Android - Activity lifecycle and Thread
This example is to download from a link then view it in the app.
manifest
main.xml
import java.io.IOException; import org.apache.http.HttpEntity; import org.apache.http.HttpResponse; import org.apache.http.StatusLine; import org.apache.http.client.HttpClient; import org.apache.http.client.methods.HttpGet; import org.apache.http.client.methods.HttpUriRequest; import org.apache.http.impl.client.DefaultHttpClient; import org.apache.http.util.EntityUtils; import android.app.Activity; import android.app.ProgressDialog; import android.content.Context; import android.graphics.Bitmap; import android.graphics.BitmapFactory; import android.os.Bundle; import android.os.Handler; import android.os.Message; import android.view.View; import android.widget.ImageView; public class MainActivity extends Activity { // Static so that the thread access the latest attribute private static ProgressDialog dialog; private static Bitmap downloadBitmap; private static Handler handler; private ImageView imageView; private Thread downloadThread; /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); // Create a handler to update the UI handler = new Handler() { @Override public void handleMessage(Message msg) { imageView.setImageBitmap(downloadBitmap); dialog.dismiss(); } }; // get the latest imageView after restart of the application imageView = (ImageView) findViewById(R.id.imageView1); Context context = imageView.getContext(); System.out.println(context); // Did we already download the image? if (downloadBitmap != null) { imageView.setImageBitmap(downloadBitmap); } // Check if the thread is already running downloadThread = (Thread) getLastNonConfigurationInstance(); if (downloadThread != null && downloadThread.isAlive()) { dialog = ProgressDialog.show(this, "Download", "downloading"); } } public void resetPicture(View view) { if (downloadBitmap != null) { downloadBitmap = null; } imageView.setImageResource(R.drawable.ic_launcher); } public void downloadPicture(View view) { dialog = ProgressDialog.show(this, "Download", "downloading"); downloadThread = new MyThread(); downloadThread.start(); } // Save the thread @Override public Object onRetainNonConfigurationInstance() { return downloadThread; } // dismiss dialog if activity is destroyed @Override protected void onDestroy() { if (dialog != null && dialog.isShowing()) { dialog.dismiss(); dialog = null; } super.onDestroy(); } // Utiliy method to download image from the internet static private Bitmap downloadBitmap(String url) throws IOException { HttpUriRequest request = new HttpGet(url.toString()); HttpClient httpClient = new DefaultHttpClient(); HttpResponse response = httpClient.execute(request); StatusLine statusLine = response.getStatusLine(); int statusCode = statusLine.getStatusCode(); if (statusCode == 200) { HttpEntity entity = response.getEntity(); byte[] bytes = EntityUtils.toByteArray(entity); Bitmap bitmap = BitmapFactory.decodeByteArray(bytes, 0, bytes.length); return bitmap; } else { throw new IOException("Download failed, HTTP response code " + statusCode + " - " + statusLine.getReasonPhrase()); } } static public class MyThread extends Thread { @Override public void run() { try { // Simulate a slow network try { new Thread().sleep(4000); } catch (InterruptedException e) { e.printStackTrace(); } downloadBitmap = downloadBitmap("http://www.imaginelifestyles.com/luxuryliving/wp-content/uploads/2012/11/ferrari-f12-front.jpg"); // Updates the user interface handler.sendEmptyMessage(0); } catch (IOException e) { e.printStackTrace(); } finally { } } } }