Crash avec un ArrayAdapter ou le ListView

Question

Im juste tester avec ArrayAdapyer et ListView, Lorsque je cours ce code mon plantage de l'application. Le journal ne dit rien et ne trouve aucune erreur. ici est la classe:

et la classe:

import android.os.Bundle; 
import android.support.v7.app.AppCompatActivity; 
import android.widget.ArrayAdapter; 
import android.widget.ListView; 

import java.util.ArrayList; 

public class MainActivity extends AppCompatActivity { 

    ListView list; 
    ArrayAdapter<String> adap; 
    ArrayList<String> arr; 


    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_main); 
     list = (ListView) findViewById(R.id.list); 
     arr = new ArrayList<String>(); 
     arr.add("hello"); 
     arr.add("name is dragon"); 
     adap = new ArrayAdapter<String>(this,android.R.layout.simple_list_item_1,arr); 
     list.setAdapter(adap); 


    } 

} 

LOG:

          java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.faivel.myapplication/com.example.faivel.myapplication.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:2984) 
               at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3045) 
               at android.app.ActivityThread.-wrap14(ActivityThread.java) 
               at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1642) 
               at android.os.Handler.dispatchMessage(Handler.java:102) 
               at android.os.Looper.loop(Looper.java:154) 
               at android.app.ActivityThread.main(ActivityThread.java:6776) 
               at java.lang.reflect.Method.invoke(Native Method) 
               at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1520) 
               at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1410) 
              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.example.faivel.myapplication.MainActivity.onCreate(MainActivity.java:26) 
               at android.app.Activity.performCreate(Activity.java:6955) 
               at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1126) 
               at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2927) 
               at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3045)  
               at android.app.ActivityThread.-wrap14(ActivityThread.java)  
               at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1642)  
               at android.os.Handler.dispatchMessage(Handler.java:102)  
               at android.os.Looper.loop(Looper.java:154)  
               at android.app.ActivityThread.main(ActivityThread.java:6776)  
               at java.lang.reflect.Method.invoke(Native Method)  
               at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1520)  
               at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1410)  

quel est le problème ici? Merci! Modifier: ajouté le journal!

Answer 1

J'ai testé votre class

package com.example.nniroula.test; 

import android.os.Bundle; 
import android.support.v7.app.AppCompatActivity; 
import android.widget.ArrayAdapter; 
import android.widget.ListView; 

import java.util.ArrayList; 

public class Test extends AppCompatActivity { 

    ListView list; 
    ArrayAdapter<String> adap; 
    ArrayList<String> arr; 


    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_text); 
     list = (ListView) findViewById(R.id.list); 
     arr = new ArrayList<String>(); 
     arr.add("hello"); 
     arr.add("name is dragon"); 
     adap = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, arr); 
     list.setAdapter(adap); 


    } 

} 

et xml fichier

<?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"> 

    <ListView 
     android:id="@+id/list" 
     android:layout_width="match_parent" 
     android:layout_height="match_parent"/> 

</LinearLayout> 

Tout fonctionne très bien.