Question

我的logcat中有一个NullPointerException指向'holder.imageLoader.DisplayImage（resultp.get（BookScreen.KEY_THUMB_URL），holder.thumb_image）; '在类LazyAdapter 中。为什么将null传入该行？

public class LazyAdapter扩展了BaseAdapter {

Context context;
HashMap<String, String> resultp = new HashMap<String, String>();
private ArrayList<HashMap<String, String>> data;
private static LayoutInflater inflater = null;
public ImageLoader imageLoader;

public LazyAdapter(Context contextActivity, ArrayList<HashMap<String, String>> d) {
    this.context = contextActivity;
    data = d;
    imageLoader = new ImageLoader(context);
}

public int getCount() {
    return data.size();
}

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

public long getItemId(int position) {
    return 0;
}

static class ViewHolder {

    TextView id, title, description, bookingDate, bookingTime;
    ImageView thumb_image;
    ImageLoader imageLoader;
}

public View getView(final int position, View convertView, ViewGroup parent) {
    ViewHolder holder;
    inflater = (LayoutInflater) context
        .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    resultp = data.get(position);
    if (convertView == null) {
        convertView = inflater.inflate(R.layout.book_list_row, parent, false);
        holder = new ViewHolder();
        holder.id = (TextView) convertView.findViewById(R.id.id);
        holder.title = (TextView) convertView.findViewById(R.id.menu_name);
        holder.description = (TextView) convertView.findViewById(R.id.address);
        holder.bookingDate = (TextView) convertView.findViewById(R.id.book_date);
        holder.bookingTime = (TextView) convertView.findViewById(R.id.book_time);
        holder.thumb_image = (ImageView) convertView.findViewById(R.id.list_image);
        convertView.setTag(holder);
    } else {
        holder = (ViewHolder) convertView.getTag();
    }
    holder.id.setText(resultp.get(BookScreen.KEY_ID));
    holder.title.setText(resultp.get(BookScreen.KEY_TITLE));
    holder.description.setText(resultp.get(BookScreen.KEY_ADDRESS));
    holder.bookingDate.setText(resultp.get(BookScreen.KEY_DATE));
    holder.bookingTime.setText(resultp.get(BookScreen.KEY_TIME));
    holder.imageLoader.DisplayImage(resultp.get(BookScreen.KEY_THUMB_URL), holder.thumb_image); //NULLPOINTEREXCEPTION HERE
    return convertView;
}

}

与函数DisplayImage相关联的

ImageLoader类 ：

public class ImageLoader {

    MemoryCache memoryCache=new MemoryCache();
    FileCache fileCache;
    private Map<ImageView, String> imageViews=Collections.synchronizedMap(new WeakHashMap<ImageView, String>());
    ExecutorService executorService;

    public ImageLoader(Context context){
        fileCache=new FileCache(context);
        executorService=Executors.newFixedThreadPool(5);
    }

    final int stub_id = R.drawable.no_image;
    public void DisplayImage(String url, ImageView imageView)
    {
        imageViews.put(imageView, url);
        Bitmap bitmap=memoryCache.get(url);
        if(bitmap!=null)
            imageView.setImageBitmap(bitmap);
        else
        {
            queuePhoto(url, imageView);
            imageView.setImageResource(stub_id);
        }
    }

    private void queuePhoto(String url, ImageView imageView)
    {
        PhotoToLoad p=new PhotoToLoad(url, imageView);
        executorService.submit(new PhotosLoader(p));
    }

    private Bitmap getBitmap(String url)
    {
        File f=fileCache.getFile(url);

        //from SD cache
        Bitmap b = decodeFile(f);
        if(b!=null)
            return b;

        //from web
        try {
            Bitmap bitmap=null;
            URL imageUrl = new URL(url);
            HttpURLConnection conn = (HttpURLConnection)imageUrl.openConnection();
            conn.setConnectTimeout(30000);
            conn.setReadTimeout(30000);
            conn.setInstanceFollowRedirects(true);
            InputStream is=conn.getInputStream();
            OutputStream os = new FileOutputStream(f);
            Utils.CopyStream(is, os);
            os.close();
            bitmap = decodeFile(f);
            return bitmap;
        } catch (Exception ex){
           ex.printStackTrace();
           return null;
        }
    }

    //decodes image and scales it to reduce memory consumption
    private Bitmap decodeFile(File f){
        try {
            //decode image size
            BitmapFactory.Options o = new BitmapFactory.Options();
            o.inJustDecodeBounds = true;
            BitmapFactory.decodeStream(new FileInputStream(f),null,o);

            //Find the correct scale value. It should be the power of 2.
            final int REQUIRED_SIZE=70;
            int width_tmp=o.outWidth, height_tmp=o.outHeight;
            int scale=1;
            while(true){
                if(width_tmp/2<REQUIRED_SIZE || height_tmp/2<REQUIRED_SIZE)
                    break;
                width_tmp/=2;
                height_tmp/=2;
                scale*=2;
            }

            //decode with inSampleSize
            BitmapFactory.Options o2 = new BitmapFactory.Options();
            o2.inSampleSize=scale;
            return BitmapFactory.decodeStream(new FileInputStream(f), null, o2);
        } catch (FileNotFoundException e) {}
        return null;
    }

    //Task for the queue
    private class PhotoToLoad
    {
        public String url;
        public ImageView imageView;
        public PhotoToLoad(String u, ImageView i){
            url=u;
            imageView=i;
        }
    }

    class PhotosLoader implements Runnable {
        PhotoToLoad photoToLoad;
        PhotosLoader(PhotoToLoad photoToLoad){
            this.photoToLoad=photoToLoad;
        }

        @Override
        public void run() {
            if(imageViewReused(photoToLoad))
                return;
            Bitmap bmp=getBitmap(photoToLoad.url);
            memoryCache.put(photoToLoad.url, bmp);
            if(imageViewReused(photoToLoad))
                return;
            BitmapDisplayer bd=new BitmapDisplayer(bmp, photoToLoad);
            Activity a=(Activity)photoToLoad.imageView.getContext();
            a.runOnUiThread(bd);
        }
    }

    boolean imageViewReused(PhotoToLoad photoToLoad){
        String tag=imageViews.get(photoToLoad.imageView);
        if(tag==null || !tag.equals(photoToLoad.url))
            return true;
        return false;
    }

    //Used to display bitmap in the UI thread
    class BitmapDisplayer implements Runnable
    {
        Bitmap bitmap;
        PhotoToLoad photoToLoad;
        public BitmapDisplayer(Bitmap b, PhotoToLoad p){bitmap=b;photoToLoad=p;}
        public void run()
        {
            if(imageViewReused(photoToLoad))
                return;
            if(bitmap!=null)
                photoToLoad.imageView.setImageBitmap(bitmap);
            else
                photoToLoad.imageView.setImageResource(stub_id);
        }
    }

    public void clearCache() {
        memoryCache.clear();
        fileCache.clear();
    }

}

XML文件：

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:orientation="horizontal"
    android:padding="5dip" >

    <!-- ListRow Left sied Thumbnail image -->

    <LinearLayout
        android:id="@+id/thumbnail"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentLeft="true"
        android:layout_marginRight="5dip"
        android:padding="3dip" >

        <ImageView
            android:id="@+id/list_image"
            android:layout_width="50dip"
             android:src="@drawable/logo"
            android:layout_height="50dip" 
            />
    </LinearLayout>

    <!-- Menu name -->

    <TextView
        android:id="@+id/menu_name"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignTop="@+id/thumbnail"
        android:layout_toRightOf="@+id/thumbnail"
        android:text="@string/book_name"
        android:textColor="#040404"
        android:textSize="15sp"
        android:textStyle="bold"
        android:typeface="sans" />

    <!-- Description -->

    <TextView
        android:id="@+id/address"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_alignBottom="@+id/thumbnail"
        android:layout_below="@id/menu_name"
        android:layout_marginTop="1dip"
        android:layout_toRightOf="@+id/thumbnail"
        android:text="@string/book_address"
        android:textColor="#343434"
        android:textSize="10sp"
        tools:ignore="SmallSp" />

    <!-- Price -->

    <TextView
        android:id="@+id/book_date"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentRight="true"
        android:layout_alignTop="@id/menu_name"
        android:layout_marginRight="5dip"
        android:gravity="right"
        android:text="@string/book_date"
        android:textColor="#10bcc9"
        android:textSize="10sp"
        android:textStyle="bold"
        tools:ignore="SmallSp" />

    <TextView
        android:id="@+id/book_time"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignLeft="@+id/book_date"
        android:layout_centerVertical="true"
        android:gravity="right"
        android:text="@string/book_time"
        android:textColor="#10bcc9"
        android:textSize="10sp"
        android:textStyle="bold"
        tools:ignore="SmallSp" />

    <TextView 
        android:id="@+id/id"
        android:layout_width="0dp"
        android:layout_height="0dp"
        android:layout_alignParentTop="true"
        android:layout_centerHorizontal="true"
       > </TextView>

</RelativeLayout>

logcat的：

12-02 12:30:33.210: E/AndroidRuntime(890): FATAL EXCEPTION: main
12-02 12:30:33.210: E/AndroidRuntime(890): Process: com.example.clinicbooker, PID: 890
12-02 12:30:33.210: E/AndroidRuntime(890): java.lang.NullPointerException
12-02 12:30:33.210: E/AndroidRuntime(890):  at com.example.clinicbooker.LazyAdapter.getView(LazyAdapter.java:75)
12-02 12:30:33.210: E/AndroidRuntime(890):  at android.widget.AbsListView.obtainView(AbsListView.java:2263)
12-02 12:30:33.210: E/AndroidRuntime(890):  at android.widget.ListView.measureHeightOfChildren(ListView.java:1263)
12-02 12:30:33.210: E/AndroidRuntime(890):  at android.widget.ListView.onMeasure(ListView.java:1175)
12-02 12:30:33.210: E/AndroidRuntime(890):  at android.view.View.measure(View.java:16458)
12-02 12:30:33.210: E/AndroidRuntime(890):  at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125)
12-02 12:30:33.210: E/AndroidRuntime(890):  at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1404)
12-02 12:30:33.210: E/AndroidRuntime(890):  at android.widget.LinearLayout.measureVertical(LinearLayout.java:695)
12-02 12:30:33.210: E/AndroidRuntime(890):  at android.widget.LinearLayout.onMeasure(LinearLayout.java:588)
12-02 12:30:33.210: E/AndroidRuntime(890):  at android.view.View.measure(View.java:16458)
12-02 12:30:33.210: E/AndroidRuntime(890):  at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125)
12-02 12:30:33.210: E/AndroidRuntime(890):  at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
12-02 12:30:33.210: E/AndroidRuntime(890):  at android.view.View.measure(View.java:16458)
12-02 12:30:33.210: E/AndroidRuntime(890):  at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125)
12-02 12:30:33.210: E/AndroidRuntime(890):  at com.android.internal.widget.ActionBarOverlayLayout.onMeasure(ActionBarOverlayLayout.java:327)
12-02 12:30:33.210: E/AndroidRuntime(890):  at android.view.View.measure(View.java:16458)
12-02 12:30:33.210: E/AndroidRuntime(890):  at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125)
12-02 12:30:33.210: E/AndroidRuntime(890):  at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
12-02 12:30:33.210: E/AndroidRuntime(890):  at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2289)
12-02 12:30:33.210: E/AndroidRuntime(890):  at android.view.View.measure(View.java:16458)
12-02 12:30:33.210: E/AndroidRuntime(890):  at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:1914)
12-02 12:30:33.210: E/AndroidRuntime(890):  at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1111)
12-02 12:30:33.210: E/AndroidRuntime(890):  at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1293)
12-02 12:30:33.210: E/AndroidRuntime(890):  at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:998)
12-02 12:30:33.210: E/AndroidRuntime(890):  at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5582)
12-02 12:30:33.210: E/AndroidRuntime(890):  at android.view.Choreographer$CallbackRecord.run(Choreographer.java:749)
12-02 12:30:33.210: E/AndroidRuntime(890):  at android.view.Choreographer.doCallbacks(Choreographer.java:562)
12-02 12:30:33.210: E/AndroidRuntime(890):  at android.view.Choreographer.doFrame(Choreographer.java:532)
12-02 12:30:33.210: E/AndroidRuntime(890):  at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:735)
12-02 12:30:33.210: E/AndroidRuntime(890):  at android.os.Handler.handleCallback(Handler.java:733)
12-02 12:30:33.210: E/AndroidRuntime(890):  at android.os.Handler.dispatchMessage(Handler.java:95)
12-02 12:30:33.210: E/AndroidRuntime(890):  at android.os.Looper.loop(Looper.java:137)
12-02 12:30:33.210: E/AndroidRuntime(890):  at android.app.ActivityThread.main(ActivityThread.java:4998)
12-02 12:30:33.210: E/AndroidRuntime(890):  at java.lang.reflect.Method.invokeNative(Native Method)
12-02 12:30:33.210: E/AndroidRuntime(890):  at java.lang.reflect.Method.invoke(Method.java:515)
12-02 12:30:33.210: E/AndroidRuntime(890):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:777)
12-02 12:30:33.210: E/AndroidRuntime(890):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:593)
12-02 12:30:33.210: E/AndroidRuntime(890):  at dalvik.system.NativeStart.main(Native Method)

Answer 1

您的holder.imageLoader方法中

Initialized不是getView。

holder是instance ViewHolder的{{1}}和ViewHolder类Class中的imageLoader。

Answer 2

想出来。

imageLoader.DisplayImage(resultp.get(BookScreen.KEY_THUMB_URL), holder.thumb_image);

而不是

holder.imageLoader.DisplayImage(resultp.get(BookScreen.KEY_THUMB_URL), holder.thumb_image);

XML-parser为什么将null传递给thumb_image？

2 个答案: