FlingViewGroup.java

FlingViewGroup.java

package org.videolan.vlc.android.widget;


import android.content.Context;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.VelocityTracker;
import android.view.View;
import android.view.ViewConfiguration;
import android.view.ViewGroup;
import android.widget.Scroller;

public class FlingViewGroup extends ViewGroup {
	public static final String TAG = "VLC/FlingViewGroup";
	private final static int TOUCH_STATE_MOVE = 0;
	private final static int TOUCH_STATE_REST = 1;
	
	private int mCurrentView = 0;
	private Scroller mScroller;
	private VelocityTracker mVelocityTracker;
	
	private int mTouchState = TOUCH_STATE_REST;
	private int mInterceptTouchState = TOUCH_STATE_REST;
	private int mTouchSlop;
	private int mMaximumVelocity;
	
	private float mLastX;
	private float mLastInterceptDownY;
	private ViewSwitchListener mViewSwitchListener;
	
	public FlingViewGroup(Context context, AttributeSet attrs) {
		super(context, attrs);
		this.setLayoutParams(new ViewGroup.LayoutParams(
				ViewGroup.LayoutParams.WRAP_CONTENT,
				ViewGroup.LayoutParams.FILL_PARENT));
		
		mScroller = new Scroller(context);
		ViewConfiguration config = ViewConfiguration.get(getContext());
		mTouchSlop = config.getScaledTouchSlop();
		mMaximumVelocity = config.getScaledMaximumFlingVelocity();
	}

	@Override
	protected void onLayout(boolean changed, int l, int t, int r, int b) {
		int childLeft = 0;

		final int count = getChildCount();
		for (int i = 0; i < count; i++) {
			final View child = getChildAt(i);
			if (child.getVisibility() != View.GONE) {
				final int childWidth = child.getMeasuredWidth();
				child.layout(childLeft, 0, childLeft + childWidth,
						child.getMeasuredHeight());
				childLeft += childWidth;
			}
		}
	}
	
	@Override
	protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
		super.onMeasure(widthMeasureSpec, heightMeasureSpec);

		final int width = MeasureSpec.getSize(widthMeasureSpec);
		final int widthMode = MeasureSpec.getMode(widthMeasureSpec);
		final int heightMode = MeasureSpec.getMode(heightMeasureSpec);
		if (widthMode != MeasureSpec.EXACTLY ||
				heightMode != MeasureSpec.EXACTLY) {
			throw new IllegalStateException("can only be used in EXACTLY mode.");
		}

		final int count = getChildCount();
		for (int i = 0; i < count; i++) {
			getChildAt(i).measure(widthMeasureSpec, heightMeasureSpec);
		}
		
		scrollTo(mCurrentView * width, 0);
	}
	
	@Override
	public void computeScroll() {
		if (mScroller.computeScrollOffset()) {
			scrollTo(mScroller.getCurrX(), mScroller.getCurrY());
			postInvalidate();
		}
	}
	
	public void setPosition(int position) {
		mCurrentView = position;
	}
	
	@Override
	public boolean onInterceptTouchEvent(MotionEvent ev) {
		if (getChildCount() == 0)
			return false;

		final float x =  ev.getX();
		final float y =  ev.getY();
						
		switch (ev.getAction()) {
		case MotionEvent.ACTION_DOWN:
			mLastX = x;
			mLastInterceptDownY = ev.getY();
			mTouchState = mScroller.isFinished() ? 
					TOUCH_STATE_REST : TOUCH_STATE_MOVE; 
			mInterceptTouchState = TOUCH_STATE_REST;
			break;
		case MotionEvent.ACTION_MOVE:
			if (mInterceptTouchState == TOUCH_STATE_MOVE)
				return false;
			if (Math.abs(mLastInterceptDownY - y) > mTouchSlop)
				mInterceptTouchState = TOUCH_STATE_MOVE;			
			if (Math.abs(mLastX - x) > mTouchSlop)
				mTouchState = TOUCH_STATE_MOVE;
			break;
		case MotionEvent.ACTION_UP:
		case MotionEvent.ACTION_CANCEL:
			mInterceptTouchState = TOUCH_STATE_REST;
			break;
		}
		
		return mTouchState == TOUCH_STATE_MOVE;
	}
	
	@Override
	public boolean onTouchEvent(MotionEvent event) {
		if (getChildCount() == 0)
			return false;
		
		if (mVelocityTracker == null)
			mVelocityTracker = VelocityTracker.obtain();
		mVelocityTracker.addMovement(event);
		
		final int action = event.getAction();
		final float x = event.getX();
		
		switch (action) {
		case MotionEvent.ACTION_DOWN:
			if (!mScroller.isFinished())
				mScroller.abortAnimation();
			mLastX = x;
			break;
		case MotionEvent.ACTION_MOVE:
			int delta = (int) (mLastX - x);
			mLastX = x;
			final int scrollX = getScrollX();
			if (delta < 0) {
				if (scrollX > 0) {
					scrollBy(Math.max(-scrollX, delta), 0);
				}
			} else if (delta > 0) {
				final int availableToScroll = 
					getChildAt(getChildCount() - 1).getRight() - scrollX - getWidth();
				if (availableToScroll > 0) {
					scrollBy(Math.min(availableToScroll, delta), 0);
				}
			}
			break;
		case MotionEvent.ACTION_UP:
		case MotionEvent.ACTION_CANCEL:
			final VelocityTracker velocityTracker = mVelocityTracker;
			velocityTracker.computeCurrentVelocity(1000, mMaximumVelocity);
			int velocityX = (int) velocityTracker.getXVelocity();

			if (velocityX > 1000 && mCurrentView > 0) {
				snapToScreen(mCurrentView - 1);
			} else if (velocityX < -1000
					&& mCurrentView < getChildCount() - 1) {
				snapToScreen(mCurrentView + 1);
			} else {
				snapToDestination();
			}

			if (mVelocityTracker != null) {
				mVelocityTracker.recycle();
				mVelocityTracker = null;
			}
			
			break;
		}
		
		return true;
	}
	
	@Override
	protected void onScrollChanged(int l, int t, int oldl, int oldt) {
		super.onScrollChanged(l, t, oldl, oldt);
		if (mViewSwitchListener != null) {
			float progress = (float)l / (float)(getWidth() * (getChildCount() - 1)); 
			mViewSwitchListener.onSwitching(progress);
		}
	}
	
	private void snapToDestination() {
		final int screenWidth = getWidth();
		final int whichScreen = (getScrollX() + (screenWidth / 2)) / screenWidth;
		snapToScreen(whichScreen);
	}

	public void snapToScreen(int position) {
		mCurrentView = position;
		final int delta = (position * getWidth()) - getScrollX();
		mScroller.startScroll(getScrollX(), 0, delta, 0, Math.abs(delta));
		invalidate();
		if (mViewSwitchListener != null) {
			mViewSwitchListener.onSwitched(position);
		}
	}
	
	public void setOnViewSwitchedListener(ViewSwitchListener l) {
		mViewSwitchListener = l;
	}
	
	public static interface ViewSwitchListener {
		void onSwitching(float progress);
		void onSwitched(int position);
	}

}