我想将网址中的某个图片加载到我的ListView中。但是在加载时我得到NullPointerException。我从一个返回JSON响应的Url中获取数据。我已将响应转换为HashMap，这很好。但是在加载图像时我得到NullPointerException
有人可以指出解决方案吗？ 谢谢 这是我的代码： -
MainActivity.java
JSONArray jObject = new JSONArray(responseBody);
for (int i = 0; i < jObject.length(); i++)
{
JSONObject menuObject = jObject.getJSONObject(i);
String title= menuObject.getString("NewsSourceTitle");
String description= menuObject.getString("Title");
String thumbnail= menuObject.getString("ThumbnailPath");
String newsUrl = menuObject.getString("Url");
HashMap<String, String> map = new HashMap<String,String>();
map.put(NEWSSOURCETITLE, title);
map.put(TITLE, description);
map.put(THUMBNAILPATH, thumbnail);
myNewsList.add(map);
}
itemsAdapter = new LazyAdapter(this, myNewsList);
newsList.setAdapter(itemsAdapter);
LazyAdapter.java
public class LazyAdapter extends BaseAdapter
{
private Activity activity;
private ArrayList<HashMap<String, String>> data;
private static LayoutInflater inflater = null;
public ImageLoader imageLoader;
public LazyAdapter(Activity a, ArrayList<HashMap<String, String>> d)
{
activity = a;
data=d;
inflater = (LayoutInflater)activity.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
imageLoader=new ImageLoader();
}
@Override
public int getCount()
{
// TODO Auto-generated method stub
return data.size();
}
@Override
public Object getItem(int position)
{
// TODO Auto-generated method stub
return position;
}
@Override
public long getItemId(int position)
{
// TODO Auto-generated method stub
return position;
}
@Override
public View getView(int position, View convertView, ViewGroup parent)
{
View vi=convertView;
if(convertView==null)
vi = inflater.inflate(R.layout.list_row, null);
TextView title = (TextView)vi.findViewById(R.id.title); // title
TextView description = (TextView)vi.findViewById(R.id.description); // artist name
ImageView thumb_image=(ImageView)vi.findViewById(R.id.list_image); // thumb image
HashMap<String, String> song = new HashMap<String, String>();
song = data.get(position);
// Setting all values in listview
title.setText(song.get("NewsSourceTitle"));
description.setText(song.get("Title"));
imageLoader.DisplayImage(song.get("ThumbnailPath"), thumb_image);
return vi;
}
ImageLoader.java
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);
}
public ImageLoader() {
// TODO Auto-generated constructor stub
}
final int stub_id = com.zevenpooja.attini.R.drawable.myimage;
public void DisplayImage(String url, ImageView thumb_image)
{
// TODO Auto-generated method stub
imageViews.put(thumb_image, url);
Bitmap bitmap=memoryCache.get(url);
if(bitmap!=null)
thumb_image.setImageBitmap(bitmap);
else
{
queuePhoto(url, thumb_image);
thumb_image.setImageResource(stub_id);
}
}
private void queuePhoto(String url, ImageView thumb_image)
{
// TODO Auto-generated method stub
PhotoToLoad p=new PhotoToLoad(url, thumb_image); // ERROR HERE
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);
URI uri = new URI(imageUrl.getProtocol(), imageUrl.getUserInfo(), imageUrl.getHost(), imageUrl.getPort(), imageUrl.getPath(), imageUrl.getQuery(), imageUrl.getRef());
imageUrl = uri.toURL();
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();
}
logcat的
03-19 08:45:28.132: E/AndroidRuntime(3296): FATAL EXCEPTION: main
03-19 08:45:28.132: E/AndroidRuntime(3296): java.lang.NullPointerException
03-19 08:45:28.132: E/AndroidRuntime(3296): at Utility.ImageLoader.queuePhoto(ImageLoader.java:59)
03-19 08:45:28.132: E/AndroidRuntime(3296): at Utility.ImageLoader.DisplayImage(ImageLoader.java:50)
03-19 08:45:28.132: E/AndroidRuntime(3296): at Utility.LazyAdapter.getView(LazyAdapter.java:73)
03-19 08:45:28.132: E/AndroidRuntime(3296): at android.widget.AbsListView.obtainView(AbsListView.java:2267)
03-19 08:45:28.132: E/AndroidRuntime(3296): at android.widget.ListView.measureHeightOfChildren(ListView.java:1244)
03-19 08:45:28.132: E/AndroidRuntime(3296): at android.widget.ListView.onMeasure(ListView.java:1156)
03-19 08:45:28.132: E/AndroidRuntime(3296): at android.view.View.measure(View.java:15172)
03-19 08:45:28.132: E/AndroidRuntime(3296): at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4814)
03-19 08:45:28.132: E/AndroidRuntime(3296): at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1390)
03-19 08:45:28.132: E/AndroidRuntime(3296): at android.widget.LinearLayout.measureVertical(LinearLayout.java:681)
03-19 08:45:28.132: E/AndroidRuntime(3296): at android.widget.LinearLayout.onMeasure(LinearLayout.java:574)
03-19 08:45:28.132: E/AndroidRuntime(3296): at android.view.View.measure(View.java:15172)
03-19 08:45:28.132: E/AndroidRuntime(3296): at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4814)
03-19 08:45:28.132: E/AndroidRuntime(3296): at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
03-19 08:45:28.132: E/AndroidRuntime(3296): at android.view.View.measure(View.java:15172)
03-19 08:45:28.132: E/AndroidRuntime(3296): at android.widget.LinearLayout.measureVertical(LinearLayout.java:833)
03-19 08:45:28.132: E/AndroidRuntime(3296): at android.widget.LinearLayout.onMeasure(LinearLayout.java:574)
03-19 08:45:28.132: E/AndroidRuntime(3296): at android.view.View.measure(View.java:15172)
03-19 08:45:28.132: E/AndroidRuntime(3296): at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4814)
03-19 08:45:28.132: E/AndroidRuntime(3296): at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
03-19 08:45:28.132: E/AndroidRuntime(3296): at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2148)
03-19 08:45:28.132: E/AndroidRuntime(3296): at android.view.View.measure(View.java:15172)
03-19 08:45:28.132: E/AndroidRuntime(3296): at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:1848)
03-19 08:45:28.132: E/AndroidRuntime(3296): at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1100)
03-19 08:45:28.132: E/AndroidRuntime(3296): at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1273)
03-19 08:45:28.132: E/AndroidRuntime(3296): at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:998)
03-19 08:45:28.132: E/AndroidRuntime(3296): at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:4212)
03-19 08:45:28.132: E/AndroidRuntime(3296): at android.view.Choreographer$CallbackRecord.run(Choreographer.java:725)
03-19 08:45:28.132: E/AndroidRuntime(3296): at android.view.Choreographer.doCallbacks(Choreographer.java:555)
03-19 08:45:28.132: E/AndroidRuntime(3296): at android.view.Choreographer.doFrame(Choreographer.java:525)
03-19 08:45:28.132: E/AndroidRuntime(3296): at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:711)
03-19 08:45:28.132: E/AndroidRuntime(3296): at android.os.Handler.handleCallback(Handler.java:615)
03-19 08:45:28.132: E/AndroidRuntime(3296): at android.os.Handler.dispatchMessage(Handler.java:92)
03-19 08:45:28.132: E/AndroidRuntime(3296): at android.os.Looper.loop(Looper.java:137)
03-19 08:45:28.132: E/AndroidRuntime(3296): at android.app.ActivityThread.main(ActivityThread.java:4745)
03-19 08:45:28.132: E/AndroidRuntime(3296): at java.lang.reflect.Method.invokeNative(Native Method)
03-19 08:45:28.132: E/AndroidRuntime(3296): at java.lang.reflect.Method.invoke(Method.java:511)
03-19 08:45:28.132: E/AndroidRuntime(3296): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
03-19 08:45:28.132: E/AndroidRuntime(3296): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
03-19 08:45:28.132: E/AndroidRuntime(3296): at dalvik.system.NativeStart.main(Native Method)
答案 0 :(得分：0)
崩溃日志会有所帮助，也可以看看这个Volley Lib https://developers.google.com/events/io/sessions/325304728 maby它会帮助你获得更好的性能，同时我也看到你的适配器没有这个方法
@Override
public int getCount() {
// TODO Auto-generated method stub
return data.size();
}
也试试这个
if(convertView==null)
vi = inflater.inflate(R.layout.list_row, parent,false);