Backendless:我无法访问检索到的数据
Backendless:我无法访问检索到的数据
提问于 2016-03-14 16:34:14
使用Android项目这里，RestaurantListActivity在Backendless中显示了从Restaurant表检索到的Restaurants列表，到目前为止没有问题。
问题:我这两天一直在尝试检索代码中其他地方的餐馆列表，或者使用totalRestaurants列表。
我试过：
1-此代码导致NullPointerException：
Backendless.Data.of( Restaurant.class ).findFirst();2-使用Github中的相同代码:我可以在括号内访问totalRestaurants列表，但是在这段代码之后，它会显示totalRestaurants列表是空的。
Backendless.Data.of( Restaurant.class ).find( query, new LoadingCallback<BackendlessCollection<Restaurant>>( this, getString( R.string.loading_restaurants ), true )
{
@Override
public void handleResponse( BackendlessCollection<Restaurant> restaurantsBackendlessCollection )
{
restaurants = restaurantsBackendlessCollection;
addMoreItems( restaurantsBackendlessCollection );
super.handleResponse( restaurantsBackendlessCollection );
}
} );3-在后台站点中使用自动加载方法进行轻微的编辑:同样的事情再次发生。在回调中，我可以打印Restaurant对象的名称，并将每个对象添加到copylist中，但是在代码的末尾，copylist是空的！
LoadingCallback<BackendlessCollection<Restaurant>> callback=new LoadingCallback<BackendlessCollection<Restaurant>>(this, getString( R.string.loading_restaurants ), true)
{
@Override
public void handleResponse( BackendlessCollection<Restaurant> restaurants )
{
System.out.println( "Loaded " + restaurants.getCurrentPage().size() + " restaurant objects" );
System.out.println( "Total restaurants in the Backendless storage - " + restaurants.getTotalObjects() );
Iterator<Restaurant> iterator=restaurants.getCurrentPage().iterator();
while( iterator.hasNext() )
{
Restaurant restaurant=iterator.next();
copylist.add(restaurant);
System.out.println( "\nRestaurant name = " + restaurant.getName() );
}
}
};
Backendless.Data.of( Restaurant.class ).find( callback );非常感谢您的帮助！
回答 3
Stack Overflow用户
回答已采纳
发布于 2016-03-16 20:04:26
好吧，我是这样做的：
带有getter和setter的TaxiList类
public class TaxiList {
private String ime; //in database
private String telefon1; //in database
private String telefon2; //in database
public String getIme(String ime) {
return this.ime;
}
public void setIme(String ime) {
this.ime = ime;
}
public String getTelefon1(String telefon1) {
return this.telefon1;
}
public void setTelefon1(String telefon1) {
this.telefon1 = telefon1;
}
public String getTelefon2(String telefon2) {
return this.telefon2;
}
public void setTelefon2(String telefon2) {
this.telefon2 = telefon2;
}}
接下来是适配器
public class TaxiAdapter extends BaseAdapter {
private final LayoutInflater inflater;
private List<TaxiList> taxiLists = null;
public TaxiAdapter(Context context,List<TaxiList> taxiLists) {
Context mContext = context;
this.taxiLists = taxiLists;
inflater = LayoutInflater.from(mContext);
}
public class ViewHolder {
TextView ime;
TextView telefon1;
TextView telefon2;
}
@Override
public int getCount() {
return taxiLists.size();
}
@Override
public TaxiList getItem(int position) {
return taxiLists.get(position);
}
@Override
public long getItemId(int position) {
return position;
}
public View getView(final int position, View view, ViewGroup parent) {
final ViewHolder holder;
if (view == null) {
holder = new ViewHolder();
view = inflater.inflate(R.layout.one_row_taxi, parent, false);
holder.ime = (TextView) view.findViewById(R.id.textIme);
holder.telefon1 = (TextView) view.findViewById(R.id.textTelefon1);
holder.telefon2 = (TextView) view.findViewById(R.id.textTelefon2);
view.setTag(holder);
} else {
holder = (ViewHolder) view.getTag();
}
holder.ime.setText(taxiLists.get(position).getIme("ime"));
holder.telefon1.setText(taxiLists.get(position).getTelefon1("telefon1"));
holder.telefon2.setText(taxiLists.get(position).getTelefon2("telefon2"));
return view;
}}
最后，这就是从Backendless (对我来说，在片段中)检索东西的方法。
public class Taxi extends Fragment {
private ListView listview;
private ProgressBar progressBar;
private List<TaxiList> taxiLists = new ArrayList<>();
@Nullable
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_taxi, container, false);
listview = (ListView) rootView.findViewById(R.id.listview);
progressBar = (ProgressBar) rootView.findViewById(R.id.progressBar);
progressBar.setVisibility(View.VISIBLE);
BackendlessDataQuery query = new BackendlessDataQuery();
QueryOptions queryOptions = new QueryOptions();
String whereClause = "created";
queryOptions.addSortByOption(whereClause);
query.setQueryOptions(queryOptions);
Backendless.Data.of(TaxiList.class).find(query, new AsyncCallback<BackendlessCollection<TaxiList>>() {
@Override
public void handleResponse(BackendlessCollection<TaxiList> taxiListBackendlessCollection) {
TaxiList taxiList;
for (TaxiList total : taxiListBackendlessCollection.getCurrentPage()) {
taxiList = new TaxiList();
taxiList.setIme(total.getIme("ime"));
taxiList.setTelefon1(total.getTelefon1("telefon1"));
taxiList.setTelefon2(total.getTelefon2("telefon2"));
taxiLists.add(taxiList);
TaxiAdapter adapter = new TaxiAdapter(getActivity(), taxiLists);
listview.setAdapter(adapter);
progressBar.setVisibility(View.GONE);
}
}
@Override
public void handleFault(BackendlessFault backendlessFault) {
}
});
return rootView;
}}
希望这能对你有所帮助
Stack Overflow用户
发布于 2016-03-15 07:43:12
(1)请提供堆栈跟踪，如果没有任何细节，就很难诊断出问题
(2)和(3)记住，handleResponse方法的执行是异步的。如果您尝试在调用"copyList“方法之前访问"handleResponse”或“handleResponse”，数据将根本不存在。
Stack Overflow用户
发布于 2016-03-16 11:47:18
创建一个可序列化的类
public class SharedClass implements Serializable{
public List<String> copylist = new ArrayList<>();
void additem(String s){
copylist.add(s);
}
}因为handleResponse在(2)调用中添加了addMoreItems。编辑它以填充copylist并移动到另一个名为NewActivity的活动。
private void addMoreItems( BackendlessCollection<Restaurant> nextPage )
{
totalRestaurants.addAll( nextPage.getCurrentPage() );
Intent restaurantListingIntent = new Intent( this, NewActivity.class );
SharedClass sharedlist=new SharedClass();
for(int i=0;i<totalRestaurants.size();i++){
sharedlist.additem(totalRestaurants.get(i).getName());
System.out.println("Added "+totalRestaurants.get(i).getName());
}
restaurantListingIntent.putExtra("sharedlist", sharedlist);
startActivity(restaurantListingIntent);
}在NewActivity内部，我打印copylist大小
Intent intent=getIntent();
SharedClass sharedObject= (SharedClass) intent.getSerializableExtra("sharedlist");
System.out.println("copy list size"+ sharedObject.copylist.size());页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/35993055
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