Updating TextView

Question

I have a loop which contains TextView.append("what eve text here") in side a loop how can I send the new strings to the TextView like the Eclipse console where everything is showing. I am trying to basically have the loop run and add each output to the bottom of the TextView in real time.

package com.example.assignment2_android;

import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Calendar;
import java.util.LinkedList;
import java.util.Queue;
import java.util.Random;

import android.os.AsyncTask;
import android.os.Bundle;
import android.app.Activity;
import android.content.Intent;
import android.drm.DrmStore.Action;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

public class station extends Activity implements View.OnClickListener
{
    Button run, clear, home;
    EditText userinput;
    TextView useroutput;

    //LinkedList Customer Queue created here.
    public static Queue<String> line = new  LinkedList<String> ();
    private static String time;   //Time variable stored here.
    //DateFormat variable  stored here
    private static DateFormat dateFormat = new SimpleDateFormat("HH:mm:ss");

    private int intervals; //Random arrival integer stored here
    private int cashiers; //User input of number of cashiers stored here
    private int processing_time; //Random processing time stored here

    protected void onCreate(Bundle savedInstanceState) 
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.reverser);

        userinput = (EditText)findViewById(R.id.r_userinput);
        useroutput = (TextView)findViewById(R.id.r_useroutput);

        run = (Button)findViewById(R.id.button_run);
        clear = (Button)findViewById(R.id.button_clear);
        home = (Button)findViewById(R.id.button_home);

        if (run != null)
        {
            run.setOnClickListener(this);
        }
        if (clear != null)
        {
            clear.setOnClickListener(this);
        }
        if (home != null)
        {
            home.setOnClickListener(this);
        }

    }

    public void onClick(View view) 
    {
          if (view == run)
          {
              cashiers = Integer.parseInt(userinput.getText().toString());//Get the Integer value the user inputs from the TextArea
              arrival();
          }
          else if (view == clear) 
          {
            userinput.setText("Line Cleared"); //Use string resource !
            useroutput.setText("");
            System.out.println("cleared"); // Use string resource
          } 
          else if (view == home) 
          {
            Intent a = new Intent(this, MainActivity.class);
            startActivity(a);
          }
    }

    private void arrival()
    {
        Thread arrival = new Thread();
        {
            useroutput.append("CUSTOMERS ARE COMING !!!! !!!!" + "\n" + "\n");
            //Array of all the customer that will enter the queue.
            String list[] = {"Naqi", "Monty", "Mohin", "Yasmin", "Maighjoo", "Ashish", "Paal", "Kevin", "Ruhail", "Tony"};
            //2nd ArrayList which customer are added to and removed later on so no duplicates arise.
            ArrayList<String> customer = new ArrayList<String>(Arrays.asList(list));

            int array_customer_list = list.length; //Recording the number of customers in the array.

            //While statement containing for loop add customers to the empty LinkedList object.
            while (line.isEmpty())
            {
                for (int x = 0; x < array_customer_list; x++ )
                {
                    try
                    {
                        Thread.sleep(ran_interval() * 1000);   //Sleep method to hold the arrival time by 1-2 seconds. 
                        int cus = (int) (Math.random() * customer.size());   //Random customer is picked here. 
                        String new_cus = customer.get(cus);   //New customer object is created ere.
                        line.add(new_cus);   //Customer objects are added to the empty LinkedList queue.
                        customer.remove(cus);
                        //For loop statement to outputting the queue.
                        for (String s : line)
                        {
                            useroutput.append("[" + s.toString() + " " + "]" + "\n");; //Outputting each customer and using the ".name" method so customers are readable.
                        }
                        //Outputting the whole queue and stating who has joined the queue.
                        useroutput.append("\n" + "The queue has " + line.size() + " customers so far" + "\n" + 
                        new_cus.toString() + " Has Joined the Queue " + " <=== WAITING" + "\n" + "\n");
                    }
                    catch(Exception a)   //ERROR handler for sleep method.
                    {
                        System.out.println("Intervals error: " + a);   //Outputting the ERROR message.
                        System.exit(0);   //If ERROR found exit system.
                    }

                }
            }
            useroutput.append("\n");
            useroutput.append("CUSTOMERS ARE WAITING !!!! !!!!" + "\n" + "\n");
            useroutput.append("Processing START !!!!" + "\n" + "\n");

            while (!line.isEmpty())   //While statement with for loop to remove each customer from LinkedList queue.
            {
                try 
                {
                    String cus = line.remove(); //Method to remove customer from LinkedList queue.
                    String time = getTime();
                    Thread.sleep((processing_time() * 1000) / cashiers); //Sleep method to hold the processing by 1-3 seconds.
                    for (String s : line)
                    {
                        useroutput.append("[" + s.toString() + " " + "]" + "\n"); //Outputting each customer and using the ".name" method so customers are readable.
                    }
                    //Outputting the whole queue and stating who has joined the queue.
                    useroutput.append("\n" + "The queue has " + line.size() + " customers left" + "\n" + 
                    cus.toString()+ " waited for " + time + " <=== SERVED" + "\n" + "\n");
                }
                catch(Exception a)   //ERROR handler for sleep method.
                {
                    System.out.println("Cashiers_wait error: " + a);   //Outputting the ERROR message.
                    System.exit(0);   //If ERROR found exit system.
                }
            }
            useroutput.append("Processing FINISHED !!!!" + "\n");
            System.out.println("working" + "\n" + "random arrival time is :" + intervals + "\n" + 
            "random processing time is :" + processing_time);
        }; arrival.start();
    };

    static String getTime()   //Time Constructor
    {
       Calendar cal = Calendar.getInstance();
       time = dateFormat.format(cal.getTime());   //Getting the current system time.
       return time;   //Return time.
    }

    public int ran_interval()
     {
         Random rand = new Random(); //Random object created here.
         int interval = this.intervals = rand.nextInt(2) + 1; //Random number between 1-2 is generated for customer arrival here.

         return interval;
     }

    public int processing_time()
     {
         Random ran = new Random();    //Random object created here.
         int time = this.processing_time = ran.nextInt(4) + 1;  //Random number between 1-3 is generated for customer arrival here.

         return time;
     }
}

Answer 1

it seems you use a long running loop on the UI thread, and this can cause ANR and actually update what the user sees only after it ends.

a possible solution:

use a thread that runs in the background , and each time you wish to update the textView, you can use a Handler instance (that you need to create on the UI thread) to post messages/runnables that will cause the textview to update itself with new data.

Answer 2

Your arrival method is running on the UI thread. You should put it in an AsyncTask. This method would become the doInBackground and whenever you wanted to update the UI (basically, whenever you called append) you would call publishProgress. Then you override onProgressUpdate to invalidate the EditText, which would cause it to repaint itself with the new text.