Java: onClick not working to set a value in an empty field

Question

I am trying to build a simple calculator to learn Android programming. I've got my UI all sorted but the "Submit" button doesn't seem to be working, which should do logic on two user submitted values and output the result.

Here is the method:

@Override
public void onClick(View view){
    String num1 = etfirst.getText().toString();
    String num2 = etsecond.getText().toString();
    String amount = etamount.getText().toString();
    switch(view.getId()){
        case R.id.btnSubmit:
            int divide =  (Integer.parseInt(num2) / Integer.parseInt(num1)) +1;
            int multiply = divide * Integer.parseInt(amount);
            tvResult.setText(String.valueOf(multiply));
            break;
    }
}

I've declared all my variables before hand and initialized them. All variable names match but the ID of the elements in the UI so I'm not sure what the problem is.

Here is the logcat as requested: https://i.stack.imgur.com/6RurY.png. Posted to Imgur as 10 reputation is needed to post images.

Answer 1

   public class MainActivity extends ActionBarActivity implements View.OnClickListener{
    private Button btnSubmit;
    private TextView tvResult;
    private EditText etfirst, etsecond, etamount;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        btnSubmit = (Button) findViewById(R.id.btnSubmit);
        tvResult = (TextView) findViewById(R.id.tvResult);
        etfirst = (EditText) findViewById(R.id.etFirst);
        etsecond = (EditText) findViewById(R.id.etSecond);
        etamount = (EditText) findViewById(R.id.etAmount);
        btnSubmit.setOnClickListener(this);
    }


    @Override
    public void onClick(View view) {
        switch (view.getId()) {
        case R.id.btnSubmit:

            if(etfirst.getText().toString().length()==0){
                Toast.makeText(getBaseContext(), "First edittext empty", Toast.LENGTH_LONG).show();
                }
            else if(etsecond.getText().toString().length()==0){
                Toast.makeText(getBaseContext(), "Second edittext empty", Toast.LENGTH_LONG).show();
                }
            else if(etamount.getText().toString().length()==0){
                Toast.makeText(getBaseContext(), "Amount edittext empty", Toast.LENGTH_LONG).show();
                }
            else{
            int divide = (Integer.parseInt(etsecond.getText().toString()) / Integer.parseInt(etfirst.getText().toString())) + 1;
            int multiply = divide * Integer.parseInt(etamount.getText().toString());
            tvResult.setText(String.valueOf(multiply));
            }
            break;
        }
    }

}

Answer 2

From the explanation, and the Logs, I can clearly see that it is a null pointer problem; may be caused either by not getting a correct reference to the button or the text view.

In your onCreate make sure you have this:

Button button = (Button) findViewById(R.id.enter_button);
button.setOnclickListener(this);

Make sure the resource Id from the XML file matches your reference.
And for the textView where you display the output, get a correct reference like

TextView theText = (TextView) findViewById(R.id.the_text);

Again make sure you have a correct XML resource ID (the reference)
Then the null pointer should be solved.

Double check your whole code and make sure your are getting a correct reference for the button and textView.

Answer 3

Try this:

Button btnSubmit;
TextView tvResult;
EditText etfirst,etsecond,etamount;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    btnSubmit = (Button) findViewById(R.id.btnSubmit);
    tvResult = (TextView)findViewById(R.id.tvResult);
    etfirst = (EditText)findViewById(R.id.etFirst);
    etsecond = (EditText)findViewById(R.id.etSecond);
    etamount = (EditText)findViewById(R.id.etAmount); //You wasnt definind this in the original code
    btnSubmit.setOnClickListener(this);
}





@Override
public void onClick(View view){
    String num1 = etfirst.getText().toString();
    String num2 = etsecond.getText().toString();
    String amount = etamount.getText().toString();
    switch(view.getId()){
        case R.id.btnSubmit:
            int divide =  (Integer.parseInt(num2) / Integer.parseInt(num1)) +1;
            int multiply = divide * Integer.parseInt(amount);
            tvResult.setText(String.valueOf(multiply));
            break;
    }
}