我可以毫无问题地在模拟器上运行我的应用程序，但是当我尝试在手机上播放时出现此错误
＆＃34;无法启动活动ComponentInfo {br.com.pedro.pedrodaumas / br.com.pedro.pedrodaumas.MainActivity}：java.lang.NullPointerException：尝试调用虚方法＆＃39; void android。 widget.ListView.setAdapter（android.widget.ListAdapter）＆＃39;在空对象引用＆＃34;。
据我所知，我应该能够通过我的activity_main访问movieListView = (ListView) findViewById(R.id.movieListView);，就像我拥有的那样：
<include android:id="@+id/content" layout="@layout/content_main" />
所以我不确定为什么我会收到此错误。
MainActivity.java
package br.com.pedro.pedrodaumas;
import android.annotation.TargetApi;
import android.content.Context;
import android.content.Intent;
import android.os.AsyncTask;
import android.os.Build;
import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.design.widget.TextInputEditText;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.text.Layout;
import android.view.LayoutInflater;
import android.view.View;
import android.view.Menu;
import android.view.MenuItem;
import android.view.ViewGroup;
import android.view.Window;
import android.view.inputmethod.InputMethodManager;
import android.widget.AdapterView;
import android.widget.LinearLayout;
import android.widget.ListView;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;
import java.net.URLEncoder;
import java.util.ArrayList;
import java.util.List;
public class MainActivity extends AppCompatActivity {
private List<Movie> movieList = new ArrayList<>();
private MovieArrayAdapter movieArrayAdapter;
private ListView movieListView;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
movieListView = (ListView) findViewById(R.id.movieListView);
movieArrayAdapter = new MovieArrayAdapter(this, movieList);
movieListView.setAdapter(movieArrayAdapter);
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) {
TextInputEditText search_bar;
search_bar = (TextInputEditText) findViewById(R.id.search_bar);
URL url = createURL(search_bar.getText().toString());
if(url != null){
dismissKeyboard(search_bar);
GetMovieTask getLocalMovieTask = new GetMovieTask();
getLocalMovieTask.execute(url);
}else {
Snackbar.make(findViewById(R.id.coordinatorLayout), R.string.invalid_url,
Snackbar.LENGTH_LONG).show();
}
}
});
movieListView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
switch (position) {
default:
Movie review = movieArrayAdapter.getItem(position);
Intent nextActivity = new Intent(MainActivity.this, ShortReview.class);
nextActivity.putExtra("summary", review.getsummary());
startActivity(nextActivity);
break;
}
}
});
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
private void dismissKeyboard (View view){
InputMethodManager imm = (InputMethodManager)getSystemService(Context.INPUT_METHOD_SERVICE);
imm.hideSoftInputFromWindow(view.getWindowToken(),0);
}
private URL createURL (String movie){
String apiKey = getString (R.string.api_key);
String baseUrl = getString(R.string.nyt_url);
try{
String urlString = baseUrl + "?api_key=" + apiKey + "&query=" + URLEncoder.encode (movie, "UTF-8");
return new URL(urlString);
}
catch( Exception e){
e.printStackTrace();
}
return null;
}
private class GetMovieTask extends AsyncTask<URL, Void, JSONObject> {
@TargetApi(Build.VERSION_CODES.KITKAT)
@Override
protected JSONObject doInBackground(URL... params) {
HttpURLConnection connection = null;
try {
connection = (HttpURLConnection) params[0].openConnection();
int response = connection.getResponseCode();
if (response == HttpURLConnection.HTTP_OK){
StringBuilder builder = new StringBuilder ();
try (BufferedReader reader = new BufferedReader(new InputStreamReader(connection.getInputStream()))){
String line;
while ((line = reader.readLine()) != null){
builder.append(line);
}
}
catch (IOException e){
Snackbar.make(findViewById(R.id.coordinatorLayout), R.string.read_error, Snackbar.LENGTH_LONG).show();
e.printStackTrace();
}
return new JSONObject(builder.toString());
}
}
catch (Exception e){
Snackbar.make(findViewById(R.id.coordinatorLayout), R.string.connect_error, Snackbar.LENGTH_LONG).show();
e.printStackTrace();
}
finally{
if (connection != null){
connection.disconnect();
}
}
return null;
}
protected void onPostExecute(JSONObject movie) {
convertJSONToArrayList (movie);
movieArrayAdapter.notifyDataSetChanged();
movieListView.smoothScrollToPosition(0);
}
}
private void convertJSONToArrayList (JSONObject forecast){
movieList.clear();
try{
JSONArray results = forecast.getJSONArray("results");
for (int i = 0; i < results.length(); i++) {
JSONObject movie = results.getJSONObject(i);
if(movie.isNull("multimedia")){
movieList.add(new Movie(movie.getString("display_title"),
movie.getString("publication_date"),
"image", movie.getString("summary_short")));
}else {
JSONObject multimedia = movie.getJSONObject("multimedia");
movieList.add(new Movie(movie.getString("display_title"),
movie.getString("publication_date"),
multimedia.getString("src"), movie.getString("summary_short")));
}
}
if(results.length() == 0){
Snackbar.make(findViewById(R.id.coordinatorLayout), R.string.no_movie,
Snackbar.LENGTH_LONG).show();
}
}
catch (JSONException e){
e.printStackTrace();
}
}
}
Movie.java
package br.com.pedro.pedrodaumas;
public class Movie {
public final String title;
public final String publication_date;
public final String iconURL;
public final String short_summary ;
public Movie(String title,String publication_date, String iconName, String short_summary) {
this.title = title;
this.publication_date = publication_date;
this.iconURL = iconName;
this.short_summary = short_summary;
}
public String getsummary() {
return short_summary;
}
}
MovieArrayAdapter.java
package br.com.pedro.pedrodaumas;
import android.annotation.TargetApi;
import android.content.Context;
import android.content.Intent;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.AsyncTask;
import android.os.Build;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.ImageView;
import android.widget.TextView;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
public class MovieArrayAdapter extends ArrayAdapter<Movie> {
private static class ViewHolder{
ImageView movieImage;
TextView description;
TextView publication_date;
}
private Map<String, Bitmap> bitmaps = new HashMap<>();
public MovieArrayAdapter (Context context, List<Movie>
forecast){
super (context, -1, forecast);
}
public View getView(int position, View convertView, ViewGroup parent) {
Movie review = getItem (position);
ViewHolder viewHolder;
if (convertView == null){
viewHolder = new ViewHolder();
LayoutInflater inflater = LayoutInflater.from(getContext());
convertView = inflater.inflate(R.layout.complete_review, parent, false);
viewHolder.movieImage = (ImageView)convertView.findViewById(R.id.movieImage);
viewHolder.description = (TextView)convertView.findViewById(R.id.description);
viewHolder.publication_date = (TextView)convertView.findViewById(R.id.publication_date);
convertView.setTag(viewHolder);
}
else{
viewHolder = (ViewHolder)convertView.getTag();
}
if(review.iconURL == "image"){
viewHolder.movieImage.setImageResource(R.drawable.ic_import_contacts_white_24dp);
}
else{
new LoadImageTask (viewHolder.movieImage).execute (review.iconURL);
}
viewHolder.description.setText(review.title);
viewHolder.publication_date.setText(review.publication_date);
return convertView;
}
private class LoadImageTask extends AsyncTask<String, Void, Bitmap> {
private ImageView imageView;
public LoadImageTask (ImageView imageView){
this.imageView = imageView;
}
@TargetApi(Build.VERSION_CODES.KITKAT)
@Override
protected Bitmap doInBackground(String... params) {
Bitmap bitmap = null;
HttpURLConnection connection = null;
try{
URL url = new URL(params[0]);
connection = (HttpURLConnection) url.openConnection();
try(InputStream inputStream = connection.getInputStream ()){
bitmap = BitmapFactory.decodeStream(inputStream);
bitmaps.put (params[0], bitmap);
}
catch (Exception e){
e.printStackTrace();
}
}
catch (Exception e){
e.printStackTrace();
}
finally{
connection.disconnect();
}
return bitmap;
}
protected void onPostExecute(Bitmap bitmap) {
imageView.setImageBitmap(bitmap);
}
}
}
activity_main.xml中
<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout 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"
android:fitsSystemWindows="true"
tools:context="br.com.pedro.pedrodaumas.MainActivity"
android:id="@+id/coordinatorLayout">
<android.support.design.widget.AppBarLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:theme="@style/AppTheme.AppBarOverlay">
<android.support.v7.widget.Toolbar
android:id="@+id/toolbar"
android:layout_width="match_parent"
android:layout_height="?attr/actionBarSize"
android:background="?attr/colorPrimary"
app:popupTheme="@style/AppTheme.PopupOverlay"
android:elevation="@dimen/toolbar_elevation" />
</android.support.design.widget.AppBarLayout>
<android.support.design.widget.FloatingActionButton
android:id="@+id/fab"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="top|end"
android:layout_marginTop="@dimen/fab_magin_top"
android:layout_marginEnd="@dimen/fab_margin"
android:layout_marginBottom="@dimen/fab_margin"
android:layout_marginStart="@dimen/fab_margin"
app:elevation="@dimen/rested_button_elevation"
android:src="@drawable/ic_action_search" />
<include android:id="@+id/content"
layout="@layout/content_main" />
</android.support.design.widget.CoordinatorLayout>
Content_main.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
app:layout_behavior="@string/appbar_scrolling_view_behavior"
tools:context="br.com.pedro.pedrodaumas.MainActivity"
tools:showIn="@layout/activity_main"
android:orientation="vertical">
<android.support.design.widget.TextInputLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:id="@+id/view">
<android.support.design.widget.TextInputEditText android:layout_width="match_parent"
android:layout_height="wrap_content"
android:id="@+id/search_bar"
android:singleLine="true"
android:hint="@string/hint_text"
android:elevation="@dimen/rested_search_elevation"
tools:targetApi="lollipop" />
</android.support.design.widget.TextInputLayout>
<ListView
android:layout_width="match_parent"
android:layout_height="0dp"
android:id="@+id/movieListView"
android:layout_weight="1" />
</LinearLayout>
错误消息
07-28 21:18:00.812 5123-5123/br.com.pedro.pedrodaumas E/Zygote: no v2
07-28 21:18:00.822 5123-5123/br.com.pedro.pedrodaumas I/SELinux: Function: selinux_compare_spd_ram, SPD-policy is existed. and_ver=SEPF_SM-J110M_5.1.1 ver=48
07-28 21:18:00.822 5123-5123/br.com.pedro.pedrodaumas I/SELinux: Function: selinux_compare_spd_ram , priority [1] , priority version is VE=SEPF_SM-J110M_5.1.1_0048
07-28 21:18:00.822 5123-5123/br.com.pedro.pedrodaumas E/SELinux: [DEBUG] get_category: variable seinfo: default sensitivity: NULL, cateogry: NULL
07-28 21:18:00.822 5123-5123/br.com.pedro.pedrodaumas I/art: Late-enabling -Xcheck:jni
07-28 21:18:00.842 5123-5123/br.com.pedro.pedrodaumas I/SAMP: ActivityThread() - SAMP_ENABLE : true
07-28 21:18:00.862 5123-5123/br.com.pedro.pedrodaumas W/ResourcesManager: getTopLevelResources: null for user 0
07-28 21:18:01.012 5123-5123/br.com.pedro.pedrodaumas W/ResourcesManager: getTopLevelResources: null for user 0
07-28 21:18:01.022 5123-5123/br.com.pedro.pedrodaumas D/DisplayManager: DisplayManager()
07-28 21:18:01.022 5123-5123/br.com.pedro.pedrodaumas W/ResourcesManager: getTopLevelResources: null for user 0
07-28 21:18:01.092 5123-5123/br.com.pedro.pedrodaumas W/art: Before Android 4.1, method android.graphics.PorterDuffColorFilter android.support.graphics.drawable.VectorDrawableCompat.updateTintFilter(android.graphics.PorterDuffColorFilter, android.content.res.ColorStateList, android.graphics.PorterDuff$Mode) would have incorrectly overridden the package-private method in android.graphics.drawable.Drawable
07-28 21:18:01.172 5123-5123/br.com.pedro.pedrodaumas D/PhoneWindow: *FMB* installDecor mIsFloating : false
07-28 21:18:01.172 5123-5123/br.com.pedro.pedrodaumas D/PhoneWindow: *FMB* installDecor flags : -2139029248
07-28 21:18:01.362 5123-5138/br.com.pedro.pedrodaumas I/art: Background partial concurrent mark sweep GC freed 3506(700KB) AllocSpace objects, 0(0B) LOS objects, 27% free, 5MB/7MB, paused 7.831ms total 22.235ms
07-28 21:18:01.372 5123-5123/br.com.pedro.pedrodaumas I/TextInputLayout: EditText added is not a TextInputEditText. Please switch to using that class instead.
07-28 21:18:01.412 5123-5123/br.com.pedro.pedrodaumas D/AndroidRuntime: Shutting down VM
07-28 21:18:01.412 5123-5123/br.com.pedro.pedrodaumas E/AndroidRuntime: FATAL EXCEPTION: main
Process: br.com.pedro.pedrodaumas, PID: 5123
java.lang.RuntimeException: Unable to start activity ComponentInfo{br.com.pedro.pedrodaumas/br.com.pedro.pedrodaumas.MainActivity}: 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:2697)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2771)
at android.app.ActivityThread.access$900(ActivityThread.java:177)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1432)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5912)
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:1405)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1200)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ListView.setAdapter(android.widget.ListAdapter)' on a null object reference
at br.com.pedro.pedrodaumas.MainActivity.onCreate(MainActivity.java:44)
at android.app.Activity.performCreate(Activity.java:6178)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1118)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2650)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2771)
at android.app.ActivityThread.access$900(ActivityThread.java:177)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1432)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5912)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1405)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1200)
07-28 21:29:10.422 8489-8489/br.com.pedro.pedrodaumas W/art: Before Android 4.1, method android.graphics.PorterDuffColorFilter android.support.graphics.drawable.VectorDrawableCompat.updateTintFilter(android.graphics.PorterDuffColorFilter, android.content.res.ColorStateList, android.graphics.PorterDuff$Mode) would have incorrectly overridden the package-private method in android.graphics.drawable.Drawable
07-28 21:29:10.522 8489-8489/br.com.pedro.pedrodaumas D/PhoneWindow: *FMB* installDecor mIsFloating : false
07-28 21:29:10.522 8489-8489/br.com.pedro.pedrodaumas D/PhoneWindow: *FMB* installDecor flags : -2139029248
07-28 21:29:10.612 8489-8489/br.com.pedro.pedrodaumas I/TextInputLayout: EditText added is not a TextInputEditText. Please switch to using that class instead.
07-28 21:29:10.612 8489-8489/br.com.pedro.pedrodaumas D/AndroidRuntime: Shutting down VM
07-28 21:29:10.612 8489-8489/br.com.pedro.pedrodaumas E/AndroidRuntime: FATAL EXCEPTION: main
Process: br.com.pedro.pedrodaumas, PID: 8489
java.lang.RuntimeException: Unable to start activity ComponentInfo{br.com.pedro.pedrodaumas/br.com.pedro.pedrodaumas.MainActivity}: 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:2697)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2771)
at android.app.ActivityThread.access$900(ActivityThread.java:177)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1432)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5912)
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:1405)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1200)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ListView.setAdapter(android.widget.ListAdapter)' on a null object reference
at br.com.pedro.pedrodaumas.MainActivity.onCreate(MainActivity.java:44)
at android.app.Activity.performCreate(Activity.java:6178)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1118)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2650)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2771)
at android.app.ActivityThread.access$900(ActivityThread.java:177)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1432)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5912)
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:1405)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1200)
答案 0 :(得分：0)
对不起伙计们，我真的很蠢，因为我的项目是针对Android 4.0 +而我在布局上使用了elvation（只支持5.0 +），android studio制作了2种不同的布局，一种用于5.0 - 和一个5.0 + +由于某种原因5.0 +的layour没有ListView。 我刚刚在v21 / content_main上添加了ListView，它确实有效！
感谢每个人的帮助，并为愚蠢的错误和不良解释感到抱歉