我正在创建一个简单的应用程序，它读取JSON数据并将其显示在ListView中。我创建了一个名为MyAdapter.java的自定义适配器类。我成功地膨胀了行，但是findViewById返回null（在注释中指出）。我计划向Row.xml添加更多wigets，但仅仅是为了测试我添加了TextView。有什么帮助吗？
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical" android:layout_width="match_parent"
android:layout_height="match_parent"
android:padding="6dp">
<TextView
android:id="@+id/tvnew_title"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:textStyle="italic"/>
</LinearLayout>
package com.test.rajat.contacts;
import android.content.Context;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.TextView;
import java.util.ArrayList;
import java.util.HashMap;
public class MyAdapter extends ArrayAdapter<HashMap<String,String>> {
private ArrayList<HashMap<String,String>> movies_list;
private Context context;
private TextView title;
public MyAdapter(Context context, int resource,ArrayList<HashMap<String,String>> movies_list) {
super(context, resource,movies_list);
this.context=context;
this.movies_list=movies_list;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
View v=convertView;
if(v==null){
LayoutInflater inflater=(LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
inflater.inflate(R.layout.row,null);
Log.d("IR","row inflated");
}
HashMap<String,String> movie=movies_list.get(position);
if(movie!=null){
/********This line returns null on findViewById********/
title=(TextView)v.findViewById(R.id.tvnew_title);
title.setText(movie.get("title"));
}
return v;
}
}
package com.test.rajat.contacts;
import android.app.SearchManager;
import android.content.Context;
import android.content.Intent;
import android.os.AsyncTask;
import android.os.Bundle;
import android.support.v7.app.ActionBarActivity;
import android.support.v7.widget.SearchView;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.ListView;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import java.util.ArrayList;
import java.util.HashMap;
public class MainActivity extends ActionBarActivity {
private ListView list_movies;
private MyAdapter adapter;
private SearchView searchView;
JSONParser parser;
ArrayList<HashMap<String,String>> movies_list;
private static String url="https://api.themoviedb.org/3/search/movie?api_key=<pasted key>&&query=";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
list_movies=(ListView) findViewById(R.id.list_movies);
handleIntent(getIntent());
parser=new JSONParser();
}
@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);
SearchManager searchManager =
(SearchManager) getSystemService(Context.SEARCH_SERVICE);
searchView=
(SearchView) menu.findItem(R.id.action_search).getActionView();
searchView.setSearchableInfo(
searchManager.getSearchableInfo(getComponentName()));
searchView.setIconifiedByDefault(false);
final SearchView.OnQueryTextListener queryTextListener = new SearchView.OnQueryTextListener() {
@Override
public boolean onQueryTextChange(String newText) {
return true;
}
@Override
public boolean onQueryTextSubmit(String query) {
String newquery=url+query.replaceAll(" ","%20");
new RetrieveJSON().execute(newquery);
searchView.clearFocus();
return true;
}
};
searchView.setOnQueryTextListener(queryTextListener);
return true;
}
private void handleIntent(Intent intent) {
if (Intent.ACTION_SEARCH.equals(intent.getAction())) {
String query = intent.getStringExtra(SearchManager.QUERY);
//use the query to search your data somehow
}
}
@Override
protected void onNewIntent(Intent intent) {
handleIntent(intent);
}
@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();
//noinspection SimplifiableIfStatement
switch(id)
{
case R.id.action_settings:
return true;
case R.id.action_search:
}
return super.onOptionsItemSelected(item);
}
class RetrieveJSON extends AsyncTask<String,String,Void>
{
@Override
protected void onPreExecute() {
super.onPreExecute();
movies_list=new ArrayList<HashMap<String,String>>();
}
@Override
protected Void doInBackground(String... params) {
String str_json= parser.getJSONFromUrl(params[0]);
try {
JSONObject json=new JSONObject(str_json);
JSONArray jsonArray=new JSONArray(json.getString("results"));
for(int i=0;i<jsonArray.length();i++)
{
JSONObject tmp=jsonArray.getJSONObject(i);
String title=tmp.getString("title");
String release_date=tmp.getString("release_date");
String overview=tmp.getString("overview");
String rating=tmp.getString("vote_average");
String poster_path=tmp.getString("poster_path");
HashMap<String,String> movie=new HashMap<>();
movie.put("title",title);
movie.put("release_date",release_date);
movie.put("overview",overview);
movie.put("rating",rating);
movie.put("poster_path",poster_path);
movies_list.add(movie);
}
}
catch(JSONException e)
{
}
return null;
}
@Override
protected void onPostExecute(Void result) {
super.onPostExecute(result);
adapter=new MyAdapter(MainActivity.this,R.layout.row,movies_list);
list_movies.setAdapter(adapter);
}
}
}
07-14 19:31:57.182 12606-12606/com.test.rajat.contacts D/IR﹕ row inflated
07-14 19:31:57.183 12606-12606/com.test.rajat.contacts D/AndroidRuntime﹕ Shutting down VM
07-14 19:31:57.189 12606-12606/com.test.rajat.contacts E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.test.rajat.contacts, PID: 12606
java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.View.findViewById(int)' on a null object reference
at com.test.rajat.contacts.MyAdapter.getView(MyAdapter.java:40)
at android.widget.AbsListView.obtainView(AbsListView.java:2349)
at android.widget.ListView.onMeasure(ListView.java:1154)
at android.view.View.measure(View.java:17554)
at android.widget.ScrollView.measureChildWithMargins(ScrollView.java:1260)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:436)
at android.widget.ScrollView.onMeasure(ScrollView.java:337)
at android.view.View.measure(View.java:17554)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5536)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:436)
at android.view.View.measure(View.java:17554)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5536)
at android.support.v7.internal.widget.ActionBarOverlayLayout.onMeasure(ActionBarOverlayLayout.java:453)
at android.view.View.measure(View.java:17554)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5536)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:436)
at android.view.View.measure(View.java:17554)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5536)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1436)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:722)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:613)
at android.view.View.measure(View.java:17554)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5536)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:436)
at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2871)
at android.view.View.measure(View.java:17554)
at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2015)
at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1173)
at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1379)
at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1061)
at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5891)
at android.view.Choreographer$CallbackRecord.run(Choreographer.java:767)
at android.view.Choreographer.doCallbacks(Choreographer.java:580)
at android.view.Choreographer.doFrame(Choreographer.java:550)
at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:753)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5293)
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:904)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:699)
答案 0 :(得分：1)
从
改变 inflater.inflate(R.layout.row,null);
到
v= inflater.inflate(R.layout.row,null);
应解决问题