Question

我已设置GridView来保存从SD卡加载的一些图像。但是，有很多图像需要加载，因此我决定使用AsyncTask在后台线程上运行加载和重新采样任务，并在加载完图像后将图像添加到GridView。不幸的是，每当我运行代码时，我都会遇到这个错误：

01-01 19:49:40.239: E/AndroidRuntime(3851): FATAL EXCEPTION: main
01-01 19:49:40.239: E/AndroidRuntime(3851): java.lang.NullPointerException
01-01 19:49:40.239: E/AndroidRuntime(3851): at com.stullich.tim.woistmeinphoto.PhotoGalleryActivity.addImage(PhotoGalleryActivity.java:199)
01-01 19:49:40.239: E/AndroidRuntime(3851): at <packagename>.PhotoGalleryActivity.access$0(PhotoGalleryActivity.java:195)
01-01 19:49:40.239: E/AndroidRuntime(3851): at <packagename>.PhotoGalleryActivity$FileFetcher.onProgressUpdate(PhotoGalleryActivity.java:226)
01-01 19:49:40.239: E/AndroidRuntime(3851): at <packagename>.PhotoGalleryActivity$FileFetcher.onProgressUpdate(PhotoGalleryActivity.java:1)
01-01 19:49:40.239: E/AndroidRuntime(3851): at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:618)
01-01 19:49:40.239: E/AndroidRuntime(3851): at android.os.Handler.dispatchMessage(Handler.java:99)
01-01 19:49:40.239: E/AndroidRuntime(3851): at android.os.Looper.loop(Looper.java:137)
01-01 19:49:40.239: E/AndroidRuntime(3851): at android.app.ActivityThread.main(ActivityThread.java:4514)
01-01 19:49:40.239: E/AndroidRuntime(3851): at java.lang.reflect.Method.invokeNative(Native Method)
01-01 19:49:40.239: E/AndroidRuntime(3851): at java.lang.reflect.Method.invoke(Method.java:511)
01-01 19:49:40.239: E/AndroidRuntime(3851): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:790)
01-01 19:49:40.239: E/AndroidRuntime(3851): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:557)
01-01 19:49:40.239: E/AndroidRuntime(3851): at dalvik.system.NativeStart.main(Native Method)

这是似乎造成麻烦的代码：

final class FileFetcher extends AsyncTask<Void, LoadedImage, Void> 
{
  private Context mContext;

  public FileFetcher(Context context)
  {
     mContext = context;
  }

  @Override
  protected void onPreExecute()
  {
     loadImages(new File("/mnt/extSdCard/Bilder"));         
  }

  @Override
  public void onProgressUpdate(LoadedImage... value)
  {
     addImage(value);
  }

  @Override
  protected Void doInBackground(Void... rootDir) 
  {
     int i = 1;
     for (File f : directories)
     {
        File[] anImage = f.listFiles();
        if (anImage.length > 0)
        {
           Bitmap aMap = decodeSampledBitmapFromFile(anImage[0], 120, 120);
           publishProgress(new LoadedImage(aMap));
           i++;
        }
     }
     return null;

  }
}

//My addImage method
private void addImage(LoadedImage... value) 
{
  for (LoadedImage image : value) 
  {
      adapter.addPhoto(image);
      adapter.notifyDataSetChanged();
  }
}

每次调用addImage方法时都会发生崩溃。总是返回一个位图，所以我不知道可以抛出NullPointerException的位置。任何帮助都会非常感激，因为我已经在这个问题上待了很长一段时间。

Answer 1

我忘了在onCreate中初始化我的适配器，导致应用程序崩溃。

将图像添加到GridView时AsyncTask崩溃

1 个答案: