Android自定义控件进阶：自定义LayoutManager

if (Math.abs(realDx) < 0.00000001f) {
return 0;
}

mHorizontalOffset += dx;

dx = fill(recycler, state, dx);

return dx;
}

private int fill(RecyclerView.Recycler recycler, RecyclerView.State state, int dx) {
int resultDelta = dx;
resultDelta = fillHorizontalLeft(recycler, state, dx);
recycleChildren(recycler);
return resultDelta;
}

private int fillHorizontalLeft(RecyclerView.Recycler recycler, RecyclerView.State state, int dx) {
//----------------1、边界检测-----------------
if (dx < 0) {
// 已到达左边界
if (mHorizontalOffset < 0) {
mHorizontalOffset = dx = 0;
}
}

if (dx > 0) {
if (mHorizontalOffset >= getMaxOffset()) {
// 根据最大偏移量来计算滑动到最右侧边缘
mHorizontalOffset = (long) getMaxOffset();
dx = 0;
}
}

// 分离全部的view，加入到临时缓存
detachAndScrapAttachedViews(recycler);

float startX = 0;
float fraction = 0f;
boolean isChildLayoutLeft = true;

View tempView = null;
int tempPosition = -1;

if (onceCompleteScrollLength == -1) {
// 因为mFirstVisiPos在下面可能被改变，所以用tempPosition暂存一下
tempPosition = mFirstVisiPos;
tempView = recycler.getViewForPosition(tempPosition);
measureChildWithMargins(tempView, 0, 0);
childWidth = getDecoratedMeasurementHorizontal(tempView);
}

// 修正第一个可见view mFirstVisiPos 已经滑动了多少个完整的onceCompleteScrollLength就代表滑动了多少个item
firstChildCompleteScrollLength = getWidth() / 2 + childWidth / 2;
if (mHorizontalOffset >= firstChildCompleteScrollLength) {
startX = normalViewGap;
onceCompleteScrollLength = childWidth + normalViewGap;
mFirstVisiPos = (int) Math.floor(Math.abs(mHorizontalOffset - firstChildCompleteScrollLength) / onceCompleteScrollLength) + 1;
fraction = (Math.abs(mHorizontalOffset - firstChildCompleteScrollLength) % onceCompleteScrollLength) / (onceCompleteScrollLength * 1.0f);
} else {
mFirstVisiPos = 0;
startX = getMinOffset();
onceCompleteScrollLength = firstChildCompleteScrollLength;
fraction = (Math.abs(mHorizontalOffset) % onceCompleteScrollLength) / (onceCompleteScrollLength * 1.0f);
}

// 临时将mLastVisiPos赋值为getItemCount() - 1，放心，下面遍历时会判断view是否已溢出屏幕，并及时修正该值并结束布局
mLastVisiPos = getItemCount() - 1;

float normalViewOffset = onceCompleteScrollLength * fraction;
boolean isNormalViewOffsetSetted = false;

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