下面是“Android 自定义RecyclerView 实现真正的Gallery效果的完整攻略”的详细讲解，包括实现步骤、示例说明等方面。
实现步骤
要实现真正的Gallery效果，需要自定义RecyclerView，具体步骤如下：
- 创建一个自定义LayoutManager，继承自RecyclerView.LayoutManager，用于控制RecyclerView中子View的布局和位置。
-
在自定义LayoutManager中重写以下方法：
-
onLayoutChildren()：用于对子View进行布局。
- scrollHorizontallyBy()：用于控制RecyclerView的水平滚动。
-
canScrollHorizontally()：用于判断RecyclerView是否可以水平滚动。
-
在自定义LayoutManager中添加以下属性：
-
mItemWidth：子View的宽度。
- mItemHeight：子View的高度。
- mItemCount：子View的数量。
-
mScrollOffset：RecyclerView的滚动偏移量。
-
在自定义LayoutManager中添加以下方法：
-
getOffsetForPosition()：用于获取指定位置的子View的偏移量。
-
getSnapOffset()：用于获取RecyclerView的滚动偏移量，使子View居中显示。
-
在自定义LayoutManager中添加以下常量：
-
MAX_SCROLL_DISTANCE：RecyclerView的最大滚动距离。
-
MAX_VISIBLE_ITEMS：RecyclerView中最多可见的子View数量。
-
在自定义LayoutManager中添加以下枚举：
-
ScrollDirection：RecyclerView的滚动方向，包括LEFT和RIGHT。
-
创建一个自定义RecyclerView.Adapter，继承自RecyclerView.Adapter，用于控制RecyclerView中子View的数据。
-
在自定义RecyclerView.Adapter中添加以下属性：
-
mData：子View的数据。
-
在自定义RecyclerView.Adapter中添加以下方法：
-
onCreateViewHolder()：用于创建ViewHolder。
- onBindViewHolder()：用于绑定ViewHolder和数据。
-
getItemCount()：用于获取子View的数量。
-
创建一个自定义ViewHolder，继承自RecyclerView.ViewHolder，用于控制RecyclerView中子View的视图。
示例说明
下面是两个示例，分别演示了如何实现真正的Gallery效果。
示例1：使用自定义LayoutManager和RecyclerView.Adapter
public class GalleryLayoutManager extends RecyclerView.LayoutManager {
private int mItemWidth;
private int mItemHeight;
private int mItemCount;
private int mScrollOffset;
private int mMaxScrollDistance;
private int mMaxVisibleItems;
private ScrollDirection mScrollDirection = ScrollDirection.RIGHT;
public GalleryLayoutManager(Context context, int itemWidth, int itemHeight, int itemCount) {
mItemWidth = itemWidth;
mItemHeight = itemHeight;
mItemCount = itemCount;
mMaxScrollDistance = (mItemCount - mMaxVisibleItems) * mItemWidth;
}
@Override
public RecyclerView.LayoutParams generateDefaultLayoutParams() {
return new RecyclerView.LayoutParams(mItemWidth, mItemHeight);
}
@Override
public void onLayoutChildren(RecyclerView.Recycler recycler, RecyclerView.State state) {
if (getItemCount() == 0) {
removeAndRecycleAllViews(recycler);
return;
}
if (getChildCount() == 0 && state.isPreLayout()) {
return;
}
detachAndScrapAttachedViews(recycler);
int left = getPaddingLeft();
int top = getPaddingTop();
int right = getWidth() - getPaddingRight();
int bottom = getHeight() - getPaddingBottom();
int visibleCount = Math.min(mMaxVisibleItems, getItemCount());
int start = Math.max(0, getPosition(getChildAt(0)));
int end = Math.min(start + visibleCount, getItemCount());
for (int i = start; i < end; i++) {
View view = recycler.getViewForPosition(i);
addView(view);
measureChildWithMargins(view, 0, 0);
layoutDecorated(view, left, top, left + mItemWidth, top + mItemHeight);
left += mItemWidth;
}
}
@Override
public int scrollHorizontallyBy(int dx, RecyclerView.Recycler recycler, RecyclerView.State state) {
if (getChildCount() == 0 || dx == 0) {
return 0;
}
int scrolled = dx;
if (mScrollOffset + dx < 0) {
scrolled = -mScrollOffset;
} else if (mScrollOffset + dx > mMaxScrollDistance) {
scrolled = mMaxScrollDistance - mScrollOffset;
}
mScrollOffset += scrolled;
offsetChildrenHorizontal(-scrolled);
if (mScrollOffset == 0 || mScrollOffset == mMaxScrollDistance) {
return scrolled;
}
int start = getPosition(getChildAt(0));
int end = getPosition(getChildAt(getChildCount() - 1));
if (scrolled > 0) {
if (end == getItemCount() - 1) {
return scrolled;
}
if (end == getItemCount() - 2) {
View view = recycler.getViewForPosition(end + 1);
addView(view);
measureChildWithMargins(view, 0, 0);
layoutDecorated(view, getChildAt(getChildCount() - 1).getRight(), 0,
getChildAt(getChildCount() - 1).getRight() + mItemWidth, mItemHeight);
}
} else {
if (start == 0) {
return scrolled;
}
if (start == 1) {
View view = recycler.getViewForPosition(start - 1);
addView(view, 0);
measureChildWithMargins(view, 0, 0);
layoutDecorated(view, getChildAt(0).getLeft() - mItemWidth, 0,
getChildAt(0).getLeft(), mItemHeight);
}
}
return scrolled;
}
@Override
public boolean canScrollHorizontally() {
return true;
}
@Override
public int computeHorizontalScrollOffset(RecyclerView.State state) {
return mScrollOffset;
}
@Override
public int computeHorizontalScrollRange(RecyclerView.State state) {
return mMaxScrollDistance;
}
@Override
public int computeHorizontalScrollExtent(RecyclerView.State state) {
return getWidth();
}
private enum ScrollDirection {
LEFT, RIGHT
}
}
public class GalleryAdapter extends RecyclerView.Adapter<GalleryAdapter.ViewHolder> {
private List<Integer> mData;
public GalleryAdapter(List<Integer> data) {
mData = data;
}
@Override
public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_gallery, parent, false);
return new ViewHolder(view);
}
@Override
public void onBindViewHolder(ViewHolder holder, int position) {
holder.mImageView.setImageResource(mData.get(position));
}
@Override
public int getItemCount() {
return mData.size();
}
public static class ViewHolder extends RecyclerView.ViewHolder {
public ImageView mImageView;
public ViewHolder(View itemView) {
super(itemView);
mImageView = itemView.findViewById(R.id.image_view);
}
}
}
示例2：使用自定义RecyclerView
public class GalleryRecyclerView extends RecyclerView {
private GalleryLayoutManager mLayoutManager;
public GalleryRecyclerView(Context context) {
super(context);
init();
}
public GalleryRecyclerView(Context context, @Nullable AttributeSet attrs) {
super(context, attrs);
init();
}
public GalleryRecyclerView(Context context, @Nullable AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
init();
}
private void init() {
mLayoutManager = new GalleryLayoutManager(getContext(), 200, 200, 10);
setLayoutManager(mLayoutManager);
setAdapter(new GalleryAdapter(getData()));
}
private List<Integer> getData() {
List<Integer> data = new ArrayList<>();
data.add(R.drawable.image1);
data.add(R.drawable.image2);
data.add(R.drawable.image3);
data.add(R.drawable.image4);
data.add(R.drawable.image5);
data.add(R.drawable.image6);
data.add(R.drawable.image7);
data.add(R.drawable.image8);
data.add(R.drawable.image9);
data.add(R.drawable.image10);
return data;
}
}
结论
本文为您提供了“Android 自定义RecyclerView 实现真正的Gallery效果的完整攻略”，包括实现步骤、示例说明等方面。在实际应用中，可以根据具体需求自定义LayoutManager和RecyclerView.Adapter，从而实现各种效果。
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