怕自己说的不清不楚，先来一个郭神的文章镇楼：
github:
先贴一个自己画的ZrcListView的UML类图（学习ing。。。）
首先说下他的整个大体的布局
SimpleHeader是依据状态来draw自己的。通常是不画空白。下拉时把setHeadable设置的SimpleHeader给画出来；然后假设你把MainActivity中loadMore凝视掉你拉倒底部你会发现载入很多其它的动画一直在跑，说明它从始至终都在那的并没有须要做什么处理。 这里的SimpleHeader和SimpleFooter有且仅仅有一个；并且他也实现了ListView的HeaderView和FooterView的功能，可是在他这个项目里没实用到（上一篇文章说的有一个就是利用HeaderView来实现下拉刷新动画），这个后面会说到怎么实现的。
滚动的实现
想知道滚动方面的实现要看什么呢？当然是触摸事件的监听啦。而onTouchEvent仅仅有在ZrcAbsListView中才有实现，看来是在这里实现的了。
@Override public boolean onTouchEvent(MotionEvent ev) { try { if (!isEnabled()) { return isClickable() || isLongClickable(); } if (!mIsAttached) { return false; } initVelocityTrackerIfNotExists(); mVelocityTracker.addMovement(ev); final int actionMasked = ev.getActionMasked(); switch (actionMasked) { case MotionEvent.ACTION_DOWN: { onTouchDown(ev); break; } case MotionEvent.ACTION_MOVE: { onTouchMove(ev); break; } case MotionEvent.ACTION_UP: { onTouchUp(ev); break; } case MotionEvent.ACTION_CANCEL: { onTouchCancel(); break; } case MotionEvent.ACTION_POINTER_UP: { onSecondaryPointerUp(ev); final int x = mMotionX; final int y = mMotionY; final int motionPosition = pointToPosition(x, y); if (motionPosition >= 0) { mMotionPosition = motionPosition; } mLastY = y; break; } case MotionEvent.ACTION_POINTER_DOWN: { final int index = ev.getActionIndex(); final int id = ev.getPointerId(index); final int x = (int) ev.getX(index); final int y = (int) ev.getY(index); mMotionCorrection = 0; mActivePointerId = id; mMotionX = x; mMotionY = y; final int motionPosition = pointToPosition(x, y); if (motionPosition >= 0) { mMotionPosition = motionPosition; } mLastY = y; break; } } return true; } catch (Throwable e) { e.printStackTrace(); return false; } } 看起来似乎非常复杂，可是事实上仅仅须要关心ACTION_MOVE就可以；
private void onTouchMove(MotionEvent ev) { if (mTouchMode == TOUCH_MODE_INVALID) { mTouchMode = TOUCH_MODE_SCROLL; } int pointerIndex = ev.findPointerIndex(mActivePointerId); if (pointerIndex == -1) { pointerIndex = 0; mActivePointerId = ev.getPointerId(pointerIndex); } if (mDataChanged) { layoutChildren(); } final int x = (int) ev.getX(pointerIndex); final int y = (int) ev.getY(pointerIndex); switch (mTouchMode) { case TOUCH_MODE_DOWN: case TOUCH_MODE_TAP: case TOUCH_MODE_DONE_WAITING: startScrollIfNeeded(x, y); break; case TOUCH_MODE_SCROLL: scrollIfNeeded(x, y); break; } } startScrollIfNeeded中最后也还是调用scrollIfNeeded；直接看看scrollIfNeeded
private void scrollIfNeeded(int x, int y) { final int rawDeltaY = y - mMotionY; final int deltaY = rawDeltaY - mMotionCorrection; int incrementalDeltaY = mLastY != Integer.MIN_VALUE ? y - mLastY : deltaY; if (mTouchMode == TOUCH_MODE_SCROLL) { if (y != mLastY) { if (Math.abs(rawDeltaY) > mTouchSlop) { final ViewParent parent = getParent(); if (parent != null) { parent.requestDisallowInterceptTouchEvent(true); } } boolean atEdge = false; if (incrementalDeltaY != 0) { atEdge = trackMotionScroll(deltaY, incrementalDeltaY); } if (atEdge) { if (mVelocityTracker != null) { mVelocityTracker.clear(); } } mMotionX = x; mMotionY = y; mLastY = y; } } }
trackMotionScroll跟进去；这里就是重点
boolean trackMotionScroll(int deltaY, int incrementalDeltaY) { final int childCount = getChildCount(); final int firstPosition = mFirstPosition; final int firstTop = childCount == 0 ? mFirstTop : getChildAt(0) .getTop(); int lastBottom = childCount == 0 ? firstTop : getChildAt(childCount - 1).getBottom(); if (firstPosition + childCount >= mItemCount - 1) { if (!isRefreshing && !isLoadingMore && isLoadMoreOn && onLoadMoreStart != null) { isLoadingMore = true; onLoadMoreStart.onStart(); } } if (isRefreshing || isLoadingMore) { if (mZrcFooter != null) { lastBottom += mZrcFooter.getHeight(); } } final int mPaddingBottom = getPaddingBottom(); final int mPaddingTop = getPaddingTop(); final Rect listPadding = mListPadding; int effectivePaddingTop = 0; int effectivePaddingBottom = 0; final int spaceAbove = effectivePaddingTop - firstTop; final int end = getHeight() - effectivePaddingBottom; final int spaceBelow = lastBottom - end; final int height = getHeight() - mPaddingBottom - mPaddingTop; if (incrementalDeltaY < 0) { incrementalDeltaY = Math.max(-(height - 1), incrementalDeltaY); } else { incrementalDeltaY = Math.min(height - 1, incrementalDeltaY); } final Headable zrcHeader = mZrcHeader; final boolean isTooShort = childCount == mItemCount && lastBottom - firstTop < getHeight(); final int topOffset = firstTop - (listPadding.top + mFirstTopOffset + (showHeader ? zrcHeader .getHeight() : 0)); final int bottomOffset = isTooShort ?
firstTop - listPadding.top : lastBottom - getHeight() + listPadding.bottom + mLastBottomOffset; final boolean isOutOfTop = firstPosition == 0 && topOffset > 0; final boolean isOutOfBottom = firstPosition + childCount == mItemCount && bottomOffset < 0; final boolean cannotScrollDown = (isOutOfTop && incrementalDeltaY > 0); final boolean cannotScrollUp = (isOutOfBottom && incrementalDeltaY <= 0); if (isTooShort && cannotScrollDown && mTouchMode == TOUCH_MODE_RESCROLL) { mTouchMode = TOUCH_MODE_FLING; return true; } if (isOutOfTop || isOutOfBottom) { if (mTouchMode == TOUCH_MODE_SCROLL) { incrementalDeltaY /= 1.7f; if (zrcHeader != null && isOutOfTop) { final int state = zrcHeader.getState(); if (topOffset >= zrcHeader.getHeight()) { if (state == Headable.STATE_PULL || state == Headable.STATE_REST) { zrcHeader.stateChange(Headable.STATE_RELEASE, null); } } else { if (state == Headable.STATE_RELEASE || state == Headable.STATE_REST) { zrcHeader.stateChange(Headable.STATE_PULL, null); } } } } if (mTouchMode == TOUCH_MODE_RESCROLL && false) { if (isOutOfTop && zrcHeader != null) { final int state = zrcHeader.getState(); if (topOffset < 10 && (state == Headable.STATE_SUCCESS || state == Headable.STATE_FAIL)) { zrcHeader.stateChange(Headable.STATE_REST, null); removeCallbacks(mResetRunnable); } } } if (mTouchMode == TOUCH_MODE_FLING) { if (cannotScrollDown) { incrementalDeltaY /= 1.7f; int duration = firstTop - listPadding.top; if (duration > getHeight() / 6) { return true; } } else if (cannotScrollUp && !isOutOfTop) { incrementalDeltaY /= 1.7f; int duration = bottomOffset; if (duration < -getHeight() / 6) { return true; } } } else { if (incrementalDeltaY > 0) { int duration = firstTop - listPadding.top; if (duration > getHeight() / 2) { return true; } } else if (incrementalDeltaY < 0 && !isOutOfTop) { int duration = bottomOffset; if (duration < -getHeight() / 2) { return true; } } } if (onScrollStateListener != null) { if (mScrollState != OnScrollStateListener.EDGE) { mScrollState = OnScrollStateListener.EDGE; onScrollStateListener.onChange(OnScrollStateListener.EDGE); } } } else { if (zrcHeader != null) { if (zrcHeader.getState() == Headable.STATE_PULL) { zrcHeader.stateChange(Headable.STATE_REST, null); } } if (incrementalDeltaY > 5) { if (onScrollStateListener != null) { if (mScrollState != OnScrollStateListener.UP) { mScrollState = OnScrollStateListener.UP; onScrollStateListener .onChange(OnScrollStateListener.UP); } } } else if (incrementalDeltaY < -5) { if (onScrollStateListener != null) { if (mScrollState != OnScrollStateListener.DOWN) { mScrollState = OnScrollStateListener.DOWN; onScrollStateListener .onChange(OnScrollStateListener.DOWN); } } } } //---------------------美丽的切割线----------------- final boolean down = incrementalDeltaY < 0; final int headerViewsCount = getHeaderViewsCount(); final int footerViewsStart = mItemCount - getFooterViewsCount(); int start = 0; int count = 0; if (down) { int top = -incrementalDeltaY; for (int i = 0; i < childCount; i++) { final View child = getChildAt(i); if (child.getBottom() >= top + Math.min(0, bottomOffset)) { break; } else { count++; int position = firstPosition + i; if (position >= headerViewsCount && position < footerViewsStart) { mRecycler.addScrapView(child, position); } } } } else { int bottom = getHeight() - incrementalDeltaY; for (int i = childCount - 1; i >= 0; i--) { final View child = getChildAt(i); if (child.getTop() <= bottom + Math.max(0, topOffset)) { break; } else { start = i; count++; int position = firstPosition + i; if (position >= headerViewsCount && position < footerViewsStart) { mRecycler.addScrapView(child, position); } } } } mBlockLayoutRequests = true; if (count > 0) { detachViewsFromParent(start, count); mRecycler.removeSkippedScrap(); } if (!awakenScrollBars()) { invalidate(); } offsetChildrenTopAndBottom(incrementalDeltaY); if (down) { mFirstPosition += count; } final int absIncrementalDeltaY = Math.abs(incrementalDeltaY); if (spaceAbove < absIncrementalDeltaY || spaceBelow < absIncrementalDeltaY) { fillGap(down); } mFirstTop = getChildCount() == 0 ?
mFirstTop + incrementalDeltaY : getChildAt(0).getTop(); if (mSelectorPosition != INVALID_POSITION) { final int childIndex = mSelectorPosition - mFirstPosition; if (childIndex >= 0 && childIndex < getChildCount()) { positionSelector(INVALID_POSITION, getChildAt(childIndex)); } } else { mSelectorRect.setEmpty(); } mBlockLayoutRequests = false; invokeOnItemScrollListener(); return false; }
代码虽多可是事实上做了两件事，第一件切割符上面的推断并设置SimpleHeader的状态，SimpleHeader会依据状态做不同的变化；第二件依据须要调用fillGap(down)、offsetTopAndBottom使得ListView滚动起来。贴一下SimpleHeader的draw代码
@Override public boolean draw(Canvas canvas, int left, int top, int right, int bottom) { boolean more = false; final int width = right - left; final int height = mHeight; final int offset = bottom - top; canvas.save(); if (isClipCanvas) { canvas.clipRect(left + 5, 1, right + 5, bottom - 1); } switch (mState) { case STATE_REST: break; case STATE_PULL: case STATE_RELEASE: if (offset < 10) { break; } mPaint.setColor(mPointColor); for (int i = 0; i < mPice; i++) { int angleParam; if (offset < height * 3 / 4) { angleParam = offset * 16 / height - 3;// 每1%转0.16度; } else { angleParam = offset * 300 / height - 217;// 每1%转3度; } float angle = -(i * (360 / mPice) - angleParam) * PI / 180; float radiusParam; if (offset <= height) { radiusParam = offset / (float) height; radiusParam = 1 - radiusParam; radiusParam *= radiusParam; radiusParam = 1 - radiusParam; } else { radiusParam = 1; } float radius = width / 2 - radiusParam * (width / 2 - mCircleRadius); float x = (float) (width / 2 + radius * Math.cos(angle)); float y = (float) (offset / 2 + radius * Math.sin(angle)); canvas.drawCircle(x, y + top, mPointRadius, mPaint); } break; case STATE_LOADING: more = true; mPaint.setColor(mPointColor); for (int i = 0; i < mPice; i++) { int angleParam = mTime * 5; float angle = -(i * (360 / mPice) - angleParam) * PI / 180; float radius = mCircleRadius; float x = (float) (width / 2 + radius * Math.cos(angle)); float y; if (offset < height) { y = (float) (offset - height / 2 + radius * Math.sin(angle)); } else { y = (float) (offset / 2 + radius * Math.sin(angle)); } canvas.drawCircle(x, y + top, mPointRadius, mPaint); } mTime++; break; case STATE_SUCCESS: case STATE_FAIL: more = true; final int time = mTime; if (time < 30) { mPaint.setColor(mPointColor); for (int i = 0; i < mPice; i++) { int angleParam = mTime * 10; float angle = -(i * (360 / mPice) - angleParam) * PI / 180; float radius = mCircleRadius + time * mCircleRadius; float x = (float) (width / 2 + radius * Math.cos(angle)); float y; if (offset < height) { y = (float) (offset - height / 2 + radius * Math.sin(angle)); } else { y = (float) (offset / 2 + radius * Math.sin(angle)); } canvas.drawCircle(x, y + top, mPointRadius, mPaint); } mPaint.setColor(mTextColor); mPaint.setAlpha(time * 255 / 30); String text = mMsg != null ? mMsg : mState == STATE_SUCCESS ? "载入成功" : "载入失败"; float y; if (offset < height) { y = offset - height / 2; } else { y = offset / 2; } canvas.drawText(text, width / 2, y + top + mFontOffset, mPaint); } else { mPaint.setColor(mTextColor); String text = mMsg != null ? mMsg : mState == STATE_SUCCESS ?
"载入成功" : "载入失败"; float y; if (offset < height) { y = offset - height / 2; mPaint.setAlpha(offset * 255 / height); } else { y = offset / 2; } canvas.drawText(text, width / 2, y + top + mFontOffset, mPaint); } mTime++; break; } canvas.restore(); return more; }
这里有个问题那么draw这个函数什么时候调用呢，事实上是这种：ZrcListView再画自己的时候会调用draw–>onDraw–>dispatchDraw而在ZrcAbsListView中重写了，在这里调用了header和footer的draw方法。这样ZrcListView在画自己的时候也会去画header和footer了。
另一个关键点是ListView内部是怎么滚动起来的呢？我也是看了上面郭神的文章才了解的，详细大家能够细细去看，我这里写一个我理解的流程。fillGap主要是填充载入View到ListView中fillGap–>fillUp/fillDown–>makeAndAddView–>obtainView(真正把View从无到有的方法。假设缓存里没有就是从这里获得)–>setupChild（这种方法里View已经增加了。这时候就是滚动了）–>offsetTopAndBottom（移动）
最后一点ListView整个控件又是怎么移动的呢？我们知道下拉的时候它须要往下移动（一般移动量是手指移动的一半，这样比較有下拉的感觉）让出一定空间好让SimpleHeader能够展示自己。
关于这个分为两部分，第一部分：ListView尾随手指移动而移动它的二分之中的一个量；第二部分松开手指（可能会播放动画也可能不会）后ListView上移值原始位置 首先看第一部分。找了N久没找到他是怎么移动的；后来我一步步跟踪代码最后我把offsetTopAndBottom这段移动ListView内部的代码凝视掉发现子View动不了（肯定的）整个ListView也不会移动。于是有了例如以下猜想：
所以事实上ListView内部子view的offsetTopAndBottom就是整个ListView的移动他并没有在外面包一层View。心中一万仅仅某马奔腾而过。。 。待验证？？？？？
再然后说说第二部分：一句话概括就是在ACTION_UP里利用Scroller让ListView自然的飘逸的移动到原来的位置Adapter
ZrcListView的Adapter须要说下。看上面的类图能够看到一个HeaderViewListAdapter，这个是干嘛的呢？我把getView代码贴出来
public View getView(int position, View convertView, ViewGroup parent) { // Header (negative positions will throw an IndexOutOfBoundsException) int numHeaders = getHeadersCount(); if (position < numHeaders) { return mHeaderViewInfos.get(position).view; } // Adapter final int adjPosition = position - numHeaders; int adapterCount = 0; if (mAdapter != null) { adapterCount = mAdapter.getCount(); if (adjPosition < adapterCount) { return mAdapter.getView(adjPosition, convertView, parent); } } // Footer (off-limits positions will throw an IndexOutOfBoundsException) return mFooterViewInfos.get(adjPosition - adapterCount).view; } 还记得刚開始那个布局图吗，那个结构就是在这里进行处理的。
private final ListAdapter mAdapter; // These two ArrayList are assumed to NOT be null. // They are indeed created when declared in ListView and then shared. ArrayListmHeaderViewInfos; ArrayList mFooterViewInfos;
没错，这个就是实现ListView的HeaderView和FooterView功能的地方。HeaderViewListAdapter这个类里的这三个。mAdapter就是ListView的视图仅仅有一个，mHeaderViewInfos和mFooterViewInfos则能够有多个，你能够一直addHeaderView往里面加各种View。效果就是ListView.addHeaderView的效果
小白一枚，学习记录，轻喷