How to parse a double from EditText to TextView? (Android)

Question

I'm realy beginning to learn Java. When I run this code everything works fine till I leave my EditText boxes in the from empty and hit the run button. Then I get:

ERROR/AndroidRuntime(866): FATAL EXCEPTION: main
ERROR/AndroidRuntime(866): java.lang.NumberFormatException: 
ERROR/AndroidRuntime(866):     at org.apache.harmony.luni.util.FloatingPointParser.parseDouble(FloatingPointParser.java:267)

I guess when I try to parse a Double from string it doesn't get any value and creates an error. I was wondering how to avoid this error and give some kind of a value to the variable so it is never empty? Thanks for all the help!

import android.app.Activity;
import android.os.Bundle;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Button;
import android.view.View;
import android.view.View.OnClickListener;

public class Main extends Activity {

    private EditText noKids;
    private EditText noGumballs;
    private TextView noSum;
    private Button b;
    private Button br;
    double etKids = 0;
    double etGumballs = 0;
    private double tvSumIn = 0.00;

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        initControls();
    }


    private void initControls() {
        noKids = (EditText) findViewById(R.id.xetKids);
        noGumballs = (EditText) findViewById(R.id.xetGumballs);
        noSum = (TextView) findViewById(R.id.tvSum);


        br = (Button) findViewById(R.id.xbtnReset);
        br.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                reset();
                br.setVisibility(View.INVISIBLE);
            }

            private void reset() {
                noKids.setText("");
                noGumballs.setText("");
                noSum.setText("");

            }

        });

        b = (Button) findViewById(R.id.xbtnCalculate);
        b.setOnClickListener(new OnClickListener() {
            public void onClick(View v) {               
                calculate();
                br.setVisibility(View.VISIBLE);
                }

        private void calculate() {

            etKids = Double.parseDouble(noKids.getText().toString());
            etGumballs = Double.parseDouble(noGumballs.getText().toString());
            tvSumIn = etGumballs / etKids; 
            String thisIsIt = new Double(tvSumIn).toString();

            if(tvSumIn < 2){
                noSum.setText(thisIsIt + " This is it ");
            }else{
                noSum.setText("This is else");
            }

        }

        });



        }
    }

This is my main.xml file and I'm guessing there's nothing special to put into manifest.

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    >
    <TextView android:id="@+id/textView1" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="How many kids have you got?"></TextView>
    <EditText android:layout_width="match_parent" android:layout_height="wrap_content" android:inputType="number" android:id="@+id/xetKids">
        <requestFocus></requestFocus>
    </EditText>
    <TextView android:id="@+id/textView2" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="How many gumballs have you got?"></TextView>
    <EditText android:layout_width="match_parent" android:layout_height="wrap_content" android:inputType="number" android:id="@+id/xetGumballs"></EditText>
    <Button android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="Calculate" android:id="@+id/xbtnCalculate"></Button>
    <TextView android:layout_width="match_parent" android:layout_height="wrap_content" android:id="@+id/tvSum"></TextView>
    <Button android:layout_width="wrap_content" android:layout_height="wrap_content" android:id="@+id/xbtnReset" android:text="Reset" android:onClick="selfDestruct" android:visibility="invisible"></Button>
</LinearLayout>

Answer 1

Here is the JavaDoc for java.lang.Double class, parseDouble method:

/**
 * Parses the specified string as a double value.
 * 
 * @param string
 *            the string representation of a double value.
 * @return the primitive double value represented by {@code string}.
 * @throws NumberFormatException
 *             if {@code string} is {@code null}, has a length of zero or
 *             can not be parsed as a double value.
 * @since Android 1.0
 */

Empty values are not considered to be parseable. That's why you get this exception.

You can intoduce an additional check to your code to see if string in the noKids EditText is empty and if so, manually set the value to 0.0:

noKidsStr = noKids.getText().toString();

if(noKidsStr == null || noKidsStr.isEmpty()) {

  etKids = 0.0;

} else {

  etKids = Double.parseDouble(noKids.getText().toString());

}

I suggest writing some sort of convenience utility method that you can re-use for all similar situations in the future.

Answer 2

you should wrap the Double.parseDouble.. statements in a try/catch clause, to catch any NumberFormatExceptions, and set other values where they fail

edit:

try{
    etKids = Double.parseDouble(noKids.getText().toString());
} catch (final NumberFormatException e) {
    etKids = 1.0;
}
try{
    etGumballs = Double.parseDouble(noGumballs.getText().toString());
} catch (final NumberFormatException e) {
    etGumballs = 1.0;
} 

Answer 3

Two things you can do: First, only allow numeric data in your EditText field. Actually, I see you already did that. I usually use android:numeric - this is the first I've seen of android:inputType. Thanks for that. =)

Second, ensure that you have text in your EditText with a simple check.

if(noKids.getText().length() > 0)
{
    etKids = Double.parseDouble(noKids.getText().toString());
}