我正在使用Volley库来获取json数据。我还修改了Manifest添加必要的Internet权限。但是当我运行应用程序时它会崩溃。
主要活动.java
package com.example.sans.myapplication1;
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.view.View;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.ListView;
import android.widget.Toast;
import com.android.volley.Request;
import com.android.volley.RequestQueue;
import com.android.volley.Response;
import com.android.volley.VolleyError;
import com.android.volley.toolbox.JsonObjectRequest;
import com.android.volley.toolbox.Volley;
import org.json.JSONArray;
import org.json.JSONObject;
import java.util.ArrayList;
import java.util.List;
public class MainActivity extends AppCompatActivity {
ListView listView;
RequestQueue requestQueue;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
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();
}
});
listView=(ListView)findViewById(R.id.list);
RequestQueue requestQueue= Volley.newRequestQueue(this);
JsonObjectRequest jsonObjectRequest=new JsonObjectRequest(Request.Method.GET, "http://api.themoviedb.org/3/movie/popular?api_key=fa468af9e769ba5fbc027e9e933130ed",
new Response.Listener<JSONObject>() {
@Override
public void onResponse(JSONObject response) {
ArrayList<Movie> movieList= new ArrayList<Movie>();
try{
JSONArray jsonArray=response.getJSONArray("results");
for (int i=0;i< jsonArray.length();i++){
JSONObject jsonObject= jsonArray.getJSONObject(i);
String title= jsonObject.getString("title");
movieList.add(new Movie(title));
MovieAdapter adapter= new MovieAdapter(getApplicationContext(),movieList);
listView.setAdapter(adapter);
}
}catch(Exception e){
Toast.makeText(getApplicationContext(), "Error getting data", Toast.LENGTH_LONG).show();
}
}
},
new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
Toast.makeText(getApplicationContext(),"Error",Toast.LENGTH_LONG).show();
}
});
requestQueue.add(jsonObjectRequest);
}
}
$ MovieAdapter.java
package com.example.sans.myapplication1;
import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.TextView;
import java.util.List;
/**
* Created by sans on 13/7/16.
*/
public class MovieAdapter extends ArrayAdapter<Movie> {
public MovieAdapter(Context context, List<Movie> objects) {
super(context,0, objects);
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
Movie movie=getItem(position);
if(convertView==null){
convertView= LayoutInflater.from(getContext()).inflate(R.layout.list_row, parent);
}
TextView title=(TextView)convertView.findViewById(R.id.title);
title.setText(movie.getTitle());
return convertView;
}
}
$ Movie.java
package com.example.sans.myapplication1;
import android.app.Activity;
import android.content.Context;
import android.widget.Toast;
import com.android.volley.Request;
import com.android.volley.RequestQueue;
import com.android.volley.Response;
import com.android.volley.VolleyError;
import com.android.volley.toolbox.JsonObjectRequest;
import com.android.volley.toolbox.Volley;
import org.json.JSONArray;
import org.json.JSONObject;
import java.util.ArrayList;
/**
* Created by sans on 13/7/16.
*/
public class Movie {
private String title;
public Movie(String title){
this.title=title;
}
public void setTitle(String title) {
this.title = title;
}
public String getTitle() {
return title;
}
}
$ list_row.xml
<?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="20dp">
<TextView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:minHeight="?attr/listPreferredItemHeight"
android:id="@+id/title"/>
</LinearLayout>
$ content_main.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"
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="com.example.sans.myapplication1.MainActivity"
tools:showIn="@layout/activity_main">
<ListView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/list" />
</RelativeLayout>
记录错误
FATAL EXCEPTION: main
Process: com.example.sans.myapplication1, PID: 4252
java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.View.findViewById(int)' on a null object reference
at com.example.sans.myapplication1.MovieAdapter.getView(MovieAdapter.java:29)
at android.widget.AbsListView.obtainView(AbsListView.java:2346)
at android.widget.ListView.measureHeightOfChildren(ListView.java:1280)
at android.widget.ListView.onMeasure(ListView.java:1188)
at android.view.View.measure(View.java:18788)
at android.widget.RelativeLayout.measureChildHorizontal(RelativeLayout.java:715)
at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:461)
at android.view.View.measure(View.java:18788)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at android.support.design.widget.CoordinatorLayout.onMeasureChild(CoordinatorLayout.java:668)
at android.support.design.widget.CoordinatorLayout.onMeasure(CoordinatorLayout.java:735)
at android.view.View.measure(View.java:18788)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
at android.support.v7.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:135)
at android.view.View.measure(View.java:18788)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1465)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:748)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:630)
at android.view.View.measure(View.java:18788)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
at android.view.View.measure(View.java:18788)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1465)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:748)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:630)
at android.view.View.measure(View.java:18788)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
at com.android.internal.policy.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2643)
at android.view.View.measure(View.java:18788)
at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2100)
at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1216)
at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1452)
at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1107)
at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6013)
at android.view.Choreographer$CallbackRecord.run(Choreographer.java:858)
at android.view.Choreographer.doCallbacks(Choreographer.java:670)
at android.view.Choreographer.doFrame(Choreographer.java:606)
at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:844)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
07-13 17:37:39.746 1532-1903/? W/ActivityManager: Force finishing activity com.example.sans.myapplication1/.MainActivity
答案 0 :(得分：0)
在MovieAdapter.java中，将convertView!=null更改为convertView==null
＆安培;在 list_row.xml 文件中
而不是android:minHeight="?attr/listPreferredItemHeight"
将其更改为android:minHeight="?android:attr/listPreferredItemHeight"