recyclerview 水平向左滚动 [英] recyclerview horizontal scrolling to left
本文介绍了recyclerview 水平向左滚动的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
我正在制作一个应用程序，其中我使用 RecyclerView 和 SnapHelper 类来制作可滚动的水平卡片堆.我已经成功实现了，但是我的问题是卡片向右滑动，而我想向左滑动卡片.
I'm making an app where I'm using RecyclerView with SnapHelper class to make a scrollable horizontal card stack. I have implemented that successfully however my problem is that the cards swipe to right direction and I want to swipe the cards on left direction.
I did some research on SO and found 1 and 2
但我还是不知道如何将滚动位置设置为向左而不是向右.
But I still couldn't figure out how to set the scrolling position to left instead of right.
请任何帮助将不胜感激
更新:我仍在努力解决这个问题，几乎没有想明白，因为在 recyclerview 中改变滚动方向仍然很困难，所以欢迎任何人仍然想帮助我.
Update: I'm still working on this hardly figured out much because it is still difficult to change the direction of scrolling in recyclerview so anyone still wants to help me are welcome.
我还发现 FindSnapView 方法传递了滚动位置和方向，也许我错了，但下面的代码可能是解决方案
I also found that FindSnapView method passes the scroll position and direcion maybe i'm wrong but beow code might be the solution
**@Override
public View findSnapView(RecyclerView.LayoutManager layoutManager) {
if (layoutManager instanceof LadderLayoutManager) {
int pos = ((LadderLayoutManager) layoutManager).getFixedScrollPosition(
mDirection, mDirection != 0 ? 0.8f : 0.5f);
mDirection = 0;
if (pos != RecyclerView.NO_POSITION) {
return layoutManager.findViewByPosition(pos);
}
}
return null;
}**
我的主课
public class MainActivity extends AppCompatActivity {
LadderLayoutManager llm;
RecyclerView rcv;
HSAdapter adapter;
int scrollToPosition;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
llm = new LadderLayoutManager(1.5f, 0.85f, LadderLayoutManager.HORIZONTAL).
setChildDecorateHelper(new LadderLayoutManager
.DefaultChildDecorateHelper(getResources().getDimension(R.dimen.item_max_elevation)));
llm.setChildPeekSize((int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP,
30, getResources().getDisplayMetrics()));
llm.setMaxItemLayoutCount(5);
rcv = (RecyclerView) findViewById(R.id.rcv);
rcv.setLayoutManager(llm);
new LadderSimpleSnapHelper().attachToRecyclerView(rcv);
adapter = new HSAdapter();
rcv.setAdapter(adapter);
final SeekBar sb = (SeekBar) findViewById(R.id.sb);
}
我的自定义 LayoutManager 代码
My code for custom LayoutManager
public class LadderLayoutManager extends RecyclerView.LayoutManager implements RecyclerView.SmoothScroller.ScrollVectorProvider {
private static final int INVALIDATE_SCROLL_OFFSET = Integer.MAX_VALUE;
private static final float DEFAULT_CHILD_LAYOUT_OFFSET = 0.2f;
public static final int UNLIMITED = 0;
public static final int VERTICAL = 1;
public static final int HORIZONTAL = 0;
private boolean mCheckedChildSize;
private int[] mChildSize;
private int mChildPeekSize;
private int mChildPeekSizeInput;
private boolean mReverse;
private int mScrollOffset = INVALIDATE_SCROLL_OFFSET;
private float mItemHeightWidthRatio;
private float mScale;
private int mChildCount;
private float mVanishOffset = 0;
private Interpolator mInterpolator;
private int mOrientation;
private ChildDecorateHelper mDecorateHelper;
private int mMaxItemLayoutCount;
public LadderLayoutManager(float itemHeightWidthRatio) {
this(itemHeightWidthRatio, 0.9f, VERTICAL);
}
public LadderLayoutManager(float itemHeightWidthRatio, float scale, int orientation) {
this.mItemHeightWidthRatio = itemHeightWidthRatio;
this.mOrientation = orientation;
this.mScale = scale;
this.mChildSize = new int[2];
this.mInterpolator = new DecelerateInterpolator();
}
@Override
public RecyclerView.LayoutParams generateDefaultLayoutParams() {
return new RecyclerView.LayoutParams(mChildSize[0], mChildSize[1]);
}
public LadderLayoutManager setChildDecorateHelper(ChildDecorateHelper layoutHelper) {
mDecorateHelper = layoutHelper;
return this;
}
public void setMaxItemLayoutCount(int count) {
mMaxItemLayoutCount = Math.max(2, count);
if (getChildCount() > 0) {
requestLayout();
}
}
public void setVanishOffset(float offset) {
mVanishOffset = offset;
if (getChildCount() > 0) {
requestLayout();
}
}
public void setChildPeekSize(int childPeekSize) {
mChildPeekSizeInput = childPeekSize;
mCheckedChildSize = false;
if (getChildCount() > 0) {
requestLayout();
}
}
public void setItemHeightWidthRatio(float itemHeightWidthRatio) {
mItemHeightWidthRatio = itemHeightWidthRatio;
mCheckedChildSize = false;
if (getChildCount() > 0) {
requestLayout();
}
}
public void setReverse(boolean reverse) {
if (mReverse != reverse) {
mReverse = reverse;
if (getChildCount() > 0) {
requestLayout();
}
}
}
public boolean isReverse() {
return mReverse;
}
public int getFixedScrollPosition(int direction, float fixValue) {
if (mCheckedChildSize) {
if (mScrollOffset % mChildSize[mOrientation] == 0) {
return RecyclerView.NO_POSITION;
}
float position = mScrollOffset * 1.0f / mChildSize[mOrientation];
return convert2AdapterPosition((int) (direction > 0 ? position + fixValue : position + (1 - fixValue)) - 1);
}
return RecyclerView.NO_POSITION;
}
@Override
public void onMeasure(RecyclerView.Recycler recycler, RecyclerView.State state, int widthSpec, int heightSpec) {
super.onMeasure(recycler, state, widthSpec, heightSpec);
mCheckedChildSize = false;
}
@Override
public void onLayoutChildren(RecyclerView.Recycler recycler, RecyclerView.State state) {
if (state.getItemCount() == 0) {
removeAndRecycleAllViews(recycler);
return;
}
if (!mCheckedChildSize) {
if (mOrientation == VERTICAL) {
mChildSize[0] = getHorizontalSpace();
mChildSize[1] = (int) (mItemHeightWidthRatio * mChildSize[0]);
} else {
mChildSize[1] = getVerticalSpace();
mChildSize[0] = (int) (mChildSize[1] / mItemHeightWidthRatio);
}
mChildPeekSize = mChildPeekSizeInput == 0 ?
(int) (mChildSize[mOrientation] * DEFAULT_CHILD_LAYOUT_OFFSET) : mChildPeekSizeInput;
mCheckedChildSize = true;
}
int itemCount = getItemCount();
if (mReverse) {
mScrollOffset += (itemCount - mChildCount) * mChildSize[mOrientation];
}
mChildCount = itemCount;
mScrollOffset = makeScrollOffsetWithinRange(mScrollOffset);
fill(recycler);
}
public void fill(RecyclerView.Recycler recycler) {
int bottomItemPosition = (int) Math.floor(mScrollOffset / mChildSize[mOrientation]);//>=1
int bottomItemVisibleSize = mScrollOffset % mChildSize[mOrientation];
final float offsetPercent = mInterpolator.getInterpolation(
bottomItemVisibleSize * 1.0f / mChildSize[mOrientation]);//[0,1)
final int space = mOrientation == VERTICAL ? getVerticalSpace() : getHorizontalSpace();
ArrayList<ItemLayoutInfo> layoutInfos = new ArrayList<>();
for (int i = bottomItemPosition - 1, j = 1, remainSpace = space - mChildSize[mOrientation];
i >= 0; i--, j++) {
double maxOffset = mChildPeekSize * Math.pow(mScale, j);
int start = (int) (remainSpace - offsetPercent * maxOffset);
ItemLayoutInfo info = new ItemLayoutInfo(start,
(float) (Math.pow(mScale, j - 1) * (1 - offsetPercent * (1 - mScale))),
offsetPercent,
start * 1.0f / space
);
layoutInfos.add(0, info);
if (mMaxItemLayoutCount != UNLIMITED && j == mMaxItemLayoutCount - 1) {
if (offsetPercent != 0) {
info.start = remainSpace;
info.positionOffsetPercent = 0;
info.layoutPercent = remainSpace / space;
info.scaleXY = (float) Math.pow(mScale, j - 1);
}
break;
}
remainSpace -= maxOffset;
if (remainSpace <= 0) {
info.start = (int) (remainSpace + maxOffset);
info.positionOffsetPercent = 0;
info.layoutPercent = info.start / space;
info.scaleXY = (float) Math.pow(mScale, j - 1);
break;
}
}
if (bottomItemPosition < mChildCount) {
final int start = space - bottomItemVisibleSize;
layoutInfos.add(new ItemLayoutInfo(start, 1.0f,
bottomItemVisibleSize * 1.0f / mChildSize[mOrientation], start * 1.0f / space).
setIsBottom());
} else {
bottomItemPosition -= 1;
}
int layoutCount = layoutInfos.size();
final int startPos = bottomItemPosition - (layoutCount - 1);
final int endPos = bottomItemPosition;
final int childCount = getChildCount();
for (int i = childCount - 1; i >= 0; i--) {
View childView = getChildAt(i);
int pos = convert2LayoutPosition(getPosition(childView));
if (pos > endPos || pos < startPos) {
removeAndRecycleView(childView, recycler);
}
}
detachAndScrapAttachedViews(recycler);
for (int i = 0; i < layoutCount; i++) {
fillChild(recycler.getViewForPosition(convert2AdapterPosition(startPos + i)), layoutInfos.get(i));
}
}
private void fillChild(View view, ItemLayoutInfo layoutInfo) {
addView(view);
measureChildWithExactlySize(view);
final int scaleFix = (int) (mChildSize[mOrientation] * (1 - layoutInfo.scaleXY) / 2);
final float gap = (mOrientation == VERTICAL ? getHorizontalSpace() : getVerticalSpace())
- mChildSize[(mOrientation + 1) % 2] * layoutInfo.scaleXY;
if (mOrientation == VERTICAL) {
int left = (int) (getPaddingLeft() + (gap * 0.5 * mVanishOffset));
layoutDecoratedWithMargins(view, left, layoutInfo.start - scaleFix
, left + mChildSize[0], layoutInfo.start + mChildSize[1] - scaleFix);
} else {
int top = (int) (getPaddingTop() + (gap * 0.5 * mVanishOffset));
layoutDecoratedWithMargins(view, layoutInfo.start - scaleFix, top
, layoutInfo.start + mChildSize[0] - scaleFix, top + mChildSize[1]);
}
ViewCompat.setScaleX(view, layoutInfo.scaleXY);
ViewCompat.setScaleY(view, layoutInfo.scaleXY);
if (mDecorateHelper != null) {
mDecorateHelper.decorateChild(view, layoutInfo.positionOffsetPercent, layoutInfo.layoutPercent, layoutInfo.isBottom);
}
}
private void measureChildWithExactlySize(View child) {
RecyclerView.LayoutParams lp = (RecyclerView.LayoutParams) child.getLayoutParams();
final int widthSpec = View.MeasureSpec.makeMeasureSpec(
mChildSize[0] - lp.leftMargin - lp.rightMargin, View.MeasureSpec.EXACTLY);
final int heightSpec = View.MeasureSpec.makeMeasureSpec(
mChildSize[1] - lp.topMargin - lp.bottomMargin, View.MeasureSpec.EXACTLY);
child.measure(widthSpec, heightSpec);
}
private int makeScrollOffsetWithinRange(int scrollOffset) {
return Math.min(Math.max(mChildSize[mOrientation], scrollOffset), mChildCount * mChildSize[mOrientation]);
}
@Override
public int scrollVerticallyBy(int dy, RecyclerView.Recycler recycler, RecyclerView.State state) {
int pendingScrollOffset = mScrollOffset + dy;
mScrollOffset = makeScrollOffsetWithinRange(pendingScrollOffset);
fill(recycler);
return mScrollOffset - pendingScrollOffset + dy;
}
@Override
public int scrollHorizontallyBy(int dx, RecyclerView.Recycler recycler, RecyclerView.State state) {
int pendingScrollOffset = mScrollOffset + dx;
mScrollOffset = makeScrollOffsetWithinRange(pendingScrollOffset);
fill(recycler);
return mScrollOffset - pendingScrollOffset + dx;
}
@Override
public void smoothScrollToPosition(RecyclerView recyclerView, RecyclerView.State state, int position) {
final LinearSmoothScroller linearSmoothScroller = new LinearSmoothScroller(recyclerView.getContext()) {
@Override
public int calculateDyToMakeVisible(final View view, final int snapPreference) {
if (mOrientation == VERTICAL) {
return -calculateDistanceToPosition(getPosition(view));
}
return 0;
}
@Override
public int calculateDxToMakeVisible(final View view, final int snapPreference) {
if (mOrientation == HORIZONTAL) {
return -calculateDistanceToPosition(getPosition(view));
}
return 0;
}
};
linearSmoothScroller.setTargetPosition(position);
startSmoothScroll(linearSmoothScroller);
}
public int calculateDistanceToPosition(int targetPos) {
int pendingScrollOffset = mChildSize[mOrientation] * (convert2LayoutPosition(targetPos) + 1);
return pendingScrollOffset - mScrollOffset;
}
@Override
public void scrollToPosition(int position) {
if (position > 0 && position < mChildCount) {
mScrollOffset = mChildSize[mOrientation] * (convert2LayoutPosition(position) + 1);
requestLayout();
}
}
@Override
public boolean canScrollVertically() {
return mOrientation == VERTICAL;
}
@Override
public boolean canScrollHorizontally() {
return mOrientation == HORIZONTAL;
}
public int convert2AdapterPosition(int layoutPosition) {
return mReverse ? mChildCount - 1 - layoutPosition : layoutPosition;
}
public int convert2LayoutPosition(int adapterPostion) {
return mReverse ? mChildCount - 1 - adapterPostion : adapterPostion;
}
public int getVerticalSpace() {
return getHeight() - getPaddingTop() - getPaddingBottom();
}
public int getHorizontalSpace() {
return getWidth() - getPaddingLeft() - getPaddingRight();
}
@Override
public PointF computeScrollVectorForPosition(int targetPosition) {
int pos = convert2LayoutPosition(targetPosition);
int scrollOffset = (pos + 1) * mChildSize[mOrientation];
return mOrientation == VERTICAL ? new PointF(0, Math.signum(scrollOffset - mScrollOffset))
: new PointF(Math.signum(scrollOffset - mScrollOffset), 0);
}
private static class ItemLayoutInfo {
float scaleXY;
float layoutPercent;
float positionOffsetPercent;
int start;
boolean isBottom;
ItemLayoutInfo(int top, float scale, float positonOffset, float percent) {
this.start = top;
this.scaleXY = scale;
this.positionOffsetPercent = positonOffset;
this.layoutPercent = percent;
}
ItemLayoutInfo setIsBottom() {
isBottom = true;
return this;
}
}
@Override
public Parcelable onSaveInstanceState() {
SavedState savedState = new SavedState();
savedState.scrollOffset = mScrollOffset;
savedState.reverse = mReverse;
savedState.vanishOffset = mVanishOffset;
savedState.scale = mScale;
savedState.childLayoutOffsetInput = mChildPeekSizeInput;
savedState.itemHeightWidthRatio = mItemHeightWidthRatio;
savedState.orientation = mOrientation;
return savedState;
}
@Override
public void onRestoreInstanceState(Parcelable state) {
if (state instanceof SavedState) {
SavedState s = (SavedState) state;
mScrollOffset = s.scrollOffset;
mReverse = s.reverse;
mVanishOffset = s.vanishOffset;
mScale = s.scale;
mChildPeekSizeInput = s.childLayoutOffsetInput;
mItemHeightWidthRatio = s.itemHeightWidthRatio;
mOrientation = s.orientation;
requestLayout();
}
}
public static class SavedState implements Parcelable {
int scrollOffset, childLayoutOffsetInput, orientation;
float itemHeightWidthRatio, scale, elevation, vanishOffset;
boolean reverse;
public SavedState() {
}
SavedState(LadderLayoutManager.SavedState other) {
scrollOffset = other.scrollOffset;
childLayoutOffsetInput = other.childLayoutOffsetInput;
orientation = other.orientation;
itemHeightWidthRatio = other.itemHeightWidthRatio;
scale = other.scale;
elevation = other.elevation;
vanishOffset = other.vanishOffset;
reverse = other.reverse;
}
SavedState(Parcel in) {
scrollOffset = in.readInt();
childLayoutOffsetInput = in.readInt();
orientation = in.readInt();
itemHeightWidthRatio = in.readFloat();
scale = in.readFloat();
elevation = in.readFloat();
vanishOffset = in.readFloat();
reverse = in.readInt() == 1;
}
@Override
public void writeToParcel(Parcel dest, int flags) {
dest.writeInt(scrollOffset);
dest.writeInt(childLayoutOffsetInput);
dest.writeInt(orientation);
dest.writeFloat(itemHeightWidthRatio);
dest.writeFloat(scale);
dest.writeFloat(elevation);
dest.writeFloat(vanishOffset);
dest.writeInt(reverse ? 1 : 0);
}
@Override
public int describeContents() {
return 0;
}
public static final Creator<SavedState> CREATOR
= new Creator<SavedState>() {
@Override
public LadderLayoutManager.SavedState createFromParcel(Parcel in) {
return new LadderLayoutManager.SavedState(in);
}
@Override
public LadderLayoutManager.SavedState[] newArray(int size) {
return new LadderLayoutManager.SavedState[size];
}
};
}
public interface ChildDecorateHelper {
void decorateChild(View child, float posOffsetPercent, float layoutPercent, boolean isBottom);
}
public static class DefaultChildDecorateHelper implements ChildDecorateHelper {
private float mElevation;
public DefaultChildDecorateHelper(float maxElevation) {
mElevation = maxElevation;
}
@Override
public void decorateChild(View child, float posOffsetPercent, float layoutPercent, boolean isBottom) {
ViewCompat.setElevation(child, (float) (layoutPercent * mElevation * 0.7 + mElevation * 0.3));
}
}
}
这是我的 snaphelper 代码
Here is my code for snaphelper
public class LadderSimpleSnapHelper extends SnapHelper {
private int mDirection;
//int position = layoutManager.getPosition(centerView);
@Override
public int[] calculateDistanceToFinalSnap(
@NonNull RecyclerView.LayoutManager layoutManager, @NonNull View targetView) {
if (layoutManager instanceof LadderLayoutManager) {
int[] out = new int[2];
if (layoutManager.canScrollHorizontally()) {
out[0] = ((LadderLayoutManager) layoutManager).calculateDistanceToPosition(
layoutManager.getPosition(targetView));
out[1] = 0;
} else {
out[0] = 0;
out[1] = ((LadderLayoutManager) layoutManager).calculateDistanceToPosition(
layoutManager.getPosition(targetView));
}
return out;
}
return null;
}
@Override
public int findTargetSnapPosition(RecyclerView.LayoutManager layoutManager, int velocityX,
int velocityY) {
if (layoutManager.canScrollHorizontally()) {
mDirection = velocityX;
} else {
mDirection = velocityY;
}
return RecyclerView.NO_POSITION;
}
@Override
public View findSnapView(RecyclerView.LayoutManager layoutManager) {
if (layoutManager instanceof LadderLayoutManager) {
int pos = ((LadderLayoutManager) layoutManager).getFixedScrollPosition(
mDirection, mDirection != 0 ? 0.8f : 0.5f);
mDirection = 0;
if (pos != RecyclerView.NO_POSITION) {
return layoutManager.findViewByPosition(pos);
}
}
return null;
}
}
推荐答案
in xml:从右到左
in xml: right to left
android:layoutDirection="rtl"
从左到右
android:layoutDirection="ltr"
这篇关于recyclerview 水平向左滚动的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
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