Application retrieving image from URL and displaying in Android application crashes

Question

I have this simple program which retrieves an image from a URL ----- saves at bitmap --- displays as image view. However, it keeps on crashes when I try to run it. I have the downloadBitmap method to convert a url into a bitmap and then I want to set image to ImageBitmap?

package com.example.bitmapdisplay;

import java.io.IOException;
import java.io.InputStream;

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.HttpStatus;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.DefaultHttpClient;

import com.fasterxml.jackson.core.JsonParseException;

import android.app.Activity;
import android.app.ProgressDialog;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.drawable.BitmapDrawable;
import android.os.Bundle;
import android.util.Log;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.ImageView;

public class MainActivity extends Activity {

    Bitmap image;
    BitmapDrawable bd;
    ImageView temp;
    ProgressDialog pd;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        temp = (ImageView) findViewById(R.id.ivImage);


        Thread retrieveImage = new Thread() {
            public void run(){
                try {

                    image = downloadBitmap("http://i1.cpcache.com/product_zoom/617914535/dickbutt_2_mug.jpg?side=Back&height=250&width=250&padToSquare=true");

                } catch (JsonParseException e) {

                    e.printStackTrace();
                } catch (IOException e) {

                    e.printStackTrace();
                }
                finally {

                    temp.setImageBitmap(image);
                }
            }
        };
        retrieveImage.run();

    }

     private Bitmap downloadBitmap(String url) throws JsonParseException, IOException{

         // initilize the default HTTP client object
         final DefaultHttpClient client = new DefaultHttpClient();

         //forming a HttoGet request 
         final HttpGet getRequest = new HttpGet(url);

         HttpResponse response = client.execute(getRequest);

             //check 200 OK for success
             final int statusCode = response.getStatusLine().getStatusCode();

             if (statusCode != HttpStatus.SC_OK) {
                 Log.w("ImageDownloader", "Error " + statusCode + 
                         " while retrieving bitmap from " + url);
                 return null;

             }

             final HttpEntity entity = response.getEntity();
             if (entity != null) {
                 InputStream inputStream = null;
                 try {
                     // getting contents from the stream 
                     inputStream = entity.getContent();

                     // decoding stream data back into image Bitmap that android understands
                     image = BitmapFactory.decodeStream(inputStream);


                 } finally {
                     if (inputStream != null) {
                         inputStream.close();
                     }
                     entity.consumeContent();
                 }
             }

         return image;
     }
}

Logcat? Looks like trying to update the UI on a background thread — codeMagic, May 30 '14 at 18:33
So would I put the temp.setImageBitmap(image); after the retrieveImage.run()? Wouldn't that create an error though because it is still processing downloadBitmap while trying to execute that statement (isn't that the whole point of threads? ) — Stickerbomby, May 30 '14 at 18:35
Yes so you would need a callback for when it is finished or use an `AsyncTask` and update the UI in `onPostExecute()` — codeMagic, May 30 '14 at 18:36

score 0 · Accepted Answer · edited May 23 '17 at 12:05

The problem is that

temp.setImageBitmap(image);

is inside of a background Thread. Since we can't update UI elements on any Thread other than the UI Thread we either need to post a callback when the download thread is done or use an AsyncTask which has methods for doing background work and methods for doing work on the UI Thread.

This example shows the basic set up for an AsyncTask

AsyncTask Docs

Application retrieving image from URL and displaying in Android application crashes

1 Answers1