Android在自定义适配器ListView上还原过滤器

Question

从一个活动开始，我打开另一个活动并过滤自定义列表视图的结果。

这是第一个活动：

import UIKit

class FirstViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()

        // Do any additional setup after loading the view.
    }


    @IBAction func goToSecondVC(_ sender: UIButton) {

        // Go from first VC to second VC

        let storyBoard : UIStoryboard = UIStoryboard(name: "Main", bundle:nil)
        let showSecondVC = storyBoard.instantiateViewController(withIdentifier: "goSecondVC") as! SecondViewController
        self.present(showSecondVC, animated:true, completion:nil)
    }


}

这是过滤器活动：

public class PersonaFragment extends Fragment {
    private PersonaAdapter personaAdapter;
    private ListView personeListView;
    private ArrayList<Persona> personeList = new ArrayList<Persona>();
    private ArrayList<String> listIdClas = new ArrayList<String>();
    private final static int INSERT_REQUEST = 1;
    private final static int FILTER_REQUEST = 2;

    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.persona_fragment, null);
        setHasOptionsMenu(true);

        personaAdapter = new PersonaAdapter(getActivity(), personeList, R.layout.persona_row_layout);
        personeListView = view.findViewById(R.id.lvPersone);
        personeListView.setAdapter(personaAdapter);

        blsRequest request = new blsRequest(getActivity(), blsVolleyResponse());
        request.add(blsUrl.listaPersone(), "00");

        return view;
    }

    private void startFilterActivity() {
        Intent intent = new Intent(getActivity(), PersonaFilterActivity.class);
        intent.putStringArrayListExtra("listIdClas", this.listIdClas);
        startActivityForResult(intent, FILTER_REQUEST);
    }

    @Override
    public void onActivityResult(int requestCode, int resultCode, Intent data) {     
        if (requestCode == FILTER_REQUEST) {
            if (resultCode == RESULT_OK) {
                this.listIdClas = data.getStringArrayListExtra("listIdClas");
                personaAdapter.filterManual(this.listIdClas);
            }
        }
    }

    private blsVolleyResponse blsVolleyResponse() {
        return new blsVolleyResponse() {
            @Override
            public void onResponse(String result, String tag) {
                switch (tag) {
                    case "00":
                        personeList = blsJSON.ParseList(result, tag);
                        personaAdapter.updateData(personeList);
                        break;
                }
            }

            @Override
            public void onError(VolleyError error, String tag) {
                Toast.makeText(getActivity(), "Ops! Qualcosa è andato storto", Toast.LENGTH_SHORT).show();
                blsLog.i("blsVolleyResponse.onError: TAG = " + tag + " ERROR = " + error);
            }
        };
    }
}

如您所见，我没有使用：

public class PersonaFilterActivity extends AppCompatActivity {
    private ClasseAdapter classeAdapter;
    private ListView classiListView;
    private ArrayList<Classe> classiList = new ArrayList<Classe>();
    private ArrayList<String> listIdClas = new ArrayList<>();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.persona_filter_activity);

        Bundle extras = getIntent().getExtras();
        if (extras != null) {
            listIdClas = extras.getStringArrayList("listIdClas");
        }

        classiListView = findViewById(R.id.lvClassi);
        classeAdapter = new ClasseAdapter(this, classiList);
        classiListView.setAdapter(classeAdapter);
        classiListView.addOnLayoutChangeListener(onListLoaded);

        blsRequest request = new blsRequest(this, blsVolleyResponse());
        request.add(blsUrl.listaClassi(), "00");
    }

    private View.OnLayoutChangeListener onListLoaded = new View.OnLayoutChangeListener() {
        @Override
        public void onLayoutChange(View view, int i, int i1, int i2, int i3, int i4, int i5, int i6, int i7) {
            setFilter();
        }
    };

    private void applyFilter() {
        fillListId();

        Intent returnIntent = new Intent();
        returnIntent.putStringArrayListExtra("listIdClas", listIdClas);
        setResult(Activity.RESULT_OK, returnIntent);
        finish();
    }

    private void fillListId() {
        listIdClas.clear();

        for (int i = 0; i < classiListView.getChildCount(); i++) {
            View child = classiListView.getChildAt(i);
            Classe classe = (Classe) classiListView.getItemAtPosition(i);
            Switch aSwitch = child.findViewById(R.id.swFlt);

            if (aSwitch.isChecked())
                listIdClas.add(classe.getId());
        }

    }

    private void ReturnValue(int Result) {
        Intent returnIntent = new Intent();
        setResult(Result, returnIntent);
        finish();
    }

    private void clearFilter() {
        listIdClas.clear();

        for (int i = 0; i < classiListView.getChildCount(); i++) {
            View child = classiListView.getChildAt(i);
            Switch aSwitch = child.findViewById(R.id.swFlt);
            aSwitch.setChecked(false);
        }
    }

    private void setFilter() {
        for (int i = 0; i < classiListView.getChildCount(); i++) {
            for (String idCat : listIdClas) {
                View child = classiListView.getChildAt(i);
                Switch aSwitch = child.findViewById(R.id.swFlt);
                Classe classe = (Classe) classiListView.getItemAtPosition(i);

                if (classe.getId().compareTo(idCat) == 0)
                    aSwitch.setChecked(true);
            }
        }
    }

    private blsVolleyResponse blsVolleyResponse() {
        return new blsVolleyResponse() {
            @Override
            public void onResponse(String result, String tag) {
                switch (tag) {
                    case "00":
                        classiList = blsJSON.ParseList(result, tag);
                        classeAdapter.updateData(classiList);
                        break;
                }
            }

            @Override
            public void onError(VolleyError error, String tag) {
                Toast.makeText(PersonaFilterActivity.this, "Ops! Qualcosa è andato storto", Toast.LENGTH_SHORT).show();
                blsLog.i("blsVolleyResponse.onError: TAG = " + tag + " ERROR = " + error);
            }
        };
    }
}

但是

classiListView.getCount()

因为过滤器listview上有很多项目，如果我使用“ getCount（）”，则会收到类似以下的错误： “尝试在空对象引用上调用虚拟方法'android.view.View android.view.View.findViewById（int）'”

我没有任何问题可以过滤列表视图的自定义适配器：使用数组列表，存储选择的行ID，并将其应用于第一个活动列表视图。现在，我需要打开第二个活动并为每行设置已选中的Switch对象（如果/未选中），但是当我重新单击过滤器按钮以添加其他过滤器时，过滤器项的列表视图无法正确还原，由于使用了“ getChildCount（）”。

希望我很清楚。我该如何执行？