在學(xué)習(xí)用RecyclerView實現(xiàn)ExpandableListView時候,讀drawthink/ExpandableRecyclerView
發(fā)現(xiàn)如下的代碼:
/**
* collapseGroup
* @param position showingDatas position
*/
private int collapseGroup(int position) {
Object item = showingDatas.get(position);
if (null == item) {
return -1;
}
if (!(item instanceof GroupItem)) {
return -1;
}
if (!((GroupItem) item).isExpand()) {
return -1;
}
int tempSize = showingDatas.size();
List<BaseItem> tempChilds;
if (((GroupItem) item).hasChilds()) {
tempChilds = ((GroupItem) item).getChildDatas();
((GroupItem) item).onExpand();
showingDatas.removeAll(tempChilds);
notifyItemRangeRemoved(position+1,tempChilds.size());
notifyItemRangeChanged(position+1,tempSize-(position+1));
return position;
}
return -1;
}
其中notifyItemRangeRemoved() 和 notifyItemRangeChanged()不知如何區(qū)別
參考:
關(guān)于Adapter調(diào)用notifyItemRemoved后數(shù)組越界和數(shù)據(jù)錯亂的問題
RecyclerView里notifyItemRemoved的坑
1: 重現(xiàn)crash
- 構(gòu)造十條數(shù)據(jù):
public class MainActivity extends AppCompatActivity {
RecyclerView recyclerView;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
recyclerView = findViewById(R.id.rc_view);
List<String> datas = new ArrayList<>();
for (int i = 0; i < 10; i++) {
datas.add(String.format("第%s個數(shù)據(jù)", i));
}
RcAdapter rcAdapter = new RcAdapter(this, datas);
recyclerView.setLayoutManager(new LinearLayoutManager(this));
recyclerView.setAdapter(rcAdapter);
}
}
- Adapter:
public class RcAdapter extends RecyclerView.Adapter<RcAdapter.RcViewHolder> {
private List<String> datas;
private Context mContext;
public RcAdapter(Context mContext, List<String> datas) {
this.mContext = mContext;
this.datas = datas;
}
@NonNull
@Override
public RcViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
View itemView = LayoutInflater.from(mContext).inflate(R.layout.rc_item, parent, false);
return new RcViewHolder(itemView);
}
@Override
public void onBindViewHolder(@NonNull RcViewHolder holder, final int position) {
holder.rcItemTv.setText(datas.get(position));
holder.itemView.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Log.d("RcAdapter", "點擊 position -> " + position);
datas.remove(position);
notifyItemRemoved(position);
}
});
}
@Override
public int getItemCount() {
return datas.size();
}
class RcViewHolder extends RecyclerView.ViewHolder {
TextView rcItemTv;
public RcViewHolder(View itemView) {
super(itemView);
rcItemTv = itemView.findViewById(R.id.textView);
}
}
}
xml rc_item很簡單,就不貼了
共有10條數(shù)據(jù),position 0 -> 9
datas.remove(position);
notifyItemRemoved(position);
點擊item時候,先移除List里的數(shù)據(jù),然后再notifyItemRemoved(pos)
比如我們先點擊"第1個數(shù)據(jù)",正常刪除了,沒有異常,
此時我們再點擊"第9個數(shù)據(jù)",嘗試刪除最后一條,就crash了
繼續(xù)試驗,發(fā)現(xiàn)此時position已經(jīng)錯亂了,比如我們點擊第二個item 刪除掉的可能是 第三個item
究其原因:
當我們 datas.remove(position) 數(shù)據(jù)集刷新了,但是界面上Item所持有的數(shù)據(jù)沒有刷新,比如: 現(xiàn)在的第二個ItemView 是之前的第三個ItemView,我們點擊第二個itemView 觸發(fā)onBindViewHolder(,,position),這個position = 3 ,然后我們又datas.remove(3),就是這個造成了點擊第二個,移除了第三個的原因,如果不湊巧,我們點擊的ItemView的position 超過了當前datas的size,那么自然就IndexOutOfRange了
2: 解決辦法
- 2.1 notifyDataSetChanged
這個,干凈利索快,不留后遺癥,相當于對適配器重新綁定一次數(shù)據(jù),啥問題不會再有,就是如果數(shù)據(jù)過多,會損耗性能能
@Override
public void onBindViewHolder(@NonNull RcViewHolder holder, final int position) {
holder.rcItemTv.setText(datas.get(position));
holder.itemView.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Log.d("RcAdapter", "點擊 position -> " + position);
datas.remove(position);
notifyDataSetChanged();
}
});
}
但是,隨之而來的,刪除Item的動畫沒了
- 2.2 notifyItemRangeChanged
@Override
public void onBindViewHolder(@NonNull RcViewHolder holder, final int position) {
holder.rcItemTv.setText(datas.get(position));
holder.itemView.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Log.d("RcAdapter", "點擊 position -> " + position);
datas.remove(position);
notifyItemRemoved(position);
/*
* @param positionStart Position of the first item that has changed
* position : 第一個 改變的 item的position ( 舊的 position)
* @param itemCount Number of items that have changed
* itemCount : 已經(jīng)變更的 item 的數(shù)量 (包括自己,因此: datas.size() - position)
*
*/
notifyItemRangeChanged(position, datas.size() - position);
}
});
}
說明一下notifyItemRangeChanged(int positionStart, int itemCount)的兩個參數(shù)
/**
* Notify any registered observers that the <code>itemCount</code> items starting at
* position <code>positionStart</code> have changed.
* Equivalent to calling <code>notifyItemRangeChanged(position, itemCount, null);</code>.
*
* <p>This is an item change event, not a structural change event. It indicates that
* any reflection of the data in the given position range is out of date and should
* be updated. The items in the given range retain the same identity.</p>
*
* @param positionStart Position of the first item that has changed
* @param itemCount Number of items that have changed
*
* @see #notifyItemChanged(int)
*/
這個方法,是通知所有觀察者: 從positinStart開始的itemCount這些個item已經(jīng)改變了,與notifyItemRangeChanged(position, itemCount, null)等價
positionStart : 是從哪個界面位置開始Item開始變化,比如你點擊界面上的第二個ItemView positionStart是1
itemCount : 是以經(jīng)發(fā)生變化的item的個數(shù)(包括自己,即正在點擊這個),比如,你點擊界面上的第二個ItemView,position [1,9] 發(fā)生變化,共計9個,因此我們上邊計算是`datas.size() - position
再返回文章開頭
notifyItemRangeRemoved(position+1,tempChilds.size());
notifyItemRangeChanged(position+1,tempSize-(position+1));
原作者批量移除數(shù)據(jù)后,調(diào)用notifyItemRangeChanged(),是統(tǒng)樣道理,這里要再解釋為什么原作者 position + 1,因為原作者是要實現(xiàn)ExpandableListView的功能,點擊 position,要移除這個position之后的若干個數(shù)據(jù),因此是開始移除的位置是 position + 1
好了,本篇文章到此告一段落
祝生活愉快 ヾ(@▽@)ノ
