Android Studio app keeps crashing after button click

Question

Im a beginner in java but I'm trying to build exercises and I ran into this problem. The user types in a donation, presses the button and the value of donations increments. Ive written the entire code but when I click the button to add to the donation count, the app crashes. Ive followed all the teachings of my teacher. I create a method in the activity, the in the ui builder I go to the button on click property and set it to that method. It should go smoothly but it crashes whenever I click the button. This is my activity which I set the onClick property to computeDonation.

public void computeDonation(View v){

    String addedText = ((EditText)findViewById(R.id.AmountText)).getText().toString();

    DonationModel donation = new DonationModel(addedText);
    String answer = donation.calcDonation();

    ((TextView)findViewById(R.id.totalText)).setText(answer);
}

This is the model:

String textAdded;
double addedDonation;

public DonationModel(String y) {
    textAdded = y;
}

public String calcDonation(){
    double counter = Double.parseDouble(textAdded);
    addedDonation += counter;

    Locale locale = new Locale("en", "CA");
    NumberFormat fmt = NumberFormat.getCurrencyInstance(locale);

    return fmt.format(addedDonation);

}

Ive even tried without the number format just to see if it sends back to the activity but it doesn't. BTW for my class I'm using an older version of android studio.

This is the logcat:

02-15 17:12:28.797 21619-21619/ca.roumani.donations E/AndroidRuntime: FATAL EXCEPTION: main Process: ca.roumani.donations, PID: 21619 java.lang.IllegalStateException: Could not execute method for android:onClick at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:293) at android.view.View.performClick(View.java:5197) at android.view.View$PerformClick.run(View.java:20909) at android.os.Handler.handleCallback(Handler.java:739) at android.os.Handler.dispatchMessage(Handler.java:95) at android.os.Looper.loop(Looper.java:145) at android.app.ActivityThread.main(ActivityThread.java:5942) at java.lang.reflect.Method.invoke(Native Method) at java.lang.reflect.Method.invoke(Method.java:372) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1399) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1194) Caused by: java.lang.reflect.InvocationTargetException at java.lang.reflect.Method.invoke(Native Method) at java.lang.reflect.Method.invoke(Method.java:372) at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:288) at android.view.View.performClick(View.java:5197)  at android.view.View$PerformClick.run(View.java:20909)  at android.os.Handler.handleCallback(Handler.java:739)  at android.os.Handler.dispatchMessage(Handler.java:95)  at android.os.Looper.loop(Looper.java:145)  at android.app.ActivityThread.main(ActivityThread.java:5942)  at java.lang.reflect.Method.invoke(Native Method)  at java.lang.reflect.Method.invoke(Method.java:372)  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1399)  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1194)  Caused by: java.lang.NumberFormatException: Invalid double: "" at java.lang.StringToReal.invalidReal(StringToReal.java:63) at java.lang.StringToReal.parseDouble(StringToReal.java:267) at java.lang.Double.parseDouble(Double.java:301) at ca.roumani.donations.DonationModel.calcDonation(DonationModel.java:20) at ca.roumani.donations.DonationActivity.computeDonation(DonationActivity.java:24) at java.lang.reflect.Method.invoke(Native Method)  at java.lang.reflect.Method.invoke(Method.java:372)  at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:288)  at android.view.View.performClick(View.java:5197)  at android.view.View$PerformClick.run(View.java:20909)  at android.os.Handler.handleCallback(Handler.java:739)  at android.os.Handler.dispatchMessage(Handler.java:95)  at android.os.Looper.loop(Looper.java:145)  at android.app.ActivityThread.main(ActivityThread.java:5942)  at java.lang.reflect.Method.invoke(Native Method)  at java.lang.reflect.Method.invoke(Method.java:372)  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1399)  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1194) 

Answer 1

It seems like your textAdded is an empty String, which causes the NumberFormatException and crashes your app. What you can do to prevent this, is to check if your textAdded is not empty before parsing it:

public String calcDonation() {
    if (TextUtils.isEmpty(textAdded)) {
        //textAdded is empty, so just return an empty String
        return "";
    }
    //We're sure that textAdded has a value, so we can try to parse it
    double counter = Double.parseDouble(textAdded);
    addedDonation += counter;

    Locale locale = new Locale("en", "CA");
    NumberFormat fmt = NumberFormat.getCurrencyInstance(locale);

    return fmt.format(addedDonation);
} 

Or just prevent the method from being invoked before the user has entered a value in the EditText view:

public void computeDonation(View v){
    String addedText = ((EditText)findViewById(R.id.AmountText)).getText().toString();
    if (TextUtils.isEmpty(textAdded)) {
        Toast.makeText(context, "Please enter a valid number", Toast.LENGTH_SHORT).show();
    } else {
        DonationModel donation = new DonationModel(addedText);
        String answer = donation.calcDonation();
        ((TextView)findViewById(R.id.totalText)).setText(answer);
    }
}