How to syncronisize two Listview positions

Question

I have two ListViews. Is there any way to synchronize the position of ListViews when I scroll any one of the Lists. Im implementing an AbsListView.OnScrollListener, registering to the ListView. When the ListView is scrolled, the onScroll() method of OnScrollListener will be triggered, then i call `smoothScrollToPosition()'. But it doent work properly. Can someone provide me any code example for this?

Answer 1

If the position is visible smoothScrollToPosition() won't scroll. You can thought use scrollTo or scrollBy on the other list that is not scrolling at the moment, but be careful to not enter a recursion with each list calling the other to scroll.

Answer 2

Here is a working code sample of what nininho is suggesting

MainActivity

public class MainActivity extends Activity {

public static String[] Cheeses = new String[] { "Abbaye de Belloc", "Abbaye du Mont des Cats",
        "Abertam", "Abondance", "Ackawi", "Acorn", "Adelost", "Affidelice au Chablis",
        "Afuega'l Pitu", "Airag", "Airedale", "Aisy Cendre", "Allgauer Emmentaler", "Alverca",
        "Ambert", "American Cheese", };

ListView list1;
ListView list2;

boolean isLeftListEnabled = true;
boolean isRightListEnabled = true;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    ListAdapter adapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1,
            Cheeses);

    list1 = (ListView) findViewById(R.id.list1);
    list1.setAdapter(adapter);

    list2 = (ListView) findViewById(R.id.list2);
    list2.setAdapter(adapter);

    // IF YOU DO NOT OVERRIDE THIS
    // ONLY THE ONE THAT IS TOUCHED WILL SCROLL OVER
    list1.setOverScrollMode(ListView.OVER_SCROLL_NEVER);
    list2.setOverScrollMode(ListView.OVER_SCROLL_NEVER);

    list1.setOnScrollListener(new OnScrollListener() {

        @Override
        public void onScrollStateChanged(AbsListView view, int scrollState) {
            // onScroll will be called and there will be an infinite loop.
            // That's why i set a boolean value
            if (scrollState == SCROLL_STATE_TOUCH_SCROLL) {
                isRightListEnabled = false;
            } else if (scrollState == SCROLL_STATE_IDLE) {
                isRightListEnabled = true;
            }
        }

        @Override
        public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount,
                int totalItemCount) {
            View c = view.getChildAt(0);
            if (c != null && isLeftListEnabled) {
                list2.setSelectionFromTop(firstVisibleItem, c.getTop());
            }
        }
    });

    list2.setOnScrollListener(new OnScrollListener() {
        @Override
        public void onScrollStateChanged(AbsListView view, int scrollState) {
            if (scrollState == SCROLL_STATE_TOUCH_SCROLL) {
                isLeftListEnabled = false;
            } else if (scrollState == SCROLL_STATE_IDLE) {
                isLeftListEnabled = true;
            }
        }

        @Override
        public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount,
                int totalItemCount) {
            View c = view.getChildAt(0);
            if (c != null && isRightListEnabled) {
                list1.setSelectionFromTop(firstVisibleItem, c.getTop());
            }
        }
    });
}
}

the XML

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="match_parent">

<LinearLayout
    android:orientation="horizontal"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:splitMotionEvents="true">
    <ListView android:id="@+id/list1"
              android:layout_width="0dip"
              android:layout_height="match_parent"
              android:layout_weight="1" />
    <ListView android:id="@+id/list2"
              android:layout_width="0dip"
              android:layout_height="match_parent"
              android:layout_weight="1" />
</LinearLayout>