portfoliobuilder portfoliobuilder - 4 months ago 16
Android Question

How to do circular scrolling on ViewPager?

I would like to set my ViewPager to do circular scrolling. I want the first page to be able to scroll to page 2 AND the last page. And I would like my last page to scroll to [last page -1] AND the first page. I have made an attempt, although I am not sure when to call the method I have created. There does not seem to be a method in ViewPager that handles this sort of thing, so I created the below.

public ViewPagerAdapter(final ViewPager pager, int... pageIDs) {
super();
int actualNoOfIDs = pageIDs.length;
count = actualNoOfIDs + 2;
Log.d(TAG, "actualNoOfIDs: " + actualNoOfIDs +
"count: " + count);

pageIDsArray = new int[count];
for (int i = 0; i < actualNoOfIDs; i++) {
pageIDsArray[ i + 1] = pageIDs[i];
}
pageIDsArray[0] = pageIDs[actualNoOfIDs - 1];
pageIDsArray[count - 1] = pageIDs[0];

Log.d(TAG, "actualNoOfIDs#2: " + actualNoOfIDs +
"count#2: " + count);
pager.setOnPageChangeListener(new OnPageChangeListener() {
@Override
public void onPageSelected(int position) {
int pageCount = getCount();
if (position == 0) {
pager.setCurrentItem(pageCount - 2, false);
} else if (position == pageCount - 1) {
pager.setCurrentItem(1, false);
}
}

@Override
public void onPageScrollStateChanged(int state) {
// TODO Auto-generated method stub
Log.d(TAG, "onPageScrollStateChanged()");
// if (state == ViewPager.SCROLL_STATE_IDLE) {
// int pageCount = getCount();
// int currentItem = pager.getCurrentItem();
// if (currentItem == 0) {
// pager.setCurrentItem(pageCount - 2, false);
// } else if (currentItem == pageCount - 1) {
// pager.setCurrentItem(1, false);
// }
// }

}

@Override
public void onPageScrolled(int position, float positionOffset,
int positionOffsetPixels) {
// TODO Auto-generated method stub
Log.d(TAG, "onPageScrolled()");

}
});
}


My entire code is sort of lengthy, but if it helps I can post it.

public class ViewPagerAdapter extends PagerAdapter {
public static String TAG = ViewPagerAdapter.class.getSimpleName();

private int count;
private int[] pageIDsArray;

private TextToSpeech btnTTS;
private TtsButton tTSBtn;

String inputTxt;
Context context;
View itemView;

TextView tvNumber; // container for atomic number
TextView tvSymbol; // container for symbol
TextView tvWeight; // container for weight
TextView tvName; // container for name
TextView tvGroup; // container for group
TextView tvPeriod; // container for period
TextView tvBlock; // container for block
TextView tvFamily; // container for family
TextView tvColor; // container for color
TextView tvPhase; // container for phase
TextView tvMelt; // container for melting point
TextView tvBoil; // container for boiling point
TextView tvNeutrons; // container for neutrons
TextView tvProtons; // container for protons
TextView tvElectrons; // container for electrons
TextView tvUrl; // container for electrons

public ViewPagerAdapter(Context context, List<Integer> arrayAtomicNum,
List<String> arrayName, List<String> arraySymbol, List<String> arrayFamily,
List<String> arrayPhase, List<String> arrayColor, List<Integer> arrayGroup,
List<Integer> arrayPeriod, List<String> arrayBlock, List<Integer> arrayProtons,
List<Integer> arrayNeutrons, List<Integer> arrayElectrons, List<Double> arrayWeight,
List<Double> arrayMelt, List<Double> arrayBoil, List<String> arrayUrl) {
this.context = context;
ElementStructure.arrayAtomicNum = arrayAtomicNum;
ElementStructure.arrayName = arrayName;
ElementStructure.arraySymbol = arraySymbol;
ElementStructure.arrayFamily = arrayFamily;
ElementStructure.arrayPhase = arrayPhase;
ElementStructure.arrayColor = arrayColor;
ElementStructure.arrayGroup = arrayGroup;
ElementStructure.arrayPeriod = arrayPeriod;
ElementStructure.arrayBlock = arrayBlock;
ElementStructure.arrayProtons = arrayProtons;
ElementStructure.arrayNeutrons = arrayNeutrons;
ElementStructure.arrayElectrons = arrayElectrons;
ElementStructure.arrayWeight = arrayWeight;
ElementStructure.arrayMelt = arrayMelt;
ElementStructure.arrayBoil = arrayBoil;
ElementStructure.arrayUrl = arrayUrl;
}


public ViewPagerAdapter(final ViewPager pager, int... pageIDs) {
super();
int actualNoOfIDs = pageIDs.length;
count = actualNoOfIDs + 2;
Log.d(TAG, "actualNoOfIDs: " + actualNoOfIDs +
"count: " + count);

pageIDsArray = new int[count];
for (int i = 0; i < actualNoOfIDs; i++) {
pageIDsArray[ i + 1] = pageIDs[i];
}
pageIDsArray[0] = pageIDs[actualNoOfIDs - 1];
pageIDsArray[count - 1] = pageIDs[0];

Log.d(TAG, "actualNoOfIDs#2: " + actualNoOfIDs +
"count#2: " + count);
pager.setOnPageChangeListener(new OnPageChangeListener() {
@Override
public void onPageSelected(int position) {
int pageCount = getCount();
if (position == 0) {
pager.setCurrentItem(pageCount - 2, false);
} else if (position == pageCount - 1) {
pager.setCurrentItem(1, false);
}
}

@Override
public void onPageScrollStateChanged(int state) {
// TODO Auto-generated method stub
Log.d(TAG, "onPageScrollStateChanged()");
// if (state == ViewPager.SCROLL_STATE_IDLE) {
// int pageCount = getCount();
// int currentItem = pager.getCurrentItem();
// if (currentItem == 0) {
// pager.setCurrentItem(pageCount - 2, false);
// } else if (currentItem == pageCount - 1) {
// pager.setCurrentItem(1, false);
// }
// }

}

@Override
public void onPageScrolled(int position, float positionOffset,
int positionOffsetPixels) {
// TODO Auto-generated method stub
Log.d(TAG, "onPageScrolled()");

}
});
}

@Override
public int getCount() {
// TODO Auto-generated method stub
return ElementStructure.arrayAtomicNum.size();

}

@Override
public boolean isViewFromObject(View view, Object object) {
// TODO Auto-generated method stub
return view == ((RelativeLayout) object);
}

@Override
public Object instantiateItem(ViewGroup container, final int position) {

LayoutInflater inflater = (LayoutInflater) context
.getSystemService(Context.LAYOUT_INFLATER_SERVICE);

int layoutColorId = ElementStructure.arrayLayoutColor.get(position);

if (layoutColorId == 1) {
itemView = inflater.inflate(R.layout.frame_learn_a, container,
false);
} else if (layoutColorId == 2) {
itemView = inflater.inflate(R.layout.frame_learn_b, container,
false);
} else if (layoutColorId == 3) {
itemView = inflater.inflate(R.layout.frame_learn_c, container,
false);
} else if (layoutColorId == 4) {
itemView = inflater.inflate(R.layout.frame_learn_d, container,
false);
}

Button btnSpeak = (Button)itemView.findViewById(R.id.btnaudio);

btnSpeak.setOnClickListener(new OnClickListener() {

@Override
public void onClick(View v) {
// TODO Auto-generated method stub
inputTxt = ElementStructure.arrayName.get(position);
tTSBtn = new TtsButton(this, inputTxt);
}

});

// atomic number textView
tvNumber = (TextView)itemView.findViewById(R.id.metanumber);

// symbol textView
tvSymbol = (TextView)itemView.findViewById(R.id.metasymbol);

// weight textView
tvWeight = (TextView)itemView.findViewById(R.id.metaweight);

// name textView
tvName = (TextView)itemView.findViewById(R.id.metaname);

// group textView
tvGroup = (TextView)itemView.findViewById(R.id.metagroup);

// period textView
tvPeriod = (TextView)itemView.findViewById(R.id.metaperiod);

// block textView
tvBlock = (TextView)itemView.findViewById(R.id.metablock);

// family textView
tvFamily = (TextView)itemView.findViewById(R.id.metafamily);

// color textView
tvColor = (TextView)itemView.findViewById(R.id.metacolor);

// phase textView
tvPhase = (TextView)itemView.findViewById(R.id.metaphase);

// melting point textView
tvMelt = (TextView)itemView.findViewById(R.id.metamelt);

// boiling point textView
tvBoil = (TextView)itemView.findViewById(R.id.metaboil);

// neutrons textView
tvNeutrons = (TextView)itemView.findViewById(R.id.metaneutrons);

// protons textView
tvProtons = (TextView)itemView.findViewById(R.id.metaprotons);

// electrons textView
tvElectrons = (TextView)itemView.findViewById(R.id.metaelectrons);

// url textView
tvUrl = (TextView)itemView.findViewById(R.id.metaurl);

// capture position and set to the TextViews
tvNumber.setText(String.valueOf(ElementStructure.arrayAtomicNum.get(position)));
tvSymbol.setText(ElementStructure.arraySymbol.get(position));
tvWeight.setText(String.valueOf(ElementStructure.arrayWeight.get(position)));
tvName.setText(ElementStructure.arrayName.get(position));
tvPeriod.setText(String.valueOf(ElementStructure.arrayPeriod.get(position)));
tvBlock.setText(String.valueOf(ElementStructure.arrayBlock.get(position)));
tvFamily.setText(ElementStructure.arrayFamily.get(position));
tvColor.setText(ElementStructure.arrayColor.get(position));
tvPhase.setText(ElementStructure.arrayPhase.get(position));
tvNeutrons.setText(String.valueOf(ElementStructure.arrayNeutrons.get(position)));
tvProtons.setText(String.valueOf(ElementStructure.arrayProtons.get(position)));
tvElectrons.setText(String.valueOf(ElementStructure.arrayElectrons.get(position)));
tvUrl.setText(ElementStructure.arrayUrl.get(position));

// capture position, adjust for 0 value cases
if (ElementStructure.arrayGroup.get(position) == 0) {
tvGroup.setText("n/a");
} else {
tvGroup.setText(String.valueOf(ElementStructure.arrayGroup.get(position)));
}

if (ElementStructure.arrayMelt.get(position) == 0) {
tvMelt.setText("n/a");
} else {
tvMelt.setText(String.valueOf(ElementStructure.arrayMelt.get(position)));
}

if (ElementStructure.arrayBoil.get(position) == 0) {
tvBoil.setText("n/a");
} else {
tvBoil.setText(String.valueOf(ElementStructure.arrayBoil.get(position)));
}

// add fragments to container (ViewPager)
((ViewPager) container).addView(itemView);
return itemView;

}

@Override
public void destroyItem(ViewGroup container, int position, Object object) {
Log.d(TAG, "destroyItem()");
// remove fragments from container (ViewPager)
((ViewPager) container).removeView((RelativeLayout) object);
}


@Override
public void finishUpdate(View container) {
// TODO Auto-generated method stub
Log.d(TAG, "finishUpdate()");
}

@Override
public void restoreState(Parcelable state, ClassLoader loader) {
// TODO Auto-generated method stub
Log.d(TAG, "restoreState()");
}

@Override
public Parcelable saveState() {
// TODO Auto-generated method stub
Log.d(TAG, "saveState()");
return null;
}

@Override
public void startUpdate(View container) {
// TODO Auto-generated method stub
Log.d(TAG, "startUpdate()");
}




public class TtsButton extends Activity implements OnInitListener {

public TtsButton(OnClickListener onClickListener, String inputTxt) {
super();
tTSCheck(inputTxt);
}

private void tTSCheck (String inputTxt) {

int resultCodeCheck = TextToSpeech.Engine.CHECK_VOICE_DATA_PASS;
if (resultCodeCheck == 1) {
btnTTS = new TextToSpeech(context, this);
} else {
Intent installTTSFiles = new Intent(); //missing data, install it
installTTSFiles.setAction(TextToSpeech.Engine.ACTION_INSTALL_TTS_DATA);
startActivity(installTTSFiles);
}
}

@Override
public void onInit(int status) {
// TODO Auto-generated method stub
if(status == TextToSpeech.SUCCESS)
{
Log.i(TAG, "TTS INIT: SUCCESS");
btnTTS.setLanguage(Locale.US);
btnTTS.speak(inputTxt, TextToSpeech.QUEUE_FLUSH, null);
}
else if(status == TextToSpeech.ERROR)
{
Log.e(TAG, "TTS INIT: ERROR");
}
}

@Override
public void onPause() {
if (btnTTS != null) {
btnTTS.stop();
btnTTS.shutdown();
}
super.onPause();
}

} //end embedded class

} //end ViewPagerAdapter


Thanks in advance. I was thinking about trying to use motion gesture, however, I really do not understand why my method won't work so long that I can call it in the correct spot. My initial thought was to call it in "Object instantiateItem(ViewGroup container, final int position)" every time the position changes, and if the conditions were correct. But I'm not sure if that is best.

Answer

Ok, I have an answer. It was actually easier than I expected, but it does take some trickery. First, let me begin with the set up. Lets say, for example, you have three pages (A-B-C) that you are scrolling through in your ViewPager. And you want to set it up so that if you continue scrolling on C (pg. 3), it goes to A (pg. 1) and if you scrolled backwards on A (pg. 1) it goes to C (pg. 3).

I am not saying my solution is the best, but it works and I do not see any issues. First, you have to create two "fake" pages. The fake pages represent the first and last pages of your ViewPager. The next thing you will need is to set up an onPageChangeListener(), and use the method onPageSelected(). The reason why you need the fake pages is because onPageSelected() only registers after you have moved (swiped). In other words, without this method the end user would have to scroll to page 2 and back to page 1 to receive a hit on page 1, which also means that page 1 would be skipped depending on your code logic.

The setup is really the entire answer. Once you have your fake pages, it is just a matter of using setCurrentItem() inside the necessary method.

Here is how my code looks. Be sure to place this inside your public Object instantiateItem(final ViewGroup container, final int position) method, just before you return your view inside of your container.

((ViewPager) container).setOnPageChangeListener(new OnPageChangeListener() {
            @Override
            public void onPageSelected(int position) {
                Log.d(TAG, "onPageSelected() :: " + "position: " + position);

                // skip fake page (first), go to last page
                if (position == 0) {
                    ((ViewPager) container).setCurrentItem(118, false);
                }

                // skip fake page (last), go to first page
                if (position == 119) {
                    ((ViewPager) container).setCurrentItem(1, false); //notice how this jumps to position 1, and not position 0. Position 0 is the fake page!
                }

            }

That's it, it does the trick! The only other thing to do is start your ViewPager on position 1 (which is the second page: fake page = pg 1, my real starting page = pg 2). Now, every time I scroll to the fake page, I redirect it backwards to the last real page. And every time I scroll forward to the last fake page, I redirect it forwards to the real starting page (pg 2).

Also, do not try to put any code in onPageScrollStateChanged. That method is bizarre, it seems that the state value is uncontrollable. It constantly jumps from one state to another. Even without scrolling. That is just a tip I picked up.

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