Android: ViewPager gets stuck in between views

Question

I have a ViewPager which swipes between Fragments. I\'m using a FragmentStatePagerAdapter to feed the Fragments to the ViewPager. If the user swipes left at a normal pace, and t

Answer 1

Try the following sample code and modify it as per your requirement(I guess your are loading the image on main UI thread and not caching it, its just a guess). In this code i am downloading and caching the images from the internet : Create a Activity class named SomeFragTest

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.lang.ref.WeakReference;
import java.util.ArrayList;
import java.util.List;
import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.HttpStatus;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.DefaultHttpClient;
import android.app.ActivityManager;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Bitmap.Config;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.graphics.PorterDuff.Mode;
import android.graphics.PorterDuffXfermode;
import android.graphics.Rect;
import android.graphics.RectF;
import android.os.AsyncTask;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentActivity;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentPagerAdapter;
import android.support.v4.util.LruCache;
import android.support.v4.view.ViewPager;
import android.util.Log;
import android.widget.ImageView;
public class SomeFragTest extends FragmentActivity{
private LruCache cache;
private List strings;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_layout);
ViewPager mViewPager = (ViewPager)findViewById(R.id.viewPager);

strings=new ArrayList();
setData();
int memClass = ( ( ActivityManager )getSystemService(           Context.ACTIVITY_SERVICE ) ).getMemoryClass();
int cacheSize = 1024 * 1024 * memClass / 8;

cache=new LruCache(cacheSize){
    @Override
    protected int sizeOf(String key, Bitmap value) {
        return value.getByteCount()/1024;
    }
};
mViewPager.setOffscreenPageLimit(strings.size());
mViewPager.setAdapter(new MyPageAdapter(getSupportFragmentManager()));
}
private void setData()
{
for (int i = 1; i <= 10; i++) {
    strings.add("http://dummyimage.com/600x400/000/0011ff.png&text="+i);
}
}
public void loadBitmap(int position , ImageView imageView) {
imageView.setImageResource(R.drawable.ic_launcher);
imageView.setTag(strings.get(position));
BitmapDownloaderTask task = new BitmapDownloaderTask(imageView);
task.execute(strings.get(position));
}
class MyPageAdapter extends FragmentPagerAdapter
{
public MyPageAdapter(FragmentManager fm) {
    super(fm);
    // TODO Auto-generated constructor stub
}

@Override
public Fragment getItem(int arg0) {
    Fragment fragment=new ChildFrag();
    Bundle bundle=new Bundle();
    bundle.putInt("POS", arg0);
    fragment.setArguments(bundle);
    return fragment;
}

@Override
public int getCount() {
    return strings.size();
}


 }
class BitmapDownloaderTask extends AsyncTask {
public String url;
private final WeakReference imageViewReference;


public BitmapDownloaderTask(ImageView imageView) {
    imageViewReference = new WeakReference(imageView);

}

@Override
// Actual download method, run in the task thread
protected Bitmap doInBackground(String... params) {

     // params comes from the execute() call: params[0] is the url.
    url=params[0];
    if(cache.get(url)!=null){
        Log.e("FROM ", "CACHE");
        return cache.get(url);
    }
     return downloadBitmap(params[0]);
}
private Bitmap downloadBitmap(String url) {
    Log.e("FROM ", "URL");
   HttpClient client=new DefaultHttpClient();
    //final AndroidHttpClient client =     AndroidHttpClient.newInstance("Android");
    final HttpGet getRequest = new HttpGet(url);

    try {
        HttpResponse response = client.execute(getRequest);
        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 {
                inputStream = entity.getContent(); 
                //final Bitmap bitmap = BitmapFactory.decodeStream(inputStream);
                return decodeBitmapWithGiveSizeFromResource(inputStream);
            } finally {
                if (inputStream != null) {
                    inputStream.close();  
                }
                entity.consumeContent();
            }
        }
    } catch (Exception e) {
        // Could provide a more explicit error message for IOException or IllegalStateException
        getRequest.abort();
        Log.w("ImageDownloader", "Error while retrieving bitmap from " + url);
        Log.e("ERROR", " " +e.getLocalizedMessage());
    } finally {
        if (client != null) {
            //client.close();
        }
    }
    return null;
}

/***************/
private void copy(InputStream inputStream,ByteArrayOutputStream arrayOutputStream)
{

            byte[] buffer = new byte[1024];
    int len;
    try {
        while ((len = inputStream.read(buffer)) > -1 ) {
           arrayOutputStream.write(buffer, 0, len);
        }
        arrayOutputStream.flush();
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

}
private  Bitmap decodeBitmapWithGiveSizeFromResource(InputStream inputStream) {
    //BufferedInputStream bufferedInputStream=new BufferedInputStream(inputStream);
    final BitmapFactory.Options options = new BitmapFactory.Options();
    ByteArrayOutputStream out = new ByteArrayOutputStream();
    copy(inputStream,out);
   InputStream in2 = new ByteArrayInputStream(out.toByteArray());

    options.inJustDecodeBounds = true;

        BitmapFactory.decodeStream(inputStream, null, options);
    // Calculate inSampleSize
    options.inSampleSize = calculateInSampleSize(options);

    // Decode bitmap with inSampleSize set
    options.inJustDecodeBounds = false;
    Bitmap bitmap=BitmapFactory.decodeStream(in2,null, options);
    try {
        inputStream.close();
        in2.close();
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

    return scaleDown(bitmap,false);
}
private  Bitmap scaleDown(Bitmap realImage, boolean filter) {

    Bitmap newBitmap = Bitmap.createScaledBitmap(realImage, 100,
            100, filter);

    Bitmap output = Bitmap.createBitmap(newBitmap.getWidth(), newBitmap
            .getHeight(), Config.ARGB_8888);
    Canvas canvas = new Canvas(output);

    final int color = 0xff424242;
    final Paint paint = new Paint();
    final Rect rect = new Rect(0, 0, newBitmap.getWidth(), newBitmap.getHeight());
    final RectF rectF = new RectF(rect);
    final float roundPx = 10;

    paint.setAntiAlias(true);
    canvas.drawARGB(0, 0, 0, 0);
    paint.setColor(color);
    canvas.drawRoundRect(rectF, roundPx, roundPx, paint);

    paint.setXfermode(new PorterDuffXfermode(Mode.SRC_IN));
    canvas.drawBitmap(newBitmap, rect, rect, paint);

    return output;
}
private  int calculateInSampleSize(BitmapFactory.Options options) {
    // Raw height and width of image
    final int height = options.outHeight;
    final int width = options.outWidth;
    int inSampleSize = 1;
    if (height > 100 || width > 100) {

        final int halfHeight = height / 2;
        final int halfWidth = width / 2;

        // Calculate the largest inSampleSize value that is a power of 2 and keeps both
        // height and width larger than the requested height and width.
        while ((halfHeight / inSampleSize) >100
                && (halfWidth / inSampleSize) >100) {
            inSampleSize *= 2;
        }
    }

    return inSampleSize;
} 
@Override
// Once the image is downloaded, associates it to the imageView
protected void onPostExecute(Bitmap bitmap) {
    if (isCancelled()) {
        bitmap = null;
    }

    if (imageViewReference != null) {
        cache.put(url, bitmap);
        ImageView imageView = imageViewReference.get();

   //     BitmapDownloaderTask bitmapDownloaderTask = getBitmapDownloaderTask(imageView);
        // Change bitmap only if this process is still associated with it

        if (((String)imageView.getTag()).equalsIgnoreCase(url)) {
            imageView.setImageBitmap(bitmap);

        }
    }
}
   }
}

After this create the xml for it, named activity_layout

Now we have create the Fragment class that we want to inflate in the ViewPager: Create a class named ChildFrag as follows

import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.TextView;

public class ChildFrag extends Fragment {
private int index;
private ImageView imageView;

@Override
@Nullable
public View onCreateView(LayoutInflater inflater,
        @Nullable ViewGroup container, @Nullable Bundle savedInstanceState)     {
    View view = inflater.inflate(R.layout.fragtest, container, false);
    index = getArguments().getInt("POS");
    ((TextView) view.findViewById(R.id.textView1)).setText("" + index);
    imageView = (ImageView) view.findViewById(R.id.imageView1);
    return view;
}

@Override
public void onActivityCreated(@Nullable Bundle savedInstanceState) {
    super.onActivityCreated(savedInstanceState);
    ((SomeFragTest) getActivity()).loadBitmap(index, imageView);
}
}

Now we have create the xml for the fragment as fragtest:

Add the following permission in the AndroidManifest.xml