SwipeListItemWrapper.java

/*
 * Copyright (C) 2009 Android Shuffle Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.dodgybits.shuffle.android.list.view;

import android.R;
import android.content.Context;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.widget.AdapterView;
import android.widget.FrameLayout;
import android.widget.ListView;

public class SwipeListItemWrapper extends FrameLayout {
    private static final String cTag = "SwipeListItemWrapper";

	private int mStartX;
	private int mStartY;
	private SwipeListItemListener mListener;
	private int mPosition;
	
	public SwipeListItemWrapper(Context context) {
		super(context);
	}

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

	public SwipeListItemWrapper(Context context, AttributeSet attrs, int defStyle) {
		super(context, attrs, defStyle);
	}
	
    @Override
    public boolean onInterceptTouchEvent(MotionEvent ev) {
        final int action = ev.getAction();
        
        final int x = (int)ev.getX(); 
        final int y = (int)ev.getY();

        boolean stealEvent = false;
        
        switch (action) {
            case MotionEvent.ACTION_MOVE:
                Log.d(cTag, "move event");
                if (isValidSwipe(x, y)) {
                	stealEvent = true;
                }
                break;

            case MotionEvent.ACTION_DOWN:
                Log.d(cTag, "down event");
                mStartX = x;
                mStartY = y;
                break;

            case MotionEvent.ACTION_CANCEL:
                Log.d(cTag, "cancel event");
                mPosition = AdapterView.INVALID_POSITION;
            	// some parent component has stolen the event
            	// nothing to do
            	break;
            	
            case MotionEvent.ACTION_UP:
                Log.d(cTag, "up event");
                break;
        }

        return stealEvent;
    }	
	
	@Override
	public boolean onTouchEvent(MotionEvent event) {
		if (event.getAction() == MotionEvent.ACTION_UP) {
			// we've got a valid swipe event. Notify the listener (if any)
			
			if (mPosition != AdapterView.INVALID_POSITION && mListener != null) {
				mListener.onListItemSwiped(mPosition);
			}
		}
		return true;
	}
	
	public void setSwipeListItemListener(SwipeListItemListener listener) {
		mListener = listener;
	}

	/**
	 * Check if this appears to be a swipe event.
	 * 
	 * Consider it a swipe if it traverses at least a third of the screen, 
	 * and is mostly horizontal.
	 */
	private boolean isValidSwipe(final int x, final int y) {
		final int screenWidth = getWidth();
		final int xDiff = Math.abs(x - mStartX);
		final int yDiff = Math.abs(y - mStartY);
		boolean horizontalValid = xDiff >= (screenWidth / 3);
		boolean verticalValid = yDiff > 0 && (xDiff / yDiff) > 4;

		mPosition = AdapterView.INVALID_POSITION;
		if (horizontalValid && verticalValid) {
			ListView list = (ListView) findViewById(R.id.list);
			if (list != null) {
				// adjust for list not being at top of screen
				mPosition = list.pointToPosition(mStartX, mStartY - list.getTop());
			}
		}
		
		Log.d(cTag, "isValidSwipe hValid=" + horizontalValid + 
				" vValid=" + verticalValid + " position=" + mPosition);
        
		return horizontalValid && verticalValid;
	}

}