引起：java.lang.NumberFormatException：空字符串

Question

this is my calculator app when we normally click on equals button without add any calculation, that time app is crashing on this code

 case R.id.equal:
            int item1=s1.getSelectedItemPosition();
            int item2=s2.getSelectedItemPosition();
            double value1=Double.parseDouble(e1.getText().toString());
            double result=evaluate(item1,item2,value1);
            e2.setText(result+"");
            break;

App is crashing on 3rd line

Answer 1

You can't parse to double if you have an empty string, The string you're trying to parse as double is empty. You need to check if the getText() method returns a non-empty string before trying to do the parsing.

case R.id.equal:
    int item1=s1.getSelectedItemPosition();
    int item2=s2.getSelectedItemPosition();
    double value1=ParseDouble(e1.getText().toString());
    double result=evaluate(item1,item2,value1);
    e2.setText(result+"");
    break;

double ParseDouble(String strNumber) {
    if (strNumber != null && strNumber.length() > 0) {
        try {
            return Double.parseDouble(strNumber);
            } 
        catch(Exception e) {
            return -1;   // or a default value to mark this field is wrong.
            }
        }
    else return 0;
}