騷年，如果你還在用ListView趕緊換RecyclerView吧，用了之后你會發現從此你再也不想用ListView了。下面我說說兩者的優缺點，listView簡單易用，google工程師已經把很多功能封裝好了，比如點擊事件，分割線，頭部，尾部。缺點：性能差，可拓展性不好。RecyclerView用法稍微復雜。但是功能強大，可拓展性好。依靠LayoutManager（通俗叫法布局管理器）可以實現多種效果，比如listview，graidview，以及瀑布流效果。并且可以設置動畫，點擊效果那叫一個狂拽酷炫啊。Google工程師呢也是留下了很多東西讓開發者自己去發揮。條目點擊我們得自己寫，最惡心的是分割線和grid形式的間距設置有點惡心。還有一點我發現對于api22以上（開發時的編譯版本）和api22以下是有差異的。比如我要設置recyclerview高度為wrap_content，但是視圖并沒有包裹而是占了一個頁面。解決方式是寫一個可包裹的L愛有天Mannager。對于api22以上不需要考慮，可以正常設置。這點算一個版本bug吧。那么無論listview還是recyclerview最重要的就是適配器了。終于講到正題了。那么下面我們來聊聊Adapter
適配器其實就是把數據適配成view。通俗點說就像是一個模具，你把料（數據）放進來，我們倒個模出來。平時開發中這個列表需求是很多的，那么意味著我們要用很多次這種控件。每次用我們又得寫適配器。是不是很煩，一大堆相同代碼。寫得手疼，于是想著要把這些相同的代碼是不是可以做個封裝，我們只需要把布局，把數據這些不同業務提供給外面實現。基于這個想法，有了今天我們要講的這個主題。
業務需求1.普通常見列表。不包含頭尾。要求只給一個布局，一些數據可以實現需求。
分析：數據寫死肯定是不行的，這里采用泛型設計。數據設置我們可以寫一個set方法設置。布局得抽象出去實現，還有數據和view之間的綁定也得抽象出去。holder也需要根據布局來重新寫。
適配器代碼如下：
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);
}
/*數據操作*/
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();
}
/*寫一個接口回調點擊事件*/
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.使用過程中發現ViewHolder以及查找id并不好用，把上面的適配器升級一下，我們來一個BaseViewHolder把一些數據裝配操作也封裝起來。BaseViewHolder封裝了一些常用控件的數據操作，事件監聽等。基于這些想法，我們再做升級改造。
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表示滑動，true表示不滑動
private View headerView, footerView; //頭和尾的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);
}
/*數據操作*/
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，就不去綁定數據
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) {
//頭尾都不為空
totalList = mDatas.size() + 2;
} else if (headerView == null && footerView == null) {
//頭尾都為空
totalList = mDatas.size();
} else {
//頭尾有一個不為空
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;
}
}
/*
* 需要根據實際情況設置的部分抽象出去
* */
protected abstract void convert(BaseViewHolder holder, int p, T t);
/*接口回調點擊和長按事件*/
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的代碼如下
public class BaseViewHolder extends RecyclerView.ViewHolder {
/*
* 數據量不大，最好在千級以內
* key必須為int類型，這中情況下的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; //集合類，layout里包含的View,以view的id作為key，value是view對象
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;
}
// 封裝一些常用的控件 根據對應的id獲取控件
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.使用中發現對于GridLayout，瀑布流這種會導致頭部和尾部變成其中的item。這顯然不是我們想要的。那么就對著兩種情況特殊處理。
怎么做呢？在adapter中重寫onAttachedToRecyclerView
但是這種做法無法解決瀑布流的問題，對于StaggeredGridLayoutManager我們需要重寫onViewAttachedToWindow
/**
* @param recyclerView 處理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可以控制列數
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并沒有setSpanSizeLookup這個方法，所以此路不通
StaggeredGridLayoutManager staggeredManager = (StaggeredGridLayoutManager) manager;
}*/
}
/**
* @param holder
* 處理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，我們的目的就達到了，使用起來超簡單可以繼承BaseRecyclerAdapter，也可以直接用它的匿名內部類。這里就不贅述了。使用本類可以減少你Adapter百分之70的代碼，趕緊拿去擼吧！
