Picasso + RxJava2：方法调用应该从主线程发生

Question

This was my initial Question:

I am trying to show a few images in the AutoScrollViewPager . I am using Picasso to achieve the same. However, I would like to do the same with using Rxjava2 + Picasso. I am kinda new to this RxJava concept. So if anyone can help me with details if possible, to convert the below into RxJava code, I would really appreciate it.

This is what I do in onViewCreated()

imageAdapter = new ImageAdapter(getActivity());
autoScrollViewPager.setAdapter(imageAdapter);
autoScrollViewPager.setCurrentItem(imageAdapter.getCount() - 1);
autoScrollViewPager.startAutoScroll();
autoScrollViewPager.setInterval(4000);

This is my ImageAdapter

ImageAdapter(Context context){
    this.context=context;
    mLayoutInflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
}

@Override
public int getCount() {
    return GalImages.length;
}

@Override
public boolean isViewFromObject(View view, Object object) {
    return view == ((RelativeLayout) object);
}

@Override
public Object instantiateItem(ViewGroup container, int position) {
    LayoutInflater inflater = (LayoutInflater) container.getContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    View view = inflater.inflate(R.layout.pager_item,null);
    ((ViewPager) container).addView(view);
    final ImageView img = (ImageView) view.findViewById(R.id.imageView);
    Picasso.with(context)
            .load(GalImages[position])
            .fit()
            .into(img);
    return view;
}

@Override
public void destroyItem(ViewGroup container, int position, Object object) {
    container.removeView((RelativeLayout)object);
}

How can I convert this into RxJava code? Any help will be appreciated.

This is what I tried to do

I changed my ImageAdapter a bit:

@Override
public Object instantiateItem(ViewGroup container, int position) {
    LayoutInflater inflater = (LayoutInflater) container.getContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    View view = inflater.inflate(R.layout.pager_item,null);
    ((ViewPager) container).addView(view);
    img = (ImageView) view.findViewById(R.id.imageView);
    loadImagesWithPicasso(position)
        .subscribeOn(Schedulers.newThread())
        .observeOn(AndroidSchedulers.mainThread())
        .subscribe();
    return view;
}

public Completable loadImagesWithPicasso(int position) {
   return Completable.fromAction(new Action() {
       @Override
       public void run() throws Exception {
           Picasso.with(context)
                  .load(GalImages[position])
                  .fit()
                  .into(new Target() {
                            @Override
                            public void onBitmapLoaded(Bitmap bitmap, Picasso.LoadedFrom from) {

                            }

                            @Override
                            public void onBitmapFailed(Drawable errorDrawable) {

                            }

                            @Override
                            public void onPrepareLoad(Drawable placeHolderDrawable) {
                                img.setImageDrawable(placeHolderDrawable);
                            }
                        });
       }
   });
}

But this, unfortunately, did not work and I ended up with this error:

java.lang.IllegalStateException: Method call should happen from the main thread.
at com.squareup.picasso.Utils.checkMain(Utils.java:136)
at com.squareup.picasso.RequestCreator.into(RequestCreator.java:496)
at com.kaaddevelopers.myprescriptor.ImageAdapter$1.run(ImageAdapter.java:79)
at io.reactivex.internal.operators.completable.CompletableFromAction.subscribeActual(CompletableFromAction.java:34)
at io.reactivex.Completable.subscribe(Completable.java:1613)
at io.reactivex.internal.operators.completable.CompletableSubscribeOn$SubscribeOnObserver.run(CompletableSubscribeOn.java:64)
at io.reactivex.Scheduler$1.run(Scheduler.java:134)
at io.reactivex.internal.schedulers.ScheduledRunnable.run(ScheduledRunnable.java:59)
at io.reactivex.internal.schedulers.ScheduledRunnable.call(ScheduledRunnable.java:51)
at java.util.concurrent.FutureTask.run(FutureTask.java:237)
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:269)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1113)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:588)
at java.lang.Thread.run(Thread.java:818)

Any help will be appreciated. :)

Answer 1

You are loading the image from the executor thread, which Picasso doesn't allow (this is pour choice if you ask me, there are better ways to deal with sync issues, but that's the way it is now).

You can see the details of this decision in this thread :

It was a mistake from Picasso to allow external callers to invoke into() other than the main thread. Those methods deal with view recycling and canceling without synchronization, hence in Picasso 2.3 we added the checks.

There are several options for you. You can do the whole instantiateItem work in the UI thread, if you pass Looper.getMainLooper() in, or you can use RequestCreator.get() method instead of RequestCreator.into() , or wrap your Picasso work with:

context.runOnUiThread(new Runnable() {
    @Override
    public void run() {
         // Can call RequestCreator.into here
    }
});