我的应用程序不断崩溃，大概是因为空对象引用错误，但我不知道为啥
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【中文标题】我的应用程序不断崩溃，大概是因为空对象引用错误，但我不知道为啥【英文标题】：My app keeps crashing, presumably because of null object reference error but I can't figure out why我的应用程序不断崩溃，大概是因为空对象引用错误，但我不知道为什么 【发布时间】：2018-12-23 07:13:14 【问题描述】：我目前正在构建的应用程序有点问题。它启动得很好，但每次我让它进入关键字搜索活动时，它都会崩溃。我查看了 logcat，第 49 行的 listview.setadapter 似乎有问题，但我不知道为什么？我在这里寻找答案，但我无法让它发挥作用。如果你们能帮忙就太好了。
错误
07-15 15:47:19.273 2204-4369/com.google.android.gms E/Herrevad: [309] RemoteReportsRefreshChimeraService.a: want to send authenticated request, but no Google account on device
07-15 15:47:19.310 1180-1618/? E/Drm: Failed to find drm plugin
07-15 15:47:19.387 2204-2769/com.google.android.gms E/Volley: [150] BasicNetwork.performRequest: Unexpected response code 307 for https://android.googleapis.com/nova/herrevad/network_quality_info
07-15 15:50:44.074 4411-4411/? E/libprocessgroup: failed to make and chown /acct/uid_10058: Read-only file system
07-15 15:50:46.582 4411-4411/com.android.dreamworker.droomapp E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.android.dreamworker.droomapp, PID: 4411
java.lang.RuntimeException: Unable to start activity ComponentInfocom.android.dreamworker.droomapp/com.android.dreamworker.droomapp.Keywordsearch: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ListView.setAdapter(android.widget.ListAdapter)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2325)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2387)
at android.app.ActivityThread.access$800(ActivityThread.java:151)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5254)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ListView.setAdapter(android.widget.ListAdapter)' on a null object reference
at com.android.dreamworker.droomapp.Keywordsearch.onCreate(Keywordsearch.java:49)
at android.app.Activity.performCreate(Activity.java:5990)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1106)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2278)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2387)
at android.app.ActivityThread.access$800(ActivityThread.java:151)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5254)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
07-15 15:50:48.783 1536-1589/system_process E/InputDispatcher: channel '3e3c931 com.android.dreamworker.droomapp/com.android.dreamworker.droomapp.MainActivity (server)' ~ Channel is unrecoverably broken and will be disposed!
关键字搜索.java
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.app.ActionBar;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.widget.SearchView;
import android.text.TextUtils;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.ListView;
import java.util.ArrayList;
public class Keywordsearch extends AppCompatActivity
ListView keywordlist;
KeywordlistAdapter adapter;
String[] title;
String[] description;
int[] icon;
ArrayList<Model> arrayList = new ArrayList<Model>();
@Override
protected void onCreate(Bundle savedInstanceState)
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
ActionBar actionBar = getSupportActionBar();
if (actionBar != null)
actionBar.setTitle("Items List");
title = new String[]"Battery", "Cpu", "Display", "Memory", "Sensor";
description = new String[]"Battery detail...", "Cpu detail...", "Display detail...", "Memory detail...", "Sensor detail...";
keywordlist = findViewById(R.id.keywordlist);
for (int i =0; i<title.length; i++)
Model model = new Model(title[i], description[i]);
arrayList.add(model);
adapter = new KeywordlistAdapter(this, arrayList);
//this is were it goes wrong according to catlog
keywordlist.setAdapter(adapter);
@Override
public boolean onCreateOptionsMenu(Menu menu)
getMenuInflater().inflate(R.menu.menu, menu);
MenuItem myActionMenuItem = menu.findItem(R.id.action_search);
SearchView searchView = (SearchView)myActionMenuItem.getActionView();
searchView.setOnQueryTextListener(new SearchView.OnQueryTextListener()
@Override
public boolean onQueryTextSubmit(String s)
return false;
@Override
public boolean onQueryTextChange(String s)
if (TextUtils.isEmpty(s))
adapter.filter("");
keywordlist.clearTextFilter();
else
adapter.filter(s);
return true;
);
return true;
@Override
public boolean onOptionsItemSelected(MenuItem item)
int id = item.getItemId();
if (id==R.id.action_settings)
return true;
return super.onOptionsItemSelected(item);
activity_keywordsearch.xml
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_
android:layout_
tools:context=".Keywordsearch"
android:background="@drawable/achtergrond">
<ListView
android:id="@+id/keywordlist"
android:layout_
android:layout_>
</ListView>
</RelativeLayout>
KeywordlistAdapter.java
import android.widget.BaseAdapter;
import android.content.Context;
import android.content.Intent;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
import com.android.dreamworker.droomapp.com.android.dreamworker.droomapp.keywordactivity.NewActivity;
import java.util.ArrayList;
import java.util.List;
import java.util.Locale;
public class KeywordlistAdapter extends BaseAdapter
Context mContext;
LayoutInflater inflater;
List<Model> modellist;
ArrayList<Model> arrayList;
public KeywordlistAdapter(Context context, List<Model> modellist)
mContext = context;
this.modellist = modellist;
inflater = LayoutInflater.from(mContext);
this.arrayList = new ArrayList<Model>();
this.arrayList.addAll(modellist);
public class ViewHolder
TextView mTitleTv, mDescTv;
@Override
public int getCount()
return modellist.size();
@Override
public Object getItem(int i)
return modellist.get(i);
@Override
public long getItemId(int i)
return i;
@Override
public View getView(final int postition, View view, ViewGroup parent)
ViewHolder holder;
if (view==null)
holder = new ViewHolder();
view = inflater.inflate(R.layout.row, parent, false);
holder.mTitleTv = view.findViewById(R.id.mainTitle);
holder.mDescTv = view.findViewById(R.id.mainDesc);
view.setTag(holder);
else
holder = (ViewHolder)view.getTag();
holder.mTitleTv.setText(modellist.get(postition).getTitle());
holder.mDescTv.setText(modellist.get(postition).getDesc());
view.setOnClickListener(new View.OnClickListener()
@Override
public void onClick(View view)
if (modellist.get(postition).getTitle().equals("Battery"))
Intent intent = new Intent(mContext, NewActivity.class);
mContext.startActivity(intent);
if (modellist.get(postition).getTitle().equals("Cpu"))
Intent intent = new Intent(mContext, NewActivity.class);
mContext.startActivity(intent);
if (modellist.get(postition).getTitle().equals("Display"))
Intent intent = new Intent(mContext, NewActivity.class);
mContext.startActivity(intent);
if (modellist.get(postition).getTitle().equals("Memory"))
Intent intent = new Intent(mContext, NewActivity.class);
mContext.startActivity(intent);
if (modellist.get(postition).getTitle().equals("Sensor"))
Intent intent = new Intent(mContext, NewActivity.class);
mContext.startActivity(intent);
);
return view;
public void filter(String charText)
charText = charText.toLowerCase(Locale.getDefault());
modellist.clear();
if (charText.length()==0)
modellist.addAll(arrayList);
else
for (Model model : arrayList)
if (model.getTitle().toLowerCase(Locale.getDefault())
.contains(charText))
modellist.add(model);
notifyDataSetChanged();
您可能不需要这些，但如果您在此处使用它们
Model.java
public class Model
String title;
String desc;
//constructor
public Model(String title, String desc)
this.title = title;
this.desc = desc;
//getters
public String getTitle()
return this.title;
public String getDesc()
return this.desc;
row.xml
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_
android:layout_
android:orientation="horizontal"
android:gravity="center"
android:padding="10dp">
<LinearLayout
android:layout_
android:layout_
android:orientation="vertical"
android:gravity="center"
android:layout_marginLeft="5dp"
android:layout_marginStart="5dp">
<TextView
android:id="@+id/mainTitle"
android:text="Title"
android:textStyle="bold"
android:textSize="20sp"
android:layout_
android:layout_ />
<TextView
android:id="@+id/mainDesc"
android:text="Description"
android:textSize="20sp"
android:layout_
android:layout_ />
</LinearLayout>
</RelativeLayout>
再次，如果你们中的任何人可以帮助我，那将是 太棒了！ 谢谢！
【问题讨论】：
setContentView(R.layout.activity_main);。您设置了错误的布局，这反过来使 findViewById(R.id.keywordlist) 返回 null （因为您设置了另一个不包含此视图的布局）。试试setContentView(R.layout.activity_keywordsearch);。
【参考方案1】：
这将返回 null，因此 keywordlist 是 null 导致 NPE：
keywordlist = findViewById(R.id.keywordlist);
显然R.id.keywordlist在当前布局中不存在。
原因是在Keywordsearch.onCreate() 你这样做：
setContentView(R.layout.activity_main);
当您可能想要这样做时：
setContentView(R.layout.activity_keywordsearch);
【讨论】：
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