Main

package com.example.hanakpiskozub;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.view.View;
import android.widget.Adapter;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Spinner;
import android.widget.Toast;

import java.util.InputMismatchException;

public class MainActivity extends AppCompatActivity implements AdapterView.OnItemSelectedListener {

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

        String[] spinnerOptions = {"+", "-"};

        EditText realisA = findViewById(R.id.textBoxAr);
        EditText realisB = findViewById(R.id.textBoxBr);
        EditText imaginarisA = findViewById(R.id.textBoxAi);
        EditText imaginarisB = findViewById(R.id.textBoxBi);
        Button plus = findViewById(R.id.buttonPlus);
        Button minus = findViewById(R.id.buttonMinus);
        SpinnerM spinner = findViewById(R.id.spinner);
        ArrayAdapter adaptor = new ArrayAdapter(this, android.R.layout.simple_spinner_item,spinnerOptions);
        adaptor.setDropDownViewResource(android.R.layout.select_dialog_singlechoice);


        spinner.setOnItemSelectedListener(this);

        spinner.setAdapter(adaptor);

        plus.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                try {
                    double resultRealis = Double.parseDouble(realisA.getText().toString()) +
                            Double.parseDouble(realisB.getText().toString());
                    double resultImaginaris = Double.parseDouble(imaginarisA.getText().toString()) +
                            Double.parseDouble(imaginarisB.getText().toString());
                    String result = (resultRealis == 0) ? "0" : Double.toString(resultRealis);
                    result += (resultImaginaris > 0) ? "+" : "";
                    result += (resultImaginaris == 0) ? "" : Double.toString(resultImaginaris) + "i";
                    Toast.makeText(getApplicationContext(),"Result: " + result,Toast.LENGTH_SHORT).show();
                } catch (Exception e){
                    Toast.makeText(getApplicationContext(),"WRONG INPUT, NOT A NUMBER",Toast.LENGTH_SHORT).show();
                }
            }
        });
        minus.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                try {
                    double resultRealis = Double.parseDouble(realisA.getText().toString()) -
                            Double.parseDouble(realisB.getText().toString());
                    double resultImaginaris = Double.parseDouble(imaginarisA.getText().toString()) -
                            Double.parseDouble(imaginarisB.getText().toString());
                    String result = (resultRealis == 0) ? "0" : Double.toString(resultRealis);
                    result += (resultImaginaris > 0) ? "+" : "";
                    result += (resultImaginaris == 0) ? "" : Double.toString(resultImaginaris) + "i";
                    Toast.makeText(getApplicationContext(),"Result: " + result,Toast.LENGTH_SHORT).show();
                } catch (Exception e){
                    Toast.makeText(getApplicationContext(),"WRONG INPUT, NOT A NUMBER",Toast.LENGTH_SHORT).show();
                }
            }
        });

    }

    @Override
    public void onItemSelected(AdapterView<?> adapterView, View view, int i, long l) {
        if(adapterView.getItemAtPosition(i).equals("+")) {
            try {
                EditText realisA = findViewById(R.id.textBoxAr);
                EditText realisB = findViewById(R.id.textBoxBr);
                EditText imaginarisA = findViewById(R.id.textBoxAi);
                EditText imaginarisB = findViewById(R.id.textBoxBi);
                double resultRealis = Double.parseDouble(realisA.getText().toString()) +
                        Double.parseDouble(realisB.getText().toString());
                double resultImaginaris = Double.parseDouble(imaginarisA.getText().toString()) +
                        Double.parseDouble(imaginarisB.getText().toString());
                String result = (resultRealis == 0) ? "0" : Double.toString(resultRealis);
                result += (resultImaginaris > 0) ? "+" : "";
                result += (resultImaginaris == 0) ? "" : Double.toString(resultImaginaris) + "i";
                Toast.makeText(getApplicationContext(),"Result: " + result,Toast.LENGTH_SHORT).show();
            } catch (Exception e){
                Toast.makeText(getApplicationContext(),"WRONG INPUT, NOT A NUMBER",Toast.LENGTH_SHORT).show();
            }
        }
        else if (adapterView.getItemAtPosition(i).equals("-")) {
            try {
                EditText realisA = findViewById(R.id.textBoxAr);
                EditText realisB = findViewById(R.id.textBoxBr);
                EditText imaginarisA = findViewById(R.id.textBoxAi);
                EditText imaginarisB = findViewById(R.id.textBoxBi);
                double resultRealis = Double.parseDouble(realisA.getText().toString()) -
                        Double.parseDouble(realisB.getText().toString());
                double resultImaginaris = Double.parseDouble(imaginarisA.getText().toString()) -
                        Double.parseDouble(imaginarisB.getText().toString());
                String result = (resultRealis == 0) ? "0" : Double.toString(resultRealis);
                result += (resultImaginaris > 0) ? "+" : "";
                result += (resultImaginaris == 0) ? "" : Double.toString(resultImaginaris) + "i";
                Toast.makeText(getApplicationContext(),"Result: " + result,Toast.LENGTH_SHORT).show();
            } catch (Exception e){
                Toast.makeText(getApplicationContext(),"WRONG INPUT, NOT A NUMBER",Toast.LENGTH_SHORT).show();
            }
        }
    }

    @Override
    public void onNothingSelected(AdapterView<?> adapterView) {

    }
}