OnKeyListener problem enabling a button

Thanks in advance for your answers. I am working on a basic tax calculator to help me better understand the fundamentals to the Android SDK. The user enters a subtotal and a tax rate (.08) a开发者_运维知识库nd they press calculate to calculate the solution. I disable the calculate button until both fields have contents. My problem is that when the user enters numbers for both of the fields, the calculate button is still disabled. I posted the code I currently am running (the OnKeyListener). The edittext fields are registered to the listener.

private OnKeyListener mKeyListener = new OnKeyListener()
{
    @Override
    public boolean onKey(View v, int keyCode, KeyEvent event)
    {
        switch(v.getId())
        {
        case R.id.txtSub:
            cmdSubmit.setEnabled(txtTax.getText().length()>0
                    && txtSub.getText().length() > 0);
            break;
        case R.id.txtTax:
            cmdSubmit.setEnabled(txtTax.getText().length()>0
                    && txtSub.getText().length() > 0);
            break;
        }
        return false;
    }

};

If you look at the spec for OnKeyListener you'll notice that it gets invoked BEFORE the KeyEvent is given to the view. Other than that this looks right: I would suspect you aren't binding the listener to the right view. Put a break point in the method and make sure it is getting invoked correctly.

I've personally found the TextWatchers a much nicer way of keeping track of whether an EditText has data or not:

TextWatcher tw = new TextWatcher() {
  @Override
  public void afterTextChanged(Editable s) {
    cmdSubmit.setEnabled(!Utils.isStringBlank(txtTax.getText().toString()) && 
                         !Utils.isStringBlank(txtSub.getText().toString()));
  }

  @Override
  public void beforeTextChanged(CharSequence s, int start, int count, int after) {}
  @Override
  public void onTextChanged(CharSequence s, int start, int before, int count) {}
};
txtTax.addTextChangedListener(tw); 
txtSub.addTextChangedListener(tw);