package com.mcoy.snapscrollview;
 
import android.content.Context;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.view.VelocityTracker;
import android.view.View;
import android.view.ViewConfiguration;
import android.view.ViewGroup;
import android.widget.Scroller;
 
/**
 * @author jiangxinxing---mcoy in English
 * 
 * 了解此ViewGroup之前， 有兩點(diǎn)一定要做到心中有數(shù)
 * 一個是對Scroller的使用， 另一個是對onInterceptTouchEvent和onTouchEvent要做到很熟悉
 * 以下幾個網(wǎng)站可以做參考用
 * http://blog.csdn.net/bigconvience/article/details/26697645
 * http://blog.csdn.net/androiddevelop/article/details/8373782
 * http://blog.csdn.net/xujainxing/article/details/8985063
 */
public class McoySnapPageLayout extends ViewGroup {
 
  。。。。
 
 
 public interface McoySnapPage {
 /**
 * 返回page根節(jié)點(diǎn)
 * 
 * @return
 */
 View getRootView();
 
 /**
 * 是否滑動到最頂端
 * 第二頁必須自己實(shí)現(xiàn)此方法，來判斷是否已經(jīng)滑動到第二頁的頂部
 * 并決定是否要繼續(xù)滑動到第一頁
 */
 boolean isAtTop();
 
 /**
 * 是否滑動到最底部
 * 第一頁必須自己實(shí)現(xiàn)此方法，來判斷是否已經(jīng)滑動到第二頁的底部
 * 并決定是否要繼續(xù)滑動到第二頁
 */
 boolean isAtBottom();
 }
 
 public interface PageSnapedListener {
 
 /**
 * @mcoy
 * 當(dāng)從某一頁滑動到另一頁完成時的回調(diào)函數(shù)
 */
 void onSnapedCompleted(int derection);
 }
 
  。。。。。。
 
 /**
 * 設(shè)置上下頁面
 * @param pageTop
 * @param pageBottom
 */
 public void setSnapPages(McoySnapPage pageTop, McoySnapPage pageBottom) {
 mPageTop = pageTop;
 mPageBottom = pageBottom;
 addPagesAndRefresh();
 }
 
 private void addPagesAndRefresh() {
 // 設(shè)置頁面id
 mPageTop.getRootView().setId(0);
 mPageBottom.getRootView().setId(1);
 addView(mPageTop.getRootView());
 addView(mPageBottom.getRootView());
 postInvalidate();
 }
 
 /**
 * @mcoy add
 * computeScroll方法會調(diào)用postInvalidate()方法， 而postInvalidate()方法中系統(tǒng)
 * 又會調(diào)用computeScroll方法， 因此會一直在循環(huán)互相調(diào)用， 循環(huán)的終結(jié)點(diǎn)是在computeScrollOffset()
 * 當(dāng)computeScrollOffset這個方法返回false時，說明已經(jīng)結(jié)束滾動。
 * 
 * 重要：真正的實(shí)現(xiàn)此view的滾動是調(diào)用scrollTo(mScroller.getCurrX(), mScroller.getCurrY());
 */
 @Override
 public void computeScroll() {
 //先判斷mScroller滾動是否完成
 if (mScroller.computeScrollOffset()) {
 if (mScroller.getCurrY() == (mScroller.getFinalY())) {
 if (mNextDataIndex > mDataIndex) {
  mFlipDrection = FLIP_DIRECTION_DOWN;
  makePageToNext(mNextDataIndex);
 } else if (mNextDataIndex < mDataIndex) {
  mFlipDrection = FLIP_DIRECTION_UP;
  makePageToPrev(mNextDataIndex);
 }else{
  mFlipDrection = FLIP_DIRECTION_CUR;
 }
 if(mPageSnapedListener != null){
  mPageSnapedListener.onSnapedCompleted(mFlipDrection);
 }
 }
 //這里調(diào)用View的scrollTo()完成實(shí)際的滾動
 scrollTo(mScroller.getCurrX(), mScroller.getCurrY());
 //必須調(diào)用該方法，否則不一定能看到滾動效果
 postInvalidate();
 }
 }
 
 private void makePageToNext(int dataIndex) {
 mDataIndex = dataIndex;
  mCurrentScreen = getCurrentScreen();
 }
 
 private void makePageToPrev(int dataIndex) {
 mDataIndex = dataIndex;
  mCurrentScreen = getCurrentScreen();
 }
 
 public int getCurrentScreen() {
 for (int i = 0; i < getChildCount(); i++) {
 if (getChildAt(i).getId() == mDataIndex) {
 return i;
 }
 }
 return mCurrentScreen;
 }
 
 public View getCurrentView() {
 for (int i = 0; i < getChildCount(); i++) {
 if (getChildAt(i).getId() == mDataIndex) {
 return getChildAt(i);
 }
 }
 return null;
 }
 
 /*
 * (non-Javadoc)
 * 
 * @see
 * android.view.ViewGroup#onInterceptTouchEvent(android.view.MotionEvent)
 * 重寫了父類的onInterceptTouchEvent()，主要功能是在onTouchEvent()方法之前處理
 * touch事件。包括：down、up、move事件。
 * 當(dāng)onInterceptTouchEvent()返回true時進(jìn)入onTouchEvent()。
 */
 @Override
 public boolean onInterceptTouchEvent(MotionEvent ev) {
 final int action = ev.getAction();
 if ((action == MotionEvent.ACTION_MOVE)
 && (mTouchState != TOUCH_STATE_REST)) {
 return true;
 }
 final float x = ev.getX();
 final float y = ev.getY();
 
 switch (action) {
 case MotionEvent.ACTION_MOVE:
 // 記錄y與mLastMotionY差值的絕對值。
   // yDiff大于gapBetweenTopAndBottom時就認(rèn)為界面拖動了足夠大的距離，屏幕就可以移動了。
 final int yDiff = (int)(y - mLastMotionY);
 boolean yMoved = Math.abs(yDiff) > gapBetweenTopAndBottom;
 if (yMoved) {
 if(MCOY_DEBUG) {
  Log.e(TAG, "yDiff is " + yDiff);
  Log.e(TAG, "mPageTop.isFlipToBottom() is " + mPageTop.isAtBottom());
  Log.e(TAG, "mCurrentScreen is " + mCurrentScreen);
  Log.e(TAG, "mPageBottom.isFlipToTop() is " + mPageBottom.isAtTop());
 }
 if(yDiff < 0 && mPageTop.isAtBottom() && mCurrentScreen == 0 
  || yDiff > 0 && mPageBottom.isAtTop() && mCurrentScreen == 1){
  Log.e("mcoy", "121212121212121212121212");
  mTouchState = TOUCH_STATE_SCROLLING;
 }
 }
 break;
 case MotionEvent.ACTION_DOWN:
 // Remember location of down touch
 mLastMotionY = y;
 Log.e("mcoy", "mScroller.isFinished() is " + mScroller.isFinished());
 mTouchState = mScroller.isFinished() ? TOUCH_STATE_REST
  : TOUCH_STATE_SCROLLING;
 break;
 case MotionEvent.ACTION_CANCEL:
 case MotionEvent.ACTION_UP:
 // Release the drag
 mTouchState = TOUCH_STATE_REST;
 break;
 }
 boolean intercept = mTouchState != TOUCH_STATE_REST;
 Log.e("mcoy", "McoySnapPageLayout---onInterceptTouchEvent return " + intercept);
 return intercept;
 }
 
 /*
 * (non-Javadoc)
 * 
 * @see android.view.View#onTouchEvent(android.view.MotionEvent)
 * 主要功能是處理onInterceptTouchEvent()返回值為true時傳遞過來的touch事件
 */
 @Override
 public boolean onTouchEvent(MotionEvent ev) {
 Log.e("mcoy", "onTouchEvent--" + System.currentTimeMillis());
  if (mVelocityTracker == null) {
   mVelocityTracker = VelocityTracker.obtain();
  }
  mVelocityTracker.addMovement(ev);
  
 final int action = ev.getAction();
 final float x = ev.getX();
 final float y = ev.getY();
 switch (action) {
 case MotionEvent.ACTION_DOWN:
 if (!mScroller.isFinished()) {
 mScroller.abortAnimation();
 }
 break;
 case MotionEvent.ACTION_MOVE:
  if(mTouchState != TOUCH_STATE_SCROLLING){
     // 記錄y與mLastMotionY差值的絕對值。
     // yDiff大于gapBetweenTopAndBottom時就認(rèn)為界面拖動了足夠大的距離，屏幕就可以移動了。
    final int yDiff = (int) Math.abs(y - mLastMotionY);
    boolean yMoved = yDiff > gapBetweenTopAndBottom;
    if (yMoved) {
     mTouchState = TOUCH_STATE_SCROLLING;
    }
   }
   // 手指拖動屏幕的處理
   if ((mTouchState == TOUCH_STATE_SCROLLING)) {
    // Scroll to follow the motion event
    final int deltaY = (int) (mLastMotionY - y);
    mLastMotionY = y;
    final int scrollY = getScrollY();
    if(mCurrentScreen == 0){//顯示第一頁，只能上拉時使用
     if(mPageTop != null && mPageTop.isAtBottom()){
     scrollBy(0, Math.max(-1 * scrollY, deltaY));
     }
    }else{
     if(mPageBottom != null && mPageBottom.isAtTop()){
     scrollBy(0, deltaY);
     }
    }
   }
 break;
 case MotionEvent.ACTION_CANCEL:
 case MotionEvent.ACTION_UP:
 // 彈起手指后，切換屏幕的處理
 if (mTouchState == TOUCH_STATE_SCROLLING) {
  final VelocityTracker velocityTracker = mVelocityTracker;
    velocityTracker.computeCurrentVelocity(1000, mMaximumVelocity);
    int velocityY = (int) velocityTracker.getYVelocity();
    if (Math.abs(velocityY) > SNAP_VELOCITY) {
     if( velocityY > 0 && mCurrentScreen == 1 && mPageBottom.isAtTop()){
      snapToScreen(mDataIndex-1);
     }else if(velocityY < 0 && mCurrentScreen == 0){
      snapToScreen(mDataIndex+1);
     }else{
      snapToScreen(mDataIndex);
     }
    } else {
     snapToDestination();
    }
    if (mVelocityTracker != null) {
     mVelocityTracker.recycle();
     mVelocityTracker = null;
    }
 }else{
 }
 mTouchState = TOUCH_STATE_REST;
 break;
 
 default:
 break;
 }
 return true;
 }
 
 private void clearOnTouchEvents(){
 mTouchState = TOUCH_STATE_REST;
 if (mVelocityTracker != null) {
    mVelocityTracker.recycle();
    mVelocityTracker = null;
   }
 }
 
 private void snapToDestination() {
 // 計(jì)算應(yīng)該去哪個屏
 final int flipHeight = getHeight() / 8;
  
  int whichScreen = -1;
  final int topEdge = getCurrentView().getTop();
 
  if(topEdge < getScrollY() && (getScrollY()-topEdge) >= flipHeight && mCurrentScreen == 0){
   //向下滑動 
   whichScreen = mDataIndex + 1;
  }else if(topEdge > getScrollY() && (topEdge - getScrollY()) >= flipHeight && mCurrentScreen == 1){
   //向上滑動
   whichScreen = mDataIndex - 1;
  }else{
   whichScreen = mDataIndex;
  }
  Log.e(TAG, "snapToDestination mDataIndex = " + mDataIndex);
  Log.e(TAG, "snapToDestination whichScreen = " + whichScreen);
  snapToScreen(whichScreen);
 }
 
 private void snapToScreen(int dataIndex) {
  if (!mScroller.isFinished())
   return;
  
  final int direction = dataIndex - mDataIndex;
  mNextDataIndex = dataIndex;
  boolean changingScreens = dataIndex != mDataIndex;
  View focusedChild = getFocusedChild();
  if (focusedChild != null && changingScreens) {
   focusedChild.clearFocus();
  }
  //在這里判斷是否已到目標(biāo)位置~
  int newY = 0;
 switch (direction) {
 case 1: //需要滑動到第二頁
 Log.e(TAG, "the direction is 1");
 newY = getCurrentView().getBottom(); // 最終停留的位置
 break;
 case -1: //需要滑動到第一頁
 Log.e(TAG, "the direction is -1");
 Log.e(TAG, "getCurrentView().getTop() is "
  + getCurrentView().getTop() + " getHeight() is "
  + getHeight());
 newY = getCurrentView().getTop() - getHeight(); // 最終停留的位置
 break;
 case 0: //滑動距離不夠， 因此不造成換頁，回到滑動之前的位置
 Log.e(TAG, "the direction is 0");
 newY = getCurrentView().getTop(); //第一頁的top是0， 第二頁的top應(yīng)該是第一頁的高度
 break;
 default:
 break;
 }
  final int cy = getScrollY(); // 啟動的位置
  Log.e(TAG, "the newY is " + newY + " cy is " + cy);
  final int delta = newY - cy; // 滑動的距離，正值是往左滑<—，負(fù)值是往右滑—>
  mScroller.startScroll(0, cy, 0, delta, Math.abs(delta));
  invalidate();
 }
 

 
}