Update Textview Android Using Handler

Question

I started Programming now on Android, and I need to update a Textview after receiving a string from a Socket connection. I get the string correctly but the apk closes giving an exception:

10-01 11:05:57.470: E/androidruntime(753): FATAL EXCEPTION: Thread-94

I saw that this exception is caused by updating the ui by a thread outside the main thread, in that the serial solution use Handler to update the ui, however I could not get an example of how to do this and would like to help to implement it in my code:

Searching the web, I found a simple way using a thread apart to update the ui, in the following codigods I show what I did:

Update Class xto(thread that has the function of changing text in Textview)

package com.example.palioteste;

public class AtualizarTexto implements Runnable {

            private String text;

            public AtualizarTexto(final String text) {
                this.text = text;
            }

            @Override
            public void run() {

                MainActivity.textorecebido.setText(text);
            }

        }

Mainactivity

    package com.example.palioteste;

    import java.io.BufferedReader; import java.io.BufferedWriter; import java.io.IOException; import java.io.OutputStreamWriter; import java.net.Socket;
    import android.app.Activity; import android.os.Bundle; import android.view.Menu; import android.view.MenuItem; import android.view.View; import android.view.View.OnClickListener; import android.widget.Button; import android.widget.TextView;

    public class MainActivity extends Activity {

    private Button button;
    private TextView textView1;
    static TextView textorecebido;

    @Override   
    protected void onCreate(Bundle savedInstanceState) {        
        super.onCreate(savedInstanceState);         
        setContentView(R.layout.activity_main);
        button = (Button) findViewById(R.id.button);        
        textView1 = (TextView)  findViewById(R.id.textView1);
        textorecebido = (TextView) findViewById(R.id.textorecebido);

        button.setOnClickListener(new OnClickListener() {           
            @Override           
            public void onClick(View arg0) {
                textView1.setText("Botao Cliquado");
                abrirSocket rodar = new abrirSocket();
                rodar.execute();            
            }
            });     
        }

    @Override   
    public boolean onCreateOptionsMenu(Menu menu) {         
        // Inflate the menu; this adds items to the action bar if it is present.        
        getMenuInflater().inflate(R.menu.main, menu);       
        return true;    
    }

    @Override   
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will      
        // automatically handle clicks on the Home/Up button, so long       
        // as you specify a parent activity in AndroidManifest.xml.         
        int id = item.getItemId();
        if (id == R.id.action_settings) {
            return true;
        }       
            return super.onOptionsItemSelected(item);
        } 
}

Thread that makes the socket connection

package com.example.palioteste;

import android.os.AsyncTask;

import java.io.BufferedReader; 
import java.io.BufferedWriter; 
import java.io.DataOutputStream; 
import java.io.IOException; 
import java.io.InputStreamReader; 
import java.io.OutputStreamWriter; 
import java.net.Socket; 
import java.util.Arrays;

public class abrirSocket extends AsyncTask { 
private static final String hostname = "192.168.43.127"; 
private static final int portaServidor = 9837; 
int valorconvertido;

    @Override
    protected String doInBackground(String... params) {
    try {
        Socket socket = new Socket(hostname, portaServidor);

        //dados enviados para o servidor

        BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(socket.getOutputStream()));
        bw.write("2");
        bw.newLine();
        bw.flush();

        BufferedReader br = new BufferedReader(new InputStreamReader(socket.getInputStream()));
        //String retorno =  "Dados Recebidos " + br.readLine(); //retornar ok

        Thread t = new Thread(new AtualizarTexto(br.readLine()));
        t.start();
        // socket.close();
    }
    catch(IOException e) {
        return e.getMessage();
    }
    return null;

    }     
}

This implementation did not work and I want to try to use Handler, but the examples I found I could not adapt to my code and I ask the members for help for this.

Answer 1

You can use this method to run on the UI thread

runOnUiThread(new Runnable(){

        @Override
        public void run() {
            // TODO Auto-generated method stub
            textorecebido.setText(text);
        }

    });

Or you can use the Asynctask methods that also wheels on the main thread as shown in the link

Try this:

'@Override
protected String doInBackground(String... params) {
    try {
        Socket socket = new Socket(hostname, portaServidor);

        //dados enviados para o servidor

        BufferedWriter bw = new BufferedWriter(new     OutputStreamWriter(socket.getOutputStream()));
        bw.write("2");
        bw.newLine();
        bw.flush();

        BufferedReader br = new BufferedReader(new    InputStreamReader(socket.getInputStream()));
    //String retorno =  "Dados Recebidos " + br.readLine(); //retornar ok

        return br.readLine();

       // socket.close();

    }
    catch(IOException e) {
        return e.getMessage();
    }         return null;
}

@Override
protected void onPostExecute(String resultado) {

    //...
    seuTextview.setText(resultado());
}