DRAG AND DROP

MainActivity.java

package com.furq.dragableimagecollage;

import android.animation.Animator;
import android.animation.AnimatorListenerAdapter;
import android.animation.ValueAnimator;
import android.graphics.Rect;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.widget.GridLayout;
import android.view.DragEvent;
import android.view.LayoutInflater;
import android.view.View;
import android.view.animation.OvershootInterpolator;
import android.widget.ScrollView;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity {

    private static final int ITEMS = 10;
    private GridLayout mGrid;
    private ScrollView mScrollView;
    private ValueAnimator mAnimator;
    private Boolean isScroll = false;

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

        mScrollView = (ScrollView)findViewById(R.id.scrollView);
        mScrollView.setSmoothScrollingEnabled(true);

        mGrid = (GridLayout) findViewById(R.id.grid);

        mGrid.setOnDragListener(new DragListener());

        final LayoutInflater inflater = LayoutInflater.from(this);
        for (int i = 0; i < ITEMS; i++) {
            final View itemView = inflater.inflate(R.layout.item, mGrid, false);
            final TextView text = (TextView) itemView.findViewById(R.id.text);
            text.setText(String.valueOf(i + 1));
            itemView.setOnLongClickListener(new LongPressListener());
            mGrid.addView(itemView);
        }
    }

    class DragListener implements View.OnDragListener {
        @Override
        public boolean onDrag(View v, DragEvent event) {
            final View view = (View) event.getLocalState();
            switch (event.getAction()) {
                case DragEvent.ACTION_DRAG_LOCATION:
                    if (view == v) return true;
                    // get the new list index
                    final int index = calculateNextIndex(event.getX(), event.getY());

                    final Rect rect = new Rect();
                    mScrollView.getHitRect(rect);
                    final int scrollY = mScrollView.getScrollY();

                    if (event.getY() -  scrollY > mScrollView.getBottom() - 250) {
                        startScrolling(scrollY, mGrid.getHeight());
                    } else if (event.getY() - scrollY < mScrollView.getTop() + 250) {
                        startScrolling(scrollY, 0);
                    } else {
                        stopScrolling();
                    }

                    // remove the view from the old position
                    mGrid.removeView(view);
                    //add new view
                    mGrid.addView(view, index);
                    break;
                case DragEvent.ACTION_DROP:
                    view.setVisibility(View.VISIBLE);
                    break;
                case DragEvent.ACTION_DRAG_ENDED:
                    if (!event.getResult()) {
                        view.setVisibility(View.VISIBLE);
                    }
                    break;
            }
            return true;
        }
    }

    private void startScrolling(int from, int to) {
        if (from != to && mAnimator == null) {
            isScroll=true;
            mAnimator = new ValueAnimator();
            mAnimator.setInterpolator(new OvershootInterpolator());
            mAnimator.setDuration(Math.abs(to - from));
            mAnimator.setIntValues(from, to);
            mAnimator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
                @Override
                public void onAnimationUpdate(ValueAnimator valueAnimator) {
                    mScrollView.smoothScrollTo(0, (int) valueAnimator.getAnimatedValue());
                }
            });
            mAnimator.addListener(new AnimatorListenerAdapter() {
                @Override
                public void onAnimationEnd(Animator animation) {
                    isScroll=false;
                    mAnimator = null;
                }
            });
            mAnimator.start();
        }
    }

    private void stopScrolling() {
        if (mAnimator != null) {
            mAnimator.cancel();
        }
    }

    private int calculateNextIndex(float x, float y) {
        // calculate which column to move to
        final float cellWidth = mGrid.getWidth() / mGrid.getColumnCount();
        final int column = (int)(x / cellWidth);

        final float cellHeight = mGrid.getHeight() / mGrid.getRowCount();
        final int row = (int)Math.floor(y / cellHeight);

        int index = row * mGrid.getColumnCount() + column;
        if (index >= mGrid.getChildCount()) {
            index = mGrid.getChildCount() - 1;
        }

        return index;
    }
}

Hi Furq, Can i get complete source of this proj ?