NumberFormatingExcepton 如果应用程序是第一次启动

Question

I have 4 TextView s. 3 of them display results of EditText input value in another activity, and it's saved with shared preferences.

The fourth TextView needs to display sum of that previous 3 TextView s.

I get the error: NumberFormatingException invalid double ""

This is my code:

// GETTING VALUES FOR FIRST 3 TEXTVIEWS
textViewRezultat1RMPotisakSKlupe.setText(settings.getString("benchSave", null));
textViewRezultat1RMCucanj.setText(settings.getString("squatSave", null));
textViewRezultat1RMMrtvoDizanje.setText(settings.getString("deadSave", null));

//LITTLE BIT OF MATH TO GET VALUE OF FOURTH
double prvo = Double.parseDouble(textViewRezultat1RMPotisakSKlupe.getText().toString());
double drugo = Double.parseDouble(textViewRezultat1RMCucanj.getText().toString());
double trece = Double.parseDouble(textViewRezultat1RMMrtvoDizanje.getText().toString());
double rezultat = 0;

rezultat = (prvo + drugo + trece);

textViewRezultat1RMUkupno.setText(Double.toString(rezultat));

That works like a charm.

The problem is, I get the error I mentioned above if the app is launched for the first time (with no stored data).

Can anyone help me solve it?

Answer 1

Actually the problem occurs when trying to parse a double from a string that is not representing a number or just simply null.

parseDouble

public static double parseDouble(String s) throws NumberFormatException

Returns a new double initialized to the value represented by the specified String, as performed by the valueOf method of class Double.

Parameters : s - the string to be parsed.

Returns : the double value represented by the string argument.

Throws :

NullPointerException - if the string is null

NumberFormatException - if the string does not contain a parsable double.

So you need to test both scenarios to be sure you are not in either of the faulty cases.

String prvoString = textViewRezultat1RMPotisakSKlupe.getText().toString();
Double prvo; 
if(prvoString != null) { //shouldn't occur
  try {
    prvo = Double.parseDouble(prvoString); 
  } catch (NumberFormatException ex) { //inputs like "" or "banana"
     //Tell the user he is entering invalid input
  }
}

So why is this occuring when your app is running for the first time? The code that is parseDouble is executed when your view is loaded and trying to parse empty ("") strings.

Answer 2

Before doing double prvo = Double.parseDouble() always check whether your Strings are valid or not because if your String is empty, that is like "" , you can't convert this to Double as its not a number.

So before every Double.parseDouble check like this -

if (!TextUtils.isEmpty(yourString))
    Double.parseDouble(yourString);