Volley Library的ImageLoader如何使用？

Question

我正在使用 volley 库从网络加载图像并出现空指针异常。我在 Adapter class.Is 中使用它，在获取实例时有任何问题或我没有得到什么。 getView() 抛出 nullpointerexception

VolleySingleton.java

package com.w3nuts.babaa.helper;

import android.content.Context;
import android.graphics.Bitmap;
import android.support.v4.util.LruCache;

import com.android.volley.RequestQueue;
import com.android.volley.toolbox.ImageLoader;
import com.android.volley.toolbox.Volley;

public class VolleySingleton {

 private static VolleySingleton instance;
 private RequestQueue requestQueue;
 private static ImageLoader imageLoader;

 private VolleySingleton(Context context) {
  requestQueue = Volley.newRequestQueue(context);

  imageLoader = new ImageLoader(requestQueue,
    new ImageLoader.ImageCache() {
     private final LruCache<String, Bitmap> cache = new LruCache<String, Bitmap>(
       20);

     @Override
     public Bitmap getBitmap(String url) {
      return cache.get(url);
     }

     @Override
     public void putBitmap(String url, Bitmap bitmap) {
      cache.put(url, bitmap);
     }
    });
 }

 public static VolleySingleton getInstance(Context context) {
  if (instance == null) {
   instance = new VolleySingleton(context);
  }
  return instance;
 }

 public RequestQueue getRequestQueue() {
  return requestQueue;
 }

 public static ImageLoader getImageLoader() {
  return imageLoader;
 }
}


ServiceListAdapter.class

package com.w3nuts.babaa.adapter;

import java.util.ArrayList;

import android.app.Activity;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.ImageView;
import android.widget.RatingBar;
import android.widget.TextView;

import com.android.volley.VolleyError;
import com.android.volley.toolbox.ImageLoader;
import com.android.volley.toolbox.ImageLoader.ImageContainer;
import com.android.volley.toolbox.ImageLoader.ImageListener;
import com.android.volley.toolbox.NetworkImageView;
import com.w3nuts.babaa.R;
import com.w3nuts.babaa.getterSetter.ServiceDetailGetterSetter;
import com.w3nuts.babaa.helper.VolleySingleton;

public class ServiceListAdapter extends BaseAdapter {

 private Activity activity;
 private LayoutInflater inflater;
 private ArrayList<ServiceDetailGetterSetter> serviceDetailList;

 // Typeface tfRegular, tfLight;

 public ServiceListAdapter(Activity activity,
   ArrayList<ServiceDetailGetterSetter> serviceDetailList) {
  this.activity = activity;
  this.serviceDetailList = serviceDetailList;
 }

 @Override
 public int getCount() {
  return serviceDetailList.size();
 }

 @Override
 public Object getItem(int position) {
  return serviceDetailList.get(position);
 }

 @Override
 public long getItemId(int position) {
  return position;
 }

 private class ViewHolder {
  RatingBar ratingBar;
  TextView name;
  TextView location;
  TextView rating;
  NetworkImageView image;
 }

 @Override
 public View getView(int position, View convertView, ViewGroup parent) {
  final ViewHolder holder;

  View view = convertView;
  if (convertView == null) {
   inflater = activity.getLayoutInflater();
   convertView = inflater.inflate(R.layout.service_list_item, null);

   holder = new ViewHolder();
   holder.name = (TextView) convertView.findViewById(R.id.name);
   holder.location = (TextView) convertView
     .findViewById(R.id.location);
   holder.rating = (TextView) convertView
     .findViewById(R.id.rating_text);
   holder.image = (NetworkImageView) convertView
     .findViewById(R.id.task_image);
   holder.ratingBar = (RatingBar) convertView
     .findViewById(R.id.rating_bar);
   convertView.setTag(holder);
  } else {
   holder = (ViewHolder) convertView.getTag();
  }

  holder.name.setText(serviceDetailList.get(position).getTitle());
  holder.location.setText(serviceDetailList.get(position).getLocation());
  holder.rating.setText(serviceDetailList.get(position).getRating() + "");
  holder.ratingBar.setRating((float) serviceDetailList.get(position)
    .getRating());
  // ////VOLLEY IMAGE LOADER
  String url = serviceDetailList.get(position).getImage();
  ImageLoader imageLoader = VolleySingleton.getImageLoader();

  imageLoader.get(url, new ImageListener() {

   public void onErrorResponse(VolleyError error) {
    holder.image.setImageResource(R.drawable.ic_launcher);
   }

   public void onResponse(ImageContainer response, boolean arg1) {
    if (response.getBitmap() != null) {
     holder.image.setImageBitmap(response.getBitmap());
    }
   }
  });

  Log.i("title", serviceDetailList.get(position).getTitle());
  Log.i("location", serviceDetailList.get(position).getLocation());
  Log.i("image", serviceDetailList.get(position).getImage());
  // SET TEXT AND IMAGE HERE

  return convertView;
 }
}



Service_list_item.xml

 <LinearLayout
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:orientation="horizontal" >

        <com.android.volley.toolbox.NetworkImageView
            android:id="@+id/task_image"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:adjustViewBounds="true"
            android:scaleType="centerInside"
            android:src="@drawable/task_demo_image" />
    </LinearLayout>

03-03 18:40:14.909：E/AndroidRuntime(6317)：致命异常：main 03-03 18:40:14.909: E/AndroidRuntime(6317): java.lang.NullPointerException 03-03 18:40:14.909: E/AndroidRuntime(6317): 在 com.w3nuts.babaa.adapter.ServiceListAdapter.getView(ServiceListAdapter.java:93) 03-03 18:40:14.909: E/AndroidRuntime(6317): 在 android.widget.AbsListView.obtainView(AbsListView.java:2177) 03-03 18:40:14.909: E/AndroidRuntime(6317): 在 android.widget.ListView.makeAndAddView(ListView.java:1840) 03-03 18:40:14.909: E/AndroidRuntime(6317): 在 android.widget.ListView.fillDown(ListView.java:675) 03-03 18:40:14.909: E/AndroidRuntime(6317): 在 android.widget.ListView.fillFromTop(ListView.java:736) 03-03 18:40:14.909: E/AndroidRuntime(6317): 在 android.widget.ListView.layoutChildren(ListView.java:1655) 03-03 18:40:14.909: E/AndroidRuntime(6317): 在 android.widget.AbsListView.onLayout(AbsListView.java:2012) 03-03 18:40:14.909: E/AndroidRuntime(6317): 在 android.view.View.layout(View.java:14289) 03-03 18:40:14.909: E/AndroidRuntime(6317): 在 android.view.ViewGroup.layout(ViewGroup.java:4562) 03-03 18:40:14.909: E/AndroidRuntime(6317): 在 android.widget.LinearLayout.setChildFrame(LinearLayout.java:1671) 03-03 18:40:14.909: E/AndroidRuntime(6317): 在 android.widget.LinearLayout.layoutHorizontal(LinearLayout.java:1660) 03-03 18:40:14.909: E/AndroidRuntime(6317): 在 android.widget.LinearLayout.onLayout(LinearLayout.java:1436) 03-03 18:40:14.909: E/AndroidRuntime(6317): 在 android.view.View.layout(View.java:14289) 03-03 18:40:14.909: E/AndroidRuntime(6317): 在 android.view.ViewGroup.layout(ViewGroup.java:4562) 03-03 18:40:14.909: E/AndroidRuntime(6317): 在 android.widget.FrameLayout.onLayout(FrameLayout.java:448) 03-03 18:40:14.909: E/AndroidRuntime(6317): 在 android.view.View.layout(View.java:14289) 03-03 18:40:14.909: E/AndroidRuntime(6317): 在 android.view.ViewGroup.layout(ViewGroup.java:4562) 03-03 18:40:14.909: E/AndroidRuntime(6317): 在 android.widget.LinearLayout.setChildFrame(LinearLayout.java:1671) 03-03 18:40:14.909: E/AndroidRuntime(6317): 在 android.widget.LinearLayout.layoutVertical(LinearLayout.java:1525) 03-03 18:40:14.909: E/AndroidRuntime(6317): 在 android.widget.LinearLayout.onLayout(LinearLayout.java:1434) 03-03 18:40:14.909: E/AndroidRuntime(6317): 在 android.view.View.layout(View.java:14289) 03-03 18:40:14.909: E/AndroidRuntime(6317): 在 android.view.ViewGroup.layout(ViewGroup.java:4562) 03-03 18:40:14.909: E/AndroidRuntime(6317): 在 android.widget.FrameLayout.onLayout(FrameLayout.java:448) 03-03 18:40:14.909: E/AndroidRuntime(6317): 在 android.view.View.layout(View.java:14289) 03-03 18:40:14.909: E/AndroidRuntime(6317): 在 android.view.ViewGroup.layout(ViewGroup.java:4562) 03-03 18:40:14.909: E/AndroidRuntime(6317): 在 android.widget.FrameLayout.onLayout(FrameLayout.java:448) 03-03 18:40:14.909: E/AndroidRuntime(6317): 在 android.view.View.layout(View.java:14289) 03-03 18:40:14.909: E/AndroidRuntime(6317): 在 android.view.ViewGroup.layout(ViewGroup.java:4562) 03-03 18:40:14.909: E/AndroidRuntime(6317): 在 android.widget.FrameLayout.onLayout(FrameLayout.java:448) 03-03 18:40:14.909: E/AndroidRuntime(6317): 在 android.view.View.layout(View.java:14289) 03-03 18:40:14.909: E/AndroidRuntime(6317): 在 android.view.ViewGroup.layout(ViewGroup.java:4562) 03-03 18:40:14.909: E/AndroidRuntime(6317): 在 android.widget.LinearLayout.setChildFrame(LinearLayout.java:1671) 03-03 18:40:14.909: E/AndroidRuntime(6317): 在 android.widget.LinearLayout.layoutVertical(LinearLayout.java:1525) 03-03 18:40:14.909: E/AndroidRuntime(6317): 在 android.widget.LinearLayout.onLayout(LinearLayout.java:1434) 03-03 18:40:14.909: E/AndroidRuntime(6317): 在 android.view.View.layout(View.java:14289) 03-03 18:40:14.909: E/AndroidRuntime(6317): 在 android.view.ViewGroup.layout(ViewGroup.java:4562) 03-03 18:40:14.909: E/AndroidRuntime(6317): 在 android.widget.FrameLayout.onLayout(FrameLayout.java:448) 03-03 18:40:14.909: E/AndroidRuntime(6317): 在 android.view.View.layout(View.java:14289) 03-03 18:40:14.909: E/AndroidRuntime(6317): 在 android.view.ViewGroup.layout(ViewGroup.java:4562) 03-03 18:40:14.909: E/AndroidRuntime(6317): 在 android.widget.RelativeLayout.onLayout(RelativeLayout.java:1076) 03-03 18:40:14.909: E/AndroidRuntime(6317): 在 android.view.View.layout(View.java:14289) 03-03 18:40:14.909: E/AndroidRuntime(6317): 在 android.view.ViewGroup.layout(ViewGroup.java:4562) 03-03 18:40:14.909: E/AndroidRuntime(6317): 在 android.widget.FrameLayout.onLayout(FrameLayout.java:448) 03-03 18:40:14.909: E/AndroidRuntime(6317): 在 android.view.View.layout(View.java:14289) 03-03 18:40:14.909: E/AndroidRuntime(6317): 在 android.view.ViewGroup.layout(ViewGroup.java:4562) 03-03 18:40:14.909: E/AndroidRuntime(6317): 在 android.widget.LinearLayout.setChildFrame(LinearLayout.java:1671) 03-03 18:40:14.909: E/AndroidRuntime(6317): 在 android.widget.LinearLayout.layoutVertical(LinearLayout.java:1525) 03-03 18:40:14.909: E/AndroidRuntime(6317): 在 android.widget.LinearLayout.onLayout(LinearLayout.java:1434) 03-03 18:40:14.909: E/AndroidRuntime(6317): 在 android.view.View.layout(View.java:14289) 03-03 18:40:14.909: E/AndroidRuntime(6317): 在 android.view.ViewGroup.layout(ViewGroup.java:4562) 03-03 18:40:14.909: E/AndroidRuntime(6317): 在 android.widget.FrameLayout.onLayout(FrameLayout.java:448) 03-03 18:40:14.909: E/AndroidRuntime(6317): 在 android.view.View.layout(View.java:14289) 03-03 18:40:14.909: E/AndroidRuntime(6317): 在 android.view.ViewGroup.layout(ViewGroup.java:4562) 03-03 18:40:14.909: E/AndroidRuntime(6317): 在 android.view.ViewRootImpl.performLayout(ViewRootImpl.java:1976) 03-03 18:40:14.909: E/AndroidRuntime(6317): 在 android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1730) 03-03 18:40:14.909: E/AndroidRuntime(6317): 在 android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1004) 03-03 18:40:14.909: E/AndroidRuntime(6317): 在 android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5481) 03-03 18:40:14.909: E/AndroidRuntime(6317): 在 android.view.Choreographer$CallbackRecord.run(Choreographer.java:749) 03-03 18:40:14.909: E/AndroidRuntime(6317): 在 android.view.Choreographer.doCallbacks(Choreographer.java:562) 03-03 18:40:14.909: E/AndroidRuntime(6317): 在 android.view.Choreographer.doFrame(Choreographer.java:532) 03-03 18:40:14.909: E/AndroidRuntime(6317): 在 android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:735) 03-03 18:40:14.909: E/AndroidRuntime(6317): 在 android.os.Handler.handleCallback(Handler.java:730) 03-03 18:40:14.909: E/AndroidRuntime(6317): 在 android.os.Handler.dispatchMessage(Handler.java:92) 03-03 18:40:14.909: E/AndroidRuntime(6317): 在 android.os.Looper.loop(Looper.java:137) 03-03 18:40:14.909: E/AndroidRuntime(6317): 在 android.app.ActivityThread.main(ActivityThread.java:5103) 03-03 18:40:14.909: E/AndroidRuntime(6317): 在 java.lang.reflect.Method.invokeNative（本机方法） 03-03 18:40:14.909: E/AndroidRuntime(6317): 在 java.lang.reflect.Method.invoke(Method.java:525) 03-03 18:40:14.909: E/AndroidRuntime(6317): 在 com.andr

Answer 1

问题是你创建了 imageLoader static，你只在 VolleySingleton 构造函数中初始化它，它只在 getInstance().[=19 期间调用=]

使 imageLoader 非 static，并使 getImageLoader 方法也非 static，并将您的代码替换为如下所示：

ImageLoader imageLoader = VolleySingleton.getInstance(context).getImageLoader()

Volley Library的ImageLoader如何使用？

How to use ImageLoader of Volley Library?

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