Edittext to String and multiply with Spinner

[Adde Berg]

I´m currently working on a currency converter project for school. I have an array with currencies (USD,EUR etc) and one with values (6.54, 9.56 etc).

I have two spinners and one EditText and you choose From unit in one spinner and To unit in the other. Then it should consider the amount in editText and show the "live" result in textView. If you change spinners or editText the value in textview should update directly.

Let's say that the value inserted in editText is 10.0, and we want to convert it from USD to EUR, the calculation will look like this: 10.0*6.54/9.56=

But I can't figure out how to add the editText in to the calculation. And I also get an error message saying I have an empty String

import android.app.Activity;
import android.os.Bundle;
import android.text.Editable;
import android.text.TextWatcher;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.Spinner;
import android.widget.TextView;
import android.widget.EditText;

public class MainActivity extends Activity {
    private String [] currency;
    private ArrayAdapter<String> adapter;
    private Spinner spin1, spin2;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        setUpTheSpinners();

    }


    private void setUpTheSpinners() {
        currency = getResources().getStringArray(R.array.currency);
        adapter= new ArrayAdapter<String>(this, android.R.layout.simple_spinner_item, currency);
        adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
        AdapterView.OnItemSelectedListener listener = new currencySelectedListener();
        spin1 = (Spinner)findViewById(R.id.spinner1);
        spin1.setAdapter(adapter);
        spin1.setOnItemSelectedListener(listener);
        spin2 = (Spinner)findViewById(R.id.spinner2);
        spin2.setAdapter(adapter);
        spin2.setOnItemSelectedListener(listener);
    }



    private void calculateSum() {
        EditText et_value = (EditText) findViewById(R.id.editText);
        String [] price = getResources().getStringArray(R.array.price);
        int index1 = spin1.getSelectedItemPosition();
        int index2 = spin2.getSelectedItemPosition();
        double fromCurrency = Double.parseDouble( price[index1] );
        double toCurrency = Double.parseDouble( price[index2] );
        double value = Double.parseDouble(et_value.getText().toString());
        double totalCost = (fromCurrency / toCurrency) * value;
        TextView totalCostText = (TextView)findViewById(R.id.textView5);
        totalCostText.setText("" + totalCost);

    }

private class currencySelectedListener implements AdapterView.OnItemSelectedListener {
    public void onItemSelected(AdapterView<?> parent, View view, int pos, long id) {
        calculateSum();

    }
private class MyTextWatcher implements TextWatcher {
    public void onTextChanged(CharSequence s, int start, int before,
                              int count) {
        calculateSum();

    }

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

    }

    public void afterTextChanged(Editable s) {
    }

}
        public void onNothingSelected(AdapterView<?> parent) {
        }
    }
}

Here is the error log:

        --------- beginning of crash
E/AndroidRuntime: FATAL EXCEPTION: main
                  Process: com.example.adamp.currencyconverter3, PID: 2457
                  java.lang.NumberFormatException: empty String
                      at java.lang.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:1071)
                      at java.lang.Double.parseDouble(Double.java:547)
                      at com.example.adamp.currencyconverter3.MainActivity.calculateSum(MainActivity.java:50)
                      at com.example.adamp.currencyconverter3.MainActivity.access$100(MainActivity.java:14)
                      at com.example.adamp.currencyconverter3.MainActivity$currencySelectedListener.onItemSelected(MainActivity.java:59)
                      at android.widget.AdapterView.fireOnSelected(AdapterView.java:931)
                      at android.widget.AdapterView.dispatchOnItemSelected(AdapterView.java:920)
                      at android.widget.AdapterView.-wrap1(AdapterView.java)
                      at android.widget.AdapterView$SelectionNotifier.run(AdapterView.java:890)
                      at android.os.Handler.handleCallback(Handler.java:751)
                      at android.os.Handler.dispatchMessage(Handler.java:95)
                      at android.os.Looper.loop(Looper.java:154)
                      at android.app.ActivityThread.main(ActivityThread.java:6077)
                      at java.lang.reflect.Method.invoke(Native Method)
                      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:865)
                      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755)

[Campbell Ritchie]

Welcome to the Ranch

Doesn't the error message make it plain? NumberFormatException(←link) and “empty string”. It means you cannot get a number out of your text box until you put some content in it.
I suggest you use a Scanner. Did you know that you can create a Scanner from a text box? Well, actually, you can't, but you can do the next best thing: create a Scanner dealing with the contents of a text box:-

BigDecimal originalAmount;
// ...
/*
 * Consider using a loop until valid
 * input is obtained.
 */
String text = originalAmountTextBox.getText();
Scanner originalTextScan = new Scanner(text);
if (originalTextScan.hasNextBigDecimal())
{
   originalAmount = originalTextScan.nextBigDecimal();
}
else
{
   // some sort of error message or similar
}

Beware: if you enter "123.456 Adde Berg" in the text box, it will happily give you a return value of a BigDecimal containing 123.456.