AsyncTask

package br.exemplothreadprincipal;

import android.app.Activity;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.AsyncTask;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.ProgressBar;

import java.io.IOException;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;

public class MainActivity extends Activity {
public ImageView iv;
    public ProgressBar progressBar;
    public Button button;


@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
        button = (Button) findViewById(R.id.botao);
        iv = (ImageView) findViewById(R.id.imagem);
        progressBar = (ProgressBar)findViewById(R.id.progressBar);
    }

    public void disableprogressbar(){
        progressBar.setVisibility(View.GONE);
    }

    public void setView(Bitmap bitmap){
        iv.setImageBitmap(bitmap);
    }

    public void baixarImagemWeb(View view) {
        Download download = new Download();
        download.execute();
    }
    private class Download extends AsyncTask<Void, Void, Bitmap> {

        @Override
        protected Bitmap doInBackground(Void... params) {
            Bitmap imagem = null;
            try {

                URL url = new URL("http://www.thiengo.com.br/img/system/logo/thiengo-80-80.png ");
                HttpURLConnection connection;
                connection = (HttpURLConnection) url.openConnection();
                connection.setDoInput(true);
                connection.connect();
                InputStream input = connection.getInputStream();
                final Bitmap imagem = BitmapFactory.decodeStream(input);

                Log.i("livro", "baixou imagem.");
            }
            catch (MalformedURLException e) {
                e.printStackTrace();
            }
            catch (IOException e) {
                e.printStackTrace();
            }
            return imagem;
        }

        @Override
        protected void onPostExecute(Bitmap imagem) {
            super.onPostExecute( imagem );
            disableprogressbar();
            setView( imagem );
        }
    }
}