アプリにスピナーを追加するとクラッシュする

Question

私のアプリにスピナーが追加され、アプリケーションがクラッシュしてビルドしません。スピナーは、ストレージから.mp3ファイル名の項目を表示しました。誰かがクラッシュする理由を伝えることはできますか？私のコードで何が間違っていますか？ コードが必要な場合は教えてください。ここ

これらはマニフェスト

<?xml version="1.0" encoding="utf-8"?> 
<manifest xmlns:android="http://schemas.android.com/apk/res/android" 
package="com.nati_1.ImageGallerySwitching_v8_2"> 

<uses-permission android:name="android.permission.WAKE_LOCK" /> 
<uses-permission android:name="android.permission.INTERNET" /> 
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" /> 
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" /> 


<application 
    android:allowBackup="true" 
    android:icon="@mipmap/ic_launcher" 
    android:label="@string/app_name" 
    android:supportsRtl="true" 
    android:theme="@style/Theme.AppCompat.NoActionBar"> 

song_item.xml

<?xml version="1.0" encoding="utf-8"?> 
<TextView android:id="@+id/text1" 
xmlns:android="http://schemas.android.com/apk/res/android" 
android:layout_width="match_parent" 
android:layout_height="match_parent" 
android:textSize="20dp" 
android:textStyle="bold" 
/> 

と

12-20 00:22:48.014 12887-12887/com.nati_1.ImageGallerySwitching_v6 
E/AndroidRuntime: FATAL EXCEPTION: main 

Process: com.nati_1.ImageGallerySwitching_v6, PID: 12887 



    java.lang.RuntimeException: Unable to instantiate activity  
ComponentInfo{com.nati_1.ImageGallerySwitching_v6/com.nati_1.ImageGallerySwitching_v8_2.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.Window$Callback android.view.Window.getCallback()' on a null object reference 

at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2614) 

at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2787) 

at android.app.ActivityThread.-wrap12(ActivityThread.java) 

at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1504) 

at android.os.Handler.dispatchMessage(Handler.java:102) 

at android.os.Looper.loop(Looper.java:154) 

at android.app.ActivityThread.main(ActivityThread.java:6247) 

at java.lang.reflect.Method.invoke(Native Method) 

at 


com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:872) 

at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:762) 

Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 
'android.view.Window$Callback android.view.Window.getCallback()' on a null 
object reference 

at android.support.v7.app.AppCompatDelegateImplBase.<init> 
(AppCompatDelegateImplBase.java:116) 


at android.support.v7.app.AppCompatDelegateImplV9.<init> 
(AppCompatDelegateImplV9.java:147) 

at android.support.v7.app.AppCompatDelegateImplV11.<init> 
(AppCompatDelegateImplV11.java:27) 


at android.support.v7.app.AppCompatDelegateImplV14.<init> 
(AppCompatDelegateImplV14.java:50) 

at android.support.v7.app.AppCompatDelegateImplV23.<init> 
(AppCompatDelegateImplV23.java:29) 

at android.support.v7.app.AppCompatDelegateImplN.<init> 
(AppCompatDelegateImplN.java:29) 

at 
android.support.v7.app.AppCompatDelegate.create(AppCompatDelegate.java:197) 

at 
android.support.v7.app.AppCompatDelegate.create(AppCompatDelegate.java:181) 

at 
android.support.v7.app.AppCompatActivity.getDelegate(AppCompatActivity.java:521) 

                        at android.support.v7.app.AppCompatActivity.findViewById(AppCompatActivity.java:190) 
                        at com.nati_1.ImageGallerySwitching_v8_2.MainActivity.<init>(MainActivity.java:225) 
                        at java.lang.Class.newInstance(Native Method) 
                        at android.app.Instrumentation.newActivity(Instrumentation.java:1079) 
                        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2604) 
                        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2787)  
                        at android.app.ActivityThread.-wrap12(ActivityThread.java)  
                        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1504)  
                        at android.os.Handler.dispatchMessage(Handler.java:102)  
                        at android.os.Looper.loop(Looper.java:154)  
                        at android.app.ActivityThread.main(ActivityThread.java:6247)  
                        at java.lang.reflect.Method.invoke(Native Method)  

logcatからの部品であるMainActivity

import java.io.File; 
import java.io.FilenameFilter; 
import java.io.IOException; 
import java.util.ArrayList; 
import java.util.List; 

//import android.view.Window; 



    public class MainActivity extends AppCompatActivity implements 
AdapterView.OnItemSelectedListener { 

    private Integer images[]={R.drawable.pic1, R.drawable.pic21, 
R.drawable.pic3, R.drawable.pic2, R.drawable.pic4, 
      R.drawable.pic5, R.drawable.pic6, R.drawable.pic30, 
R.drawable.pic31, R.drawable.pic26, R.drawable.pic7, R.drawable.pic25, 
R.drawable.pic8, R.drawable.pic9, 
      R.drawable.pic10, R.drawable.pic27, R.drawable.pic28, 
R.drawable.pic29, R.drawable.pic11, R.drawable.pic22, R.drawable.pic23, 
R.drawable.pic13, R.drawable.pic14, 
      R.drawable.pic15, R.drawable.pic16, R.drawable.pic24, 
R.drawable.pic17, R.drawable.pic18, R.drawable.pic19 
      , R.drawable.pic20, R.drawable.pic12}; 
......... 
......... 
// for spinner 
class Mp3Filter implements FilenameFilter { 
    public boolean accept (File dir, String name){ 
     return (name.endsWith(".mp3")); 
    } 
} 
// spinner 
public final String SD_PATH =new String("/sdcard/music/"); 
public List<String> songs = new ArrayList<String>(); 
Spinner mySpinner = (Spinner)findViewById(R.id.spinner1); 

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
..... 
..... 
    mp = MediaPlayer.create(this, R.raw.shlomoimagine); 
    mp.start(); 
    // currImage = 0; 
    setContentView(R.layout.activity_main); 


    //initializing the loop at the beginning of the app run 
    initializeImageSwitcher(); 
    setImageRotateListener(); 
    // handler.post(runnable); 
    updatePlayList(); 

... 
... 
private void updatePlayList() { 
    File home=new File(SD_PATH); 

    File[] files = home.listFiles(new Mp3Filter()); 
    if(files.length>0){ 
     for(File file:files){ 
      songs.add(file.getName()); 
     } 
     ArrayAdapter<String> songList = new ArrayAdapter<String> 
(this,R.layout.song_item,songs); 
     mySpinner.setAdapter(songList); 
     mySpinner.setOnItemSelectedListener(this); 

    } 
} 

の一部であります

Answer 1

問題は次のように定義されます

Spinner mySpinner = (Spinner)findViewById(R.id.spinner1); 

が、これは間違っている、あなた：

java.lang.NullPointerException: Attempt to invoke virtual method 
'android.view.Window$Callback android.view.Window.getCallback()' on a null object reference 

問題は、あなたがSpinnerための変数を作成すると同時に、彼らの参照を取得しているということですonCreate()メソッド内の参照を取得する必要があり、このようないくつか：

Spinner mySpinner; 

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_login); 

    mySpinner = (Spinner)findViewById(R.id.spinner1); 
    ... 
    ... 
}