Question

我想将listview中的所选项目发送到另一个包含sharedprefences的列表视图。我可以保存项目，但无法看到此项目的另一个列表视图。 活动类

TextView textUrun = (TextView) view.findViewById(R.id.textUrun);
            TextView textFiyat = (TextView) view.findViewById(R.id.textFiyat);
            String yemek = textUrun.getText().toString();
            String fiyat = textFiyat.getText().toString();
            DataProvider dataProvider = new DataProvider(yemek,fiyat);
            list.add(dataProvider);
            String jsonurun = gson.toJson(list);
            SharedPreferences sharedPreferences = getSharedPreferences("yemekbilgi", Context.MODE_PRIVATE);
            SharedPreferences.Editor editor = sharedPreferences.edit();
            editor.putString("yemek",jsonurun);
            editor.apply();
            Toast.makeText(getApplicationContext(),"Listeye Kaydedildi",Toast.LENGTH_LONG).show();

这是应该显示项目的列表类。 Listele1

SharedPreferences sharedPreferences = getSharedPreferences("urun1", Context.MODE_PRIVATE);
    List<DataProvider> list;
    String jsonurun = sharedPreferences.getString("liste1", "");
    Gson gson = new Gson();
    DataProvider[] providers = gson.fromJson(jsonurun, DataProvider[].class);
    list = Arrays.asList(providers);
    listDataAdapter = new ListDataAdapter(getApplicationContext(), list);
    listView = (ListView) findViewById(R.id.liste1);
    listView.setAdapter(listDataAdapter);

最后，这是适配器类

public class ListDataAdapter extends ArrayAdapter {
List list = new ArrayList();

public ListDataAdapter(@NonNull Context context,List<DataProvider> list) {
    super(context, R.layout.be_layout, list);
}

static class LayoutHandler{
    TextView ad,fiyat;
}

@Override
public void add(@Nullable Object object) {
    super.add(object);
    list.add(object);
}

@Override
public int getCount() {
    return list.size();
}

@Nullable
@Override
public Object getItem(int position) {
    return list.get(position);
}

@NonNull
@Override
public View getView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {
    View view = convertView;
    LayoutHandler layoutHandler;
    if (view == null){
        LayoutInflater layoutInflater = (LayoutInflater) this.getContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        view = layoutInflater.inflate(R.layout.child_layout,parent,false);
        layoutHandler = new LayoutHandler();
        layoutHandler.ad = (TextView) view.findViewById(R.id.textUrun);
        layoutHandler.fiyat = (TextView) view.findViewById(R.id.textFiyat);
        view.setTag(layoutHandler);
    }
    else
        layoutHandler = (LayoutHandler) view.getTag();
    DataProvider dataProvider = (DataProvider) this.getItem(position);
    layoutHandler.ad.setText(dataProvider.getAd());
    layoutHandler.fiyat.setText(dataProvider.getFiyat());
    return view;
}

}

Answer 1

您传入了一个列表，但您从未分配过它。

IMAX_BITS()

值得指出的是，您可能也无法执行上述操作并完全删除public class ListDataAdapter extends ArrayAdapter<DataProvider> { List<DataProvider> list; // don't assign here public ListDataAdapter(@NonNull Context context, @LayoutRes int resource,List<DataProvider> list) { super(context, resource, list); this.list = list; // see here }，list和add()，getItem()定义，然后才能执行此操作我可能会工作。

getCount()的任何用法应改为list.get(position)

Answer 2

list = new ArrayList<DataProvider>();
gson = new Gson();
SharedPreferences sharedPreferences = getSharedPreferences("yemekbilgi", Context.MODE_PRIVATE);
String yemek = sharedPreferences.getString("yemek","");
Type type = new TypeToken<List<DataProvider>>(){}.getType();
list = gson.fromJson(yemek,type);
listView = (ListView) findViewById(R.id.liste1);
listDataAdapter = new ListDataAdapter(getApplicationContext(),R.layout.child_layout,list);
listView.setAdapter(listDataAdapter);

Answer 3

    list = new ArrayList<DataProvider>();
    listView = (ListView) findViewById(R.id.liste1);
    listDataAdapter = new ListDataAdapter(getApplicationContext(),R.layout.child_layout,list);
    gson = new Gson();

    SharedPreferences sharedPreferences = getSharedPreferences("yemekbilgi", Context.MODE_PRIVATE);
    String yemek = sharedPreferences.getString("yemek","");
    Type type = new TypeToken<List<DataProvider>>(){}.getType();
    list.addAll(gson.fromJson(yemek,type));
    listView.setAdapter(listDataAdapter);
    listDataAdapter.notitifyDataSetChanged();

ListView不显示任何内容

3 个答案: