我是Android新手，我正在尝试使用新的架构组件实现条码阅读器方案。
每次读取条形码时，我都想更新ViewModel中的列表，如果条形码不在列表中或者增加数量，则添加新元素。
以下解决方案正在运行，但是为了更新UI，在适配器上调用“notifyDataSetChanged”并不令我满意。这是因为ViewModel列表和适配器内部列表包含对相同对象的引用，因此DiffUtil不会捕获任何更改。
有更好的方法来更新UI吗？除了适配器，我应该考虑处理架构组件的任何改进吗？
视图模型
public class ScannerViewModel extends ViewModel {
private MutableLiveData<List<ProductScan>> scanListLD;
public ScannerViewModel() {
scanListLD = new MutableLiveData<>();
scanListLD.setValue(new ArrayList<ProductScan>());
}
public LiveData<List<ProductScan>> getScanList() {
return scanListLD;
}
public void addBarcode(String barcode) {
List<ProductScan> list = scanListLD.getValue();
ProductScan scan = null;
for (ProductScan item : list) {
if (item.barcode.equals(barcode)) {
scan = item;
break;
}
}
if (scan == null) {
scan = new ProductScan();
scan.barcode = barcode;
scan.qt = 0;
list.add(scan);
}
scan.qt += 1;
scanListLD.postValue(list);
}
}
适配器
public class ScannerAdapter extends RecyclerView.Adapter<ScannerAdapter.ViewHolder> {
private List<ProductScan> scans;
public interface OnItemClickListener {
void onItemClick();
}
public ScannerAdapter(List<ProductScan> scans) {
this.scans = scans;
}
@Override
public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.template_scan, parent, false);
ScannerAdapter.ViewHolder viewHolder = new ScannerAdapter.ViewHolder(view);
return viewHolder;
}
@Override
public void onBindViewHolder(ViewHolder holder, int position) {
holder.bindData(scans.get(position), position);
}
@Override
public int getItemCount() {
return scans != null ? scans.size() : 0;
}
//Not used since scans and newScans contain same objects
public void setScans(final List<ProductScan> newScans) {
if (scans == null) {
scans = new ArrayList<ProductScan>();
scans.addAll(newScans);
notifyItemRangeInserted(0, newScans.size());
} else {
DiffUtil.DiffResult result = DiffUtil.calculateDiff(new DiffUtil.Callback() {
@Override
public int getOldListSize() {
return scans != null ? scans.size() : 0;
}
@Override
public int getNewListSize() {
return newScans != null ? newScans.size() : 0;
}
@Override
public boolean areItemsTheSame(int oldItemPosition, int newItemPosition) {
ProductScan oldScan = scans.get(oldItemPosition);
ProductScan newScan = newScans.get(newItemPosition);
return Utils.equals(oldScan.barcode,newScan.barcode);
}
@Override
public boolean areContentsTheSame(int oldItemPosition, int newItemPosition) {
ProductScan oldScan = scans.get(oldItemPosition);
ProductScan newScan = newScans.get(newItemPosition);
return Utils.equals(newScan.barcode, oldScan.barcode)
&& Utils.equals(newScan.productId, oldScan.productId)
&& Utils.equals(newScan.productDescription, oldScan.productDescription)
&& Utils.equals(newScan.qt, oldScan.qt);
}
});
scans.clear();
scans.addAll(newScans);
result.dispatchUpdatesTo(this);
}
}
public class ViewHolder extends RecyclerView.ViewHolder {
private TemplateScanBinding binding;
public ViewHolder(View itemView) {
super(itemView);
binding = DataBindingUtil.bind(itemView);
}
public void bindData(ProductScan scan, int position) {
binding.setScan(scan);
binding.setBtnIncreaseQtListener(() -> {
scan.qt += 1;
notifyItemChanged(position);
});
binding.setBtnDecreaseQtListener(() -> {
scan.qt = Math.max(1, scan.qt - 1);
notifyItemChanged(position);
});
binding.edtQt.setOnEditorActionListener(new TextView.OnEditorActionListener() {
@Override
public boolean onEditorAction(TextView textView, int i, KeyEvent keyEvent) {
if (i == EditorInfo.IME_ACTION_DONE) {
binding.edtQt.clearFocus();
}
return false;
}
});
binding.edtQt.setOnFocusChangeListener(new View.OnFocusChangeListener() {
@Override
public void onFocusChange(View view, boolean b) {
if (scan.qt == null || scan.qt < 1) {
scan.qt = 1;
notifyItemChanged(position);
}
InputMethodManager imm = (InputMethodManager) binding.getRoot().getContext().getSystemService(Context.INPUT_METHOD_SERVICE);
imm.hideSoftInputFromWindow(view.getWindowToken(), 0);
}
});
}
}
}
活动
public class ScannerActivity extends ScannerBaseActivity {
@Inject
ViewModelFactory viewModelFactory;
private ScannerViewModel viewModel;
private ActivityScannerBinding binding;
private ScannerAdapter adapter;
@Override
public void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
((MyApplication) getApplication()).getComponent().inject(this);
viewModel = ViewModelProviders.of(this, viewModelFactory).get(ScannerViewModel.class);
binding = DataBindingUtil.setContentView(this, R.layout.activity_scanner);
adapter = new ScannerAdapter(viewModel.getScanList().getValue());
binding.recvScans.setLayoutManager(new LinearLayoutManager(this));
binding.recvScans.setAdapter(adapter);
viewModel.getScanList().observe(this, (list) -> {
adapter.notifyDataSetChanged();
});
binding.btnScan.setOnClickListener((v) -> {
//calls viewModel.addBarcode(String barcode)
readBarcode(readBarcodeCallback);
});
}
}
答案 0 :(得分：1)
您可以在现有适配器中使用PagedListAdapterHelper，如下所示
class UserAdapter extends RecyclerView.Adapter<UserViewHolder> {
private final PagedListAdapterHelper<User> mHelper;
public UserAdapter(PagedListAdapterHelper.Builder<User> builder) {
mHelper = new PagedListAdapterHelper(this, DIFF_CALLBACK);
}
@Override
public int getItemCount() {
return mHelper.getItemCount();
}
public void setList(PagedList<User> pagedList) {
mHelper.setList(pagedList);
}
@Override
public void onBindViewHolder(UserViewHolder holder, int position) {
User user = mHelper.getItem(position);
if (user != null) {
holder.bindTo(user);
} else {
// Null defines a placeholder item - PagedListAdapterHelper will automatically
// invalidate this row when the actual object is loaded from the database
holder.clear();
}
}
public static final DiffCallback<User> DIFF_CALLBACK = new DiffCallback<User>() {
@Override
public boolean areItemsTheSame(
@NonNull User oldUser, @NonNull User newUser) {
// User properties may have changed if reloaded from the DB, but ID is fixed
return oldUser.getId() == newUser.getId();
}
@Override
public boolean areContentsTheSame(
@NonNull User oldUser, @NonNull User newUser) {
// NOTE: if you use equals, your object must properly override Object#equals()
// Incorrectly returning false here will result in too many animations.
return oldUser.equals(newUser);
}
}
OR
class UserAdapter extends PagedListAdapter<User, UserViewHolder> {
public UserAdapter() {
super(DIFF_CALLBACK);
}
@Override
public void onBindViewHolder(UserViewHolder holder, int position) {
User user = getItem(position);
if (user != null) {
holder.bindTo(user);
} else {
// Null defines a placeholder item - PagedListAdapter will automatically invalidate
// this row when the actual object is loaded from the database
holder.clear();
}
}
public static final DiffCallback<User> DIFF_CALLBACK = new DiffCallback<User>() {
@Override
public boolean areItemsTheSame(
@NonNull User oldUser, @NonNull User newUser) {
// User properties may have changed if reloaded from the DB, but ID is fixed
return oldUser.getId() == newUser.getId();
}
@Override
public boolean areContentsTheSame(
@NonNull User oldUser, @NonNull User newUser) {
// NOTE: if you use equals, your object must properly override Object#equals()
// Incorrectly returning false here will result in too many animations.
return oldUser.equals(newUser);
}
}
答案 1 :(得分：-1)
尝试在调用适配器之前制作列表的深层副本。那么您可以使用difutil更新回收站。有关深度复制的更多信息，请参考此link。