由于某些原因，我需要自定义一个LayoutManager来实现RecyclerView的流动布局项。代码是：
public class FlowLayoutManager extends RecyclerView.LayoutManager implements
RecyclerView.SmoothScroller.ScrollVectorProvider {
final static int LAYOUT_START = -1;
final static int LAYOUT_END = 1;
public static final int HORIZONTAL = LinearLayout.HORIZONTAL;
public static final int VERTICAL = LinearLayout.VERTICAL;
public static final int INVALID_OFFSET = Integer.MIN_VALUE;
private static final int DEFAULT_HORIZONTAL_SPACE = 12;
private static final int DEFAULT_VERTICAL_SPACE = 12;
@IntDef({HORIZONTAL, VERTICAL})
public @interface Orientation {
}
private SparseArray<Rect> mScrapRects;
private SparseIntArray mColumnCountOfRow;
private SparseArray<LayoutParams> mScrapSites;
private int mOffsetX;
private int mOffsetY;
private int mItemCount;
private int mLeft, mTop, mRight, mBottom;
private int mWidth, mHeight;
private int mTotalWidth;
private int mTotalHeight;
private int mScrollOffsetX;
private int mScrollOffsetY;
private int mVerticalSpace = DEFAULT_VERTICAL_SPACE;
private int mHorizontalSpace = DEFAULT_HORIZONTAL_SPACE;
int mPendingScrollPositionOffset = INVALID_OFFSET;
@Orientation
private int mOrientation = VERTICAL;
private RecyclerView.Recycler mRecycler;
private RecyclerView.State mState;
public FlowLayoutManager() {
this(VERTICAL);
}
public FlowLayoutManager(@Orientation int orientation) {
this(orientation, DEFAULT_VERTICAL_SPACE, DEFAULT_HORIZONTAL_SPACE);
}
public FlowLayoutManager(@Orientation int orientation, int verticalSpace, int horizontalSpace) {
setOrientation(orientation);
setSpace(verticalSpace, horizontalSpace);
setAutoMeasureEnabled(true);
}
public FlowLayoutManager(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {
Properties properties = getProperties(context, attrs, defStyleAttr, defStyleRes);
setOrientation(properties.orientation);
setReverseLayout(properties.reverseLayout);
setStackFromEnd(properties.stackFromEnd);
setAutoMeasureEnabled(true);
}
public void setSpace(int verticalSpace, int horizontalSpace) {
if (verticalSpace == mVerticalSpace && horizontalSpace == mHorizontalSpace) {
return;
}
this.mVerticalSpace = verticalSpace;
this.mHorizontalSpace = horizontalSpace;
requestLayout();
}
public void setOrientation(@Orientation int orientation) {
if (orientation == mOrientation) {
return;
}
this.mOrientation = orientation;
requestLayout();
}
public void setReverseLayout(boolean reverseLayout) {
}
public void setStackFromEnd(boolean stackFromEnd) {
}
@Orientation
public int getOrientation() {
return mOrientation;
}
@Override
public LayoutParams generateDefaultLayoutParams() {
return new LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT);
}
@Override
public LayoutParams generateLayoutParams(Context c, AttributeSet attrs) {
return new LayoutParams(c, attrs);
}
@Override
public LayoutParams generateLayoutParams(ViewGroup.LayoutParams lp) {
if (lp instanceof ViewGroup.MarginLayoutParams) {
return new LayoutParams((ViewGroup.MarginLayoutParams) lp);
} else {
return new LayoutParams(lp);
}
}
@Override
public boolean checkLayoutParams(RecyclerView.LayoutParams lp) {
return lp instanceof LayoutParams;
}
@Override
public boolean supportsPredictiveItemAnimations() {
return true;
}
@Override
public void scrollToPosition(int position) {
if (position >= getItemCount()) {
return;
}
View view = findViewByPosition(position);
if (view != null) {
if (canScrollVertically()) {
scrollVerticallyBy((int) (view.getY() - mTop), mRecycler, mState);
} else if (canScrollHorizontally()) {
scrollHorizontallyBy((int) (view.getX() - mLeft), mRecycler, mState);
}
}
}
@Override
public void smoothScrollToPosition(RecyclerView recyclerView, RecyclerView.State state, int position) {
LinearSmoothScroller scroller = new LinearSmoothScroller(recyclerView.getContext());
scroller.setTargetPosition(position);
startSmoothScroll(scroller);
}
@Override
public PointF computeScrollVectorForPosition(int targetPosition) {
final int direction = calculateScrollDirectionForPosition(targetPosition);
PointF outVector = new PointF();
if (direction == 0) {
return null;
}
if (canScrollHorizontally()) {
outVector.x = direction;
outVector.y = 0;
} else if (canScrollVertically()) {
outVector.x = 0;
outVector.y = direction;
}
return outVector;
}
@Override
public void onAdapterChanged(RecyclerView.Adapter oldAdapter, RecyclerView.Adapter newAdapter) {
mPendingScrollPositionOffset = INVALID_OFFSET;
removeAllViews();
}
@Override
public void onLayoutCompleted(RecyclerView.State state) {
// mPendingScrollPositionOffset = INVALID_OFFSET;
}
@Override
public void onLayoutChildren(RecyclerView.Recycler recycler, RecyclerView.State state) {
mRecycler = recycler;
mState = state;
mItemCount = getItemCount();
if (mItemCount == 0) {
detachAndScrapAttachedViews(recycler);
return;
}
if (getChildCount() == 0 && state.isPreLayout()) {
return;
}
mScrapRects = new SparseArray<>(mItemCount);
mScrapSites = new SparseArray<>(mItemCount);
mColumnCountOfRow = new SparseIntArray();
mScrollOffsetX = 0;
mScrollOffsetY = 0;
mWidth = getWidth();
mHeight = getHeight();
mLeft = getPaddingLeft();
mTop = getPaddingTop();
mRight = getPaddingRight();
mBottom = getPaddingBottom();
mOffsetX = mLeft;
mOffsetY = mTop;
detachAndScrapAttachedViews(recycler);
if (canScrollVertically()) {
mTotalHeight = calculateVerticalChildrenSites(recycler);
scrollVerticallyBy(mPendingScrollPositionOffset, recycler, state);
} else {
mTotalWidth = calculateHorizontalChildrenSites(recycler);
scrollHorizontallyBy(mPendingScrollPositionOffset, recycler, state);
}
// fillAndRecycleView(recycler, state);
}
private int calculateVerticalChildrenSites(RecyclerView.Recycler recycler) {
final int[] maxRowHeight = {0};
final int[] totalHeight = {0};
final Point point = new Point();
for (int i = 0; i < mItemCount; i++) {
View scrap = recycler.getViewForPosition(i);
addView(scrap);
measureChildWithMargins(scrap, 0, 0);
final int width = getDecoratedMeasurementHorizontal(scrap);
final int height = getDecoratedMeasurementVertical(scrap);
if (mOffsetX + width + mHorizontalSpace > mWidth - mRight) {
mOffsetX = mLeft;
mOffsetY += maxRowHeight[0] + (i == 0 ? 0 : mVerticalSpace);
maxRowHeight[0] = 0;
point.x = 0;
point.y++;
}
maxRowHeight[0] = Math.max(height, maxRowHeight[0]);
LayoutParams lp = (LayoutParams) scrap.getLayoutParams();
lp.column = point.x++;
lp.row = point.y;
if (lp.column != 0) {
mOffsetX += mHorizontalSpace;
}
mScrapSites.put(i, lp);
mColumnCountOfRow.put(lp.row, lp.column + 1);
Rect frame = mScrapRects.get(i);
if (frame == null) {
frame = new Rect();
}
frame.set(mOffsetX, mOffsetY, mOffsetX = mOffsetX + width, mOffsetY + height);
mScrapRects.put(i, frame);
totalHeight[0] = Math.max(totalHeight[0], mOffsetY + height);
layoutDecoratedWithMargins(scrap, frame.left, frame.top, frame.right, frame.bottom);
}
return Math.max(totalHeight[0] - mTop, getVerticalSpace());
}
private int calculateHorizontalChildrenSites(RecyclerView.Recycler recycler) {
final int[] maxColumnWidth = {0};
final int[] totalWidth = {0};
final Point point = new Point();
for (int i = 0; i < mItemCount; i++) {
View scrap = recycler.getViewForPosition(i);
addView(scrap);
measureChildWithMargins(scrap, 0, 0);
final int width = getDecoratedMeasurementHorizontal(scrap);
final int height = getDecoratedMeasurementVertical(scrap);
if (mOffsetY + height + mVerticalSpace > mHeight - mBottom) {
mOffsetY = mTop;
mOffsetX += maxColumnWidth[0] + (i == 0 ? 0 : mHorizontalSpace);
maxColumnWidth[0] = 0;
point.x++;
point.y = 0;
}
maxColumnWidth[0] = Math.max(width, maxColumnWidth[0]);
LayoutParams lp = (LayoutParams) scrap.getLayoutParams();
lp.column = point.x;
lp.row = point.y++;
if (lp.row != 0) {
mOffsetY += mVerticalSpace;
}
mScrapSites.put(i, lp);
mColumnCountOfRow.put(lp.row, lp.column + 1);
Rect frame = mScrapRects.get(i);
if (frame == null) {
frame = new Rect();
}
frame.set(mOffsetX, mOffsetY, mOffsetX + width, mOffsetY = mOffsetY + height);
mScrapRects.put(i, frame);
totalWidth[0] = Math.max(totalWidth[0], mOffsetX + width);
layoutDecoratedWithMargins(scrap, frame.left, frame.top, frame.right, frame.bottom);
}
return Math.max(totalWidth[0] - mLeft, getHorizontalSpace());
}
@SuppressWarnings("unused")
private void fillAndRecycleView(RecyclerView.Recycler recycler, RecyclerView.State state) {
if (mItemCount == 0 || state.isPreLayout()) {
return;
}
Rect displayFrame = canScrollVertically()
? new Rect(mLeft, mScrollOffsetY, mWidth, mScrollOffsetY + mHeight)
: new Rect(mScrollOffsetX, mTop, mScrollOffsetX + mWidth, mHeight);
for (int i = 0; i < mItemCount; i++) {
Rect rect = mScrapRects.get(i);
if (!Rect.intersects(displayFrame, rect)) {
View scrap = getChildAt(i);
if (scrap != null) {
removeAndRecycleView(scrap, recycler);
}
return;
}
View scrap = recycler.getViewForPosition(i);
addView(scrap);
measureChildWithMargins(scrap, 0, 0);
if (canScrollVertically()) {
layoutDecoratedWithMargins(scrap, rect.left, rect.top - mScrollOffsetY, rect.right, rect.bottom - mScrollOffsetY);
} else {
layoutDecoratedWithMargins(scrap, rect.left - mScrollOffsetX, rect.top, rect.right - mScrollOffsetX, rect.bottom);
}
}
}
@Override
public boolean canScrollVertically() {
return mOrientation == VERTICAL;
}
@Override
public boolean canScrollHorizontally() {
return mOrientation == HORIZONTAL;
}
@Override
public int scrollVerticallyBy(int dy, RecyclerView.Recycler recycler, RecyclerView.State state) {
if (dy == 0 || mItemCount == 0) {
return 0;
}
int travel = dy;
if (mScrollOffsetY + travel < 0) {
travel = -mScrollOffsetY;
} else if (mScrollOffsetY + travel > mTotalHeight - getVerticalSpace()) {//如果滑动到最底部
travel = mTotalHeight - getVerticalSpace() - mScrollOffsetY;
}
mPendingScrollPositionOffset = (mScrollOffsetY += travel);
offsetChildrenVertical(-travel);
return travel;
}
@Override
public int scrollHorizontallyBy(int dx, RecyclerView.Recycler recycler, RecyclerView.State state) {
if (dx == 0 || mItemCount == 0) {
return 0;
}
int travel = dx;
if (mScrollOffsetX + travel < 0) {
travel = -mScrollOffsetX;
} else if (mScrollOffsetX + travel > mTotalWidth - getHorizontalSpace()) {//如果滑动到最底部
travel = mTotalWidth - getHorizontalSpace() - mScrollOffsetX;
}
mPendingScrollPositionOffset = (mScrollOffsetX += travel);
// detachAndScrapAttachedViews(recycler);
offsetChildrenHorizontal(-travel);
// fillAndRecycleView(recycler, state);
return travel;
}
@Nullable
public LayoutParams getLayoutParamsByPosition(int position) {
return mScrapSites.get(position);
}
public int getRow(int position) {
LayoutParams params = getLayoutParamsByPosition(position);
return params != null ? params.row : 0;
}
public int getColumn(int position) {
LayoutParams params = getLayoutParamsByPosition(position);
return params != null ? params.column : 0;
}
public int getColumnCountOfRow(int row) {
return mColumnCountOfRow.get(row, 1);
}
private int calculateScrollDirectionForPosition(int position) {
if (getChildCount() == 0) {
return LAYOUT_START;
}
return position < getFirstChildPosition() ? LAYOUT_START : LAYOUT_END;
}
int getFirstChildPosition() {
final int childCount = getChildCount();
return childCount == 0 ? 0 : getPosition(getChildAt(0));
}
private int getDecoratedMeasurementHorizontal(View view) {
final LayoutParams params = (LayoutParams) view.getLayoutParams();
return getDecoratedMeasuredWidth(view) + params.leftMargin + params.rightMargin;
}
private int getDecoratedMeasurementVertical(View view) {
final LayoutParams params = (LayoutParams) view.getLayoutParams();
return getDecoratedMeasuredHeight(view) + params.topMargin + params.bottomMargin;
}
private int getVerticalSpace() {
return mHeight - mBottom - mTop;
}
private int getHorizontalSpace() {
return mWidth - mLeft - mRight;
}
public static class LayoutParams extends RecyclerView.LayoutParams {
//Current row in the grid
public int row;
//Current column in the grid
public int column;
public LayoutParams(Context c, AttributeSet attrs) {
super(c, attrs);
}
public LayoutParams(int width, int height) {
super(width, height);
}
public LayoutParams(ViewGroup.MarginLayoutParams source) {
super(source);
}
public LayoutParams(ViewGroup.LayoutParams source) {
super(source);
}
public LayoutParams(RecyclerView.LayoutParams source) {
super(source);
}
@Override
public String toString() {
return "LayoutParams = {"
+ "width=" + width
+ ",height=" + height
+ ",row=" + row
+ ",column=" + column + "}";
}
}
}
之后，将此FlowlayoutManager设置为RecyclerView，然后我发现RecyclerView在设置显示的LinearLayoutManager时未显示滚动条。
这是xml文件中的RecyclerView：
<android.support.v7.widget.RecyclerView
android:id="@+id/recyclerview"
android:layout_width="match_parent"
android:layout_height="400dp"
android:scrollbars="vertical"/>
具有400dp的高度和scrollbars属性。
问题似乎是我自定义的FlowLayoutManager，但我真的不知道这个问题，有人可以帮忙，还是谢谢！！
答案 0 :(得分：0)
看看parentId和RecyclerView的来源，似乎自定义LayoutManager必须实现以下方法来显示滚动条：