Indicated HorizontalScrollView

IndicatedHorizontalScrollView.java

/*
	Copyright 2014 Demon Developers Ltd. All rights reserved.
	
	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.
*/

import android.content.Context;
import android.content.res.TypedArray;
import android.graphics.Canvas;
import android.graphics.Rect;
import android.graphics.drawable.Drawable;
import android.util.AttributeSet;
import android.view.Gravity;
import android.view.MotionEvent;
import android.view.SoundEffectConstants;
import android.view.View;
import android.view.ViewGroup;
import android.widget.HorizontalScrollView;


/**
 * <b>Indicated HorizontalScrollView</b>
 * 
 * <p>
 * Use it directly in your layout just like a {@link HorizontalScrollView}.
 * 
 * <p>
 * Just add these two extra attributes and point them at your drawables:
 *     android:drawableLeft="@drawable/indicator_left"
 *     android:drawableRight="@drawable/indicator_right"
 * 
 * 
 * @author Simon Lightfoot <simon@demondevelopers.com>
 *
 */
public class IndicatedHorizontalScrollView extends HorizontalScrollView
{
	private static final int[] INDICATOR_ATTRS = {
		android.R.attr.drawableLeft,
		android.R.attr.drawableRight
	};
	
	private static final int[] PRESSED_STATE = {
		android.R.attr.state_pressed
	};
	
	private static final int LEFT        = 0;
	private static final int RIGHT       = 1;
	
	private final Drawable[] mIndicator  = new Drawable[2];
	private final boolean[]  mEnabled    = new boolean[2];
	private final Rect       mContainer  = new Rect();
	private final Rect       mBounds     = new Rect();
	
	private boolean mPressed = false;
	
	
	public IndicatedHorizontalScrollView(Context context)
	{
		super(context);
		initView(context, null);
	}
	
	public IndicatedHorizontalScrollView(Context context, AttributeSet attrs)
	{
		super(context, attrs);
		initView(context, attrs);
	}
	
	public IndicatedHorizontalScrollView(Context context, AttributeSet attrs, int defStyle)
	{
		super(context, attrs, defStyle);
		initView(context, attrs);
	}
	
	protected void initView(Context context, AttributeSet attrs)
	{
		setWillNotDraw(false);
		TypedArray a = context.obtainStyledAttributes(attrs, INDICATOR_ATTRS);
		setIndicatorDrawable(LEFT,  a.getDrawable(LEFT));
		setIndicatorDrawable(RIGHT, a.getDrawable(RIGHT));
		a.recycle();
	}
	
	public void setIndicatorDrawable(int indicator, Drawable drawable)
	{
		Drawable old = mIndicator[indicator];
		if(old != null){
			old.setCallback(null);
		}
		mIndicator[indicator] = drawable;
		if(mEnabled[indicator] = (drawable != null)){
			drawable.setCallback(this);
			drawable.setState(null);
		}
	}
	
	protected void onClickIndicator(int indicator)
	{
		View child = findChildForScroll(indicator == LEFT ? 
			View.FOCUS_LEFT : View.FOCUS_RIGHT);
		if(child != null){
			scrollToChild(child);
		}
		playSoundEffect(indicator == LEFT ? 
			SoundEffectConstants.NAVIGATION_LEFT : 
			SoundEffectConstants.NAVIGATION_RIGHT);
	}
	
	@Override
	protected void onScrollChanged(int l, int t, int oldl, int oldt)
	{
		super.onScrollChanged(l, t, oldl, oldt);
		updateIndicators();
	}
	
	@Override
	protected void onLayout(boolean changed, int l, int t, int r, int b)
	{
		super.onLayout(changed, l, t, r, b);
		updateIndicators();
	}
	
	private void updateIndicators()
	{
		mEnabled[LEFT]  = (mIndicator[LEFT]  != null) && canScrollHorizontally(-1);
		mEnabled[RIGHT] = (mIndicator[RIGHT] != null) && canScrollHorizontally( 1);
		
		getDrawingRect(mContainer);
		
		if(mIndicator[LEFT] != null){
			Gravity.apply(Gravity.LEFT | Gravity.CENTER_VERTICAL, 
				mIndicator[LEFT].getIntrinsicWidth(),
				mIndicator[LEFT].getIntrinsicHeight(), 
				mContainer, mBounds);
			mIndicator[LEFT].setBounds(mBounds);
		}
		
		if(mIndicator[RIGHT] != null){
			Gravity.apply(Gravity.RIGHT | Gravity.CENTER_VERTICAL, 
				mIndicator[RIGHT].getIntrinsicWidth(),
				mIndicator[RIGHT].getIntrinsicHeight(), 
				mContainer, mBounds);
			mIndicator[RIGHT].setBounds(mBounds);
		}
	}
	
	@Override
	public boolean onInterceptTouchEvent(MotionEvent ev)
	{
		if(mPressed){
			return true;
		}
		
		if(ev.getActionMasked() == MotionEvent.ACTION_DOWN){
			final int x = (int)ev.getX() + getScrollX();
			final int y = (int)ev.getY() + getScrollY();
			if(inIndicatorBounds(LEFT, x, y) || inIndicatorBounds(RIGHT, x, y)){
				mPressed = true;
				return true;
			}
		}
		
		return super.onInterceptTouchEvent(ev);
	}
	
	@Override
	public boolean onTouchEvent(MotionEvent ev)
	{
		if(mPressed){
			final int action = ev.getActionMasked();
			final int x = (int)ev.getX() + getScrollX();
			final int y = (int)ev.getY() + getScrollY();
			switch(action){
				case MotionEvent.ACTION_DOWN:
				case MotionEvent.ACTION_MOVE:
					inIndicatorBounds(LEFT,  x, y);
					inIndicatorBounds(RIGHT, x, y);
					break;
					
				case MotionEvent.ACTION_UP:
					if(inIndicatorBounds(LEFT, x, y)){
						onClickIndicator(LEFT);
					}
					else if(inIndicatorBounds(RIGHT, x, y)){
						onClickIndicator(RIGHT);
					}
					if(mIndicator[LEFT] != null && mIndicator[LEFT].setState(null)){
						invalidate();
					}
					if(mIndicator[RIGHT] != null && mIndicator[RIGHT].setState(null)){
						invalidate();
					}
					mPressed = false;
					break;
					
				case MotionEvent.ACTION_CANCEL:
					mPressed = false;
					break;
			}
			return true;
		}
		
		return super.onTouchEvent(ev);
	}
	
	private boolean inIndicatorBounds(int indicator, int x, int y)
	{
		if(mEnabled[indicator]){
			boolean inBounds = mIndicator[indicator].getBounds().contains(x, y);
			if(mIndicator[indicator].setState(inBounds ? PRESSED_STATE : null)){
				invalidate();
			}
			return inBounds;
		}
		return false;
	}
	
	@Override
	public void draw(Canvas canvas)
	{
		super.draw(canvas);
		if(mEnabled[LEFT]){
			mIndicator[LEFT].draw(canvas);
		}
		if(mEnabled[RIGHT]){
			mIndicator[RIGHT].draw(canvas);
		}
	}
	
	@Override
	protected boolean verifyDrawable(Drawable who)
	{
		if(who == mIndicator[LEFT] || who == mIndicator[RIGHT]){
			return true;
		}
		return super.verifyDrawable(who);
	}
	
	protected View findChildForScroll(int direction)
	{
		int pos = getScrollX() - getPaddingLeft();
		ViewGroup panel = ((ViewGroup)getChildAt(0));
		final int count = panel.getChildCount();
		if(direction == View.FOCUS_LEFT){
			for(int i = count - 1; i >= 0; i--){
				View child = panel.getChildAt(i);
				if(child.getLeft() < pos){
					return child;
				}
			}
		}
		else if(direction == View.FOCUS_RIGHT){
			pos += getWidth();
			for(int i = 0; i < count; i++){
				View child = panel.getChildAt(i);
				if(child.getRight() > pos){
					return child;
				}
			}
		}
		return null;
	}
	
	private void scrollToChild(View child)
	{
		child.getDrawingRect(mBounds);
		requestChildRectangleOnScreen(child, mBounds, false);
	}
	
	@Override
	public boolean canScrollHorizontally(int direction)
	{
		final int offset = computeHorizontalScrollOffset();
		final int range  = computeHorizontalScrollRange() - computeHorizontalScrollExtent();
		if(range == 0){
			return false;
		}
		return (direction < 0) ? (offset > 0) : (offset < range - 1);
	}
}