ListView Items in Android Scroll one at a Time

Question

Is there any way in which we scroll ListView items only one at a time. Like when you swipe up it'll only scroll One item up and not normal scroll similar for scroll down only one item shifts down.

Please Help!

Here is My Code :

public class ListViewTestExample extends Activity {

    ListView listView;

    private GestureDetectorCompat mDetector;

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

        mDetector = new GestureDetectorCompat(this, new MyGestureListener());
        // Grid ListView object from XML
        listView = (ListView) findViewById(R.id.list);

        mDetector = new GestureDetectorCompat(this, new MyGestureListener());
        // Defined Array values to show in ListView

        String[] values = new String[] { "Android List View",
         "Adapter implementation", "Simple List View In Android",
         "Create List View Android", "Android Example",
         "List View Source Code", "List View Array Adapter",
         "Android Example List View" };

         ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,
         android.R.layout.simple_list_item_1, android.R.id.text1, values);

         listView.setAdapter(adapter);       
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    public boolean onTouchEvent(MotionEvent event) {
        this.mDetector.onTouchEvent(event);
        return super.onTouchEvent(event);
    }

    class MyGestureListener extends GestureDetector.SimpleOnGestureListener {
        Context context = getApplicationContext();

        public boolean onDown(MotionEvent event) {
                return true;
        }

        public void onLongPress(MotionEvent event) {
            Toast.makeText(context, "Long Press", Toast.LENGTH_SHORT).show();
        }

        public boolean onFling(MotionEvent event1, MotionEvent event2,
                float velocityX, float velocityY) {

            float sensitvity = 50;

            // TODO Auto-generated method stub
            if ((event1.getX() - event2.getX()) > sensitvity) {
                Toast.makeText(context, "Swipe Left", Toast.LENGTH_SHORT)
                    .show();
            } else if ((event2.getX() - event1.getX()) > sensitvity) {
                Toast.makeText(context, "Swipe Right", Toast.LENGTH_SHORT)
                    .show();
            }
            if ((event1.getY() - event2.getY()) > sensitvity) {
                if (event2.getPressure() > event1.getPressure()) {
                    Toast.makeText(context, "Swipe Up + Hold",
                            Toast.LENGTH_SHORT).show();
                } else {
                    Toast.makeText(context, "Swipe Up", Toast.LENGTH_SHORT).show();
                }
            } else if ((event2.getY() - event1.getY()) > sensitvity) {
                if (event2.getPressure() > event1.getPressure()) {
                    Toast.makeText(context, "Swipe Down + Hold",
                        Toast.LENGTH_SHORT).show();
                } else {
                    Toast.makeText(context, "Swipe Down", Toast.LENGTH_SHORT).show();
                }
            }
            return true;
        }

        public boolean onSingleTapConfirmed(MotionEvent event) {
            Toast.makeText(context, "Single Tap Confirmed", Toast.LENGTH_SHORT)
                .show();
            return true;
        }

        public boolean onDoubleTap(MotionEvent event) {
            Toast.makeText(context, "Double Tap Confirmed", Toast.LENGTH_SHORT).show();
            return true;
        }

    }

}

Answer 1

I know this is now an old post, but I have searched the net and not really found a solution to this. So I have found a solution that works for me. You need to make a custom ListView and override the dispatchTouchEvent function. My version checks to see if the user has flicked with a min velocity and if they have then smooth scroll to the next item. If under this velocity then check to see if the item is over half way then do a smooth scroll. Otherwise return to the current item. This code assumes that the item fills the view.

import android.content.Context;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.VelocityTracker;
import android.view.View;
import android.widget.ListView;

/**
 * Created by bradj on 11/12/13.
 */
public class SingleScrollListView extends ListView
{
    private boolean mSingleScroll = false;
    private VelocityTracker mVelocity = null;
    final private float mEscapeVelocity = 2000.0f;
    final private int mMinDistanceMoved = 20;
    private float mStartY = 0;

    public SingleScrollListView(Context context)
    {
        super(context);
    }

    public SingleScrollListView(Context context, AttributeSet attrs)
    {
        super(context, attrs);
    }

    public SingleScrollListView(Context context, AttributeSet attrs, int defStyle)
    {
        super(context, attrs, defStyle);
    }

    public void setSingleScroll(boolean aSingleScroll) { mSingleScroll = aSingleScroll; }
    public int getVerticalScrollOffset() { return getFirstVisiblePosition(); }

    @Override
    public boolean dispatchTouchEvent(MotionEvent aMotionEvent)
    {
        if (aMotionEvent.getAction() == MotionEvent.ACTION_DOWN)
        {
            if (mSingleScroll && mVelocity == null)
                mVelocity = VelocityTracker.obtain();
            mStartY = aMotionEvent.getY();
            return super.dispatchTouchEvent(aMotionEvent);
        }

        if (aMotionEvent.getAction() == MotionEvent.ACTION_UP)
        {
            if (mVelocity != null)
            {
                if (Math.abs(aMotionEvent.getY() - mStartY) > mMinDistanceMoved)
                {
                    mVelocity.computeCurrentVelocity(1000);
                    float velocity = mVelocity.getYVelocity();

                    if (aMotionEvent.getY() > mStartY)
                    {
                        // always lock
                        if (velocity > mEscapeVelocity)
                            smoothScrollToPosition(getFirstVisiblePosition());
                        else
                        {
                            // lock if over half way there
                            View view = getChildAt(0);
                            if (view != null)
                            {
                                if (view.getBottom() >= getHeight() / 2)
                                    smoothScrollToPosition(getFirstVisiblePosition());
                                else
                                    smoothScrollToPosition(getLastVisiblePosition());
                            }
                        }
                    }
                    else
                    {
                        if (velocity < -mEscapeVelocity)
                            smoothScrollToPosition(getLastVisiblePosition());
                        else
                        {
                            // lock if over half way there
                            View view = getChildAt(1);
                            if (view != null)
                            {
                                if (view.getTop() <= getHeight() / 2)
                                    smoothScrollToPosition(getLastVisiblePosition());
                                else
                                    smoothScrollToPosition(getFirstVisiblePosition());
                            }
                        }
                    }
                }
                mVelocity.recycle();
            }
            mVelocity = null;

            if (mSingleScroll)
            {
                if (Math.abs(aMotionEvent.getY() - mStartY) > mMinDistanceMoved)
                    return super.dispatchTouchEvent(aMotionEvent);
            }
            else
                return super.dispatchTouchEvent(aMotionEvent);
        }

        if (mSingleScroll)
        {
            if (mVelocity == null)
            {
                mVelocity = VelocityTracker.obtain();
                mStartY = aMotionEvent.getY();
            }
            mVelocity.addMovement(aMotionEvent);
        }

        return super.dispatchTouchEvent(aMotionEvent);
    }
}

So the code simple becomes as below. (Don't forget to change the ListView in the xml to SingleScrollListView) There is no need for a gesture listener.

listView = (SingleScrollListView) findViewById(R.id.list);
listView.setSingleScroll(true);