我的应用不断崩溃，大概是因为空对象引用错误，但我不知道为什么
[英]My app keeps crashing, presumably because of null object reference error but I can't figure out why
问题描述
我目前正在构建的应用程序存在一些问题。 它可以正常启动，但是每次我进入keywordsearch活动时，它都会崩溃。 我查看了logcat，这似乎与第49行的listview.setadapter有关，但我不知道为什么吗？ 我一直在这里寻找答案，但我无法使其正常工作。 如果你们可以帮助的话，那太好了。
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 ComponentInfo{com.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earch.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_width="match_parent"
android:layout_height="match_parent"
tools:context=".Keywordsearch"
android:background="@drawable/achtergrond">
<ListView
android:id="@+id/keywordlist"
android:layout_width="match_parent"
android:layout_height="match_parent">
</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，但是如果您在这里这样做，它们就是
模型
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_width="match_parent"
android:layout_height="wrap_content"
android:orientation="horizontal"
android:gravity="center"
android:padding="10dp">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
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_width="match_parent"
android:layout_height="wrap_content" />
<TextView
android:id="@+id/mainDesc"
android:text="Description"
android:textSize="20sp"
android:layout_width="match_parent"
android:layout_height="wrap_content" />
</LinearLayout>
</RelativeLayout>
再说一次，如果你们中有谁能帮助我，那将太棒了！ 谢谢！
1 个解决方案
解决方案1
-1 已采纳 2018-07-15 22:24:52
这将返回null ，因此keywordlist为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()执行以下操作：
setContentView(R.layout.activity_main);
当您可能想要这样做时：
setContentView(R.layout.activity_keywordsearch);
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