Question

I’ve created an android app where the user inputs a string and a number, where the number will be calculated to its factorial. Everything’s working fine but when i enclose my code inside the thread there’s no output.

here’s my source code:

package com.inputandfactorial;

import android.app.Activity;
import android.os.Bundle;
import android.text.Editable;
import android.view.Menu;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

public class MainActivity extends Activity {

    Button chkCmd;
    EditText input1, input2;
    TextView display1, display2;
    int res = 1,factint;
    String fact;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        chkCmd = (Button) findViewById(R.id.bProcess);
        input1 = (EditText) findViewById(R.id.etString);
        input2 = (EditText) findViewById(R.id.etFactorial);
        display1 = (TextView) findViewById(R.id.tvString);
        display2 = (TextView) findViewById(R.id.tvFactorial);

        chkCmd.setOnClickListener(new View.OnClickListener() {

            public void onClick(View v) {



                Thread t1 = new Thread(){
                    public void run(){
                        String change = input1.getText().toString();
                        fact = input2.getText().toString();
                        factint = Integer.parseInt(fact);
                        for (int i = 1; i <= factint; i++) {
                            res = res * i;
                        }
                        try {
                            display2.setText("The factorial of " + fact + " is " + res);
                            display1.setText("The string value is " + change);
                        } catch (Exception e) {

                        }
                    }
                };
                t1.start();
            }
        });
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.activity_main, menu);
        return true;
    }
}

I know i don’t need to put it in a thread, i just was just experiment to see if this will work and it didn’t.

Answer 1

You can only manipulate Views on the UI thread. Wrap your code in a Runnable and execute it on the main thread with Activity#runOnUiThread(Runnable action):

runOnUiThread(new Runnable() {
    @Override
    public void run() {
        display2.setText("The factorial of " + fact + " is " + res);
        display1.setText("The string value is " + change);
    }
}

That said, simple arithmetic doesn’t warrant the use of a Thread in the first place…