骚年，如果你还在用ListView赶紧换RecyclerView吧，用了之后你会发现从此你再也不想用ListView了。下面我说说两者的优缺点，listView简单易用，google工程师已经把很多功能封装好了，比如点击事件，分割线，头部，尾部。缺点：性能差，可拓展性不好。RecyclerView用法稍微复杂。但是功能强大，可拓展性好。依靠LayoutManager（通俗叫法布局管理器）可以实现多种效果，比如listview，graidview，以及瀑布流效果。并且可以设置动画，点击效果那叫一个狂拽酷炫啊。Google工程师呢也是留下了很多东西让开发者自己去发挥。条目点击我们得自己写，最恶心的是分割线和grid形式的间距设置有点恶心。还有一点我发现对于api22以上（开发时的编译版本）和api22以下是有差异的。比如我要设置recyclerview高度为wrap_content，但是视图并没有包裹而是占了一个页面。解决方式是写一个可包裹的L爱有天Mannager。对于api22以上不需要考虑，可以正常设置。这点算一个版本bug吧。那么无论listview还是recyclerview最重要的就是适配器了。终于讲到正题了。那么下面我们来聊聊Adapter
适配器其实就是把数据适配成view。通俗点说就像是一个模具，你把料（数据）放进来，我们倒个模出来。平时开发中这个列表需求是很多的，那么意味着我们要用很多次这种控件。每次用我们又得写适配器。是不是很烦，一大堆相同代码。写得手疼，于是想着要把这些相同的代码是不是可以做个封装，我们只需要把布局，把数据这些不同业务提供给外面实现。基于这个想法，有了今天我们要讲的这个主题。
业务需求1.普通常见列表。不包含头尾。要求只给一个布局，一些数据可以实现需求。
分析：数据写死肯定是不行的，这里采用泛型设计。数据设置我们可以写一个set方法设置。布局得抽象出去实现，还有数据和view之间的绑定也得抽象出去。holder也需要根据布局来重新写。
适配器代码如下：
public abstract class BaseRecyclerViewAdapter<T> extends RecyclerView.Adapter<RecyclerView.ViewHolder> {
protected Context mContext;
protected final LayoutInflater inflater;
protected List<T> mDatas;
protected int mLayoutId;
private OnItemClickListener onItemClickListener;
public BaseRecyclerViewAdapter(Context mContext, int layoutId, List<T> datas) {
this.mContext = mContext;
this.mLayoutId = layoutId;
this.mDatas = datas;
inflater = LayoutInflater.from(mContext);
}
/*数据操作*/
public void addData(T bean) {
mDatas.add(bean);
notifyDataSetChanged();
}
public void addDatas(List<T> datas) {
mDatas.addAll(datas);
notifyDataSetChanged();
}
public void remove(int index) {
if (index < 0 && index > mDatas.size()) {
throw new IndexOutOfBoundsException("index not right");
}
else mDatas.remove(index);
notifyDataSetChanged();
}
public void removeAll() {
mDatas.clear();
notifyDataSetChanged();
}
@Override
public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View view = inflater.inflate(mLayoutId, parent, false);
return onCreatHolder(view);
}
@Override
public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {
final int pos = getRealPosition(holder);
final T bean = mDatas.get(pos);
onBindHolder(holder, pos, bean);
holder.itemView.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
if (onItemClickListener != null) {
onItemClickListener.onItemClick(pos, bean);
}
}
});
}
private int getRealPosition(RecyclerView.ViewHolder holder) {
return holder.getLayoutPosition();
}
@Override
public int getItemCount() {
return mDatas == null ? 0 : mDatas.size();
}
/*写一个接口回调点击事件*/
public interface OnItemClickListener<T> {
void onItemClick(int position, T bean);
}
public void setOnItemClickListener(OnItemClickListener onItemClickListener) {
this.onItemClickListener = onItemClickListener;
}
/**
* @param view
* @return 抽象出去
*/
public abstract RecyclerView.ViewHolder onCreatHolder(View view);
protected abstract void onBindHolder(RecyclerView.ViewHolder holder, int pos, T bean);
}
2.使用过程中发现ViewHolder以及查找id并不好用，把上面的适配器升级一下，我们来一个BaseViewHolder把一些数据装配操作也封装起来。BaseViewHolder封装了一些常用控件的数据操作，事件监听等。基于这些想法，我们再做升级改造。
public abstract class BaseRecyclerAdapter<T> extends RecyclerView.Adapter<BaseViewHolder> {
protected Context mContext;
protected List<T> mDatas;
private int totalList;
private int itemLayoutId;
private OnItemClickListener onItemClickListener;
private OnItemLongClickListener onItemLongClickListener;
private final LayoutInflater mInflater;
private static final int TYPE_HEAD = 0;
private static final int TYPE_ITEM = 1;
private static final int TYPE_FOOT = 2;
private boolean isScrolling = true; //false表示滑动，true表示不滑动
private View headerView, footerView; //头和尾的view
public BaseRecyclerAdapter(Context ctx, int itemLayoutId, List<T> list) {
this.mContext = ctx;
this.itemLayoutId = itemLayoutId;
mDatas = (list != null) ? list : new ArrayList<T>();
mInflater = LayoutInflater.from(ctx);
}
/*数据操作*/
public void addData(T bean) {
mDatas.add(bean);
notifyDataSetChanged();
}
public void addDatas(List<T> datas) {
mDatas.addAll(datas);
notifyDataSetChanged();
}
public void remove(int index) {
if (index < 0 && index > mDatas.size()) {
throw new IndexOutOfBoundsException("index not right");
}
else mDatas.remove(index);
notifyDataSetChanged();
}
public void removeAll() {
mDatas.clear();
notifyDataSetChanged();
}
public void setFooterView(View view) {
this.footerView = view;
}
public void setHeaderView(View view) {
this.headerView = view;
}
@Override
public BaseViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
if (viewType == TYPE_HEAD && headerView != null) {
return new BaseViewHolder(mContext, headerView);
}
if (viewType == TYPE_FOOT && footerView != null) {
return new BaseViewHolder(mContext, footerView);
}
View view = mInflater.inflate(itemLayoutId, parent, false);
return new BaseViewHolder(mContext, view);
}
@Override
public void onBindViewHolder(BaseViewHolder holder, int position) {
if (getItemViewType(position) != TYPE_ITEM) {
//如果不是正常的Item，就不去绑定数据
return;
}
final int p = getRealPosition(position);
convert(holder, p, mDatas.get(p));
if (onItemClickListener != null) {
holder.itemView.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
onItemClickListener.onItemClick(p, mDatas.get(p));
}
});
}
if (onItemLongClickListener != null) {
holder.itemView.setOnLongClickListener(new View.OnLongClickListener() {
@Override
public boolean onLongClick(View view) {
onItemLongClickListener.onLongItemClick(p, mDatas.get(p));
return true;
}
});
}
}
private int getRealPosition(int position) {
return headerView == null ? position : position - 1;
}
@Override
public int getItemCount() {
if (mDatas == null) {
return 0;
}
if (headerView != null && footerView != null) {
//头尾都不为空
totalList = mDatas.size() + 2;
} else if (headerView == null && footerView == null) {
//头尾都为空
totalList = mDatas.size();
} else {
//头尾有一个不为空
totalList = mDatas.size() + 1;
}
return totalList;
}
@Override
public int getItemViewType(int position) {
if (position == 0 && headerView != null) {
return TYPE_HEAD;
} else if (position + 1 == getItemCount() && footerView != null) {
return TYPE_FOOT;
} else {
return TYPE_ITEM;
}
}
/*
* 需要根据实际情况设置的部分抽象出去
* */
protected abstract void convert(BaseViewHolder holder, int p, T t);
/*接口回调点击和长按事件*/
public interface OnItemClickListener<T> {
void onItemClick(int position, T bean);
}
public void setOnItemClickListener(OnItemClickListener onItemClickListener) {
this.onItemClickListener = onItemClickListener;
}
public interface OnItemLongClickListener<T> {
void onLongItemClick(int position, T bean);
}
public void setOnItemLongClickListener(OnItemLongClickListener onLongClickListener) {
this.onItemLongClickListener = onLongClickListener;
}
}
BaseViewHolder的代码如下
public class BaseViewHolder extends RecyclerView.ViewHolder {
/*
* 数据量不大，最好在千级以内
* key必须为int类型，这中情况下的HashMap可以用SparseArray代替：比如
* HashMap<Integer, Object> map = new HashMap<>();
* 用SparseArray代替:
* SparseArray<Object> array = new SparseArray<>();
* */
private SparseArray<View> mViews; //集合类，layout里包含的View,以view的id作为key，value是view对象
private Context mContext;
public BaseViewHolder(Context mContext, View itemView) {
super(itemView);
this.mContext = mContext;
mViews = new SparseArray<>();
}
public <T extends View> T getView(int viewId) {
View view = mViews.get(viewId);
if (view == null) {
view = itemView.findViewById(viewId);
mViews.put(viewId, view);
}
return (T) view;
}
// 封装一些常用的控件 根据对应的id获取控件
public TextView getTextView(int viewId) {
return (TextView) getView(viewId);
}
public Button getButton(int viewId) {
return (Button) getView(viewId);
}
public ImageView getImageView(int viewId) {
return (ImageView) getView(viewId);
}
public ImageButton getImageButton(int viewId) {
return (ImageButton) getView(viewId);
}
public EditText getEditText(int viewId) {
return (EditText) getView(viewId);
}
public BaseViewHolder setText(int viewId, String value) {
TextView textView = getView(viewId);
textView.setText(value);
return this;
}
public BaseViewHolder setBitmapImage(int viewId, int imageId) {
ImageView iv = getView(viewId);
iv.setImageResource(imageId);
return this;
}
public BaseViewHolder setImagebyUrl(int viewId, String url) {
ImageView iv = getView(viewId);
ShowImageUtils.showImageView(mContext, url, iv);
return this;
}
public BaseViewHolder setCircleImagebyUrl(int viewId, String url) {
ImageView iv = getView(viewId);
ShowImageUtils.showImageViewToCircle(mContext, R.mipmap.ic_launcher, url, iv);
return this;
}
public BaseViewHolder setBackground(int viewId, int resId) {
View view = getView(viewId);
view.setBackgroundResource(resId);
return this;
}
public BaseViewHolder setOnClickListener(int viewId, View.OnClickListener listener) {
View view = getView(viewId);
view.setOnClickListener(listener);
return this;
}
}
3.使用中发现对于GridLayout，瀑布流这种会导致头部和尾部变成其中的item。这显然不是我们想要的。那么就对着两种情况特殊处理。
怎么做呢？在adapter中重写onAttachedToRecyclerView
但是这种做法无法解决瀑布流的问题，对于StaggeredGridLayoutManager我们需要重写onViewAttachedToWindow
/**
* @param recyclerView 处理GridLayoutManager
*/
@Override
public void onAttachedToRecyclerView(RecyclerView recyclerView) {
super.onAttachedToRecyclerView(recyclerView);
RecyclerView.LayoutManager manager = recyclerView.getLayoutManager();
if (manager instanceof GridLayoutManager) {
final GridLayoutManager gridLayoutManager = (GridLayoutManager) manager;
//setSpanSizeLookup的getSpanSize可以控制列数
gridLayoutManager.setSpanSizeLookup(new GridLayoutManager.SpanSizeLookup() {
@Override
public int getSpanSize(int position) {
return (getItemViewType(position) == TYPE_HEAD || getItemViewType(position) == TYPE_FOOT) ? gridLayoutManager.getSpanCount() : 1;
}
});
}/*else if (manager instanceof StaggeredGridLayoutManager) { StaggeredGridLayoutManager并没有setSpanSizeLookup这个方法，所以此路不通
StaggeredGridLayoutManager staggeredManager = (StaggeredGridLayoutManager) manager;
}*/
}
/**
* @param holder
* 处理StaggerdGridLayoutManager
*/
@Override
public void onViewAttachedToWindow(BaseViewHolder holder) {
super.onViewAttachedToWindow(holder);
ViewGroup.LayoutParams lp = holder.itemView.getLayoutParams();
if (lp != null && lp instanceof StaggeredGridLayoutManager.LayoutParams) {
StaggeredGridLayoutManager.LayoutParams p = (StaggeredGridLayoutManager.LayoutParams) lp;
if (headerView != null && holder.getLayoutPosition() == 0) {
p.setFullSpan(true);
}
if (footerView != null && holder.getLayoutPosition() == getItemCount() - 1) {
p.setFullSpan(true);
}
}
}
至此，我们的目的就达到了，使用起来超简单可以继承BaseRecyclerAdapter，也可以直接用它的匿名内部类。这里就不赘述了。使用本类可以减少你Adapter百分之70的代码，赶紧拿去撸吧！
