java.lang.NullPointerException行53

Question

我不斷收到空指針異常錯誤，但我不知道如何解決它。以下是我的日誌貓。我認爲這個錯誤在Second.java的第53行。日誌信息下面是我的Second.java文件中的代碼。感謝任何人可以提供修復此錯誤的幫助。

10-11 13:39:10.340: E/AndroidRuntime(7905): FATAL EXCEPTION: main 
10-11 13:39:10.340: E/AndroidRuntime(7905): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.ebonybutler.cammct/com.ebonybutler.cammct.Second}: java.lang.NullPointerException 
10-11 13:39:10.340: E/AndroidRuntime(7905):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1702) 
10-11 13:39:10.340: E/AndroidRuntime(7905):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1722) 
10-11 13:39:10.340: E/AndroidRuntime(7905):  at android.app.ActivityThread.access$1500(ActivityThread.java:124) 
10-11 13:39:10.340: E/AndroidRuntime(7905):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:974) 
10-11 13:39:10.340: E/AndroidRuntime(7905):  at android.os.Handler.dispatchMessage(Handler.java:99) 
10-11 13:39:10.340: E/AndroidRuntime(7905):  at android.os.Looper.loop(Looper.java:130) 
10-11 13:39:10.340: E/AndroidRuntime(7905):  at android.app.ActivityThread.main(ActivityThread.java:3821) 
10-11 13:39:10.340: E/AndroidRuntime(7905):  at java.lang.reflect.Method.invokeNative(Native Method) 
10-11 13:39:10.340: E/AndroidRuntime(7905):  at java.lang.reflect.Method.invoke(Method.java:507) 
10-11 13:39:10.340: E/AndroidRuntime(7905):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839) 
10-11 13:39:10.340: E/AndroidRuntime(7905):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597) 
10-11 13:39:10.340: E/AndroidRuntime(7905):  at dalvik.system.NativeStart.main(Native Method) 
10-11 13:39:10.340: E/AndroidRuntime(7905): Caused by: java.lang.NullPointerException 
10-11 13:39:10.340: E/AndroidRuntime(7905):  at com.ebonybutler.cammct.Second.onCreate(Second.java:53) 
10-11 13:39:10.340: E/AndroidRuntime(7905):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047) 
10-11 13:39:10.340: E/AndroidRuntime(7905):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1666) 
10-11 13:39:10.340: E/AndroidRuntime(7905):  ... 11 more 

這裏是我的代碼：

package com.ebonybutler.cammct; 


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


public class Second extends Activity { 

//variable for selection intent 
private final int PICKER = 1; 
//variable to store the currently selected image 
private int currentPic = 0; 
//adapter for gallery view 
private PicAdapter imgAdapt;  
//gallery object 
private Gallery picGallery; 
//image view for larger display 
private ImageView picView; 


/** Called when the activity is first created. */ 
@Override 
public void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.main); 

    //get the large image view 
    picView = (ImageView) findViewById(R.id.picture); 

    //get the gallery view 
    picGallery = (Gallery) findViewById(R.id.gallery); 

    //create a new adapter 
    imgAdapt = new PicAdapter(this); 
    //set the gallery adapter 
    picGallery.setAdapter(imgAdapt); 

    //set long click listener for each gallery thumbnail item 
    picGallery.setOnItemLongClickListener(new OnItemLongClickListener() 
    { 
     //handle long clicks 
     public boolean onItemLongClick(AdapterView<?> parent, View v, 
       int position, long id) { 
      //update the currently selected position so that we assign the imported bitmap to correct item 
      currentPic = position; 
      //take the user to their chosen image selection app (gallery or file manager) 
      Intent pickIntent = new Intent(); 
      pickIntent.setType("image/*"); 
      pickIntent.setAction(Intent.ACTION_GET_CONTENT); 
      startActivityForResult(Intent.createChooser(pickIntent, "Select Picture"), PICKER); 
      return true; 
     } 
    }); 

    //set the click listener for each item in the thumbnail gallery 
    picGallery.setOnItemClickListener(new OnItemClickListener() { 
     //handles clicks 
     public void onItemClick(AdapterView<?> parent, View v, int 
       position, long id) { 
      //set the larger image view to display the chosen bitmap calling method of adapter class 
      picView.setImageBitmap(imgAdapt.getPic(position)); 
     } 
    }); 
} 

    //Base Adapter subclass creates Gallery view 

     public class PicAdapter extends BaseAdapter { 

      //use the default gallery background image 
      int defaultItemBackground; 
      //gallery context 
      private Context galleryContext; 
      //array to store bitmaps to display 
      private Bitmap[] imageBitmaps; 
      //place holder bitmap for empty spaces in gallery 
      Bitmap placeholder; 

      //constructor 
      public PicAdapter(Context c){ 
       //instantiate context 
       galleryContext = c; 
       //create bitmap array 
       imageBitmaps = new Bitmap[10]; 
       //decode the place holder image 
       placeholder = BitmapFactory.decodeResource(getResources(), R.drawable.ic_launcher); 
       //more processing 

       //set place holder as all thumb nail images in the gallery initially 
       for(int i=0; i<imageBitmaps.length; i++) 
        imageBitmaps[i]= placeholder; 

       //get the styling attributes - use default Android system resources 
       TypedArray styleAttrs = galleryContext.obtainStyledAttributes(R.styleable.PicGallery); 
       //get the background resource 
       defaultItemBackground = styleAttrs.getResourceId(R.styleable.PicGallery_android_galleryItemBackground, 0); 
       //recycle attributes 
       styleAttrs.recycle(); 

      } 

      //BaseAdapter methods 

     //return number of data items i.e. bitmap images 
     public int getCount() { 
     return imageBitmaps.length; 
     } 
     //return item t specified position 
     public Object getItem(int position) { 
      return position; 
     } 

     //return item ID at specified position 
     public long getItemId(int position) { 
      return position; 
     } 


     //get view specifies layout and display options for each thumb nail in the gallery 
     public View getView(int position, View convertView, ViewGroup parent) { 
      //create the view 
      ImageView imageView = new ImageView(galleryContext); 
      //specify the bitmap at this position in the array 
      imageView.setImageBitmap(imageBitmaps[position]); 
      //set layout options 
      imageView.setLayoutParams(new Gallery.LayoutParams(300, 200)); 
      //scale type within view area 
      imageView.setScaleType(ImageView.ScaleType.FIT_CENTER); 
      //set default gallery item background 
      imageView.setBackgroundResource(defaultItemBackground); 
      //return the view 
      return imageView; 
     } 

     //custom methods for this app 
     //helper method to add a bitmap to the gallery when the user choose one 

     public void addPic(Bitmap newPic) 
     { 
      //set at currently selected index 
      imageBitmaps[currentPic] = newPic; 
     } 

     //return bitmap at specified position for larger display 
     public Bitmap getPic(int posn) 
     { 
      //return bitmap at posn index 
      return imageBitmaps[posn]; 
     } 
     } 
     //Handle returning from gallery or file manager image selection 

     protected void onActivityResult(int requestCode, int resultCode, Intent data) { 

      if(resultCode == RESULT_OK) { 
       //check if we are returning from picture selection 
       if(requestCode == PICKER) { 

        //the returned picture URI 
        Uri pickedUri = data.getData(); 

        //declare the bitmap 
        Bitmap pic = null; 
        //declare the path string 
        String imgPath = ""; 

        //retrieve the string using media data 
        String[] medData = { MediaStore.Images.Media.DATA }; 
        //query the data 
        Cursor picCursor = managedQuery(pickedUri, medData, null, null, null); 
        if(picCursor!=null) 
        { 
         //get the path string 
         int index = picCursor.getColumnIndexOrThrow(MediaStore.Images.Media.DATA); 
         picCursor.moveToFirst(); 
         imgPath = picCursor.getString(index); 
        } 
        else 
         imgPath = pickedUri.getPath(); 

        //if and ese handle both choosing from gallery and from file manager 

        //if we have a new URI attempt to decode the image itmap 
        if(pickedUri!=null) { 

         //set the width and height we want to use as maximum display 
         int targetWidth = 600; 
         int targetHeight = 400; 

         //sample the incoming image to save on memory resources 

         //create bitmap options to calculate and use sample size 
         BitmapFactory.Options bmpOptions = new BitmapFactory.Options(); 

         //first decode image dimensions only - not the image bitmap itself 
         bmpOptions.inJustDecodeBounds = true; 
         BitmapFactory.decodeFile(imgPath, bmpOptions); 

         //work out what the sample size should be 

         //image width and height before sampling 
         int currHeight = bmpOptions.outHeight; 
         int currWidth = bmpOptions.outWidth; 

         //variable to store new sample size 
         int sampleSize = 1; 

         //calculate the sample size if the existing size is larger than target size 

         if (currHeight>targetHeight || currWidth>targetWidth) 
         { 
          //use either width of height 
          if (currWidth>currHeight) 
           sampleSize = Math.round((float)currHeight/(float)targetHeight); 
           else 
            sampleSize = Math.round((float)currWidth/(float)targetWidth); 

         } 
         //use the new sample size 
         bmpOptions.inSampleSize = sampleSize; 

         //now decode the bitmap using sample options 
         bmpOptions.inJustDecodeBounds = false; 

         //get the file as a bitmap 
         pic = BitmapFactory.decodeFile(imgPath, bmpOptions); 

         //pass bitmap to ImageAdapter to add to array 
         imgAdapt.addPic(pic); 
         //redraw the gallery thumbnails to reflect the new addition 
         picGallery.setAdapter(imgAdapt); 

         //display the newly selected image at larger size 
         picView.setImageBitmap(pic); 
         //scale options 
         picView.setScaleType(ImageView.ScaleType.FIT_CENTER); 

        } 
       } 
      } 
      //superclass method 
      super.onActivityResult(requestCode, resultCode, data); 
     } 
} 

這裏是XML：

<?xml version="1.0" encoding="utf-8"?> 
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" 
android:layout_width="fill_parent" 
android:layout_height="fill_parent" 
android:orientation="vertical"> 

<TextView android:layout_width="fill_parent" 
    android:layout_height="wrap_content" 
    android:padding="5dp" 
    android:text="@string/select_intro" 
    android:gravity="center" 
    android:textStyle="bold"/> 

<Gallery 
    android:id="@+id/gallery" 
    android:layout_width="fill_parent" 
    android:layout_height="wrap_content" /> 

<TextView android:layout_width="fill_parent" 
    android:layout_height="wrap_content" 
    android:gravity="center" 
    android:padding="5dp" 
    android:textStyle="italic" 
    android:text="@string/show_intro"/> 

<ImageView 
    android:id="@+id/picture" 
    android:layout_width="fill_parent" 
    android:layout_height="fill_parent" 
    android:contentDescription="@string/picture"/> 

</LinearLayout> 

Answer 1

53號線：

picGallery.setAdapter(imgAdapt); 

所以檢查什麼正在從返回

picGallery = (Gallery) findViewById(R.id.gallery); 

Answer 2

你試過調試嗎？嘗試調試模式在Eclipse中放置一個斷點53處

排在53排，你似乎有：

picGallery.setAdapter(imgAdapt); 

現在你不能調用picGallery一組操作，如果是零。所以你可能想檢查一下。

if (picGallery == null) { 
// do something useful, perhaps set it? I'm not familiar with android 
} 

現在看起來像picGallery應該在早些時候設置。

picGallery = (Gallery) findViewById(R.id.gallery); 

可能想查看爲什麼findViewById返回null。