Android Development: How To Use onKeyUp?

The very right way is to use TextWatcher class.

EditText tv_filter = (EditText) findViewById(R.id.filter);

TextWatcher fieldValidatorTextWatcher = new TextWatcher() {
        @Override
        public void afterTextChanged(Editable s) {
        }

        @Override
        public void beforeTextChanged(CharSequence s, int start, int count, int after) {
        }

        @Override
        public void onTextChanged(CharSequence s, int start, int before, int count) {
            if (filterLongEnough()) {
                populateList();
            }
        }

        private boolean filterLongEnough() {
            return tv_filter.getText().toString().trim().length() > 2;
        }
    };
    tv_filter.addTextChangedListener(fieldValidatorTextWatcher);

CORRECTION:

For a while, I used a generic onKeyListener. I soon found that my code was being called twice. Once with the key down and once with key up. I now use the following listener and only call the code once. "if (event.getAction() == KeyEvent.ACTION_UP)" is the key.

OnKeyListener keyListener = new OnKeyListener() {

    @Override
    public boolean onKey(View v, int keyCode, KeyEvent event) {
        if (event.getAction() == KeyEvent.ACTION_UP) {
            //do something here
        }
        return false;
    }
};

I found that onKeyUp() is called automatically for every control in the Activity. If this is what you want, add it to the Activity just like you add the onCreate()

Example:

public boolean onKeyUp(int keyCode, KeyEvent event) {
    //do something here
    return false;
};

I know this is a old question, but maybe this will help others with the same issue.

You may consider using the following code:

 @Override 
 public boolean onKeyUp(int keyCode, KeyEvent event) {
    switch (keyCode) {
        ...
        case KeyEvent.KEYCODE_J:
            if (event.isShiftPressed()) {
                fireLaser();
            } else {
                fireMachineGun();
            }
            return true;
        case KeyEvent.KEYCODE_K:
            if (event.isShiftPressed()) {
                fireSeekingMissle();
            } else {
                fireMissile();
            }
            return true;
        default:
            return super.onKeyUp(keyCode, event);
    } }

Here In the end we have called the super.onkeyUp method. Which handles the event when the user do not presses the valid key.

For more details you may consider following link.