DragNDropListView.java

package com.pinecone.technology.mcommerce.learning.android.chapter09.draganddrop;

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.PixelFormat;
import android.util.AttributeSet;
import android.view.GestureDetector;
import android.view.Gravity;
import android.view.MotionEvent;
import android.view.View;
import android.view.WindowManager;
import android.widget.ImageView;
import android.widget.ListView;

public class DragNDropListView extends ListView {

	boolean mDragMode;

	int mStartPosition;
	int mEndPosition;
	int mDragPointOffset; // Used to adjust drag view location

	ImageView mDragView;
	GestureDetector mGestureDetector;

	DropListener mDropListener;
	RemoveListener mRemoveListener;
	DragListener mDragListener;

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

	public void setDropListener(DropListener l) {
		mDropListener = l;
	}

	public void setRemoveListener(RemoveListener l) {
		mRemoveListener = l;
	}

	public void setDragListener(DragListener l) {
		mDragListener = l;
	}

	@Override
	public boolean onTouchEvent(MotionEvent ev) {
		final int action = ev.getAction();
		final int x = (int) ev.getX();
		final int y = (int) ev.getY();

		if (action == MotionEvent.ACTION_DOWN && x < this.getWidth() / 4) {
			mDragMode = true;
		}

		if (!mDragMode)
			return super.onTouchEvent(ev);

		switch (action) {
		case MotionEvent.ACTION_DOWN:
			mStartPosition = pointToPosition(x, y);
			if (mStartPosition != INVALID_POSITION) {
				int mItemPosition = mStartPosition - getFirstVisiblePosition();
				mDragPointOffset = y - getChildAt(mItemPosition).getTop();
				mDragPointOffset -= ((int) ev.getRawY()) - y;
				startDrag(mItemPosition, y);
				drag(0, y);// replace 0 with x if desired
			}
			break;
		case MotionEvent.ACTION_MOVE:
			drag(0, y);// replace 0 with x if desired
			break;
		case MotionEvent.ACTION_CANCEL:
		case MotionEvent.ACTION_UP:
		default:
			mDragMode = false;
			mEndPosition = pointToPosition(x, y);
			stopDrag(mStartPosition - getFirstVisiblePosition());
			if (mDropListener != null && mStartPosition != INVALID_POSITION
					&& mEndPosition != INVALID_POSITION)
				mDropListener.onDrop(mStartPosition, mEndPosition);
			break;
		}
		return true;
	}

	// move the drag view
	private void drag(int x, int y) {
		if (mDragView != null) {
			WindowManager.LayoutParams layoutParams = (WindowManager.LayoutParams) mDragView
					.getLayoutParams();
			layoutParams.x = x;
			layoutParams.y = y - mDragPointOffset;
			WindowManager mWindowManager = (WindowManager) getContext()
					.getSystemService(Context.WINDOW_SERVICE);
			mWindowManager.updateViewLayout(mDragView, layoutParams);

			if (mDragListener != null)
				mDragListener.onDrag(x, y, null);// change null to "this" when
													// ready to use
		}
	}

	// enable the drag view for dragging
	private void startDrag(int itemIndex, int y) {
		stopDrag(itemIndex);

		View item = getChildAt(itemIndex);
		if (item == null)
			return;
		item.setDrawingCacheEnabled(true);
		if (mDragListener != null)
			mDragListener.onStartDrag(item);

		// Create a copy of the drawing cache so that it does not get recycled
		// by the framework when the list tries to clean up memory
		Bitmap bitmap = Bitmap.createBitmap(item.getDrawingCache());

		WindowManager.LayoutParams mWindowParams = new WindowManager.LayoutParams();
		mWindowParams.gravity = Gravity.TOP;
		mWindowParams.x = 0;
		mWindowParams.y = y - mDragPointOffset;

		mWindowParams.height = WindowManager.LayoutParams.WRAP_CONTENT;
		mWindowParams.width = WindowManager.LayoutParams.WRAP_CONTENT;
		mWindowParams.flags = WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE
				| WindowManager.LayoutParams.FLAG_NOT_TOUCHABLE
				| WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON
				| WindowManager.LayoutParams.FLAG_LAYOUT_IN_SCREEN
				| WindowManager.LayoutParams.FLAG_LAYOUT_NO_LIMITS;
		mWindowParams.format = PixelFormat.TRANSLUCENT;
		mWindowParams.windowAnimations = 0;

		Context context = getContext();
		ImageView v = new ImageView(context);
		v.setImageBitmap(bitmap);

		WindowManager mWindowManager = (WindowManager) context
				.getSystemService(Context.WINDOW_SERVICE);
		mWindowManager.addView(v, mWindowParams);
		mDragView = v;
	}

	// destroy drag view
	private void stopDrag(int itemIndex) {
		if (mDragView != null) {
			if (mDragListener != null)
				mDragListener.onStopDrag(getChildAt(itemIndex));
			mDragView.setVisibility(GONE);
			WindowManager wm = (WindowManager) getContext().getSystemService(
					Context.WINDOW_SERVICE);
			wm.removeView(mDragView);
			mDragView.setImageDrawable(null);
			mDragView = null;
		}
	}

}