For some reason this is crashing and I have no idea why

Question

I'm doing a termometric scale converter in Android Studio, but when I input a number on any EditText and press the calculate button it crashes and I have no idea why.

This is the MainActivity.java code:

    private ViewHolder mViewHolder = new ViewHolder();

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

        this.mViewHolder.editValueCel = findViewById(R.id.edit_value_cel);
        this.mViewHolder.editValueFahr = findViewById(R.id.edit_value_fahr);
        this.mViewHolder.editValueKelvin = findViewById(R.id.edit_value_kelvin);
        this.mViewHolder.buttonCalculate = findViewById(R.id.button_calculate);
        this.mViewHolder.textCelsius = findViewById(R.id.tot_celcius);
        this.mViewHolder.textFahr = findViewById(R.id.tot_fahr);
        this.mViewHolder.textKelvin = findViewById(R.id.tot_kelvin);

        this.mViewHolder.buttonCalculate.setOnClickListener(this);


    }

    @Override
    public void onClick(View view) {
        if (view.getId() == R.id.button_calculate){

            String valorCel = this.mViewHolder.editValueCel.getText().toString();
            String valorFahr = this.mViewHolder.editValueFahr.getText().toString();
            String valorKelvin = this.mViewHolder.editValueKelvin.getText().toString();

            if (("".equals(valorCel)) && ("".equals(valorFahr)) && ("".equals(valorKelvin))){

                Toast.makeText(this, this.getString(R.string.informe_valor), Toast.LENGTH_SHORT).show();

            }else {

                Double celsius = Double.valueOf(valorCel);
                Double fahr = Double.valueOf(valorFahr);
                Double kelvin = Double.valueOf(valorKelvin);

                if (("".equals(valorFahr)) && ("".equals(valorKelvin))){

                    this.mViewHolder.textCelsius.setText(String.valueOf(celsius));
                    this.mViewHolder.textFahr.setText(String.valueOf((9*celsius+160)/5));
                    this.mViewHolder.textKelvin.setText(String.valueOf(celsius+273));

                }else if(("".equals(valorCel)) && ("".equals(valorKelvin))){

                    this.mViewHolder.textCelsius.setText(String.valueOf(((fahr-32)/9)*5));
                    this.mViewHolder.textFahr.setText(String.valueOf(fahr));
                    this.mViewHolder.textKelvin.setText(String.valueOf((5*fahr+2297)/9));

                }else if(("".equals(valorCel)) && ("".equals(valorFahr))){

                    this.mViewHolder.textCelsius.setText(String.valueOf(kelvin-273));
                    this.mViewHolder.textFahr.setText(String.valueOf((9*kelvin-2297)/5));
                    this.mViewHolder.textKelvin.setText(String.valueOf(kelvin));

                }else{

                    Toast.makeText(this, this.getString(R.string.erro_muitos_valores), Toast.LENGTH_SHORT).show();

                }

            }
        }
    }

    private static class ViewHolder{
        EditText editValueCel;
        EditText editValueFahr;
        EditText editValueKelvin;
        TextView textCelsius;
        TextView textFahr;
        TextView textKelvin;
        Button buttonCalculate;

    }
}

If there's need to post the activity_main.xml code here just tell me and I'll post it.

Answer 1

You convert strings to doubles first

Double celsius = Double.valueOf(valorCel);
Double fahr = Double.valueOf(valorFahr);
Double kelvin = Double.valueOf(valorKelvin);

but judging from the code that follows most likely one or more of the strings are empty which gives a NumberFormatException (or null which gives a NullPointerException ) so you need to move the conversions to be inside one of the if/else conditions.

It is better to use isEmpty() than comparing if a string equals ""

if (valorFahr.isEmpty() && valorKelvin.isEmpty()){
    Double celsius = Double.valueOf(valorCel);
    this.mViewHolder.textCelsius.setText(String.valueOf(celsius));
    this.mViewHolder.textFahr.setText(String.valueOf((9*celsius+160)/5));
    this.mViewHolder.textKelvin.setText(String.valueOf(celsius+273));
} else if(valorCel.isEmpty() && valorKelvin.isEmpty()){
    Double fahr = Double.valueOf(valorFahr);
    this.mViewHolder.textCelsius.setText(String.valueOf(((fahr-32)/9)*5));
    this.mViewHolder.textFahr.setText(String.valueOf(fahr));
    this.mViewHolder.textKelvin.setText(String.valueOf((5*fahr+2297)/9));
} else if(valorCel.isEmpty() && valorFahr.isEmpty()){
    Double kelvin = Double.valueOf(valorKelvin);
    this.mViewHolder.textCelsius.setText(String.valueOf(kelvin-273));
    this.mViewHolder.textFahr.setText(String.valueOf((9*kelvin-2297)/5));
    this.mViewHolder.textKelvin.setText(String.valueOf(kelvin));
...

Not knowing how the rest of your app works it might still be a good thing to check that not all 3 strings are empty or that any of them are null as part of this code.

So maybe before the if/else part do

if ((valorFahr == null || valorKelvin == null || valorCel == null) ||
    (valorFahr.isEmpty() && valorKelvin.isEmpty() && valorCel.isEmpty())) {
    //some error handling
}