在背景中下载图像android

我想在后台下载一个图像，以便在图像下载时应用程序不会挂起。我得到一个nullpointerexception，我不明白我做错了什么。我的日志说我正在抓取网址中的数据，因此我不确定这是不是工作原因。谢谢！在背景中下载图像android

这里是我的代码：

public class DownloadImageBackground extends AsyncTask<String, Void, Drawable> { 

ImageView imageView = null; 
String myURL = null; 

@Override 
protected Drawable doInBackground(String...strings) { 
    this.myURL = strings[0]; 
    Log.i("doInBackground", "Loading image from: "+myURL.toString()); 
    //TODO: Pass the correct URL to download_image 
    return download_Image(myURL); 
} 

@Override 
protected void onPostExecute(Drawable result) { 
    imageView.setImageDrawable(result); 
} 

private Drawable download_Image(String url) { 
    try { 
     InputStream is = (InputStream) new URL(url).getContent(); 
     Drawable d = Drawable.createFromStream(is, url); 
     return d; 
    } catch (Exception e) { 
     Log.e("download_Image", "Caught exception: "+e.getMessage()); 
     return null; 
    } 
} 
}

以下是错误：

02-27 20:07:37.815: I/doInBackground(19374): Loading image from: http://www.martingrumet.com/boxelder01may04.jpg 
02-27 20:07:37.815: I/Choreographer(19374): Skipped 92 frames! The application may be doing too much work on its main thread. 
02-27 20:07:37.840: D/dalvikvm(19374): GC_CONCURRENT freed 404K, 9% free 13752K/15047K, paused 2ms+12ms, total 24ms 
02-27 20:07:38.110: D/dalvikvm(19374): GC_FOR_ALLOC freed 72K, 9% free 13723K/15047K, paused 11ms, total 11ms 
02-27 20:07:38.110: I/dalvikvm-heap(19374): Grow heap (frag case) to 15.182MB for 1334016-byte allocation 
02-27 20:07:38.125: D/dalvikvm(19374): GC_CONCURRENT freed 0K, 9% free 15026K/16391K, paused 2ms+1ms, total 12ms 
02-27 20:07:38.125: D/dalvikvm(19374): WAIT_FOR_CONCURRENT_GC blocked 11ms 
02-27 20:07:38.395: D/AndroidRuntime(19374): Shutting down VM 
02-27 20:07:38.395: W/dalvikvm(19374): threadid=1: thread exiting with uncaught exception (group=0x40cf14a0) 
02-27 20:07:38.395: E/AndroidRuntime(19374): FATAL EXCEPTION: main 
02-27 20:07:38.395: E/AndroidRuntime(19374): java.lang.NullPointerException 
02-27 20:07:38.395: E/AndroidRuntime(19374): at com.ourbenefactors.treeidentification2.DownloadImageBackground.onPostExecute(DownloadImageBackground.java:27) 
02-27 20:07:38.395: E/AndroidRuntime(19374): at com.ourbenefactors.treeidentification2.DownloadImageBackground.onPostExecute(DownloadImageBackground.java:1) 
02-27 20:07:38.395: E/AndroidRuntime(19374): at android.os.AsyncTask.finish(AsyncTask.java:631) 
02-27 20:07:38.395: E/AndroidRuntime(19374): at android.os.AsyncTask.access$600(AsyncTask.java:177) 
02-27 20:07:38.395: E/AndroidRuntime(19374): at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:644) 
02-27 20:07:38.395: E/AndroidRuntime(19374): at android.os.Handler.dispatchMessage(Handler.java:99) 
02-27 20:07:38.395: E/AndroidRuntime(19374): at android.os.Looper.loop(Looper.java:137) 
02-27 20:07:38.395: E/AndroidRuntime(19374): at android.app.ActivityThread.main(ActivityThread.java:4898) 
02-27 20:07:38.395: E/AndroidRuntime(19374): at java.lang.reflect.Method.invokeNative(Native Method) 
02-27 20:07:38.395: E/AndroidRuntime(19374): at java.lang.reflect.Method.invoke(Method.java:511) 
02-27 20:07:38.395: E/AndroidRuntime(19374): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1008) 
02-27 20:07:38.395: E/AndroidRuntime(19374): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:775) 
02-27 20:07:38.395: E/AndroidRuntime(19374): at dalvik.system.NativeStart.main(Native Method)

来源

2013-02-28 Our_Benefactors

空你必须要在一个DownloadImageBackground.java:27'NullPointerException'。那是什么？ – midhunhk 2013-02-28 04:23:12