error while executing doInBackground - android-asynctask

Question

An error occured while executing doInBackground()
I am new to android studio and am trying to download different bitmap pictures to show in imageview by AsyncTask class.my error log follows:
FATAL EXCEPTION: AsyncTask #1
Process: com.example.sayareh.http2, PID: 32302
java.lang.RuntimeException: An error occured while executing doInBackground()
at android.os.AsyncTask$3.done(AsyncTask.java:300)
at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:355)
at java.util.concurrent.FutureTask.setException(FutureTask.java:222)
at java.util.concurrent.FutureTask.run(FutureTask.java:242)
at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
at java.lang.Thread.run(Thread.java:818)
Caused by: java.lang.RuntimeException: Can't create handler inside thread that has not called Looper.prepare()
at android.os.Handler.<init>(Handler.java:200)
at android.os.Handler.<init>(Handler.java:114)
at android.widget.Toast$TN.<init>(Toast.java:561)
at android.widget.Toast.<init>(Toast.java:129)
at android.widget.Toast.makeText(Toast.java:419)
at com.example.sayareh.http2.MainActivity.OpenHttpConnection(MainActivity.java:65)
at com.example.sayareh.http2.MainActivity.DownloadImage(MainActivity.java:75)
at com.example.sayareh.http2.MainActivity.access$100(MainActivity.java:32)
at com.example.sayareh.http2.MainActivity$DownloadImageTask.doInBackground(MainActivity.java:87)
at com.example.sayareh.http2.MainActivity$DownloadImageTask.doInBackground(MainActivity.java:83)
at android.os.AsyncTask$2.call(AsyncTask.java:288)
at java.util.concurrent.FutureTask.run(FutureTask.java:237)
at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231) 
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112) 
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587) 
at java.lang.Thread.run(Thread.java:818) 
This is my MainActivityClass:
public class MainActivity extends AppCompatActivity {
ImageView imageView;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
imageView=(ImageView) findViewById(R.id.img);
new DownloadImageTask().execute(
"http://kocholo.org/img/images/lk4nnpetjq7rf10zf8r.jpg",
"http://media.mnn.com/assets/images/2016/01/stern-baby.jpg.838x0_q80.jpg",
"http://www.raisesmartkid.com/wp-content/uploads/baby-watching-tv.jpg",
"http://creativemisha.com/wp-content/uploads/2014/07/Cute-Baby-Girl-HD-Wallpaper1.jpg");
}
private InputStream OpenHttpConnection(String urlString) throws IOException {
InputStream inputStream=null;
int response=-1;
URL url=new URL(urlString);
URLConnection conn=url.openConnection();
if(!(conn instanceof HttpURLConnection))
throw new IOException("Not an Http Connection");
try {
HttpURLConnection httpURLConnection=(HttpURLConnection) conn;
httpURLConnection.setAllowUserInteraction(false);
httpURLConnection.setInstanceFollowRedirects(true);
httpURLConnection.setRequestMethod("GET");
httpURLConnection.connect();
response=httpURLConnection.getResponseCode();
if(response==httpURLConnection.HTTP_OK)
inputStream=httpURLConnection.getInputStream();
}catch (Exception ex){
Toast.makeText(this, "NETWORKING" + ex.getLocalizedMessage(), Toast.LENGTH_LONG).show();
throw new IOException("errcoonnecting");
}
return inputStream;
}
private Bitmap DownloadImage(String url)
{
Bitmap bitmap=null;
InputStream inputStream=null;
try{
inputStream=OpenHttpConnection(url);
bitmap= BitmapFactory.decodeStream(inputStream);
inputStream.close();
}catch (IOException io){
Toast.makeText(this,io.getLocalizedMessage(),Toast.LENGTH_LONG).show();
}
return bitmap;
}
private class DownloadImageTask extends AsyncTask<String,Bitmap,Long> {
protected Long doInBackground(String... urls) {
long imgcounts =0;
for (int i = 0; i < urls.length; i++) {
Bitmap imagedownloaded = DownloadImage(urls[i]);
if (imagedownloaded != null){
imgcounts++;
try {
Thread.sleep(3000);
} catch (InterruptedException ie) {
ie.printStackTrace();
}
publishProgress(imagedownloaded);
}}
return imgcounts;
}
protected void onProgressUpdate(Bitmap... bitmaps)
{
imageView.setImageBitmap(bitmaps[0]);
}
protected void onPostExecute(Long imagedownloaded) {
Toast.makeText(getBaseContext(),"h",Toast.LENGTH_LONG).show();
}
}
can anyone help me?

Answer 1

Remove the toast from the downloadimage method, uiYou can't updatUI elements from doin background().
}catch (IOException io){
Toast.makeText(this,io.getLocalizedMessage(),Toast.LENGTH_LONG).show();
}

Answer 2

Creating and showing Toast Messages inside doInBackground() (in your case inside catch statement of DownloadImage) is causing this.
Since doInBackground() runs on separate thread and Toast requires UI Thread to show Toast messages.