Develop Reference

RecyclerView items not repeating, but retaining changes of previous item that was in its slot

I am trying to implement a list of files that can be selected from the RecyclerView Adapter class. While I understand it is not a good idea, I feel if I am able to accomplish this from within said class, it would be really helpful in the future.
My list item (Each individual item view for the RecyclerView) has the following structure:
|--------|----------------|
| ICON | DATA |
|--------|----------------|
Problem:
When a file is selected (by touching the icon portion of a file item), I change the background of that item to another color to denote that it has been selected.
However, when I scroll down to about 25 items later, another file has the same background color even though it's not selected (it does not show up in Log.d as being selected, nor was it in the test ArrayList that was used to store selected files).
It seems as though the item is only retaining the background change of the previous occupant.
Solution attempts:
Previously, only the variables related to each list item were declared in the RecyclerView ViewHolder class and all changes were made in the onBindViewHolder method. Now, all changes to be made have been moved to the ViewHolder class inside a method called bind. There was no change in behavior.
If I set the default background image during the very first step in onBindViewHolder, the behavior changes such that the items do not retain changes of previous occupants. However, on scrolling back, the background change for the target item reverts to the default background image.
Code:
public class RVA extends RecyclerView.Adapter<RVA.RVH>
{
private LayoutInflater inf;
private ArrayList<File> items;
// The var below is used to track the no. of selected items
// globally within the RVA class.
private int numberOfSelectedItems = 0;
public RVA(ArrayList<File> _items)
{
items = _items;
}
#Override
public RVA.RVH onCreateViewHolder(ViewGroup parent, int viewType)
{
inf = LayoutInflater.from(parent.getContext());
return new RVH(inf, parent);
}
#Override
public void onBindViewHolder(RVA.RVH holder, int position)
{
File listItem = items.get(position);
// 'binding' each file element to a respective host container.
holder.bind(listItem);
}
#Override
public int getItemCount()
{
return items.size();
}
#Override
public long getItemId(int position)
{
return position;
}
// The ViewHolder class.
// Initially it was just declared as class.
// There was no change observed after the 'final' modifier was added.
final class RVH extends RecyclerView.ViewHolder
{
private Context context;
private LinearLayout itemSelector;
private ImageView itemIcon;
private TextView itemName;
private TextView itemSize;
public RVH(LayoutInflater inf, ViewGroup parent)
{
super(inf.inflate(R.layout.list_item, parent, false));
context = parent.getContext();
// This is the SECOND outermost LinearLayout of each file item View.
// It was previously the parent Layout, but there was no difference due to change.
itemSelector = itemView.findViewById(R.id.item_selector);
// This is the icon ImageView.
itemIcon = itemView.findViewById(R.id.item_icon);
// These are the data TextViews.
itemName = itemView.findViewById(R.id.item_id);
itemSize = itemView.findViewById(R.id.item_size);
}
// The 'bind' method that registers changes.
public void bind(File fileItem)
{
String listItemName = fileItem.getName();
itemName.setText(listItemName);
//---- These are just changes to the icons depending on type. Works fine.
if(fileItem.isDirectory())
{
itemIcon.setImageResource(R.drawable.directory_icon);
itemSize.setText("Directory");
}
else
{
itemSize.setText(fileItem.length() + " B");
if(listItemName.endsWith(".jpg") || listItemName.endsWith(".jpeg") || listItemName.endsWith(".png") || listItemName.endsWith(".gif"))
{
Glide.with(context).load(fileItem).centerCrop().into(itemIcon);
}
else
{
itemIcon.setImageResource(R.drawable.file_icon);
}
}
//---- END
//---- This is the code which handles opening files according to type. Works fine.
itemSelector.setOnClickListener(new View.OnClickListener()
{
#Override
public void onClick(View v)
{
if(numberOfSelectedItems == 0)
{
if(!itemSize.getText().toString().endsWith(" B"))
{
Intent loadListItemIntent = new Intent(context, DirectoryViewActivity.class);
loadListItemIntent.putExtra("ITEMPATH", fileItem.getPath());
context.startActivity(loadListItemIntent);
}
else
{
if(itemName.getText().toString().endsWith(".jpg") || itemName.getText().toString().endsWith(".jpeg") || itemName.getText().toString().endsWith(".png") || itemName.getText().toString().endsWith(".gif"))
{
Glide.with(context).load(fileItem).centerCrop().into(itemIcon);
Intent loadListItemIntent = new Intent(context, ImageActivity.class);
loadListItemIntent.putExtra("ITEMPATH", fileItem.getPath());
context.startActivity(loadListItemIntent);
}
else
{
Toast.makeText(context, "File needs proper application.", Toast.LENGTH_SHORT).show();
}
}
}
}
});
//---- END
//---- !!! THIS SECTION is where the problem manifests.
itemIcon.setOnClickListener(new View.OnClickListener()
{
#Override
public void onClick(View v)
{
if(itemIcon.getTag().toString().equals("not_selected"))
{
// Incrementing based on selection.
++numberOfSelectedItems;
// Using a tag to identify/ denote whether item is selected.
itemIcon.setTag("selected");
// Changing the background & disabling file opening while in selection mode.
itemSelector.setBackgroundResource(R.drawable.list_item_selected);
itemSelector.setClickable(false);
itemSelector.setLongClickable(false);
// I use this odd method to send a message to the host Activity
// that we have entered selection mode & that the Activity should
// display some option buttons on the Action Bar.
if(context instanceof DirectoryViewActivity)
{
((DirectoryViewActivity)context).addSelectedItem(fileItem);
if(numberOfSelectedItems == 1)
{
((DirectoryViewActivity)context).setSelectionMode();
}
}
}
else
{
// Decrementing based on deselection.
--numberOfSelectedItems;
// Overwiting the tag to identify/ denote item is now unselected.
itemIcon.setTag("not_selected");
// Background changed back to default & file opening re-enabled.
itemSelector.setClickable(true);
itemSelector.setLongClickable(true);
itemSelector.setBackgroundResource(R.drawable.list_item_background);
// I use this method to send a message to the host Activity
// that we have exited selection mode & that the Activity should
// remove related option buttons from the Action Bar.
if(context instanceof DirectoryViewActivity)
{
((DirectoryViewActivity)context).removeSelectedItem(fileItem);
if(numberOfSelectedItems == 0)
{
((DirectoryViewActivity)context).voidSelectionMode();
}
}
}
}
});
}
}
}

This is because RecyclerView does not create views for all of your items in the list it create enough ViewHolder to fill up the screen and few more and when you scroll the old ViewHolder are bind to some other data in the adapter that is when the onBindViewHolder() is called , so basically what is happening here is you are setting the background of current ViewHolder on the screen and when you scroll the same ViewHolder in bind to the new data.
I think you have to check in the onBindViewHolder whether or not this is the item to which you want to set the background and then take the decision remove it if the item is not selected in the dataset set background if it is selected.

Shared Element Transition is not exiting properly

I have fragment from which I'm launching activity with shared element transition that has viewpager in it, the enter transition works fine but when i scroll in view pager and finish transition the shared image comes from left side which is not desired it should reposition itself to where it was launched, here is my code:
Intent myIntent = new Intent(getActivity(), EnlargeActivity.class);
ActivityOptionsCompat options = ActivityOptionsCompat.
makeSceneTransitionAnimation(getActivity(),
imageView,
ViewCompat.getTransitionName(imageView));
startActivity(myIntent, options.toBundle());
I'm updating view and its name in activity that contains viewpager when finishing activity, but its going with blink:
public void finishAfterTransition() {
setEnterSharedElementCallback(new SharedElementCallback() {
#Override
public void onMapSharedElements(List<String> names, Map<String, View> sharedElements) {
// Clear all current shared views and names
names.clear();
sharedElements.clear();
ViewGroup viewGroup = (ViewGroup) viewPagerDetail.getAdapter()
.instantiateItem(viewPagerDetail, viewPagerDetail.getCurrentItem());
if (viewGroup == null) {
return;
}
// Map the first shared element name to the child ImageView.
sharedElements.put(viewGroup.findViewById(R.id.img).getTransitionName(), viewGroup.findViewById(R.id.img));
// setExitSharedElementCallback((SharedElementCallback) this);
}
});
super.finishAfterTransition();

Basically, Android start the transition with your pre-defined View and transitionName and automatically use the same properties for the return transition. When you change your focused View in ViewPager, Android doesn't know about that and keep the transition on the previous one on its way back. So you need to inform Android about the changes:
Remap the transition properties: Use setEnterSharedElementCallback to change the transitionName and View to the new one before returning from Activity2.
Wait for the Activity1 to finish rendering addOnPreDrawListener.
It's a bit complex in the final implementation. But you can look at my sample code https://github.com/tamhuynhit/PhotoGallery. I try to implement the shared-element-transition from many simple to complex sections.
Your problem appeared from Level 3 and solved in Level 4.
I am writing a tutorial about this but it's not in English so hope the code can help
UPDATE 1: Work flow
Here is how I implement it in my code:
Override finishAfterTransition in Activity2 and call setEnterSharedElementCallback method to re-map the current selected item in ViewPager. Also, call setResult to pass the new selected index back to previous activity here.
#Override
#TargetApi(Build.VERSION_CODES.LOLLIPOP)
public void finishAfterTransition() {
setEnterSharedElementCallback(new SharedElementCallback() {
#Override
public void onMapSharedElements(List<String> names, Map<String, View> sharedElements) {
View selectedView = getSelectedView();
if (selectedView == null)
return;
// Clear all current shared views and names
names.clear();
sharedElements.clear();
// Store new selected view and name
String transitionName = ViewCompat.getTransitionName(selectedView);
names.add(transitionName);
sharedElements.put(transitionName, selectedView);
setExitSharedElementCallback((SharedElementCallback) null);
}
});
Intent intent = new Intent();
intent.putExtra(PHOTO_FOCUSED_INDEX, mCurrentIndex);
setResult(RESULT_PHOTO_CLOSED, intent);
super.finishAfterTransition();
}
Write a custom ShareElementCallback so I can set the callback before knowing which View is going to be used.
#TargetApi(Build.VERSION_CODES.LOLLIPOP)
private static class CustomSharedElementCallback extends SharedElementCallback {
private View mView;
/**
* Set the transtion View to the callback, this should be called before starting the transition so the View is not null
*/
public void setView(View view) {
mView = view;
}
#Override
public void onMapSharedElements(List<String> names, Map<String, View> sharedElements) {
// Clear all current shared views and names
names.clear();
sharedElements.clear();
// Store new selected view and name
String transitionName = ViewCompat.getTransitionName(mView);
names.add(transitionName);
sharedElements.put(transitionName, mView);
}
}
Override onActivityReenter in Activity1, get the selected index from the result Intent. Set setExitSharedElementCallback to re-map new selected View when the transition begins.Call supportPostponeEnterTransition to delay a bit because your new View may not be rendered at this point. Use getViewTreeObserver().addOnPreDrawListener to listen for the layout changes, find the right View by the selected index and continue the transition supportStartPostponedEnterTransition.
#Override
#TargetApi(Build.VERSION_CODES.LOLLIPOP)
public void onActivityReenter(int resultCode, Intent data) {
if (resultCode != LevelFourFullPhotoActivity.RESULT_PHOTO_CLOSED || data == null)
return;
final int selectedIndex = data.getIntExtra(LevelFourFullPhotoActivity.PHOTO_FOCUSED_INDEX, -1);
if (selectedIndex == -1)
return;
// Scroll to the new selected view in case it's not currently visible on the screen
mPhotoList.scrollToPosition(selectedIndex);
final CustomSharedElementCallback callback = new CustomSharedElementCallback();
getActivity().setExitSharedElementCallback(callback);
// Listen for the transition end and clear all registered callback
getActivity().getWindow().getSharedElementExitTransition().addListener(new Transition.TransitionListener() {
#Override
public void onTransitionStart(Transition transition) {}
#Override
public void onTransitionPause(Transition transition) {}
#Override
public void onTransitionResume(Transition transition) {}
#Override
public void onTransitionEnd(Transition transition) {
removeCallback();
}
#Override
public void onTransitionCancel(Transition transition) {
removeCallback();
}
private void removeCallback() {
if (getActivity() != null) {
getActivity().getWindow().getSharedElementExitTransition().removeListener(this);
getActivity().setExitSharedElementCallback((SharedElementCallback) null);
}
}
});
// Pause transition until the selected view is fully drawn
getActivity().supportPostponeEnterTransition();
// Listen for the RecyclerView pre draw to make sure the selected view is visible,
// and findViewHolderForAdapterPosition will return a non null ViewHolder
mPhotoList.getViewTreeObserver().addOnPreDrawListener(new ViewTreeObserver.OnPreDrawListener() {
#Override
public boolean onPreDraw() {
mPhotoList.getViewTreeObserver().removeOnPreDrawListener(this);
RecyclerView.ViewHolder holder = mPhotoList.findViewHolderForAdapterPosition(selectedIndex);
if (holder instanceof ViewHolder) {
callback.setView(((ViewHolder) holder).mPhotoImg);
}
// Continue the transition
getActivity().supportStartPostponedEnterTransition();
return true;
}
});
}
UPDATE 2: getSelectedItem
To get selected View from the ViewPager, don't use getChildAt or you get the wrong View, use findViewWithTag instead
In the PagerAdapter.instantiateItem, use position as tag for each View:
#Override
public View instantiateItem(ViewGroup container, int position) {
// Create the View
view.setTag(position)
// ...
}
Listen to onPageSelected event to get the selected index:
mViewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
#Override
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
}
#Override
public void onPageSelected(int position) {
mSelectedIndex = position;
}
#Override
public void onPageScrollStateChanged(int state) {
}
});
Call getSelectedView to get the current view by the selected index
private View getSelectedView() {
try {
return mPhotoViewPager.findViewWithTag(mSelectedIndex);
} catch (IndexOutOfBoundsException | NullPointerException ex) {
return null;
}
}

This is actually a default behavior, I was struggling SharedElementTransitions a lot, but I have nested fragments. I got my solution from an article (very recent article), it shows an implementation with a RecyclerView, which I assume you have. In short, the solution is to override onLayoutChange :
recyclerView.addOnLayoutChangeListener(
new OnLayoutChangeListener() {
#Override
public void onLayoutChange(View view,
int left,
int top,
int right,
int bottom,
int oldLeft,
int oldTop,
int oldRight,
int oldBottom) {
recyclerView.removeOnLayoutChangeListener(this);
final RecyclerView.LayoutManager layoutManager =
recyclerView.getLayoutManager();
View viewAtPosition =
layoutManager.findViewByPosition(MainActivity.currentPosition);
// Scroll to position if the view for the current position is null (not
// currently part of layout manager children), or it's not completely
// visible.
if (viewAtPosition == null
|| layoutManager.isViewPartiallyVisible(viewAtPosition, false, true)){
recyclerView.post(()
-> layoutManager.scrollToPosition(MainActivity.currentPosition));
}
}
});
Here is the article, and you will also find the project on GitHub.

Android - WebView Fullscreen video not working inside viewpager

Webview Fullscreen video not working in viewpager(fragment):
implemented fullscreen view in webview chromeclient but if click fullscreen button, it shows blank screen but audio playing. after change orientation video will appear.
WebViewFragment.java
mWebView.setWebChromeClient(new WebChromeClient() {
#Override
public void onShowCustomView(View view, CustomViewCallback callback) {
super.onShowCustomView(view, callback);
if(isAdded() && getActivity()!=null) {
DiapromaActivity activity = (DiapromaActivity) getActivity();
activity.showCustomView(view, callback);
}
}
#Override
public void onHideCustomView() {
super.onHideCustomView();
if(isAdded() && getActivity()!=null) {
DiapromaActivity activity = (DiapromaActivity) getActivity();
activity.hideCustomView();
}
}
});
DiapromaActivity.java
public void showCustomView(View view, WebChromeClient.CustomViewCallback callback) {
//If there's already a custom view, this is a duplicate call, and we should
// terminate the new view, then bail out.
if (mCustomView != null) {
callback.onCustomViewHidden();
return;
}
//Create a reusable set of FrameLayout.LayoutParams
FrameLayout.LayoutParams fullscreenParams = new FrameLayout.LayoutParams(FrameLayout.LayoutParams.MATCH_PARENT,
FrameLayout.LayoutParams.MATCH_PARENT);
//Save the drawer view into an instance variable, then hide it.
mContentView = findViewById(R.id.root_view);
mContentView.setVisibility(View.GONE);
//Create a new custom view container
mCustomViewContainer = new FrameLayout(this);
mCustomViewContainer.setLayoutParams(fullscreenParams);
mCustomViewContainer.setBackgroundResource(android.R.color.black);
//Set view to instance variable, then add to container.
mCustomView = view;
view.setLayoutParams(fullscreenParams);
mCustomViewContainer.addView(mCustomView);
mCustomViewContainer.setVisibility(View.VISIBLE);
//Save the callback an instance variable.
mCustomViewCallback = callback;
//Hide the action bar
getSupportActionBar().hide();
isFullScreen=true;
//Set the custom view container as the activity's content view.
setContentView(mCustomViewContainer);
}
/**
* Method to mirror onShowCustomView from the WebChrome client, allowing WebViews in a Fragment
* to hide custom views.
*/
public void hideCustomView() {
if (mCustomView == null) {
//Nothing to hide - return.
return;
} else {
// Hide the custom view.
mCustomView.setVisibility(View.GONE);
// Remove the custom view from its container.
mCustomViewContainer.removeView(mCustomView);
mCustomViewContainer.setVisibility(View.GONE);
mCustomViewCallback.onCustomViewHidden();
mCustomView = null;
// Show the ActionBar
getSupportActionBar().show();
// Show the content view.
mContentView.setVisibility(View.VISIBLE);
setContentView(mContentView);
isFullScreen=false;
}
}

How to modify a single list item after Asynctask is done in a BaseAdapter to

In my main activity I display a ListView which uses a custom BaseAdapter (ThoughtListAdapter).
listView = (ListView) findViewById(R.id.list);
adapter = new ThoughtListAdapter(this, resultingThoughts);
listView.setAdapter(adapter);
Every item in the ListView has a custom layout containing a TextView and two Button.
if (convertView == null) {
convertView = layoutInflater.inflate(R.layout.list_item_thought, null);
}
thoughtText = (TextView) convertView.findViewById(R.id.thought_text_view);
likeButton = (Button) convertView.findViewById(R.id.thought_like_button);
dislikeButton = (Button) convertView.findViewById(R.id.thought_dislike_button);
When a Button is clicked an AsyncTask (AsyncPost) is called which connects to my database and makes some changes.
likeButton.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
System.out.println("LIKE CLICKED");
Thought t = thoughtItems.get(position);
thoughtId = t.getId();
opinion = 1;
AsyncPost asyncPost = new AsyncPost(activity,ThoughtListAdapter.this);
asyncPost.execute(SHARE_THOUGHT_URL,
TAG_PERSON_EMAIL, "m#b.it",
TAG_THOUGHT_ID, thoughtId.toString(),
TAG_OPINION, opinion.toString());
}
});
What I need is making both Button-s of a list item disappear after the AsyncTask is done with a successful outcome. I have a method onComplete(JSONObject json) which elaborates the JSONObject returned by the AsyncTask. I try to make the buttons non visible inside the onComplete method, but this doesn't work because onComplete() doesn't know which exact button has been clicked.
How can I pass an instance of the exact clicked button inside onComplete() and make disappear only the Like and Dislike buttons of the concerned list item?
AsyncPost is a global AsyncTask used by all my other activities. I would strongly prefer to leave it alone. The onComplete() method functions as the onPostExecute() method of the AsyncTask.
Here are the getView() and onComplete() methods inside my BaseAdapter, which contain all the code shown above.
Thank you.
public View getView(final int position, View convertView, ViewGroup parent) {
if (layoutInflater == null) {
layoutInflater = (LayoutInflater) activity.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
}
if (convertView == null) {
convertView = layoutInflater.inflate(R.layout.list_item_thought, null);
}
thoughtText = (TextView) convertView.findViewById(R.id.thought_text_view);
likeButton = (Button) convertView.findViewById(R.id.thought_like_button);
dislikeButton = (Button) convertView.findViewById(R.id.thought_dislike_button);
//thoughtItems is a list of custom ojbects (Thought)
Thought t = thoughtItems.get(position);
//Here i set the content of the current TextView
thoughtText.setText(t.getText());
//the two buttons do basically the same thing when get clicked
likeButton.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
Thought t = thoughtItems.get(position);
thoughtId = t.getId();
opinion = 1;
AsyncPost asyncPost = new AsyncPost(activity,ThoughtListAdapter.this);
asyncPost.execute(SHARE_THOUGHT_URL,
TAG_PERSON_EMAIL, "m#b.it",
TAG_THOUGHT_ID, thoughtId.toString(),
TAG_OPINION, opinion.toString());
}
});
dislikeButton.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
Thought t = thoughtItems.get(position);
thoughtId = t.getId();
opinion = 0;
AsyncPost asyncPost = new AsyncPost(activity,ThoughtListAdapter.this);
asyncPost.execute(SHARE_THOUGHT_URL,
TAG_PERSON_EMAIL, "m#b.it",
TAG_THOUGHT_ID, thoughtId.toString(),
TAG_OPINION, opinion.toString());
}
});
return convertView;
}
#Override
public void onComplete(JSONObject json) {
if (json != null) {
try {
if (json.getInt(TAG_SUCCESS) == 0) {
Toast.makeText(activity, "Operazione non riuscita.", Toast.LENGTH_LONG).show();
} else {
//if everything is good i try to make the buttons of that particular list item disappear
likeButton.setVisibility(View.GONE);
dislikeButton.setVisibility(View.GONE);
}
}
catch (JSONException e) {
Log.e(TAG_LOG, "JSONException", e);
}
}
else Toast.makeText(activity, "Errore connessione!", Toast.LENGTH_LONG).show();
}

One solution to this would be to have something on your Thought object to indicate whether or not to show the buttons.
So in your getView() method you check this
likeButton = (Button) convertView.findViewById(R.id.thought_like_button);
dislikeButton = (Button) convertView.findViewById(R.id.thought_dislike_button);
Thought t = thoughtItems.get(position);
if (t.hideButtons()) {
likeButton.setVisibility(View.GONE);
dislikeButton.setVisibility(View.GONE);
}
else {
likeButton.setVisibility(View.VISIBLE);
dislikeButton.setVisibility(View.VISIBLE);
}
Then you would need to have your onComplete method return the id of the Thought object that it related to. Then inside your onComplete you could do
int id = //get your id from your JSON response
for(Thought t : thoughtItems) {
if (t.getId() == id) {
t.setHideButtons(true);
notifyDataSetChanged();
break;
}
}
By calling notifyDataSetChanged() it will redraw your list and when it does the check for whether it should show the buttons or not it will not show them because it was set on that thought item

How can I show a button when all views are viewed in viewpager?

Right now I have a save button that I want to show only if all the views inside a viewpager are shown. That means that when the user swipes between views and have seen all views inside a viewpager, then show a save button.
I want to show the save button on every view when they have seen all views hereby after.
The trouble I am having is how to set up the logic. I started out with setting the save button invisible until the last view of the viewpager. On the last view of the viewpager, show the save button. But the problem is when the user goes to the last view (there's a save button) and then goes back to a previous view, the save button is gone.
So, I was wondering how can I show the save button permanently on all views after the user has seen all views?
Here's what I have so far:
I have this snippet inside my InstantiateItem() :
if(isViewed)
{
save_button.setVisibility(Button.VISIBLE);
System.out.println("Is this called? isViewed = true");
}else if (position == numberOfPages.size()-1) {
isViewed = true;
save_button.setVisibility(Button.VISIBLE);
}
where
#Override
public void onPageSelected(int position) {
isViewed = true;
}
EDIT:
I tried the following solutions but with no luck.
Button save_button = (Button) findViewById(R.id.save);
if(isViewed[position])
{
save_button.setVisibility(Button.VISIBLE);
}
if (position == numberOfPages.length-1 && !isViewed[position]) {
isViewed[position] = true;
save_button.setVisibility(Button.VISIBLE);
}
isViewed[position] =true;
And
isViewed[position] = true;
if (isViewed[position] == isViewed[numberOfPages.length-1]) {
save_button.setVisibility(Button.VISIBLE);
}
if (isViewed[position]) {
save_button.setVisibility(Button.VISIBLE);
} else {
save_button.setVisibility(Button.INVISIBLE);
}

In your onPageSelected, do the following
if(isViewed)
{
save_button.setVisibility(Button.VISIBLE);
}
if (position == numberOfPages.size()-1) {
isViewed = true;
save_button.setVisibility(Button.VISIBLE);
}
Note the above are two seperate if statements.
Make your isViewed global and default to false.

boolean []isViewed = new boolean[noOfPages.size()];
#Override
public void onPageSelected(int position) {
if(isViewed[position])
{
save_button.setVisibility(Button.VISIBLE);
}
else {
save_button.setVisibility(Button.GONE);
}
isViewed[position] = true;
}