在 ListView 中显示选定的 Firebase 对象元素

Question

我有一个带有 ListAdapters 的复杂 FirebaseDB Datamodell，用于在 Android 的 ListView 中显示选定的对象元素。数据已在 firebase 上。

添加完整对象时出现异常，因为缺少相关的 Android-ListView-Elements ...所以我必须只添加所需的 DB 元素。

我尝试了很多，但结果字符串与 items-ArrayList 不匹配。

日志消息： 致命例外：主要 进程：com.connexibel.proficrmfree，PID：2750 java.lang.NullPointerException：尝试在空对象引用上调用虚拟方法“boolean java.util.ArrayList.add(java.lang.Object)” 在 com.connexibel.proficrmfree.lists.AccountsList$2.onChildAdded(AccountsList.java:257)

第 257 行是所描述的行（我已为您删除了所有注释行）。

有没有人正确的想法来获得正确的格式？？？

Firebase

Android ListView.class:

package com.connexibel.proficrmfree.lists;

import android.content.Intent;
import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.util.Log;
import android.view.View;
import android.view.Window;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.ListView;

import com.connexibel.proficrmfree.R;
import com.connexibel.proficrmfree.adapters.ListAdapterAccounts;
import com.connexibel.proficrmfree.datamodell.DatamodellAccounts;
import com.connexibel.proficrmfree.detailviews.AccountsDetail;
import com.google.android.gms.ads.AdRequest;
import com.google.android.gms.ads.AdView;
import com.google.firebase.database.ChildEventListener;
import com.google.firebase.database.DataSnapshot;
import com.google.firebase.database.DatabaseError;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;

import java.util.ArrayList;

public class AccountsList extends AppCompatActivity {

    ArrayList<DatamodellAccounts> items;
    ListView listView;
    ArrayAdapter arrayAdapter;

    private AdView adViewTop;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        requestWindowFeature(Window.FEATURE_NO_TITLE);
        setContentView(R.layout.activity_accounts_list);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                        .setAction("Action", null).show();
            }
        });

        getSupportActionBar().setDisplayHomeAsUpEnabled(true);


        FirebaseDatabase db = FirebaseDatabase.getInstance();
        final DatabaseReference refAccounts = db.getReference("Accounts");
        refAccounts.addChildEventListener(new ChildEventListener() {

            @Override
            public void onChildAdded(DataSnapshot dataSnapshot, String s) {
                DatamodellAccounts dm_accounts = dataSnapshot.getValue(DatamodellAccounts.class);
                dm_accounts.setAccount_id(dataSnapshot.getKey());
//this is the critical position!!! -->
                items.add(dm_accounts.getAccount_name1(), dm_accounts.getAccount_name2(), dm_accounts.getAccount_adress1(), dm_accounts.getAccount_zipcode(), dm_accounts.getAccount_city(), dm_accounts.getAccount_country(), dm_accounts.getAccount_internet());
                listView = (ListView) findViewById(R.id.listViewAccountsPortrait);
                arrayAdapter = new ListAdapterAccounts(getApplicationContext(), items);
                listView.setAdapter(arrayAdapter);
                listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {

                    @Override
                    public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                        Intent i = new Intent(getApplicationContext(), AccountsDetail.class);
                        i.putExtra("account_id", items.get(position).getAccount_id());
                        startActivity(i);
                    }
                });
            }

            @Override
            public void onChildChanged(DataSnapshot dataSnapshot, String s) {
                DatamodellAccounts dm_accounts = dataSnapshot.getValue(DatamodellAccounts.class);
                dm_accounts.setAccount_id(dataSnapshot.getKey());
                items.add(dm_accounts);
                listView = (ListView) findViewById(R.id.listViewAccountsPortrait);
                arrayAdapter = new ListAdapterAccounts(getApplicationContext(), items);
                listView.setAdapter(arrayAdapter);
                listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {

                    @Override
                    public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                        Intent i = new Intent(getApplicationContext(), AccountsDetail.class);
                        i.putExtra("account_id", items.get(position).getAccount_id());
                        startActivity(i);
                    }
                });
            }

            @Override
            public void onChildRemoved(DataSnapshot dataSnapshot) {
                DatamodellAccounts dm_accounts = dataSnapshot.getValue(DatamodellAccounts.class);
                dm_accounts.setAccount_id(dataSnapshot.getKey());
                items.remove(dm_accounts);
                listView = (ListView) findViewById(R.id.listViewAccountsPortrait);
                arrayAdapter = new ListAdapterAccounts(getApplicationContext(), items);
                listView.setAdapter(arrayAdapter);
                listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {

                    @Override
                    public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                        Intent i = new Intent(getApplicationContext(), AccountsDetail.class);
                        i.putExtra("account_id", items.get(position).getAccount_id());
                        startActivity(i);
                    }
                });
            }

            @Override
            public void onChildMoved(DataSnapshot dataSnapshot, String s) {
                DatamodellAccounts dm_accounts = dataSnapshot.getValue(DatamodellAccounts.class);
                dm_accounts.setAccount_id(dataSnapshot.getKey());
                //der bestehenden Liste neu erzeugte Objekte hinzufügen
                items.add(dm_accounts);
                listView = (ListView) findViewById(R.id.listViewAccountsPortrait);
                arrayAdapter = new ListAdapterAccounts(getApplicationContext(), items);
                listView.setAdapter(arrayAdapter);
                listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
                    @Override
                    public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                        Intent i = new Intent(getApplicationContext(), AccountsDetail.class);
                        i.putExtra("account_id", items.get(position).getAccount_id());
                        startActivity(i);
                    }
                });
            }

            @Override
            public void onCancelled(DatabaseError databaseError) {
                Log.i("Daten", databaseError.toString());

            }
        });


        adViewTop = (AdView) findViewById(R.id.adViewTop);
        AdRequest adRequest = new AdRequest.Builder()
                .addTestDevice(AdRequest.DEVICE_ID_EMULATOR)
                .build();
        adViewTop.loadAd(adRequest);
    }
}

Answer 1

您似乎从未初始化项目，您可能想要这样做：

ArrayList<DatamodellAccounts> items = new ArrayList<>();