Null Pointer Exception in Adapter

My logcat is indicating a null pointer exception, and I don't know how to solve these null pointer exceptions.

Null Pointer exception in my adapter class:

  File dir=new File(Environment.getExternalStorageDirectory(),"/myImages/");

  int count=dir.list().length; 

  String[] fileNames = dir.list();

Check the above lines... that is a value returning null.

My code:

package ImageViewExample.ImageViewExample;

   import java.io.File;

   import android.R.string;
   import android.app.Activity;
   import android.content.Context;
   import android.content.Intent;
   import android.database.Cursor;
   import android.graphics.Bitmap;
   import android.graphics.BitmapFactory;
   import android.net.Uri;
   import android.os.Bundle;
   import android.os.Environment;
   import android.provider.MediaStore;
   import android.view.View;
   import android.view.ViewGroup;
   import android.widget.AdapterView;
   import android.widget.BaseAdapter;
   import android.widget.Gallery;
   import android.widget.GridView;
   import android.widget.ImageView;
   import android.widget.AdapterView.OnItemClickListener;

    public class ImageViewExample extends Activity {
    /** Called when the activity is first created. */
    private Cursor imagecursor, actualimagecursor;
    private int image_column_index, actual_image_column_index;
    GridView imagegrid;
    private int count;
    @Override
    public void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.main);
      init_phone_image_grid();
     }
     private void init_phone_image_grid() {
      String[] img = { MediaStore.Images.Thumbnails._ID };
      imagecursor = managedQuery(MediaStore.Images.Thumbnails.EXTERNAL_CONTENT_URI, 
     img, null,null, MediaStore.Images.Thumbnails.IMAGE_ID + "");


     System.out.println("path"+managedQuery(MediaStore.Images
    .Thumbnails.EXTERNAL_CONTENT_URI, img, null,null, MediaStore.Images
     .Thumbnails.IMAGE_ID + ""));
      image_column_index =   
     imagecursor.getColumnIndexOrThrow(MediaStore.Images.Thumbnails._ID);
      System.out.println("index"+imagecursor.getColumnIndexOrThrow
     (MediaStore.Images.Thumbnails._ID));
      count = imagecursor.getCount();
      imagegrid = (GridView) findViewById(R.id.PhoneImageGrid);

      imagegrid.setAdapter(new ImAdapterh(this));
      System.out.println("index"+this);
      imagegrid.setOnItemClickListener(new OnItemClickListener() {
    public void onItemClick(AdapterView parent, View v,int position, long id) {
                          System.gc();
      String[] proj = { MediaStore.Images.Media.DATA };
    actualimagecursor = managedQuery(MediaStore.Images.Media.EXTERNAL_CONTENT_URI, 
    proj,null,null, null);
       actual_image_column_index =   
    actualimagecursor.getColumnIndexOrThrow(MediaStore.Images.Media.DATA);
                  actualimagecursor.moveToPosition(position);
                  String i = actualimagecursor.getString(actual_image_column_index);
                  System.gc();
                  Intent intent = new Intent(getApplicationContext(), ViewImage.class);
                  intent.putExtra("filename", i);
                  startActivity(intent);
            }
      });
    }


   public class ImAdapterh extends BaseAdapter{

   File dir=new File(Environment.getExternalStorageDirectory(),"/Pictures/");
   int count=dir.list().length; 
   String[] fileNames = dir.list();

    private Context mContext;

   public ImAdapterh(Context c) {
       mContext = c;
    }

      public int getCount() {
       return count;
      }

      public Object getItem(int position) {
       return null;
      }

     pu开发者_开发知识库blic long getItemId(int position) {
       return 0;
      }

   // create a new ImageView for each item referenced by the Adapter
     public View getView(int position, View convertView, ViewGroup parent) {
       ImageView imageView = null;        


     for(String bitmapFileName : fileNames)
     {
          if (convertView == null) 
          {  // if it's not recycled, initialize some attributes
              imageView = new ImageView(mContext);
              imageView.setLayoutParams(new Gallery.LayoutParams(85, 85));
              imageView.setScaleType(ImageView.ScaleType.CENTER_CROP);
              imageView.setPadding(8, 8, 8, 8);                   

              Bitmap bmp = BitmapFactory.decodeFile(dir.getPath() + "/" +   
               bitmapFileName);
              System.out.println(dir);
              imageView.setImageBitmap(bmp);  
           }else 
           {
           imageView = (ImageView) convertView;            

           }
   } 
       return imageView;
       }
      }}

Logcat error:

05-04 01:41:31.705: ERROR/AndroidRuntime(1417): FATAL EXCEPTION: main
05-04 01:41:31.705: ERROR/AndroidRuntime(1417): java.lang.RuntimeException: Unable to  
start activity  
ComponentInfo{ImageViewExample.ImageViewExample/ImageViewExample
.ImageViewExample.ImageViewExample}: java.lang.NullPointerException
05-04 01:41:31.705: ERROR/AndroidRuntime(1417):     at   
android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2663)
05-04 01:41:31.705: ERROR/AndroidRuntime(1417):     at 
android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679)
05-04 01:41:31.705: ERROR/AndroidRuntime(1417):     at 
android.app.ActivityThread.access$2300(ActivityThread.java:125)
05-04 01:41:31.705: ERROR/AndroidRuntime(1417):     at 
android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033)
05-04 01:41:31.705: ERROR/AndroidRuntime(1417):     at 
android.os.Handler.dispatchMessage(Handler.java:99)
05-04 01:41:31.705: ERROR/AndroidRuntime(1417):     at 
android.os.Looper.loop(Looper.java:123)
05-04 01:41:31.705: ERROR/AndroidRuntime(1417):     at   
android.app.ActivityThread.main(ActivityThread.java:4627)
05-04 01:41:31.705: ERROR/AndroidRuntime(1417):     at 
java.lang.reflect.Method.invokeNative(Native Method)
05-04 01:41:31.705: ERROR/AndroidRuntime(1417):     at 
java.lang.reflect.Method.invoke(Method.java:521)
05-04 01:41:31.705: ERROR/AndroidRuntime(1417):     at 
com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
05-04 01:41:31.705: ERROR/AndroidRuntime(1417):     at 
com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
05-04 01:41:31.705: ERROR/AndroidRuntime(1417):     at 
dalvik.system.NativeStart.main(Native Method)
05-04 01:41:31.705: ERROR/AndroidRuntime(1417): Caused by:   
java.lang.NullPointerException
05-04 01:41:31.705: ERROR/AndroidRuntime(1417):     at 
ImageViewExample.ImageViewExample.ImageViewExample$ImAdapterh.<init>
(ImageViewExample.java:71)
05-04 01:41:31.705: ERROR/AndroidRuntime(1417):     at 
ImageViewExample.ImageViewExample.ImageViewExample
.init_phone_image_grid(ImageViewExample.java:49)
05-04 01:41:31.705: ERROR/AndroidRuntime(1417):     at  
ImageViewExample.ImageViewExample.ImageViewExample.onCreate(ImageViewExample.java:36)
05-04 01:41:31.705: ERROR/AndroidRuntime(1417):     at 
android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
05-04 01:41:31.705: ERROR/AndroidRuntime(1417):     at   
android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2627)
05-04 01:41:31.705: ERROR/AndroidRuntime(1417):     ... 11 more

The list() method of File can return null. From the Javadoc:

Returns: An array of strings naming the files and directories in the directory denoted by this abstract pathname. The array will be empty if the directory is empty. Returns null if this abstract pathname does not denote a directory, or if an I/O error occurs.

seems to me that the list() is the one which resulting error, which can be happen because there is no file inside that folder ( "/myImages/" )

To fix that you have to check if the folder is empty or not :

File dir=new File(Environment.getExternalStorageDirectory(),"/myImages/");
if(dir!=null &&dir.list()!=null)
{
 int count=dir.list().length; 
 String[] fileNames = dir.list();
 //...<REST OF THE CODE>
}else
{
  //do empty folder handler here.
}

or

File dir=new File(Environment.getExternalStorageDirectory(),"/myImages/");
if(dir.list()==null)
{
  dir.setList(new ArrayList());// IF LIST is null, create empty list.
}
int count=dir.list().length; 
String[] fileNames = dir.list();
//..<REST OF THE CODE> ..

The null pointer exception will be raised when listing the contents or number of files of a directory that does not exist or one that you do not have permissions to.

Check the following:

1. If external storage access has been mentioned in the manifest.
2. If the directory whose files you want listed actually exists within the external storage.

Also post the stack trace and logCat outputs. That would also help people help you.

HTH,
Sriram