我有一组照片，我正在使用 RecyclerView 来显示它们。我想让我的 RecyclerView 中的第一个元素跨越 2 列和 2 行:
我知道我可以使用 setSpanSizeLookup 跨越 2 列:
GridLayoutManager gridLayoutManager = new GridLayoutManager(this, 3);
gridLayoutManager.setSpanSizeLookup(new GridLayoutManager.SpanSizeLookup() {
@Override
public int getSpanSize(int position) {
if (position == 0) {
return 2;
} else {
return 1;
}
}
});
但我怎样才能让第一个项目也跨越 2 行？
我尝试通过将不同布局的高度加倍来设置第一个项目的高度不同，但这导致与第一个项目位于同一行的每个项目也被拉伸(stretch)到该高度:
@Override
public ProfilePicViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View itemView;
if (viewType == TYPE_MAIN_PHOTO) {
itemView = LayoutInflater.from(parent.getContext()).inflate(R.layout.card_view_main_profile_photo, parent, false);
} else {
itemView = LayoutInflater.from(parent.getContext()).inflate(R.layout.card_view_profile_photo, parent, false);
}
return new ProfilePicViewHolder(itemView);
}
最佳答案
您无法使用 GridLayoutManager 实现此行为，因为它仅支持跨越多列。
Nick Butcher 目前正在实现一个自定义的 SpannedGridLayoutManager，它完全符合您的要求。它允许您同时跨越多个行和列。实现仍然是 WIP，但已经运行得很好。
SpannedGridLayoutManager.java
package io.plaidapp.ui.recyclerview;
import android.content.Context;
import android.content.res.TypedArray;
import android.graphics.PointF;
import android.graphics.Rect;
import android.support.annotation.Keep;
import android.support.annotation.NonNull;
import android.support.v7.widget.LinearSmoothScroller;
import android.support.v7.widget.RecyclerView;
import android.util.AttributeSet;
import android.util.SparseArray;
import android.view.View;
import android.view.ViewGroup;
import java.util.ArrayList;
import java.util.List;
import io.plaidapp.R;
/**
* A {@link RecyclerView.LayoutManager} which displays a regular grid (i.e. all cells are the same
* size) and allows simultaneous row & column spanning.
*/
public class SpannedGridLayoutManager extends RecyclerView.LayoutManager {
private GridSpanLookup spanLookup;
private int columns = 1;
private float cellAspectRatio = 1f;
private int cellHeight;
private int[] cellBorders;
private int firstVisiblePosition;
private int lastVisiblePosition;
private int firstVisibleRow;
private int lastVisibleRow;
private boolean forceClearOffsets;
private SparseArray<GridCell> cells;
private List<Integer> firstChildPositionForRow; // key == row, val == first child position
private int totalRows;
private final Rect itemDecorationInsets = new Rect();
public SpannedGridLayoutManager(GridSpanLookup spanLookup, int columns, float cellAspectRatio) {
this.spanLookup = spanLookup;
this.columns = columns;
this.cellAspectRatio = cellAspectRatio;
setAutoMeasureEnabled(true);
}
@Keep /* XML constructor, see RecyclerView#createLayoutManager */
public SpannedGridLayoutManager(
Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {
TypedArray a = context.obtainStyledAttributes(
attrs, R.styleable.SpannedGridLayoutManager, defStyleAttr, defStyleRes);
columns = a.getInt(R.styleable.SpannedGridLayoutManager_spanCount, 1);
parseAspectRatio(a.getString(R.styleable.SpannedGridLayoutManager_aspectRatio));
// TODO use this!
int orientation = a.getInt(
R.styleable.SpannedGridLayoutManager_android_orientation, RecyclerView.VERTICAL);
a.recycle();
setAutoMeasureEnabled(true);
}
public interface GridSpanLookup {
SpanInfo getSpanInfo(int position);
}
public void setSpanLookup(@NonNull GridSpanLookup spanLookup) {
this.spanLookup = spanLookup;
}
public static class SpanInfo {
public int columnSpan;
public int rowSpan;
public SpanInfo(int columnSpan, int rowSpan) {
this.columnSpan = columnSpan;
this.rowSpan = rowSpan;
}
public static final SpanInfo SINGLE_CELL = new SpanInfo(1, 1);
}
public static class LayoutParams extends RecyclerView.LayoutParams {
int columnSpan;
int rowSpan;
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 void onLayoutChildren(RecyclerView.Recycler recycler, RecyclerView.State state) {
calculateWindowSize();
calculateCellPositions(recycler, state);
if (state.getItemCount() == 0) {
detachAndScrapAttachedViews(recycler);
firstVisibleRow = 0;
resetVisibleItemTracking();
return;
}
// TODO use orientationHelper
int startTop = getPaddingTop();
int scrollOffset = 0;
if (forceClearOffsets) { // see #scrollToPosition
startTop = -(firstVisibleRow * cellHeight);
forceClearOffsets = false;
} else if (getChildCount() != 0) {
scrollOffset = getDecoratedTop(getChildAt(0));
startTop = scrollOffset - (firstVisibleRow * cellHeight);
resetVisibleItemTracking();
}
detachAndScrapAttachedViews(recycler);
int row = firstVisibleRow;
int availableSpace = getHeight() - scrollOffset;
int lastItemPosition = state.getItemCount() - 1;
while (availableSpace > 0 && lastVisiblePosition < lastItemPosition) {
availableSpace -= layoutRow(row, startTop, recycler, state);
row = getNextSpannedRow(row);
}
layoutDisappearingViews(recycler, state, startTop);
}
@Override
public RecyclerView.LayoutParams generateDefaultLayoutParams() {
return new LayoutParams(
ViewGroup.LayoutParams.WRAP_CONTENT,
ViewGroup.LayoutParams.WRAP_CONTENT);
}
@Override
public RecyclerView.LayoutParams generateLayoutParams(Context c, AttributeSet attrs) {
return new LayoutParams(c, attrs);
}
@Override
public RecyclerView.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 void onAdapterChanged(RecyclerView.Adapter oldAdapter, RecyclerView.Adapter newAdapter) {
removeAllViews();
reset();
}
@Override
public boolean supportsPredictiveItemAnimations() {
return true;
}
@Override
public boolean canScrollVertically() {
return true;
}
@Override
public int scrollVerticallyBy(int dy, RecyclerView.Recycler recycler, RecyclerView.State state){
if (getChildCount() == 0 || dy == 0) return 0;
int scrolled;
int top = getDecoratedTop(getChildAt(0));
if (dy < 0) { // scrolling content down
if (firstVisibleRow == 0) { // at top of content
int scrollRange = -(getPaddingTop() - top);
scrolled = Math.max(dy, scrollRange);
} else {
scrolled = dy;
}
if (top - scrolled >= 0) { // new top row came on screen
int newRow = firstVisibleRow - 1;
if (newRow >= 0) {
int startOffset = top - (firstVisibleRow * cellHeight);
layoutRow(newRow, startOffset, recycler, state);
}
}
int firstPositionOfLastRow = getFirstPositionInSpannedRow(lastVisibleRow);
int lastRowTop = getDecoratedTop(
getChildAt(firstPositionOfLastRow - firstVisiblePosition));
if (lastRowTop - scrolled > getHeight()) { // last spanned row scrolled out
recycleRow(lastVisibleRow, recycler, state);
}
} else { // scrolling content up
int bottom = getDecoratedBottom(getChildAt(getChildCount() - 1));
if (lastVisiblePosition == getItemCount() - 1) { // is at end of content
int scrollRange = Math.max(bottom - getHeight() + getPaddingBottom(), 0);
scrolled = Math.min(dy, scrollRange);
} else {
scrolled = dy;
}
if ((bottom - scrolled) < getHeight()) { // new row scrolled in
int nextRow = lastVisibleRow + 1;
if (nextRow < getSpannedRowCount()) {
int startOffset = top - (firstVisibleRow * cellHeight);
layoutRow(nextRow, startOffset, recycler, state);
}
}
int lastPositionInRow = getLastPositionInSpannedRow(firstVisibleRow, state);
int bottomOfFirstRow =
getDecoratedBottom(getChildAt(lastPositionInRow - firstVisiblePosition));
if (bottomOfFirstRow - scrolled < 0) { // first spanned row scrolled out
recycleRow(firstVisibleRow, recycler, state);
}
}
offsetChildrenVertical(-scrolled);
return scrolled;
}
@Override
public void scrollToPosition(int position) {
if (position >= getItemCount()) position = getItemCount() - 1;
firstVisibleRow = getRowIndex(position);
resetVisibleItemTracking();
forceClearOffsets = true;
removeAllViews();
requestLayout();
}
@Override
public void smoothScrollToPosition(
RecyclerView recyclerView, RecyclerView.State state, int position) {
if (position >= getItemCount()) position = getItemCount() - 1;
LinearSmoothScroller scroller = new LinearSmoothScroller(recyclerView.getContext()) {
@Override
public PointF computeScrollVectorForPosition(int targetPosition) {
final int rowOffset = getRowIndex(targetPosition) - firstVisibleRow;
return new PointF(0, rowOffset * cellHeight);
}
};
scroller.setTargetPosition(position);
startSmoothScroll(scroller);
}
@Override
public int computeVerticalScrollRange(RecyclerView.State state) {
// TODO update this to incrementally calculate
if (firstChildPositionForRow == null) return 0;
return getSpannedRowCount() * cellHeight + getPaddingTop() + getPaddingBottom();
}
@Override
public int computeVerticalScrollExtent(RecyclerView.State state) {
return getHeight();
}
@Override
public int computeVerticalScrollOffset(RecyclerView.State state) {
if (getChildCount() == 0) return 0;
return getPaddingTop() + (firstVisibleRow * cellHeight) - getDecoratedTop(getChildAt(0));
}
@Override
public View findViewByPosition(int position) {
if (position < firstVisiblePosition || position > lastVisiblePosition) return null;
return getChildAt(position - firstVisiblePosition);
}
public int getFirstVisibleItemPosition() {
return firstVisiblePosition;
}
private static class GridCell {
final int row;
final int rowSpan;
final int column;
final int columnSpan;
GridCell(int row, int rowSpan, int column, int columnSpan) {
this.row = row;
this.rowSpan = rowSpan;
this.column = column;
this.columnSpan = columnSpan;
}
}
/**
* This is the main layout algorithm, iterates over all items and places them into [column, row]
* cell positions. Stores this layout info for use later on. Also records the adapter position
* that each row starts at.
* <p>
* Note that if a row is spanned, then the row start position is recorded as the first cell of
* the row that the spanned cell starts in. This is to ensure that we have sufficient contiguous
* views to layout/draw a spanned row.
*/
private void calculateCellPositions(RecyclerView.Recycler recycler, RecyclerView.State state) {
final int itemCount = state.getItemCount();
cells = new SparseArray<>(itemCount);
firstChildPositionForRow = new ArrayList<>();
int row = 0;
int column = 0;
recordSpannedRowStartPosition(row, column);
int[] rowHWM = new int[columns]; // row high water mark (per column)
for (int position = 0; position < itemCount; position++) {
SpanInfo spanInfo;
int adapterPosition = recycler.convertPreLayoutPositionToPostLayout(position);
if (adapterPosition != RecyclerView.NO_POSITION) {
spanInfo = spanLookup.getSpanInfo(adapterPosition);
} else {
// item removed from adapter, retrieve its previous span info
// as we can't get from the lookup (adapter)
spanInfo = getSpanInfoFromAttachedView(position);
}
if (spanInfo.columnSpan > columns) {
spanInfo.columnSpan = columns; // or should we throw?
}
// check horizontal space at current position else start a new row
// note that this may leave gaps in the grid; we don't backtrack to try and fit
// subsequent cells into gaps. We place the responsibility on the adapter to provide
// continuous data i.e. that would not span column boundaries to avoid gaps.
if (column + spanInfo.columnSpan > columns) {
row++;
recordSpannedRowStartPosition(row, position);
column = 0;
}
// check if this cell is already filled (by previous spanning cell)
while (rowHWM[column] > row) {
column++;
if (column + spanInfo.columnSpan > columns) {
row++;
recordSpannedRowStartPosition(row, position);
column = 0;
}
}
// by this point, cell should fit at [column, row]
cells.put(position, new GridCell(row, spanInfo.rowSpan, column, spanInfo.columnSpan));
// update the high water mark book-keeping
for (int columnsSpanned = 0; columnsSpanned < spanInfo.columnSpan; columnsSpanned++) {
rowHWM[column + columnsSpanned] = row + spanInfo.rowSpan;
}
// if we're spanning rows then record the 'first child position' as the first item
// *in the row the spanned item starts*. i.e. the position might not actually sit
// within the row but it is the earliest position we need to render in order to fill
// the requested row.
if (spanInfo.rowSpan > 1) {
int rowStartPosition = getFirstPositionInSpannedRow(row);
for (int rowsSpanned = 1; rowsSpanned < spanInfo.rowSpan; rowsSpanned++) {
int spannedRow = row + rowsSpanned;
recordSpannedRowStartPosition(spannedRow, rowStartPosition);
}
}
// increment the current position
column += spanInfo.columnSpan;
}
totalRows = rowHWM[0];
for (int i = 1; i < rowHWM.length; i++) {
if (rowHWM[i] > totalRows) {
totalRows = rowHWM[i];
}
}
}
private SpanInfo getSpanInfoFromAttachedView(int position) {
for (int i = 0; i < getChildCount(); i++) {
View child = getChildAt(i);
if (position == getPosition(child)) {
LayoutParams lp = (LayoutParams) child.getLayoutParams();
return new SpanInfo(lp.columnSpan, lp.rowSpan);
}
}
// errrrr?
return SpanInfo.SINGLE_CELL;
}
private void recordSpannedRowStartPosition(final int rowIndex, final int position) {
if (getSpannedRowCount() < (rowIndex + 1)) {
firstChildPositionForRow.add(position);
}
}
private int getRowIndex(final int position) {
return position < cells.size() ? cells.get(position).row : -1;
}
private int getSpannedRowCount() {
return firstChildPositionForRow.size();
}
private int getNextSpannedRow(int rowIndex) {
int firstPositionInRow = getFirstPositionInSpannedRow(rowIndex);
int nextRow = rowIndex + 1;
while (nextRow < getSpannedRowCount()
&& getFirstPositionInSpannedRow(nextRow) == firstPositionInRow) {
nextRow++;
}
return nextRow;
}
private int getFirstPositionInSpannedRow(int rowIndex) {
return firstChildPositionForRow.get(rowIndex);
}
private int getLastPositionInSpannedRow(final int rowIndex, RecyclerView.State state) {
int nextRow = getNextSpannedRow(rowIndex);
return (nextRow != getSpannedRowCount()) ? // check if reached boundary
getFirstPositionInSpannedRow(nextRow) - 1
: state.getItemCount() - 1;
}
/**
* Lay out a given 'row'. We might actually add more that one row if the requested row contains
* a row-spanning cell. Returns the pixel height of the rows laid out.
* <p>
* To simplify logic & book-keeping, views are attached in adapter order, that is child 0 will
* always be the earliest position displayed etc.
*/
private int layoutRow(
int rowIndex, int startTop, RecyclerView.Recycler recycler, RecyclerView.State state) {
int firstPositionInRow = getFirstPositionInSpannedRow(rowIndex);
int lastPositionInRow = getLastPositionInSpannedRow(rowIndex, state);
boolean containsRemovedItems = false;
int insertPosition = (rowIndex < firstVisibleRow) ? 0 : getChildCount();
for (int position = firstPositionInRow;
position <= lastPositionInRow;
position++, insertPosition++) {
View view = recycler.getViewForPosition(position);
LayoutParams lp = (LayoutParams) view.getLayoutParams();
containsRemovedItems |= lp.isItemRemoved();
GridCell cell = cells.get(position);
addView(view, insertPosition);
// TODO use orientation helper
int wSpec = getChildMeasureSpec(
cellBorders[cell.column + cell.columnSpan] - cellBorders[cell.column],
View.MeasureSpec.EXACTLY, 0, lp.width, false);
int hSpec = getChildMeasureSpec(cell.rowSpan * cellHeight,
View.MeasureSpec.EXACTLY, 0, lp.height, true);
measureChildWithDecorationsAndMargin(view, wSpec, hSpec);
int left = cellBorders[cell.column] + lp.leftMargin;
int top = startTop + (cell.row * cellHeight) + lp.topMargin;
int right = left + getDecoratedMeasuredWidth(view);
int bottom = top + getDecoratedMeasuredHeight(view);
layoutDecorated(view, left, top, right, bottom);
lp.columnSpan = cell.columnSpan;
lp.rowSpan = cell.rowSpan;
}
if (firstPositionInRow < firstVisiblePosition) {
firstVisiblePosition = firstPositionInRow;
firstVisibleRow = getRowIndex(firstVisiblePosition);
}
if (lastPositionInRow > lastVisiblePosition) {
lastVisiblePosition = lastPositionInRow;
lastVisibleRow = getRowIndex(lastVisiblePosition);
}
if (containsRemovedItems) return 0; // don't consume space for rows with disappearing items
GridCell first = cells.get(firstPositionInRow);
GridCell last = cells.get(lastPositionInRow);
return (last.row + last.rowSpan - first.row) * cellHeight;
}
/**
* Remove and recycle all items in this 'row'. If the row includes a row-spanning cell then all
* cells in the spanned rows will be removed.
*/
private void recycleRow(
int rowIndex, RecyclerView.Recycler recycler, RecyclerView.State state) {
int firstPositionInRow = getFirstPositionInSpannedRow(rowIndex);
int lastPositionInRow = getLastPositionInSpannedRow(rowIndex, state);
int toRemove = lastPositionInRow;
while (toRemove >= firstPositionInRow) {
int index = toRemove - firstVisiblePosition;
removeAndRecycleViewAt(index, recycler);
toRemove--;
}
if (rowIndex == firstVisibleRow) {
firstVisiblePosition = lastPositionInRow + 1;
firstVisibleRow = getRowIndex(firstVisiblePosition);
}
if (rowIndex == lastVisibleRow) {
lastVisiblePosition = firstPositionInRow - 1;
lastVisibleRow = getRowIndex(lastVisiblePosition);
}
}
private void layoutDisappearingViews(
RecyclerView.Recycler recycler, RecyclerView.State state, int startTop) {
// TODO
}
private void calculateWindowSize() {
// TODO use OrientationHelper#getTotalSpace
int cellWidth =
(int) Math.floor((getWidth() - getPaddingLeft() - getPaddingRight()) / columns);
cellHeight = (int) Math.floor(cellWidth * (1f / cellAspectRatio));
calculateCellBorders();
}
private void reset() {
cells = null;
firstChildPositionForRow = null;
firstVisiblePosition = 0;
firstVisibleRow = 0;
lastVisiblePosition = 0;
lastVisibleRow = 0;
cellHeight = 0;
forceClearOffsets = false;
}
private void resetVisibleItemTracking() {
// maintain the firstVisibleRow but reset other state vars
// TODO make orientation agnostic
int minimumVisibleRow = getMinimumFirstVisibleRow();
if (firstVisibleRow > minimumVisibleRow) firstVisibleRow = minimumVisibleRow;
firstVisiblePosition = getFirstPositionInSpannedRow(firstVisibleRow);
lastVisibleRow = firstVisibleRow;
lastVisiblePosition = firstVisiblePosition;
}
private int getMinimumFirstVisibleRow() {
int maxDisplayedRows = (int) Math.ceil((float) getHeight() / cellHeight) + 1;
if (totalRows < maxDisplayedRows) return 0;
int minFirstRow = totalRows - maxDisplayedRows;
// adjust to spanned rows
return getRowIndex(getFirstPositionInSpannedRow(minFirstRow));
}
/* Adapted from GridLayoutManager */
private void calculateCellBorders() {
cellBorders = new int[columns + 1];
int totalSpace = getWidth() - getPaddingLeft() - getPaddingRight();
int consumedPixels = getPaddingLeft();
cellBorders[0] = consumedPixels;
int sizePerSpan = totalSpace / columns;
int sizePerSpanRemainder = totalSpace % columns;
int additionalSize = 0;
for (int i = 1; i <= columns; i++) {
int itemSize = sizePerSpan;
additionalSize += sizePerSpanRemainder;
if (additionalSize > 0 && (columns - additionalSize) < sizePerSpanRemainder) {
itemSize += 1;
additionalSize -= columns;
}
consumedPixels += itemSize;
cellBorders[i] = consumedPixels;
}
}
private void measureChildWithDecorationsAndMargin(View child, int widthSpec, int heightSpec) {
calculateItemDecorationsForChild(child, itemDecorationInsets);
RecyclerView.LayoutParams lp = (RecyclerView.LayoutParams) child.getLayoutParams();
widthSpec = updateSpecWithExtra(widthSpec, lp.leftMargin + itemDecorationInsets.left,
lp.rightMargin + itemDecorationInsets.right);
heightSpec = updateSpecWithExtra(heightSpec, lp.topMargin + itemDecorationInsets.top,
lp.bottomMargin + itemDecorationInsets.bottom);
child.measure(widthSpec, heightSpec);
}
private int updateSpecWithExtra(int spec, int startInset, int endInset) {
if (startInset == 0 && endInset == 0) {
return spec;
}
int mode = View.MeasureSpec.getMode(spec);
if (mode == View.MeasureSpec.AT_MOST || mode == View.MeasureSpec.EXACTLY) {
return View.MeasureSpec.makeMeasureSpec(
View.MeasureSpec.getSize(spec) - startInset - endInset, mode);
}
return spec;
}
/* Adapted from ConstraintLayout */
private void parseAspectRatio(String aspect) {
if (aspect != null) {
int colonIndex = aspect.indexOf(':');
if (colonIndex >= 0 && colonIndex < aspect.length() - 1) {
String nominator = aspect.substring(0, colonIndex);
String denominator = aspect.substring(colonIndex + 1);
if (nominator.length() > 0 && denominator.length() > 0) {
try {
float nominatorValue = Float.parseFloat(nominator);
float denominatorValue = Float.parseFloat(denominator);
if (nominatorValue > 0 && denominatorValue > 0) {
cellAspectRatio = Math.abs(nominatorValue / denominatorValue);
return;
}
} catch (NumberFormatException e) {
// Ignore
}
}
}
}
throw new IllegalArgumentException("Could not parse aspect ratio: '" + aspect + "'");
}
}
属性文件
<?xml version="1.0" encoding="utf-8"?>
<resources>
<declare-styleable name="SpannedGridLayoutManager">
<attr name="android:orientation" />
<attr name="spanCount" />
<attr name="aspectRatio" format="string" />
</declare-styleable>
</resources>
该代码也可用 here 。
示例用法
该代码需要 RecyclerView 23.2.0 或更高版本。
因此，如果您还没有这样做，请将以下行添加到您的 build.gradle 中。
dependencies {
compile 'com.android.support:recyclerview-v7:24.2.1'
}
为了实现初始帖子中显示的布局，我们定义了 LayoutManager 如下
recyclerView.setLayoutManager(new SpannedGridLayoutManager(
new SpannedGridLayoutManager.GridSpanLookup() {
@Override
public SpannedGridLayoutManager.SpanInfo getSpanInfo(int position) {
if (position == 0) {
return new SpannedGridLayoutManager.SpanInfo(2, 2);
} else {
return new SpannedGridLayoutManager.SpanInfo(1, 1);
}
}
},
3 /* Three columns */,
1f /* We want our items to be 1:1 ratio */));
关于带有 GridLayoutManager 的 Android RecyclerView 使项目跨越多行，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/47800508/