class ViewAdapter extends PagerAdapter{
    private List<View> list;
ViewAdapter(List<View> list){
        this.list = list;
}
    //返回view檢視的數目
@Override
public int getCount() {
        return list.size();
}
    // 當要顯示的檢視可以進行快取的時候，會呼叫這個方法進行顯示檢視的初始化，
 
    // 我們將要顯示的View加入到ViewGroup中，然後作為返回值返回即可
@Override
public Object instantiateItem(ViewGroup container, int position) {
        return super.instantiateItem(container, position);
}
    //PagerAdapter只快取一定的檢視，如果滑動的檢視超出了快取的範圍，就會呼叫這個方法，將檢視銷燬
@Override
public void destroyItem(ViewGroup container, int position, 
 
Object object) {
        super.destroyItem(container, position, object);
}
    // 來判斷顯示的是否是同檢視（物件），這裡我們將兩個引數相比較返回即可
@Override
public boolean isViewFromObject(View view, Object object) {
        return false;
}
}

public void setList(List<View>list) {
    this.list = list;
notifyDataSetChanged();
}

/**
 * This method should be called by the application if the data backing this adapter has changed
 * and associated views should update.
 */
public void notifyDataSetChanged() {
    synchronized (this) {
        if (mViewPagerObserver != null) {
            mViewPagerObserver.onChanged();
}
    }
    mObservable.notifyChanged();
}

private DataSetObserver mViewPagerObserver;

DataSetObserver 這個資料觀察者明顯是從ViewPager中去實現的

private class PagerObserver extends DataSetObserver {
    PagerObserver() {
    }

    @Override
public void onChanged() {
        dataSetChanged();
}
    @Override
public void onInvalidated() {
        dataSetChanged();
}
}

void setViewPagerObserver(DataSetObserver observer) {
    synchronized (this) {
        mViewPagerObserver = observer;
}
}

void dataSetChanged() {
    // This method only gets called if our observer is attached, so mAdapter is non-null.
final int adapterCount = mAdapter.getCount();
mExpectedAdapterCount = adapterCount;
    boolean needPopulate = mItems.size() < mOffscreenPageLimit * 2 + 1
&& mItems.size() < adapterCount;
    int newCurrItem = mCurItem;
    boolean isUpdating = false;
    for (int i = 0; i < mItems.size(); i++) {
        final ItemInfo ii = mItems.get(i);

    //通過getItemPosition（Object object）的返回值來執行的後續操作，
        final int newPos = mAdapter.getItemPosition(ii.object);
    //可以發現當返回值為POSITION_UNCHANGED 直接跳出迴圈
        if (newPos == PagerAdapter.POSITION_UNCHANGED) {
            continue;
}
    //而為 PagerAdapter.POSITION_NONE 時，才繼續執行後續操作
        if (newPos == PagerAdapter.POSITION_NONE) {
            mItems.remove(i);
i--;
            if (!isUpdating) {
                mAdapter.startUpdate(this);
isUpdating = true;
}

            mAdapter.destroyItem(this, ii.position, ii.object);
needPopulate = true;
            if (mCurItem == ii.position) {
                // Keep the current item in the valid range
newCurrItem = Math.max(0, Math.min(mCurItem, adapterCount - 1));
needPopulate = true;
}
            continue;
}

        if (ii.position != newPos) {
            if (ii.position == mCurItem) {
                // Our current item changed position. Follow it.
newCurrItem = newPos;
}

            ii.position = newPos;
needPopulate = true;
}
    }

    if (isUpdating) {
        mAdapter.finishUpdate(this);
}

    Collections.sort(mItems, COMPARATOR);
    if (needPopulate) {
        // Reset our known page widths; populate will recompute them.
final int childCount = getChildCount();
        for (int i = 0; i < childCount; i++) {
            final View child = getChildAt(i);
            final LayoutParams lp = (LayoutParams) child.getLayoutParams();
            if (!lp.isDecor) {
                lp.widthFactor = 0.f;
}
        }

        setCurrentItemInternal(newCurrItem, false, true);
requestLayout();
}
}

//為了內部檢視變換
@Override
public int getItemPosition(Object object) {
    return POSITION_NONE;
}