下面列出了android.support.v7.widget.OrientationHelper#getDecoratedStart ( ) 实例代码，或者点击链接到github查看源代码，也可以在右侧发表评论。
/**
* 当item位置变换，滚动recycler到正确的位置
* TODO: 2017/2/21 0021 整理更优雅的写法 还有scrollToPosition(0)是否必要？
*/
private void scrollToRightPositionWhenItemChanged(RecyclerView recyclerView, View itemView, int itemPos) {
final RecyclerView.LayoutManager layoutManager = recyclerView.getLayoutManager();
if (layoutManager instanceof ItemTouchHelper.ViewDropHandler) {
OrientationHelper helper = OrientationHelper.createVerticalHelper(layoutManager);
int start = helper.getDecoratedStart(itemView);
int end = helper.getDecoratedEnd(itemView);
((LinearLayoutManager) layoutManager).scrollToPositionWithOffset(
itemPos, lastItemPos > itemPos ? start : end - itemViewHeight);
// System.out.println(lastItemPos + "-" + childPos + "OrientationHelperOrientationHelper:"
// + height + "==" + itemViewHeight + "=||=" + start + "===" + end + "||||||" + myStart + "===" + itemTargetView.getHeight() );
}
if (lastItemPos == 0 || itemPos == 0) {
recyclerView.scrollToPosition(0);
}
}
private int distanceToStart(View targetView, @NonNull OrientationHelper helper, boolean fromEnd) {
if (isRtlHorizontal && !fromEnd) {
return distanceToEnd(targetView, helper, true);
}
return helper.getDecoratedStart(targetView) - helper.getStartAfterPadding();
}
private View findEndView(RecyclerView.LayoutManager layoutManager,
OrientationHelper helper) {
if (layoutManager instanceof LinearLayoutManager) {
int lastChild = ((LinearLayoutManager) layoutManager).findLastVisibleItemPosition();
if (lastChild == RecyclerView.NO_POSITION) {
return null;
}
View child = layoutManager.findViewByPosition(lastChild);
float visibleWidth;
if (isRtlHorizontal) {
visibleWidth = (float) helper.getDecoratedEnd(child)
/ helper.getDecoratedMeasurement(child);
} else {
visibleWidth = (float) (helper.getTotalSpace() - helper.getDecoratedStart(child))
/ helper.getDecoratedMeasurement(child);
}
// If we're at the start of the list, we shouldn't snap
// to avoid having the first item not completely visible.
boolean startOfList = ((LinearLayoutManager) layoutManager)
.findFirstCompletelyVisibleItemPosition() == 0;
if (visibleWidth > 0.5f && !startOfList) {
return child;
} else if (startOfList) {
return null;
} else {
// If the child wasn't returned, we need to return the previous view
return layoutManager.findViewByPosition(lastChild - 1);
}
}
return null;
}
View findOneVisibleChild(int fromIndex, int toIndex, boolean completelyVisible,
boolean acceptPartiallyVisible) {
OrientationHelper helper;
if (layoutManager.canScrollVertically()) {
helper = OrientationHelper.createVerticalHelper(layoutManager);
} else {
helper = OrientationHelper.createHorizontalHelper(layoutManager);
}
final int start = helper.getStartAfterPadding();
final int end = helper.getEndAfterPadding();
final int next = toIndex > fromIndex ? 1 : -1;
View partiallyVisible = null;
for (int i = fromIndex; i != toIndex; i += next) {
final View child = layoutManager.getChildAt(i);
final int childStart = helper.getDecoratedStart(child);
final int childEnd = helper.getDecoratedEnd(child);
if (childStart < end && childEnd > start) {
if (completelyVisible) {
if (childStart >= start && childEnd <= end) {
return child;
} else if (acceptPartiallyVisible && partiallyVisible == null) {
partiallyVisible = child;
}
} else {
return child;
}
}
}
return partiallyVisible;
}
View findOneVisibleChild(int fromIndex, int toIndex, boolean completelyVisible,
boolean acceptPartiallyVisible) {
OrientationHelper helper;
if (layoutManager.canScrollVertically()) {
helper = OrientationHelper.createVerticalHelper(layoutManager);
} else {
helper = OrientationHelper.createHorizontalHelper(layoutManager);
}
final int start = helper.getStartAfterPadding();
final int end = helper.getEndAfterPadding();
final int next = toIndex > fromIndex ? 1 : -1;
View partiallyVisible = null;
for (int i = fromIndex; i != toIndex; i += next) {
final View child = layoutManager.getChildAt(i);
final int childStart = helper.getDecoratedStart(child);
final int childEnd = helper.getDecoratedEnd(child);
if (childStart < end && childEnd > start) {
if (completelyVisible) {
if (childStart >= start && childEnd <= end) {
return child;
} else if (acceptPartiallyVisible && partiallyVisible == null) {
partiallyVisible = child;
}
} else {
return child;
}
}
}
return partiallyVisible;
}
private int getDistanceToStart(View targetView, @NonNull OrientationHelper helper) {
int distance;
// If we don't care about padding, just snap to the start of the view
if (!snapToPadding) {
int childStart = helper.getDecoratedStart(targetView);
if (childStart >= helper.getStartAfterPadding() / 2) {
distance = childStart - helper.getStartAfterPadding();
} else {
distance = childStart;
}
} else {
distance = helper.getDecoratedStart(targetView) - helper.getStartAfterPadding();
}
return distance;
}
private int distanceToStart(View targetView, @NonNull OrientationHelper helper, boolean fromEnd) {
if (isRtlHorizontal && !fromEnd) {
return distanceToEnd(targetView, helper, true);
}
return helper.getDecoratedStart(targetView) - helper.getStartAfterPadding();
}
public View findOneVisibleChild(int fromIndex, int toIndex, boolean completelyVisible,
boolean acceptPartiallyVisible) {
OrientationHelper helper;
if (layoutManager.canScrollVertically()) {
helper = OrientationHelper.createVerticalHelper(layoutManager);
} else {
helper = OrientationHelper.createHorizontalHelper(layoutManager);
}
final int start = helper.getStartAfterPadding();
final int end = helper.getEndAfterPadding();
final int next = toIndex > fromIndex ? 1 : -1;
View partiallyVisible = null;
for (int i = fromIndex; i != toIndex; i += next) {
final View child = layoutManager.getChildAt(i);
final int childStart = helper.getDecoratedStart(child);
final int childEnd = helper.getDecoratedEnd(child);
if (childStart < end && childEnd > start) {
if (completelyVisible) {
if (childStart >= start && childEnd <= end) {
return child;
} else if (acceptPartiallyVisible && partiallyVisible == null) {
partiallyVisible = child;
}
} else {
return child;
}
}
}
return partiallyVisible;
}
private int distanceToStart(View targetView, OrientationHelper helper, boolean fromEnd) {
if (mIsRtlHorizontal && !fromEnd) {
return distanceToEnd(targetView, helper, true);
}
return helper.getDecoratedStart(targetView) - helper.getStartAfterPadding();
}
private View findEndView(RecyclerView.LayoutManager layoutManager,
OrientationHelper helper) {
if (layoutManager instanceof LinearLayoutManager) {
int lastChild = ((LinearLayoutManager) layoutManager).findLastVisibleItemPosition();
if (lastChild == RecyclerView.NO_POSITION) {
return null;
}
View child = layoutManager.findViewByPosition(lastChild);
float visibleWidth;
if (mIsRtlHorizontal) {
visibleWidth = (float) helper.getDecoratedEnd(child)
/ helper.getDecoratedMeasurement(child);
} else {
visibleWidth = (float) (helper.getTotalSpace() - helper.getDecoratedStart(child))
/ helper.getDecoratedMeasurement(child);
}
// If we're at the start of the list, we shouldn't snap
// to avoid having the first item not completely visible.
boolean startOfList = ((LinearLayoutManager) layoutManager)
.findFirstCompletelyVisibleItemPosition() == 0;
if (visibleWidth > 0.5f && !startOfList) {
return child;
} else if (mSnapLastItemEnabled && startOfList) {
return child;
} else if (startOfList) {
return null;
} else {
// If the child wasn't returned, we need to return the previous view
return layoutManager.findViewByPosition(lastChild - 1);
}
}
return null;
}
private int distanceToStart(View targetView, @NonNull OrientationHelper helper, boolean fromEnd) {
if (isRtlHorizontal && !fromEnd) {
return distanceToEnd(targetView, helper, true);
}
return helper.getDecoratedStart(targetView) - helper.getStartAfterPadding();
}
private int distanceToStart(View targetView, OrientationHelper helper, boolean fromEnd) {
if (isRtlHorizontal && !fromEnd) {
return distanceToEnd(targetView, helper, true);
}
return helper.getDecoratedStart(targetView) - helper.getStartAfterPadding();
}
@Nullable
private View findStartView(RecyclerView.LayoutManager layoutManager,
@NonNull OrientationHelper helper) {
if (layoutManager instanceof LinearLayoutManager) {
LinearLayoutManager linearLayoutManager = (LinearLayoutManager) layoutManager;
boolean reverseLayout = linearLayoutManager.getReverseLayout();
int firstChild = reverseLayout ? linearLayoutManager.findLastVisibleItemPosition()
: linearLayoutManager.findFirstVisibleItemPosition();
int offset = 1;
if (layoutManager instanceof GridLayoutManager) {
offset += ((GridLayoutManager) layoutManager).getSpanCount() - 1;
}
if (firstChild == RecyclerView.NO_POSITION) {
return null;
}
View child = layoutManager.findViewByPosition(firstChild);
float visibleWidth;
if (isRtlHorizontal) {
visibleWidth = (float) (helper.getTotalSpace() - helper.getDecoratedStart(child))
/ helper.getDecoratedMeasurement(child);
} else {
visibleWidth = (float) helper.getDecoratedEnd(child)
/ helper.getDecoratedMeasurement(child);
}
boolean endOfList;
if (!reverseLayout) {
endOfList = ((LinearLayoutManager) layoutManager)
.findLastCompletelyVisibleItemPosition()
== layoutManager.getItemCount() - 1;
} else {
endOfList = ((LinearLayoutManager) layoutManager)
.findFirstCompletelyVisibleItemPosition()
== 0;
}
if (visibleWidth > 0.5f && !endOfList) {
return child;
} else if (snapLastItem && endOfList) {
return child;
} else if (endOfList) {
return null;
} else {
return reverseLayout ? layoutManager.findViewByPosition(firstChild - offset)
: layoutManager.findViewByPosition(firstChild + offset);
}
}
return null;
}
/**
* Returns the first view that we should snap to.
*
* @param layoutManager the recyclerview's layout manager
* @param helper orientation helper to calculate view sizes
* @return the first view in the LayoutManager to snap to
*/
private View findStartView(RecyclerView.LayoutManager layoutManager,
OrientationHelper helper) {
if (layoutManager instanceof LinearLayoutManager) {
int firstChild = ((LinearLayoutManager) layoutManager).findFirstVisibleItemPosition();
int offset = 1;
if (layoutManager instanceof GridLayoutManager) {
offset += ((GridLayoutManager) layoutManager).getSpanCount() - 1;
}
if (firstChild == RecyclerView.NO_POSITION) {
return null;
}
View child = layoutManager.findViewByPosition(firstChild);
float visibleWidth;
// We should return the child if it's visible width
// is greater than 0.5 of it's total width.
// In a RTL configuration, we need to check the start point and in LTR the end point
if (isRtlHorizontal) {
visibleWidth = (float) (helper.getTotalSpace() - helper.getDecoratedStart(child))
/ helper.getDecoratedMeasurement(child);
} else {
visibleWidth = (float) helper.getDecoratedEnd(child)
/ helper.getDecoratedMeasurement(child);
}
// If we're at the end of the list, we shouldn't snap
// to avoid having the last item not completely visible.
boolean endOfList = ((LinearLayoutManager) layoutManager)
.findLastCompletelyVisibleItemPosition()
== layoutManager.getItemCount() - 1;
if (visibleWidth > 0.5f && !endOfList) {
return child;
} else if (snapLastItem && endOfList) {
return child;
} else if (endOfList) {
return null;
} else {
// If the child wasn't returned, we need to return
// the next view close to the start.
return layoutManager.findViewByPosition(firstChild + offset);
}
}
return null;
}
/**
* Returns the first view that we should snap to.
*
* @param layoutManager the recyclerview's layout manager
* @param helper orientation helper to calculate view sizes
* @return the first view in the LayoutManager to snap to
*/
private View findStartView(RecyclerView.LayoutManager layoutManager,
OrientationHelper helper) {
if (layoutManager instanceof LinearLayoutManager) {
int firstChild = ((LinearLayoutManager) layoutManager).findFirstVisibleItemPosition();
if (firstChild == RecyclerView.NO_POSITION) {
return null;
}
View child = layoutManager.findViewByPosition(firstChild);
float visibleWidth;
// We should return the child if it's visible width
// is greater than 0.5 of it's total width.
// In a RTL configuration, we need to check the start point and in LTR the end point
if (isRtlHorizontal) {
visibleWidth = (float) (helper.getTotalSpace() - helper.getDecoratedStart(child))
/ helper.getDecoratedMeasurement(child);
} else {
visibleWidth = (float) helper.getDecoratedEnd(child)
/ helper.getDecoratedMeasurement(child);
}
// If we're at the end of the list, we shouldn't snap
// to avoid having the last item not completely visible.
boolean endOfList = ((LinearLayoutManager) layoutManager)
.findLastCompletelyVisibleItemPosition()
== layoutManager.getItemCount() - 1;
if (visibleWidth > 0.5f && !endOfList) {
return child;
} else if (endOfList) {
return null;
} else {
// If the child wasn't returned, we need to return
// the next view close to the start.
return layoutManager.findViewByPosition(firstChild + 1);
}
}
return null;
}
@Nullable
private View findStartView(RecyclerView.LayoutManager layoutManager,
@NonNull OrientationHelper helper) {
if (layoutManager instanceof LinearLayoutManager) {
LinearLayoutManager linearLayoutManager = (LinearLayoutManager) layoutManager;
boolean reverseLayout = linearLayoutManager.getReverseLayout();
int firstChild = reverseLayout ? linearLayoutManager.findLastVisibleItemPosition()
: linearLayoutManager.findFirstVisibleItemPosition();
int offset = 1;
if (layoutManager instanceof GridLayoutManager) {
offset += ((GridLayoutManager) layoutManager).getSpanCount() - 1;
}
if (firstChild == RecyclerView.NO_POSITION) {
return null;
}
View child = layoutManager.findViewByPosition(firstChild);
float visibleWidth;
if (isRtlHorizontal) {
visibleWidth = (float) (helper.getTotalSpace() - helper.getDecoratedStart(child))
/ helper.getDecoratedMeasurement(child);
} else {
visibleWidth = (float) helper.getDecoratedEnd(child)
/ helper.getDecoratedMeasurement(child);
}
boolean endOfList;
if (!reverseLayout) {
endOfList = ((LinearLayoutManager) layoutManager)
.findLastCompletelyVisibleItemPosition()
== layoutManager.getItemCount() - 1;
} else {
endOfList = ((LinearLayoutManager) layoutManager)
.findFirstCompletelyVisibleItemPosition()
== 0;
}
if (visibleWidth > 0.5f && !endOfList) {
return child;
} else if (snapLastItem && endOfList) {
return child;
} else if (endOfList) {
return null;
} else {
return reverseLayout ? layoutManager.findViewByPosition(firstChild - offset)
: layoutManager.findViewByPosition(firstChild + offset);
}
}
return null;
}
@Nullable
private View findEndView(RecyclerView.LayoutManager layoutManager,
@NonNull OrientationHelper helper) {
if (layoutManager instanceof LinearLayoutManager) {
LinearLayoutManager linearLayoutManager = (LinearLayoutManager) layoutManager;
boolean reverseLayout = linearLayoutManager.getReverseLayout();
int lastChild = reverseLayout ? linearLayoutManager.findFirstVisibleItemPosition()
: linearLayoutManager.findLastVisibleItemPosition();
int offset = 1;
if (layoutManager instanceof GridLayoutManager) {
offset += ((GridLayoutManager) layoutManager).getSpanCount() - 1;
}
if (lastChild == RecyclerView.NO_POSITION) {
return null;
}
View child = layoutManager.findViewByPosition(lastChild);
float visibleWidth;
if (isRtlHorizontal) {
visibleWidth = (float) helper.getDecoratedEnd(child)
/ helper.getDecoratedMeasurement(child);
} else {
visibleWidth = (float) (helper.getTotalSpace() - helper.getDecoratedStart(child))
/ helper.getDecoratedMeasurement(child);
}
boolean startOfList;
if (!reverseLayout) {
startOfList = ((LinearLayoutManager) layoutManager)
.findFirstCompletelyVisibleItemPosition() == 0;
} else {
startOfList = ((LinearLayoutManager) layoutManager)
.findLastCompletelyVisibleItemPosition()
== layoutManager.getItemCount() - 1;
}
if (visibleWidth > 0.5f && !startOfList) {
return child;
} else if (snapLastItem && startOfList) {
return child;
} else if (startOfList) {
return null;
} else {
return reverseLayout ? layoutManager.findViewByPosition(lastChild + offset)
: layoutManager.findViewByPosition(lastChild - offset);
}
}
return null;
}
private int distanceToStart(View targetView, OrientationHelper helper) {
return helper.getDecoratedStart(targetView) - helper.getStartAfterPadding();
}
private int distanceToStart(View targetView, OrientationHelper helper) {
return helper.getDecoratedStart(targetView) - helper.getStartAfterPadding();
}
/**
* Returns the first view that we should snap to.
*
* @param layoutManager the recyclerview's layout manager
* @param helper orientation helper to calculate view sizes
* @return the first view in the LayoutManager to snap to
*/
private View findStartView(RecyclerView.LayoutManager layoutManager,
OrientationHelper helper) {
if (layoutManager instanceof LinearLayoutManager) {
int firstChild = ((LinearLayoutManager) layoutManager).findFirstVisibleItemPosition();
if (firstChild == RecyclerView.NO_POSITION) {
return null;
}
View child = layoutManager.findViewByPosition(firstChild);
float visibleWidth;
// We should return the child if it's visible width
// is greater than 0.5 of it's total width.
// In a RTL configuration, we need to check the start point and in LTR the end point
if (mIsRtlHorizontal) {
visibleWidth = (float) (helper.getTotalSpace() - helper.getDecoratedStart(child))
/ helper.getDecoratedMeasurement(child);
} else {
visibleWidth = (float) helper.getDecoratedEnd(child)
/ helper.getDecoratedMeasurement(child);
}
// If we're at the end of the list, we shouldn't snap
// to avoid having the last item not completely visible.
boolean endOfList = ((LinearLayoutManager) layoutManager)
.findLastCompletelyVisibleItemPosition()
== layoutManager.getItemCount() - 1;
if (visibleWidth > 0.5f && !endOfList) {
return child;
} else if (mSnapLastItemEnabled && endOfList) {
return child;
} else if (endOfList) {
return null;
} else {
// If the child wasn't returned, we need to return
// the next view close to the start.
return layoutManager.findViewByPosition(firstChild + 1);
}
}
return null;
}