate?

Answer: Possibly!

Warning: Do not do this in production code!

Dumb Coding Experiment:

Given a static variable and a constructor in which the variable is incremented by one:

    private static int init;

    public ConfuseText() {

        init++;

        Log.d(TAG,"Constructor");

    }

We decrement the static variable in onCreate:

    @Override

    public void onCreate(Bundle inState) {

        super.onCreate(inState);

        setContentView(R.layout.main);

        init--;

        Log.d(TAG,new Integer(init).toString());

Gives us the LogCat as:

Testing was repeated by calling init++ twice in the constructor and init-- only once in onCreate.

This verifies that the init variable is not simply being cleared on restart.

Not So Stupid Experiment Two: Exceptional Methods in a Thread

Wondering: If I run an exceptional method in a thread, how will I communicate back to the UI on exception?

Answer: Using Try Methods that wrap the exceptions into a BoolString class.

Given a BoolString class and exceptional method:

//a utility class to signal success or failure, return an error message, and return a useful String value

//see Try Out in C#

public final class BoolString {

 public final boolean success;

 public final String err;

 public final String value;

 public BoolString(boolean success, String err, String value){

     this.success= success;

     this.err= err;

     this.value= value;

 }

}

BoolString class that wraps an exception.

    public String encrypt(String inString, String password) throws GeneralSecurityException {

        boolean success= true;

        String err="";

        String outString="Encrypted"; // BoolString.value

        byte[] iv;

        try {...stuff here

        }

        catch (UnsupportedEncodingException e){err="Unable to convert key to byte array."; success= false;}

        catch (InvalidKeyException e){err="Unable to generate KeySpec from key";success= false;}

        catch (InvalidKeySpecException e){err="Invalid Key Specification";success= false;}

        catch (IllegalArgumentException e){err="Illegal argument";success= false;}  

        catch (Exception e){err=e.getMessage();success= false;}

        if (!success){throw new GeneralSecurityException(err);} // converted computerTalk to peopleTalk

        return outString;

    }

Exceptional Method.

We convert the exceptional method to a try method as in:

    public BoolString tryEncrypt(String inString, String password) {

        try {

            String value= encrypt(inString, password);

            return new BoolString(true,"",value);

        }

        catch (GeneralSecurityException e){

            return new BoolString(false,e.getMessage(),"");

        }

    }

Try method that traps exceptions and wraps them into a BoolString object.

We create our inner class EncryptAsynch as in:

    private class EncryptAsynch extends AsyncTask<String, Void, BoolString>{

        protected void onPreExecute() {

            resetProgress();

            progress.show();

        }

        @Override

        protected BoolString doInBackground(String...strings) { // <== DO NOT TOUCH THE UI VIEW HERE

            // TODO Auto-generated method stub

            String inString= strings[0];

            String password= strings[1];

            return model.tryEncrypt(inString,password); // <== return value String result is sent to onPostExecute

        }

        protected void onPostExecute(BoolString result){          

            progress.dismiss();

            if (result.success){

                isValidKey= true; // not needed?                

                editTextConfusedText.setText(result.value);

                if (isShowCharCount) {

                    editTextPlainText.setText("Confused Char Count: "

                            +new Integer(result.value.length()).toString());

                }

                else {

                    editTextPlainText.setText("");

                }

            }

            else {

                   editTextConfusedText.setText("");

                editTextPassword.setError(result.err);

                editTextPassword.requestFocus();

            }

        }

    };

Where we refresh the progress dialog in the method resetProgress:

    private void resetProgress() {

        if (progress != null && progress.isShowing()){

            progress.cancel();

        }

        progress= new ProgressDialog(this);

        progress.setIndeterminate(true);

        progress.setMessage("I am thinking.");

    }

And launch our thread as in:

                // threaded code

                new EncryptAsynch().execute(inString,password);

Success.

On exception "Error".

Don't forget to implement:

    protected void onPause() {

        super.onPause();

        if (progress != null){progress.cancel();}

    }

Alternatively, consider Thread.UncaughtExceptionHandler.