ViewPager 自定义UI SlideViewPager

接下来我们将利用ViewGroup实践自定义UI，首先还是看看效果图： package com.github.songnick.viewgroup;
	import android.content.Context;
	import android.content.res.TypedArray;
	import android.support.v4.view.MotionEventCompat;
	import android.support.v4.view.VelocityTrackerCompat;
	import android.support.v4.view.ViewCompat;
	import android.support.v4.widget.ScrollerCompat;
	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.view.animation.Interpolator;
	import com.github.songnick.utils.LogUtils;
	import com.nick.library.R;
	/**
	* Created by SongNick on 15/10/26.
	*/
	public class SlideViewPager extends ViewGroup {
	private static final int MARGIN_LEFT_RIGHT = 150;
	private static final int MARGIN_TOP_BOTTOM = 400;
	private static float SCALE_RATIO = 0.8f;
	private static final int MAX_SETTLE_DURATION = 600; // ms
	/**
	* view slide direction left to right
	*/
	private static int LEFT_TO_RIGHT = 0x011;
	/***
	* view slide direction right to left
	*/
	private static int RIGHT_TO_LEFT = 0x022;
	/**
	* view slide direction invalid
	*/
	private static int INVALID_DIRECTION = 0x033;
	/**
	* A null/invalid pointer ID.
	*/
	public static final int INVALID_POINTER = -1;
	/**
	* Indicates that the pager is in an idle, settled state. The current page
	* is fully in view and no animation is in progress.
	*/
	public static final int SCROLL_STATE_IDLE = 0;
	/**
	* Indicates that the pager is currently being dragged by the user.
	*/
	public static final int SCROLL_STATE_DRAGGING = 1;
	/**
	* Indicates that the pager is in the process of settling to a final position.
	*/
	public static final int SCROLL_STATE_SETTLING = 2;
	public static int SNAP_VELOCITY = 600;
	private static final String TAG = SlideViewPager.class.getSimpleName();
	private float mDownX = 0.0f;
	private float mOriginalX = 0.0f;
	// Last known position/pointer tracking
	private int mActivePointerId = INVALID_POINTER;
	private static final int MIN_FLING_VELOCITY = 400; // dips
	private static final int MIN_DISTANCE_FOR_FLING = 25; // dips
	/**
	* determines speed during scroll
	*/
	private VelocityTracker mVelocityTracker;
	private int mMinimumVelocity;
	private int mMaximumVelocity;
	private int mFlingDistance;
	private int mCloseEnough;
	private int mCurrentPosition = 0;
	private int mCurrentDir = INVALID_DIRECTION;
	private ScrollerCompat mScroller;
	private float mMarginLeftRight = 0.0f;
	private float mGutterSize = 0.0f;
	private int mTouchSlop = 0;
	private int mSwitchSize = 0;
	private int mScrollState = SCROLL_STATE_IDLE;
	private boolean mIsBeingDragged = false;
	private boolean mIsUnableToDrag = false;
	private OnPagerChangeListener mOnPagerChangeListener = null;
	private final Runnable mEndScrollRunnable = new Runnable() {
	public void run() {
	setScrollState(SCROLL_STATE_IDLE);
	}
	};
	public interface OnPagerChangeListener{
	/**
	* this method will be invoked, when new page is selected
	* @param position the position of new page selected
	* */
	void onPageSelected(int position);
	/**
	* when the page is scrolling,
	* @param position
	* @param positionOffset
	* @param positionOffsetPixel
	* */
	void onPageScrolled(int position, float positionOffset, int positionOffsetPixel);
	/**
	* scroll state of current page
	*
	* @param state scroll state
	* @see SlideViewPager#SCROLL_STATE_DRAGGING
	* @see SlideViewPager#SCROLL_STATE_IDLE
	* @see SlideViewPager#SCROLL_STATE_SETTLING
	*
	* */
	void onPageScrollStateChanged(int state);
	}
	public SlideViewPager(Context context) {
	this(context, null);
	}
	public SlideViewPager(Context context, AttributeSet attrs) {
	this(context, attrs, 0);
	}
	public SlideViewPager(Context context, AttributeSet attrs, int defStyleAttr) {
	super(context, attrs, defStyleAttr);
	TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.ScaleViewPager, 0, 0);
	mMarginLeftRight = a.getDimension(R.styleable.ScaleViewPager_marginLeftRight, 0);
	mGutterSize = a.getDimensionPixelSize(R.styleable.ScaleViewPager_gutterSize, 0);
	a.recycle();
	init(context);
	}
	/**
	* initialize some config
	*
	* @param context this view's context
	*/
	private void init(Context context) {
	setWillNotDraw(false);
	mScroller = ScrollerCompat.create(context, sInterpolator);
	ViewConfiguration viewConfiguration = ViewConfiguration.get(context);
	mTouchSlop = viewConfiguration.getScaledTouchSlop();
	LogUtils.LogD(TAG, " touch slop == " + mTouchSlop);
	final float density = context.getResources().getDisplayMetrics().density;
	mMinimumVelocity = (int) (MIN_FLING_VELOCITY * density);
	mMaximumVelocity = viewConfiguration.getScaledMaximumFlingVelocity();
	mFlingDistance = (int) (MIN_DISTANCE_FOR_FLING * density);
	}
	/**
	* Interpolator defining the animation curve for mScroller
	*/
	private static final Interpolator sInterpolator = new Interpolator() {
	public float getInterpolation(float t) {
	t -= 1.0f;
	return t * t * t * t * t + 1.0f;
	}
	};
	@Override
	public boolean onInterceptTouchEvent(MotionEvent ev) {
	return super.onInterceptTouchEvent(ev);
	}
	private void setScrollState(int state) {
	mScrollState = state;
	if (mOnPagerChangeListener != null){
	mOnPagerChangeListener.onPageScrollStateChanged(state);
	}
	}
	/**
	* The result of a call to this method is equivalent to
	*/
	public void cancel() {
	if (mVelocityTracker != null) {
	mVelocityTracker.recycle();
	mVelocityTracker = null;
	}
	}
	@Override
	public boolean onTouchEvent(MotionEvent event) {
	LogUtils.LogD(TAG, " onInterceptTouchEvent hit touch event");
	final int actionIndex = MotionEventCompat.getActionIndex(event);
	mActivePointerId = MotionEventCompat.getPointerId(event, 0);
	if (mVelocityTracker == null) {
	mVelocityTracker = VelocityTracker.obtain();
	}
	mVelocityTracker.addMovement(event);
	switch (event.getAction() & MotionEvent.ACTION_MASK) {
	case MotionEvent.ACTION_DOWN:
	mDownX = event.getRawX();
	if (mScroller != null && !mScroller.isFinished()) {
	mScroller.abortAnimation();
	}
	break;
	case MotionEvent.ACTION_MOVE:
	//calculate moving distance
	float distance = -(event.getRawX() - mDownX);
	mDownX = event.getRawX();
	LogUtils.LogD(TAG, " current distance == " + distance);
	performDrag((int)distance);
	break;
	case MotionEvent.ACTION_UP:
	releaseViewForTouchUp();
	cancel();
	break;
	}
	return true;
	}
	/***
	* drag the this view smooth scale
	* @param distance should be drag
	* */
	private void performDrag(int distance) {
	if (mOnPagerChangeListener != null){
	mOnPagerChangeListener.onPageScrollStateChanged(SCROLL_STATE_DRAGGING);
	}
	LogUtils.LogD(TAG, " perform drag distance == " + distance);
	scrollBy(distance, 0);
	if (distance < 0) {
	dragScaleShrinkView(mCurrentPosition, LEFT_TO_RIGHT);
	} else {
	LogUtils.LogD(TAG, " current direction is right to left and current child position = " + mCurrentPosition);
	dragScaleShrinkView(mCurrentPosition, RIGHT_TO_LEFT);
	}
	}
	/**
	* user move the view and release view
	* but there is also some question for tow pointer event
	*/
	private void releaseViewForTouchUp() {
	// mVelocityTracker.computeCurrentVelocity(1000, mMaxVelocity);
	// final float xvel = clampMag(
	// VelocityTrackerCompat.getXVelocity(mVelocityTracker, mActivePointerId),
	// mMinVelocity, mMaxVelocity);
	// if (xvel != 0){
	// smoothScrollToDes();
	// }
	final VelocityTracker velocityTracker = mVelocityTracker;
	velocityTracker.computeCurrentVelocity(1000, mMaximumVelocity);
	int initialVelocity = (int) VelocityTrackerCompat.getXVelocity(
	velocityTracker, mActivePointerId);
	float xVel = mVelocityTracker.getXVelocity();
	if (xVel > SNAP_VELOCITY && mCurrentPosition > 0) {
	smoothScrollToItemView(mCurrentPosition - 1, true);
	} else if (xVel < -SNAP_VELOCITY && mCurrentPosition < getChildCount() - 1) {
	smoothScrollToItemView(mCurrentPosition + 1, true);
	} else {
	smoothScrollToDes();
	}
	setScrollState(SCROLL_STATE_SETTLING);
	}
	public void setCurrentItem(int position, boolean smooth) {
	if (position >= 0 && position <= getChildCount() - 1){
	smoothScrollToItemView(position, true);
	}
	}
	private int determineTargetPosition(int currentPosition, int velocity, int deltaX) {
	int targetPosition = 0;
	if (Math.abs(velocity) > mMinimumVelocity) {
	targetPosition = velocity > 0 ? currentPosition : currentPosition + 1;
	}
	return targetPosition;
	}
	// We want the duration of the page snap animation to be influenced by the distance that
	// the screen has to travel, however, we don't want this duration to be effected in a
	// purely linear fashion. Instead, we use this method to moderate the effect that the distance
	// of travel has on the overall snap duration.
	float distanceInfluenceForSnapDuration(float f) {
	f -= 0.5f; // center the values about 0.
	f *= 0.3f * Math.PI / 2.0f;
	return (float) Math.sin(f);
	}
	/**
	* when user touch up, invoke this method,
	* and scroll to confirmed view smoothly
	*/
	private void smoothScrollToDes() {
	int scrollX = getScrollX();
	//confirm the position to scroll
	int position = (scrollX + mSwitchSize / 2) / mSwitchSize;
	LogUtils.LogD(TAG, " smooth scroll to des position == before =" + mCurrentPosition
	+ " scroll X = " + scrollX + " switch size == " + mSwitchSize + " position == " + position);
	smoothScrollToItemView(position, mCurrentPosition == position);
	// if (mCurrentPosition != position){
	// if (mOnPagerChangeListener != null){
	// mOnPagerChangeListener.onPageSelected(position);
	// }
	// }
	// mCurrentPosition = position;
	//
	// int dx = position * (getMeasuredWidth() - (int) mMarginLeftRight * 2) - scrollX;
	// LogUtils.LogD(TAG, " smooth scroll to des position == " + position + " dx = " + dx + " scroll x == " + scrollX);
	// mScroller.startScroll(getScrollX(), 0, dx, 0, Math.min(Math.abs(dx) * 2, MAX_SETTLE_DURATION));
	// invalidate();
	}
	/**
	* scroll to confirmed position of child
	*
	* @param position the view position in this {@link #ViewGroup}
	*/
	private void smoothScrollToItemView(int position, boolean pageSelected) {
	mCurrentPosition = position;
	if (mCurrentPosition > getChildCount() - 1) {
	mCurrentPosition = getChildCount() - 1;
	}
	if (mOnPagerChangeListener != null && pageSelected){
	mOnPagerChangeListener.onPageSelected(position);
	}
	int dx = position * (getMeasuredWidth() - (int) mMarginLeftRight * 2) - getScrollX();
	mScroller.startScroll(getScrollX(), 0, dx, 0, Math.min(Math.abs(dx) * 2, MAX_SETTLE_DURATION));
	invalidate();
	}
	@Override
	public void computeScroll() {
	if (!mScroller.isFinished() && mScroller.computeScrollOffset()) {
	int dx = mCurrentPosition * mSwitchSize - mScroller.getCurrX();
	LogUtils.LogD(TAG, " compute scroll dx == " + dx + " position == " + mCurrentPosition);
	// int position = mCurrentPosition;
	// if (mCurrentDir == RIGHT_TO_LEFT){
	// LogUtils.LogD(TAG, " current direction == right to left" );
	// position = mCurrentPosition - 1;
	// }else if (mCurrentDir == LEFT_TO_RIGHT){
	// LogUtils.LogD(TAG, " current direction == left to right " );
	// position = mCurrentPosition + 1;
	// }
	dragScaleShrinkView(mCurrentPosition, mCurrentDir);
	// }
	scrollTo(mScroller.getCurrX(), 0);
	}
	completeScroll(true);
	}
	/**
	* whether the scroll animation is end
	* @param postEvents post run the runnable event
	* */
	private void completeScroll(boolean postEvents){
	boolean needPopulate = mScrollState == SCROLL_STATE_SETTLING;
	if (needPopulate){
	if (postEvents) {
	ViewCompat.postOnAnimation(this, mEndScrollRunnable);
	} else {
	mEndScrollRunnable.run();
	}
	}
	}
	/**
	* when the user drag the view, current view should be scaled or shrink and next view or previous view size should be changed
	*
	* @param position the position of dragging view
	*
	* @param direction the direction of drag
	* @see SlideViewPager#RIGHT_TO_LEFT
	* @see SlideViewPager#LEFT_TO_RIGHT
	* @see SlideViewPager#INVALID_DIRECTION
	* */
	private void dragScaleShrinkView(int position, int direction) {
	int distance = getScrollX() - position * mSwitchSize;
	mCurrentDir = direction;
	View scaleView = null;
	View shrinkView = null;
	float scaleRatio = 0.0f;
	float shrinkRatio = 0.0f;
	//if distance is bigger than zero,
	//current drag action is between current page and next page
	//otherwise is between front page and current page
	if (distance > 0) {
	int moveSize = getScrollX() - position * mSwitchSize;
	float ratio = (float) moveSize / mSwitchSize;//this value is from 0 to 1;
	if (direction == LEFT_TO_RIGHT) {//value may be from X to 0
	if (position >= 0) {
	//current view should be scaled
	scaleView = getChildAt(position);
	//next view should be shrink
	shrinkView = getChildAt(position + 1);
	shrinkRatio = SCALE_RATIO + (1.0f - SCALE_RATIO) * ratio;
	scaleRatio = 1.0f - (1.0f - SCALE_RATIO) * ratio;
	LogUtils.LogD(TAG, " current scale ratio = " + scaleRatio + " shrink ratio = " + shrinkRatio + " ratio = " + ratio);
	}
	} else if (direction == RIGHT_TO_LEFT) {
	if (position < getChildCount() - 1) {
	//
	scaleView = getChildAt(position + 1);
	shrinkView = getChildAt(position);
	scaleRatio = SCALE_RATIO + (1.0f - SCALE_RATIO) * ratio;
	;
	shrinkRatio = 1.0f - (1.0f - SCALE_RATIO) * ratio;
	}
	}
	} else if (distance < 0) {
	float moveSize = position * mSwitchSize - getScrollX();
	float ratio = moveSize / mSwitchSize;
	if (direction == LEFT_TO_RIGHT) {
	scaleView = getChildAt(position - 1);
	shrinkView = getChildAt(position);
	scaleRatio = SCALE_RATIO + (1.0f - SCALE_RATIO) * ratio;
	shrinkRatio = 1.0f - (1.0f - SCALE_RATIO) * ratio;
	} else if (direction == RIGHT_TO_LEFT) {
	scaleView = getChildAt(position);
	shrinkView = getChildAt(position - 1);
	shrinkRatio = SCALE_RATIO + (1.0f - SCALE_RATIO) * ratio;
	scaleRatio = 1.0f - (1.0f - SCALE_RATIO) * ratio;
	}
	}
	if (scaleView != null) {
	ViewCompat.setScaleX(scaleView, scaleRatio);
	ViewCompat.setScaleY(scaleView, scaleRatio);
	scaleView.invalidate();
	}
	if (shrinkView != null) {
	ViewCompat.setScaleX(shrinkView, shrinkRatio);
	ViewCompat.setScaleY(shrinkView, shrinkRatio);
	shrinkView.invalidate();
	}
	}
	/**
	* set current page change listener
	* @param onPageChangListener
	* @see com.github.songnick.viewgroup.SlideViewPager.OnPagerChangeListener
	* */
	public void setOnPageChangListener(OnPagerChangeListener onPageChangListener){
	mOnPagerChangeListener = onPageChangListener;
	}
	@Override
	protected void onLayout(boolean changed, int l, int t, int r, int b) {
	int childCount = getChildCount();
	int originLeft = (int) mMarginLeftRight;
	for (int i = 0; i < childCount; i++) {
	View child = getChildAt(i);
	int left = originLeft + child.getMeasuredWidth() * i;
	int right = originLeft + child.getMeasuredWidth() * (i + 1);
	int bottom = child.getMeasuredHeight();
	child.layout(left, 0, right, bottom);
	if (i != 0) {
	child.setScaleX(SCALE_RATIO);
	child.setScaleY(SCALE_RATIO);
	child.setTag(SCALE_RATIO);
	} else {
	child.setTag(1.0f);
	}
	}
	}
	@Override
	protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
	// For simple implementation, our internal size is always 0.
	// We depend on the container to specify the layout size of
	// our view. We can't really know what it is since we will be
	// adding and removing different arbitrary views and do not
	// want the layout to change as this happens.
	setMeasuredDimension(getDefaultSize(0, widthMeasureSpec),
	getDefaultSize(0, heightMeasureSpec));
	int measuredWidth = getMeasuredWidth();
	int measuredHeight = getMeasuredHeight();
	int childCount = getChildCount();
	int width = measuredWidth - (int) (mMarginLeftRight * 2);
	int height = measuredHeight;
	int childWidthMeasureSpec = MeasureSpec.makeMeasureSpec(width, MeasureSpec.EXACTLY);
	int childHeightMeasureSpec = MeasureSpec.makeMeasureSpec(height, MeasureSpec.EXACTLY);
	for (int i = 0; i < childCount; i++) {
	getChildAt(i).measure(childWidthMeasureSpec, childHeightMeasureSpec);
	}
	mSwitchSize = width;
	confirmScaleRatio(width, mGutterSize);
	}
	private void confirmScaleRatio(int width, float gutterSize) {
	SCALE_RATIO = (width - gutterSize * 2) / width;
	LogUtils.LogD(TAG, " confirm scale ratio == " + gutterSize + " ration == " + SCALE_RATIO + " margin lef t == " + mMarginLeftRight);
	}
	@Override
	protected void onSizeChanged(int w, int h, int oldw, int oldh) {
	LogUtils.LogD(TAG, " onSize changed com ");
	super.onSizeChanged(w, h, oldw, oldh);
	}
	}