How to Get PagerAdapter item Id for Horizontal ViewPager?

Question

I have implemented Horizontal ViewPager with Custom PagerAdapter like attached in screen. What I'm trying to achieve is to get Id of First item from list . Here is code code for everything till now .

PagerAdapter:

private static final String TAG = ViewPagerAdapter.class.getSimpleName();
private Context context;
private LayoutInflater layoutInflater;
private ArrayList<QuickActionItem> quickActionItems;

public ViewPagerAdapter(Context context, ArrayList<QuickActionItem> items) {
    this.context = context;
    this.quickActionItems = items;   
}

@Override
public float getPageWidth(int position) {
    return 0.25f;
}

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

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

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

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

    View view = layoutInflater.inflate(R.layout.item_page_slide, null);

    ImageView actionImage = view.findViewById(R.id.img_action);

    TextView actionText = view.findViewById(R.id.title_action_value);
actionImage.setImageResource(quickActionItems.get(position).getActionDrawableImage());

    actionText.setText(quickActionItems.get(position).getActionName());

    ViewPager vp = (ViewPager) container;
    vp.addView(view, 0);

    view.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View view) {

            if (quickActionItems.get(position).getActionName().equals(context.getString(R.string.quick_add_property))) {
                Log.d(TAG, "Add Property ");


            } else if (quickActionItems.get(position).getActionName().equals(context.getString(R.string.quick_add_tenant))) {
                Log.d(TAG, "Add Tenant ");

                context.startActivity(targetIntent);
            } else if (quickActionItems.get(position).getActionName().equals(context.getString(R.string.quick_add_income))) {
                Log.d(TAG, "Add Income ");

                context.startActivity(targetIntent);
            } else if (quickActionItems.get(position).getActionName().equals(context.getString(R.string.quick_add_expense))) {
                Log.d(TAG, "Add Expense ");

            }

        }
    });

    return view;
}


@Override
public void destroyItem(ViewGroup container, int position, Object object) {

      ViewPager vp = (ViewPager) container;
      View view = (View) object;
      vp.removeView(view);
     }
   }

QuickActionItem

public class QuickActionItem {

    private String actionName;
    private int actionDrawableImage;
}

MainFragment

    quickActionPager = fragmentView.findViewById(R.id.quick_actions_pager);
    sliderDotsPanel = fragmentView.findViewById(R.id.SliderDots);

    quickActionItems = new ArrayList<>();
    quickActionItems.add(new QuickActionItem(getString(R.string.quick_add_property), R.drawable.ic_add_property));
    quickActionItems.add(new QuickActionItem(getString(R.string.quick_add_tenant), R.drawable.ic_add_tenant));
    quickActionItems.add(new QuickActionItem(getString(R.string.quick_add_income), R.drawable.ic_add_income));
    quickActionItems.add(new QuickActionItem(getString(R.string.quick_add_expense), R.drawable.ic_add_expense));


    viewPagerAdapter = new ViewPagerAdapter(getActivity(), quickActionItems);
    quickActionPager.setAdapter(viewPagerAdapter);

I'm sharing only necessary part of code for MainFragment as it's very long & regardless of what I want to achieve.

Questions:

1) Is it possible that first Item get any sort of ID or not ? In my case Id for "Add Property" item

2) If possible then how to get that Id & Will I able to call findViewById on that ?

Also let me know if you need any other information or code.

Any help would be appreciated.

Answer 1

Try the following:

So, You need to get the layout of a certain page inside a viewPager and then, use findViewById() to get the layout views. You can achieve that by putting every inflated layout in instantiateItem() inside a TreeMap and removing a layout from the TreeMap when destroyed in destroyItem(). Then you can get a certain page layout by using treeMap.get(position) Below is an example:

MainActivty.class

public class MainActivity extends AppCompatActivity {

private final String TAG = MainActivity.class.getSimpleName();
private ViewPager vp;
private ViewPagerAdapter viewPagerAdapter = null;
private Button b;
private List<String> data = new ArrayList<>();
private List<Integer> color = new ArrayList<>();

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    vp = (ViewPager) findViewById(R.id.vp);

    b = (Button) findViewById(R.id.b);
    b.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            /**
             * use viewPagerAdapter.getLayout(int position) to get the layout for a certain page
             * then use findViewById() to get a certain view inside that layout
             */
            View layout = viewPagerAdapter.getLayout(vp.getCurrentItem());
            if (layout != null) {
                TextView tv = (TextView) layout.findViewById(R.id.tv);
                tv.setTextColor(color.get(vp.getCurrentItem()));
            }
        }
    });
    color.add(Color.RED);

    color.add(Color.GRAY);
    color.add(Color.BLUE);
    color.add(Color.YELLOW);
    color.add(Color.MAGENTA);
    color.add(Color.CYAN);
    color.add(Color.LTGRAY);
    color.add(Color.DKGRAY);
    for(int i=0; i<8; i++){
        data.add("Page " + (i+1));
    }
    viewPagerAdapter = new ViewPagerAdapter(MainActivity.this, data);
    vp.setAdapter(viewPagerAdapter);
}

}

ViewPagerAdapter.class

public class ViewPagerAdapter extends PagerAdapter {

private static final String TAG = ViewPagerAdapter.class.getSimpleName();
private Context context;
private LayoutInflater layoutInflater;
private List<String> data;
private TreeMap<Integer, View> layout;

public ViewPagerAdapter(Context context, List<String> data) {
    this.context = context;
    this.data = data;
    this.layout = new TreeMap<>();
}

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

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

@Override
@NonNull
public Object instantiateItem(@NonNull final ViewGroup container, final int position) {
    layoutInflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    View view = layoutInflater.inflate(R.layout.page_item, container, false);
    TextView tv = (TextView) view.findViewById(R.id.tv);
    tv.setText(data.get(position));
    /**
     * put the inflated layout inside TreeMap with key being the position
     */
    this.layout.put(position, view);
    container.addView(view);
    return view;
}


@Override
public void destroyItem(@NonNull ViewGroup container, int position, @NonNull Object object) {
    ViewPager vp = (ViewPager) container;
    View view = (View) object;
    /**
     * remove a layout with key position
     */
    this.layout.remove(position);
    vp.removeView(view);
}

/**
 * used to get a layout
 * @return TreeMap
 */
public TreeMap<Integer, View> getLayout() {
    return this.layout;
}

/**
 *
 * @param position
 * @return View at position
 */
public View getLayout(int position) {
    return this.layout.get(position);
}


}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:weightSum="100"
android:orientation="vertical">

<android.support.v4.view.ViewPager
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:layout_weight="80"
    android:id="@+id/vp">
</android.support.v4.view.ViewPager>

<Button
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:id="@+id/b"
    android:layout_weight="20"
    android:text="Change Text View Color">
</Button>

</LinearLayout>

page_item.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="match_parent"
android:id="@+id/ll"
android:layout_marginStart="20dp"
android:layout_marginRight="20dp"
android:layout_marginLeft="20dp"
android:layout_marginEnd="20dp"
android:layout_marginTop="20dp"
android:layout_marginBottom="20dp"
android:background="@color/colorAccent"
android:layout_height="match_parent">

<TextView
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:id="@+id/tv"
    android:gravity="center"
    android:layout_gravity="center"
    android:textSize="24sp"
    android:textColor="@android:color/black">
</TextView>

</LinearLayout>