java - 如何解决Logcat错误？项目 ImageView 示例

Question

嗨，现在尝试在我的画廊中创建文件夹......通常我的 GridView 单独显示图像，但我需要在我的画廊中创建文件夹。所以，我正在使用文件类...如果我运行我的项目日志 cat 指示错误如何解决这些错误？请检查我的编码......

ImageViewExample.java

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 + "");
      image_column_index = imagecursor
     .getColumnIndexOrThrow(MediaStore.Images.Thumbnails._ID);
      count = imagecursor.getCount();
      imagegrid = (GridView) findViewById(R.id.PhoneImageGrid);
      imagegrid.setAdapter(new ImAdapterh(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(),"/myImages/");

      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;
   }

   public 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 错误:

04-29 14:56:23.011: DEBUG/AndroidRuntime(415): >>>>>>>>>>>>>> AndroidRuntime START 
<<<<<<<<<<<<<<
04-29 14:56:23.021: DEBUG/AndroidRuntime(415): CheckJNI is ON
04-29 14:56:23.402: DEBUG/AndroidRuntime(415): --- registering native functions ---
04-29 14:56:24.781: DEBUG/AndroidRuntime(415): Shutting down VM
04-29 14:56:24.791: DEBUG/dalvikvm(415): Debugger has detached; object registry had 1 
entries
04-29 14:56:24.821: INFO/AndroidRuntime(415): NOTE: attach of thread 'Binder Thread 
#3' failed
04-29 14:56:25.761: DEBUG/AndroidRuntime(423): >>>>>>>>>>>>>> AndroidRuntime START 
<<<<<<<<<<<<<<
04-29 14:56:25.761: DEBUG/AndroidRuntime(423): CheckJNI is ON
04-29 14:56:26.141: DEBUG/AndroidRuntime(423): --- registering native functions ---
04-29 14:56:27.552: INFO/ActivityManager(66): Starting activity: Intent { 
act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] flg=0x10000000   
cmp=ImageViewExample.ImageViewExample/.ImageViewExample }
04-29 14:56:28.182: DEBUG/AndroidRuntime(423): Shutting down VM
04-29 14:56:28.232: DEBUG/dalvikvm(423): Debugger has detached; object registry had 1 
entries
04-29 14:56:28.291: INFO/ActivityManager(66): Start proc 
ImageViewExample.ImageViewExample for activity   
ImageViewExample.ImageViewExample/.ImageViewExample: pid=430 uid=10050 gids={}
04-29 14:56:28.312: INFO/AndroidRuntime(423): NOTE: attach of thread 'Binder Thread 
#3' failed
04-29 14:56:29.641: DEBUG/AndroidRuntime(430): Shutting down VM
04-29 14:56:29.641: WARN/dalvikvm(430): threadid=1: thread exiting with uncaught 
exception (group=0x4001d800)
04-29 14:56:29.711: ERROR/AndroidRuntime(430): FATAL EXCEPTION: main
04-29 14:56:29.711: ERROR/AndroidRuntime(430): java.lang.RuntimeException: Unable to   
start activity  
ComponentInfo{ImageViewExample.ImageViewExample/ImageViewExample.
ImageViewExample.ImageViewExample}: java.lang.NullPointerException
04-29 14:56:29.711: ERROR/AndroidRuntime(430):     at  
android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2663)
04-29 14:56:29.711: ERROR/AndroidRuntime(430):     at 
android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679)
04-29 14:56:29.711: ERROR/AndroidRuntime(430):     at  
android.app.ActivityThread.access$2300(ActivityThread.java:125)
04-29 14:56:29.711: ERROR/AndroidRuntime(430):     at  
android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033)
04-29 14:56:29.711: ERROR/AndroidRuntime(430):     at 
android.os.Handler.dispatchMessage(Handler.java:99)
04-29 14:56:29.711: ERROR/AndroidRuntime(430):     at 
android.os.Looper.loop(Looper.java:123)
04-29 14:56:29.711: ERROR/AndroidRuntime(430):     at 
android.app.ActivityThread.main(ActivityThread.java:4627)
04-29 14:56:29.711: ERROR/AndroidRuntime(430):     at 
java.lang.reflect.Method.invokeNative(Native Method)
04-29 14:56:29.711: ERROR/AndroidRuntime(430):     at   
java.lang.reflect.Method.invoke(Method.java:521)
04-29 14:56:29.711: ERROR/AndroidRuntime(430):     at   
com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
04-29 14:56:29.711: ERROR/AndroidRuntime(430):     at 
com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
04-29 14:56:29.711: ERROR/AndroidRuntime(430):     at 
dalvik.system.NativeStart.main(Native Method)
04-29 14:56:29.711: ERROR/AndroidRuntime(430): Caused by: 
java.lang.NullPointerException
04-29 14:56:29.711: ERROR/AndroidRuntime(430):     at 
ImageViewExample.ImageViewExample.ImageViewExample$ImAdapterh.<init>  
(ImageViewExample.java:73)
04-29 14:56:29.711: ERROR/AndroidRuntime(430):     at     
 ImageViewExample.ImageViewExample.ImageViewExample.init_phone_image_grid
(ImageViewExample.java:47)
04-29 14:56:29.711: ERROR/AndroidRuntime(430):     at   
ImageViewExample.ImageViewExample.ImageViewExample.onCreate
(ImageViewExample.java:36)
04-29 14:56:29.711: ERROR/AndroidRuntime(430):     at 
android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
04-29 14:56:29.711: ERROR/AndroidRuntime(430):     at     
android.app.ActivityThread.performLaunchActivity
(ActivityThread.java:2627)
04-29 14:56:29.711: ERROR/AndroidRuntime(430):     ... 11 more
04-29 14:56:29.751: WARN/ActivityManager(66):   Force finishing activity 
ImageViewExample.ImageViewExample/.ImageViewExample
04-29 14:56:30.292: WARN/ActivityManager(66): Activity pause timeout for 
HistoryRecord{4406aab0 ImageViewExample.ImageViewExample/.ImageViewExample}
04-29 14:56:36.701: DEBUG/dalvikvm(189): GC_EXPLICIT freed 162 objects / 7136 bytes in 
121ms
04-29 14:56:41.568: WARN/ActivityManager(66): Activity destroy timeout for 
HistoryRecord{4406aab0 ImageViewExample.ImageViewExample/.ImageViewExample}

请帮帮我......

Answer 1

问题几乎肯定出在这一行:

int count=dir.list().length;

证明它必须是该行的逻辑链如下:

• 创建 File 对象的语句不能在 ImAdapterh 构造函数本身中引发异常。
• 这意味着 dir 必须为非空。
• 这意味着 dir.list() 不会在 ImAdapterh 构造函数中抛出异常。
• 这只是将 String[] 引用取消引用以获取 length 值作为罪魁祸首。

最后，空指针可以通过以下事实来解释:如果 File(在本例中为 dir)，则 File.list() 返回 null >) 不存在或不表示目录...根据 File.list() javadoc .