RecyclerView现在可以说是很常用了吧？RecyclerView自然是很方便的控件，但用多了有时候对一些重复性代码也是感觉挺麻烦的，于是乎我就将一些重复性代码封装了起来，从而使 RecyclerView 的使用更加的简便
本篇博客包含的内容有：
1. 通用的单布局 RecyclerView.Adapter
2. 通用的多布局 RecyclerView.Adapter
3. 通用的 RecyclerView.ItemDecoration
4. RecyclerView 的单击和长按事件监听
5. 带头部与底部View的 RecyclerView
6. SnapHelper 的使用
一、通用的 RecyclerView.Adapter
CommonRecyclerViewAdapter 是一个抽象类，利用泛型构造了一个通用的Adapter，并通过 MultiTypeSupport 接口来实现对多布局的支持。
此外，有时候我们在刷新数据时，改变的数据可能只是List集合中的单个数据，如果都采用 Adapter.notifyDataSetChanged() 来刷新整个视图，无疑是浪费资源的，此处采用了 DiffUtil 来对比前后两个数据集，寻找出旧数据集与新数据集的最小变化量，从而对数据进行定向刷新，可以只刷新相应的Item，使得视图的刷新过程更为高效，且增添和删除数据时都伴随有相应的动画效果
/**
* 作者：叶应是叶
* 时间：2017/12/21 21:50
* 说明：通用RecyclerView Adapter
*/
public abstract class CommonRecyclerViewAdapter<T> extends RecyclerView.Adapter<CommonRecyclerViewHolder> {
//省略一些代码
......
private DiffUtil.Callback callback = new DiffUtil.Callback() {
@Override
public int getOldListSize() {
return getItemCount();
}
@Override
public int getNewListSize() {
return newDataList.size();
}
@Override
public boolean areItemsTheSame(int oldItemPosition, int newItemPosition) {
return CommonRecyclerViewAdapter.this.areItemsTheSame(oldItemPosition, newItemPosition);
}
@Override
public boolean areContentsTheSame(int oldItemPosition, int newItemPosition) {
return CommonRecyclerViewAdapter.this.areContentsTheSame(oldItemPosition, newItemPosition);
}
@Nullable
@Override
public Object getChangePayload(int oldItemPosition, int newItemPosition) {
return CommonRecyclerViewAdapter.this.getChangePayload(oldItemPosition, newItemPosition);
}
};
public void setData(final List<T> dataList) {
new Thread(new Runnable() {
@Override
public void run() {
newDataList.clear();
newDataList = CommonRecyclerViewAdapter.this.clone(dataList);
DiffUtil.DiffResult diffResult = DiffUtil.calculateDiff(callback, true);
Message message = new Message();
message.what = DIFF_UTIL_UPDATE;
message.obj = diffResult;
handler.sendMessage(message);
}
}).start();
}
@Override
public int getItemViewType(int position) {
if (multiTypeSupport != null) {
return multiTypeSupport.getLayoutId(dataList.get(position), position);
}
return DEFAULT_ITEM_VIEW_TYPE;
}
@Override
public CommonRecyclerViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
if (multiTypeSupport != null) {
layoutId = viewType;
}
return new CommonRecyclerViewHolder(layoutInflater.inflate(layoutId, parent, false));
}
@Override
public void onBindViewHolder(CommonRecyclerViewHolder holder, int position, List<Object> payloads) {
if (payloads.isEmpty()) {
onBindViewHolder(holder, position);
} else {
Bundle bundle = (Bundle) payloads.get(0);
partialBindData(holder, bundle);
}
}
@Override
public void onBindViewHolder(CommonRecyclerViewHolder holder, int position) {
entirelyBindData(holder, dataList.get(position));
if (clickListener != null) {
holder.setClickListener(clickListener);
}
if (longClickListener != null) {
holder.setLongClickListener(longClickListener);
}
}
//省略一些代码
......
private List<T> clone(List<T> dataList) {
List<T> tempDataList = new ArrayList<>(dataList.size());
for (T data : dataList) {
tempDataList.add(clone(data));
}
return tempDataList;
}
/**
* clone 指定对象，以此获得对象副本
*
* @param data 要复制的对象
* @return 对象副本
*/
protected abstract T clone(T data);
/**
* 判断数据列表刷新前后指定索引的位置是否指向同一条数据
* 此处只对比两者是否指向同一条数据，而不关心其数据内容是否有变化
*
* @param oldItemPosition 更新前的数据索引
* @param newItemPosition 更新后的数据索引
* @return 是否指向同一条数据
*/
protected abstract boolean areItemsTheSame(int oldItemPosition, int newItemPosition);
/**
* 此处来判断指向同一条数据的前后两个索引位置，其数据内容是否相同
* 只在 areItemsTheSame 返回 true 时才会调用本方法
*
* @param oldItemPosition 更新前的数据索引
* @param newItemPosition 更新后的数据索引
* @return 数据内容是否有变化
*/
protected abstract boolean areContentsTheSame(int oldItemPosition, int newItemPosition);
/**
* 获取同条数据在刷新前后是哪些数据内容发生了变化
* 只在 areContentsTheSame 返回 false 时才会调用本方法
*
* @param oldItemPosition 更新前的数据索引
* @param newItemPosition 更新后的数据索引
* @return 数据变化内容
*/
@NonNull
protected abstract Bundle getChangePayload(int oldItemPosition, int newItemPosition);
/**
* 对刷新前后的数据进行定向更新，即只更新数据发生了变化的View
*
* @param holder Holder
* @param bundle getChangePayload 方法的返回值
*/
protected abstract void partialBindData(CommonRecyclerViewHolder holder, @NonNull Bundle bundle);
/**
* 对数据进行完全绑定
*
* @param holder Holder
* @param data Data
*/
protected abstract void entirelyBindData(CommonRecyclerViewHolder holder, T data);
}
此处还需要使用到一个通用的 RecyclerView.ViewHolder
/**
* 作者：叶应是叶
* 时间：2017/12/21 21:52
* 说明：通用RecyclerView ViewHolder
*/
public class CommonRecyclerViewHolder extends RecyclerView.ViewHolder {
public interface OnClickListener {
void onClick(int position);
}
public interface OnLongClickListener {
void onLongClick(int position);
}
private OnClickListener clickListener;
private OnLongClickListener longClickListener;
//用来存放View以减少findViewById的次数
private SparseArray<View> viewSparseArray;
CommonRecyclerViewHolder(View view) {
super(view);
viewSparseArray = new SparseArray<>();
view.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
if (clickListener != null) {
clickListener.onClick(getAdapterPosition());
}
}
});
view.setOnLongClickListener(new View.OnLongClickListener() {
@Override
public boolean onLongClick(View v) {
if (longClickListener != null) {
longClickListener.onLongClick(getAdapterPosition());
}
return true;
}
});
}
void setClickListener(OnClickListener clickListener) {
this.clickListener = clickListener;
}
void setLongClickListener(OnLongClickListener longClickListener) {
this.longClickListener = longClickListener;
}
/**
* 根据 ID 来获取 View
*
* @param viewId viewID
* @param <T> 泛型
* @return 将结果强转为 View 或 View 的子类型
*/
private <T extends View> T getView(@IdRes int viewId) {
// 先从缓存中找，找到的话则直接返回
// 如果找不到则findViewById，再把结果存入缓存中
View view = viewSparseArray.get(viewId);
if (view == null) {
view = itemView.findViewById(viewId);
if (view != null) {
viewSparseArray.put(viewId, view);
}
}
return (T) view;
}
public CommonRecyclerViewHolder setText(@IdRes int viewId, CharSequence text) {
TextView textView = getView(viewId);
if (textView != null) {
textView.setText(text);
}
return this;
}
//省略一些代码
......
}
二、通用的单布局 RecyclerView.Adapter 使用示例
先来新建一个Model
/**
* 作者：叶应是叶
* 时间：2017/12/21 21:55
* 说明：
*/
public class New {
private int index;
private String title;
private String content;
public New(int index, String title, String content) {
this.index = index;
this.title = title;
this.content = content;
}
//省略一些代码
......
}
每个子项的布局包含一个索引TextView、一个标题TextView、一个内容TextView
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:background="#439af1"
android:orientation="vertical">
<TextView
android:id="@+id/tv_index"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:gravity="center"
android:padding="6dp"
android:textSize="25sp"
android:textStyle="bold" />
<TextView
android:id="@+id/tv_title"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:gravity="center"
android:padding="5dp"
android:textSize="28sp"
android:textStyle="bold" />
<TextView
android:id="@+id/tv_content"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:gravity="start"
android:padding="10dp"
android:textSize="22sp" />
</LinearLayout>
之后就是继承 CommonRecyclerViewAdapter ，泛型指定为 New ，在构造函数里直接指定要使用的布局为 R.layout.item_new，再实现几个抽象方法即可。
/**
* 作者：叶应是叶
* 时间：2017/12/21 21:55
* 说明：单个布局
*/
public class NewCommonAdapter extends CommonRecyclerViewAdapter<New> {
public NewCommonAdapter(Context context, List<New> dataList) {
super(context, dataList, R.layout.item_new);
}
@Override
protected New clone(New data) {
return new New(data.getIndex(), data.getTitle(), data.getContent());
}
@Override
protected boolean areItemsTheSame(int oldItemPosition, int newItemPosition) {
return dataList.get(oldItemPosition).getIndex() == newDataList.get(newItemPosition).getIndex();
}
@Override
protected boolean areContentsTheSame(int oldItemPosition, int newItemPosition) {
String title = dataList.get(oldItemPosition).getTitle();
String content = dataList.get(oldItemPosition).getContent();
String newTitle = newDataList.get(newItemPosition).getTitle();
String newContent = newDataList.get(newItemPosition).getContent();
return title.equals(newTitle) && content.equals(newContent);
}
@NonNull
@Override
protected Bundle getChangePayload(int oldItemPosition, int newItemPosition) {
Bundle bundle = new Bundle();
String title = dataList.get(oldItemPosition).getTitle();
String content = dataList.get(oldItemPosition).getContent();
String newTitle = newDataList.get(newItemPosition).getTitle();
String newContent = newDataList.get(newItemPosition).getContent();
if (!title.equals(newTitle)) {
bundle.putString("Title", newTitle);
}
if (!content.equals(newContent)) {
bundle.putString("Content", newContent);
}
return bundle;
}
@Override
protected void partialBindData(CommonRecyclerViewHolder holder, @NonNull Bundle bundle) {
for (String key : bundle.keySet()) {
switch (key) {
case "Title":
holder.setText(R.id.tv_title, bundle.getString(key));
break;
case "Content":
holder.setText(R.id.tv_content, bundle.getString(key));
break;
}
}
}
@Override
protected void entirelyBindData(CommonRecyclerViewHolder holder, New data) {
holder.setText(R.id.tv_title, data.getTitle())
.setText(R.id.tv_content, data.getContent());
}
}
这里省略 Activity 中对 RecyclerView 的各种初始化操作，只展现最终效果，具体代码看最下方GitHub地址。
效果图如下所示：
单布局.gif
三、通用的多布局 RecyclerView.Adapter 使用示例
在 CommonRecyclerViewAdapter 类当中，为了支持多布局，通过 MultiTypeSupport 接口来返回相应的布局文件ID，这里除了使用 单布局 中使用的 R.layout.item_new 布局文件外，同时使用另外一个布局文件 R.layout.item_new_multi ，仅仅是背景色不同而已
想要让子 Adapter 支持多布局，只要实现 CommonRecyclerViewAdapter 的另外一个构造函数即可。这里在索引为单数时使用 R.layout.item_new 布局，双数时使用 R.layout.item_new_multi 布局
/**
* 作者：叶应是叶
* 时间：2017/12/21 21:56
* 说明：多布局
*/
public class NewCommonMultiAdapter extends CommonRecyclerViewAdapter<New> {
public NewCommonMultiAdapter(Context context, List<New> dataList) {
super(context, dataList, new CommonRecyclerViewAdapter.MultiTypeSupport<New>() {
@Override
public int getLayoutId(New item, int position) {
return item.getIndex() % 2 == 0 ? R.layout.item_new_multi : R.layout.item_new;
}
});
}
//省略一些代码
......
@Override
protected void partialBindData(CommonRecyclerViewHolder holder, @NonNull Bundle bundle) {
if (bundle.size() > 0) {
int index = bundle.getInt("Index");
for (String key : bundle.keySet()) {
switch (key) {
case "Title":
if (index % 2 == 0) {
holder.setText(R.id.tv_multi_title, bundle.getString(key));
} else {
holder.setText(R.id.tv_title, bundle.getString(key));
}
break;
case "Content":
if (index % 2 == 0) {
holder.setText(R.id.tv_multi_content, bundle.getString(key));
} else {
holder.setText(R.id.tv_content, bundle.getString(key));
}
break;
}
}
}
}
@Override
protected void entirelyBindData(CommonRecyclerViewHolder holder, New data) {
if (data.getIndex() % 2 == 0) {
holder.setText(R.id.tv_multi_title, data.getTitle())
.setText(R.id.tv_multi_content, data.getContent())
.setText(R.id.tv_multi_index, String.valueOf(data.getIndex()));
} else {
holder.setText(R.id.tv_title, data.getTitle())
.setText(R.id.tv_content, data.getContent())
.setText(R.id.tv_index, String.valueOf(data.getIndex()));
}
}
}
实现的最终效果如下所示：
多布局.gif
四、带头部与底部View的 RecyclerView
为了实现带头部与底部View的 RecyclerView ，需要自定义一个Adapter来包裹实际的Adapter，重写 getItemViewType(int position) 方法，返回不同的值以区分头部View与底部View，并向外开放添加和移除头部底部View的方法
/**
* 作者：叶应是叶
* 时间：2017/12/21 21:53
* 说明：可添加头部View与底部View的RecyclerView Adapter
*/
public class WrapRecyclerViewAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder> {
private RecyclerView.Adapter<RecyclerView.ViewHolder> innerAdapter;
private SparseArray<View> headerViewArray;
private SparseArray<View> footerViewArray;
//头部View类型开始位置,用于viewType
private static int BASE_VIEW_TYPE_HEADER = 1000;
//底部View类型开始位置,用于viewType
private static int BASE_VIEW_TYPE_FOOTER = 2000;
private RecyclerView.AdapterDataObserver dataObserver = new RecyclerView.AdapterDataObserver() {
@Override
public void onChanged() {
super.onChanged();
notifyDataSetChanged();
}
@Override
public void onItemRangeChanged(int positionStart, int itemCount) {
super.onItemRangeChanged(positionStart, itemCount);
notifyItemRangeChanged(positionStart + getHeaderViewCount(), itemCount);
}
@Override
public void onItemRangeInserted(int positionStart, int itemCount) {
super.onItemRangeInserted(positionStart, itemCount);
notifyItemRangeInserted(positionStart + getHeaderViewCount(), itemCount);
}
@Override
public void onItemRangeRemoved(int positionStart, int itemCount) {
super.onItemRangeRemoved(positionStart, itemCount);
notifyItemRangeRemoved(positionStart + getHeaderViewCount(), itemCount);
}
@Override
public void onItemRangeMoved(int fromPosition, int toPosition, int itemCount) {
super.onItemRangeMoved(fromPosition, toPosition, itemCount);
int headerViewsCountCount = getHeaderViewCount();
notifyItemRangeChanged(fromPosition + headerViewsCountCount, toPosition + headerViewsCountCount + itemCount);
}
};
public WrapRecyclerViewAdapter(RecyclerView.Adapter innerAdapter) {
headerViewArray = new SparseArray<>();
footerViewArray = new SparseArray<>();
setAdapter(innerAdapter);
}
private void setAdapter(RecyclerView.Adapter<RecyclerView.ViewHolder> adapter) {
innerAdapter = adapter;
innerAdapter.registerAdapterDataObserver(dataObserver);
}
@Override
public int getItemViewType(int position) {
if (isHeaderPosition(position)) {
return headerViewArray.keyAt(position);
}
if (isFooterPosition(position)) {
return footerViewArray.keyAt(position - headerViewArray.size() - getDataItemCount());
}
return innerAdapter.getItemViewType(position - headerViewArray.size());
}
@Override
public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
if (isHeaderView(viewType)) {
return new ViewHolder(headerViewArray.get(viewType));
}
if (isFooterView(viewType)) {
return new ViewHolder(footerViewArray.get(viewType));
}
return innerAdapter.onCreateViewHolder(parent, viewType);
}
@Override
public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {
int headerViewsCountCount = getHeaderViewCount();
if (position >= headerViewsCountCount && position < headerViewsCountCount + innerAdapter.getItemCount()) {
innerAdapter.onBindViewHolder(holder, position - headerViewsCountCount);
}
}
@Override
public int getItemCount() {
return getHeaderViewCount() + getDataItemCount() + getFooterViewCount();
}
private int getDataItemCount() {
return innerAdapter == null ? 0 : innerAdapter.getItemCount();
}
public int getHeaderViewCount() {
return headerViewArray.size();
}
public int getFooterViewCount() {
return footerViewArray.size();
}
public RecyclerView.Adapter getInnerAdapter() {
return innerAdapter;
}
/**
* 判断是否是头部View
*
* @param viewType ViewType
* @return 是否是头部View
*/
private boolean isHeaderView(int viewType) {
return headerViewArray.indexOfKey(viewType) > -1;
}
/**
* 判断是否是底部View
*
* @param viewType ViewType
* @return 是否是底部View
*/
private boolean isFooterView(int viewType) {
return footerViewArray.indexOfKey(viewType) > -1;
}
/**
* 判断是否是头部View
*
* @param view View
* @return 是否是头部View
*/
public boolean isHeaderView(View view) {
return headerViewArray.indexOfValue(view) > -1;
}
/**
* 判断是否是底部View
*
* @param view View
* @return 是否是底部View
*/
public boolean isFooterView(View view) {
return footerViewArray.indexOfValue(view) > -1;
}
/**
* 根据索引判断该位置的View是否是头部View
*
* @param position 索引
* @return 是否是头部View
*/
private boolean isHeaderPosition(int position) {
return position >= 0 && position < getHeaderViewCount();
}
/**
* 根据索引判断该位置的View是否是底部View
*
* @param position 索引
* @return 是否是底部View
*/
private boolean isFooterPosition(int position) {
return position >= (getHeaderViewCount() + getDataItemCount())
&& position < (getHeaderViewCount() + getDataItemCount() + getFooterViewCount());
}
/**
* 添加头部View
*
* @param view 头部View
*/
public void addHeaderView(View view) {
if (headerViewArray.indexOfValue(view) < 0) {
headerViewArray.put(BASE_VIEW_TYPE_HEADER++, view);
notifyItemInserted(headerViewArray.size() - 1);
}
}
/**
* 添加底部View
*
* @param view 底部View
*/
public void addFooterView(View view) {
if (footerViewArray.indexOfValue(view) < 0) {
footerViewArray.put(BASE_VIEW_TYPE_FOOTER++, view);
notifyItemInserted(getHeaderViewCount() + getDataItemCount() + getFooterViewCount() - 1);
}
}
/**
* 移除头部View
*
* @param view View
*/
public void removeHeaderView(View view) {
int index = headerViewArray.indexOfValue(view);
if (index > -1) {
headerViewArray.removeAt(index);
notifyItemRemoved(index);
}
}
/**
* 移除底部View
*
* @param view View
*/
public void removeFooterView(View view) {
int index = footerViewArray.indexOfValue(view);
if (index > -1) {
footerViewArray.removeAt(index);
notifyItemRemoved(getHeaderViewCount() + getDataItemCount() + index);
}
}
private class ViewHolder extends RecyclerView.ViewHolder {
ViewHolder(View itemView) {
super(itemView);
}
}
}
WrapRecyclerViewAdapter 的使用方法也很简单，只要将实际的Adapter作为参数来构造 WrapRecyclerViewAdapter 对象，然后再传给 RecyclerView 即可，之后就可以通过 addHeaderView 和 addFooterView 方法来添加头部和底部View
RecyclerView rv_wrapDataList = (RecyclerView) findViewById(R.id.rv_wrapDataList);
NewCommonAdapter adapter = new NewCommonAdapter(this, newList);
WrapRecyclerViewAdapter wrapRecyclerViewAdapter = new WrapRecyclerViewAdapter(adapter);
rv_wrapDataList.setLayoutManager(new LinearLayoutManager(this));
rv_wrapDataList.setAdapter(wrapRecyclerViewAdapter);
使用效果如下所示：
带头部和底部View.gif
五、RecyclerView 的单击和长按事件监听
RecyclerView 的单击和长按事件一直是一个比较麻烦的地方，毕竟没有官方提供的接口，不过此处
CommonRecyclerViewAdapter 也已经提供了相应的设置方法
NewCommonMultiAdapter newCommonMultiAdapter = new NewCommonMultiAdapter(this, newList);
newCommonMultiAdapter.setClickListener(new CommonRecyclerViewHolder.OnClickListener() {
@Override
public void onClick(int position) {
toast("单击" + "\n" + newList.get(position).getTitle() + "\n" + newList.get(position).getContent());
}
});
newCommonMultiAdapter.setLongClickListener(new CommonRecyclerViewHolder.OnLongClickListener() {
@Override
public void onLongClick(int position) {
toast("长按" + "\n" + newList.get(position).getTitle() + "\n" + newList.get(position).getContent());
}
});
点击事件.gif
六、通用的 RecyclerView.ItemDecoration
想要实现Item之间的分割线，需要继承 RecyclerView.ItemDecoration 在相应的位置进行绘制，这里提供一个通用的分隔线
/**
* 作者：叶应是叶
* 时间：2017/12/21 21:52
* 说明：通用分隔线
*/
public class CommonItemDecoration extends RecyclerView.ItemDecoration{
private int orientation = LinearLayoutManager.HORIZONTAL;
private Drawable drawable;
public CommonItemDecoration(Context context, int orientation) {
this.orientation = orientation;
int[] attrs = new int[]{android.R.attr.listDivider};
TypedArray typedArray = context.obtainStyledAttributes(attrs);
drawable = typedArray.getDrawable(0);
typedArray.recycle();
}
public CommonItemDecoration(Drawable drawable, int orientation) {
this.drawable = drawable;
this.orientation = orientation;
}
@Override
public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
super.getItemOffsets(outRect, view, parent, state);
if (orientation == LinearLayoutManager.HORIZONTAL) {
outRect.set(0, 0, drawable.getIntrinsicWidth(), 0);
} else if (orientation == LinearLayoutManager.VERTICAL) {
outRect.set(0, 0, 0, drawable.getIntrinsicHeight());
}
}
@Override
public void onDraw(Canvas c, RecyclerView parent, RecyclerView.State state) {
super.onDraw(c, parent, state);
if (orientation == LinearLayoutManager.HORIZONTAL) {
drawVerticalDivider(c, parent);
} else if (orientation == LinearLayoutManager.VERTICAL) {
drawHorizontalDivider(c, parent);
}
}
private void drawVerticalDivider(Canvas c, RecyclerView parent) {
for (int i = 0; i < parent.getChildCount(); i++) {
View child = parent.getChildAt(i);
// RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) child.getLayoutParams();
// //受 child layout_marginEnd 属性的影响
// int left = child.getRight() + params.rightMargin;
//不受 child layout_marginEnd 属性的影响，会直接绘制在 child 右侧
int left = child.getRight();
int top = child.getTop();
int right = left + drawable.getIntrinsicWidth();
int bottom = child.getBottom();
drawable.setBounds(left, top, right, bottom);
drawable.draw(c);
}
}
private void drawHorizontalDivider(Canvas c, RecyclerView parent) {
for (int i = 0; i < parent.getChildCount(); i++) {
View child = parent.getChildAt(i);
int left = child.getLeft();
//不受 child layout_marginBottom 属性的影响，会直接绘制在 child 底部
int top = child.getBottom();
int right = child.getRight();
int bottom = top + drawable.getIntrinsicHeight();
//会受 child layout_marginBottom 属性的影响
//RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) child.getLayoutParams();
//int top = child.getBottom() + params.bottomMargin;
drawable.setBounds(left, top, right, bottom);
drawable.draw(c);
}
}
}
在之前的几张效果图中，其实是已经为RecyclerView添加了一条白色分隔线的，
RecyclerView rv_commonMultiDataList = (RecyclerView) findViewById(R.id.rv_commonMultiDataList);
CommonItemDecoration commonItemDecoration = new CommonItemDecoration(ContextCompat.getDrawable(this, R.drawable.divider), LinearLayoutManager.VERTICAL);
rv_commonMultiDataList.addItemDecoration(commonItemDecoration);
这里也可以传入不同的 Drawable 对象，从而实现多种风格的分隔线
分隔线.gif
七、SnapHelper的使用
顺带在这里对 SnapHelper 进行一个简单的介绍，SnapHelper 是在 Android 24.2.0 的support 包中新添加的一个支持库，是对RecyclerView的拓展。SnapHelper旨在支持RecyclerView的对齐方式，通过计算对齐RecyclerView中TargetView 的指定点或者容器中的任何像素点，可以使RecyclerView实现类似于 ViewPager 的切换效果
SnapHelper是一个抽象类，官方提供了 LinearSnapHelper 和 PagerSnapHelper 两个具体实现，这里来实现类似于第一次使用App时显示的引导页的效果
/**
* 作者：叶应是叶
* 时间：2017/12/21 22:02
* 说明：
*/
public class SnapRecyclerViewActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_snap_recycler_view);
RecyclerView rv_snap = (RecyclerView) findViewById(R.id.rv_snap);
SnapAdapter snapAdapter = new SnapAdapter(this, getData());
rv_snap.setLayoutManager(new LinearLayoutManager(this, LinearLayoutManager.HORIZONTAL, false));
// rv_snap.setLayoutManager(new LinearLayoutManager(this));
rv_snap.setAdapter(snapAdapter);
// LinearSnapHelper snapHelper = new LinearSnapHelper();
// snapHelper.attachToRecyclerView(rv_snap);
PagerSnapHelper pagerSnapHelper=new PagerSnapHelper();
pagerSnapHelper.attachToRecyclerView(rv_snap);
}
private List<Image> getData() {
List<Image> imageList = new ArrayList<>();
imageList.add(new Image(0, R.drawable.drawable_1));
imageList.add(new Image(1, R.drawable.drawable_0));
imageList.add(new Image(2, R.drawable.drawable_1));
imageList.add(new Image(3, R.drawable.drawable_0));
imageList.add(new Image(4, R.drawable.drawable_1));
imageList.add(new Image(5, R.drawable.drawable_0));
imageList.add(new Image(6, R.drawable.drawable_1));
imageList.add(new Image(7, R.drawable.drawable_0));
return imageList;
}
}
实现的效果如下所示：
Snap.gif
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