我不知道ImagaeCatche.params中的错误到底是什么,它显示了空指针异常,我在行尾指出了错误编号.

堆栈跟踪：

 E/AndroidRuntime(1464): FATAL EXCEPTION: main
 E/AndroidRuntime(1464): Process: com.gems.android, PID: 1464
 E/AndroidRuntime(1464): java.lang.NullPointerException
 E/AndroidRuntime(1464):    at com.sit.fth.util.ImageCache.getDiskCacheDir(ImageCache.java:514)
 E/AndroidRuntime(1464):    at com.sit.fth.util.ImageCache$ImageCacheParams.<init>(ImageCache.java:463)
 E/AndroidRuntime(1464):    at com.sit.fth.frgment.HomeFragment.onCreateView(HomeFragment.java:82)
 E/AndroidRuntime(1464):    at android.support.v4.app.Fragment.performCreateView(Fragment.java:1500)
 E/AndroidRuntime(1464):    at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:927)
 E/AndroidRuntime(1464):    at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1104)
 E/AndroidRuntime(1464):    at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:682)
 E/AndroidRuntime(1464):    at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1467)
 E/AndroidRuntime(1464):    at android.support.v4.app.FragmentManagerImpl.executePendingTransactions(FragmentManager.java:472)
 E/AndroidRuntime(1464):    at android.support.v4.app.FragmentPagerAdapter.finishUpdate(FragmentPagerAdapter.java:141)
 E/AndroidRuntime(1464):    at android.support.v4.view.ViewPager.populate(ViewPager.java:1068)
 E/AndroidRuntime(1464):    at android.support.v4.view.ViewPager.populate(ViewPager.java:914)
 E/AndroidRuntime(1464):    at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1436)
 E/AndroidRuntime(1464):    at android.view.View.measure(View.java:16497)
 E/AndroidRuntime(1464):    at android.widget.RelativeLayout.measureChildHorizontal(RelativeLayout.java:719)
 E/AndroidRuntime(1464):    at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:455)
 E/AndroidRuntime(1464):    at android.view.View.measure(View.java:16497)
 E/AndroidRuntime(1464):    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125)
 E/AndroidRuntime(1464):    at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
 E/AndroidRuntime(1464):    at android.view.View.measure(View.java:16497)
 E/AndroidRuntime(1464):    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125)
 E/AndroidRuntime(1464):    at com.android.internal.widget.ActionBarOverlayLayout.onMeasure(ActionBarOverlayLayout.java:327)
E/AndroidRuntime(1464):     at android.view.View.measure(View.java:16497)
 E/AndroidRuntime(1464):    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125)
 E/AndroidRuntime(1464):    at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
 E/AndroidRuntime(1464):    at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2291)
 E/AndroidRuntime(1464):    at android.view.View.measure(View.java:16497)
 E/AndroidRuntime(1464):    at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:1916)
 E/AndroidRuntime(1464):    at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1113)
 E/AndroidRuntime(1464):    at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1295)
 E/AndroidRuntime(1464):    at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1000)
 E/AndroidRuntime(1464):    at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5670)
 E/AndroidRuntime(1464):    at android.view.Choreographer$CallbackRecord.run(Choreographer.java:761)
 E/AndroidRuntime(1464):    at android.view.Choreographer.doCallbacks(Choreographer.java:574)
: E/AndroidRuntime(1464):   at android.view.Choreographer.doFrame(Choreographer.java:544)
 E/AndroidRuntime(1464):    at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:747)
 E/AndroidRuntime(1464):    at android.os.Handler.handleCallback(Handler.java:733)
 E/AndroidRuntime(1464):    at android.os.Handler.dispatchMessage(Handler.java:95)
 E/AndroidRuntime(1464):    at android.os.Looper.loop(Looper.java:136)
 E/AndroidRuntime(1464):    at android.app.ActivityThread.main(ActivityThread.java:5017)
 E/AndroidRuntime(1464):    at java.lang.reflect.Method.invokeNative(Native Method)
 E/AndroidRuntime(1464):    at java.lang.reflect.Method.invoke(Method.java:515)
 E/AndroidRuntime(1464):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
 E/AndroidRuntime(1464):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
 E/AndroidRuntime(1464):    at dalvik.system.NativeStart.main(Native Method)

ImageCatche.java：

package com.sit.fth.util;

public class ImageCache {
private static final String TAG = "ImageCache";

// Default memory cache size in kilobytes
private static final int DEFAULT_MEM_CACHE_SIZE = 1024 * 5; // 5MB

// Default disk cache size in bytes
private static final int DEFAULT_DISK_CACHE_SIZE = 1024 * 1024 * 10; // 10MB

// Compression settings when writing images to disk cache
private static final CompressFormat DEFAULT_COMPRESS_FORMAT = CompressFormat.JPEG;
private static final int DEFAULT_COMPRESS_QUALITY = 70;
private static final int DISK_CACHE_INDEX = 0;

// Constants to easily toggle various caches
private static final boolean DEFAULT_MEM_CACHE_ENABLED = true;
private static final boolean DEFAULT_DISK_CACHE_ENABLED = true;
private static final boolean DEFAULT_INIT_DISK_CACHE_ON_CREATE = false;

private DiskLruCache mDiskLruCache;
private LruCache<String, BitmapDrawable> mMemoryCache;
private ImageCacheParams mCacheParams;
private final Object mDiskCacheLock = new Object();
private boolean mDiskCacheStarting = true;

private HashSet<SoftReference<Bitmap>> mReusableBitmaps;

private ImageCache(ImageCacheParams cacheParams) {
    init(cacheParams);
   }


     public static ImageCache getInstance(
        FragmentManager fragmentManager, ImageCacheParams cacheParams) {

    // Search for, or create an instance of the non-UI RetainFragment
    final RetainFragment mRetainFragment = findOrCreateRetainFragment(fragmentManager);

    // See if we already have an ImageCache stored in RetainFragment
    ImageCache imageCache = (ImageCache) mRetainFragment.getObject();

    // No existing ImageCache, create one and store it in RetainFragment
    if (imageCache == null) {
        imageCache = new ImageCache(cacheParams);
        mRetainFragment.setObject(imageCache);
    }

    return imageCache;
}


public static class ImageCacheParams {

public int memCacheSize = DEFAULT_MEM_CACHE_SIZE;
public int diskCacheSize = DEFAULT_DISK_CACHE_SIZE;
public File diskCacheDir;
public CompressFormat compressFormat = DEFAULT_COMPRESS_FORMAT;
public int compressQuality = DEFAULT_COMPRESS_QUALITY;
public boolean memoryCacheEnabled = DEFAULT_MEM_CACHE_ENABLED;
public boolean diskCacheEnabled = DEFAULT_DISK_CACHE_ENABLED;
public boolean initDiskCacheOnCreate = DEFAULT_INIT_DISK_CACHE_ON_CREATE;


public ImageCacheParams(Context context, String diskCacheDirectoryName) {
    diskCacheDir = getDiskCacheDir(context, diskCacheDirectoryName); <-- 375th Error
}


public void setMemCacheSizePercent(float percent) {
    if (percent < 0.05f || percent > 0.8f) {
        throw new IllegalArgumentException("setMemCacheSizePercent - percent must be "
                + "between 0.05 and 0.8 (inclusive)");
    }
    memCacheSize = Math.round(percent * Runtime.getRuntime().maxMemory() / 1024);
  }
}

  private static boolean canUseForInBitmap(
    Bitmap candidate, BitmapFactory.Options targetOptions) {
  int width = targetOptions.outWidth / targetOptions.inSampleSize;
  int height = targetOptions.outHeight / targetOptions.inSampleSize;

  return candidate.getWidth() == width && candidate.getHeight() == height;
  }


 public static File getDiskCacheDir(Context context, String uniqueName) {
 // Check if media is mounted or storage is built-in, if so, try and use external cache dir
 // otherwise use internal cache dir
   final String cachePath =
        Environment.MEDIA_MOUNTED.equals(Environment.getExternalStorageState()) ||
                !isExternalStorageRemovable() ?    getExternalCacheDir(context).getPath() : <---402nd Error 
                        context.getCacheDir().getPath();

return new File(cachePath + File.separator + uniqueName);
}

}

HomeFragment.java：

package com.sit.fth.frgment;

public class HomeFragment extends BaseFragment {

    private View view;
    private ExpandableListView expListView;
    private ArrayList<String> childArrayList;

    List<String> listDataHeader;
    HashMap<String, List<String>> listDataChild = new HashMap<String, List<String>>();

    private int lastExpandedPosition = -1;
    int lastExpandedGroupPosition;
    private int mImageThumbSize;
    private ImageFetcher mImageFetcher;

    private LinearLayout loadingLayout;
    private TextView invisible;
    private List<ImgGallery> imggalleries;
    private LinearLayout listlayout;
    private int collapse = 1;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        view = inflater.inflate(R.layout.home_fragment, null);
        // mTabHost = (TabHost) mRoot.findViewById(android.R.id.tabhost);

        mImageThumbSize = getResources().getDimensionPixelSize(
                R.dimen.image_thumbnail_size);

        ((TextView) view.findViewById(R.id.txt_header)).setText("HOME");

        ImageCacheParams cacheParams = new ImageCacheParams(getActivity(),
                AppConstants.IMAGE_CACHE_DIR);  <---82nd Line Error

        cacheParams.setMemCacheSizePercent(0.25f); // Set memory cache to 25% of
                                                    // app memory

 }

如果您知道如何解决这些问题,任何人都可以帮助我.谢谢.

解决方法:

AppConstants.IMAGE_CACHE_DIR的值及其引用在函数中：

public static File getDiskCacheDir(Context context, String uniqueName) {
 // Check if media is mounted or storage is built-in, if so, try and use external cache dir
 // otherwise use internal cache dir
   final String cachePath =
        Environment.MEDIA_MOUNTED.equals(Environment.getExternalStorageState()) ||
                !isExternalStorageRemovable() ?    getExternalCacheDir(context).getPath() : <---402nd Error 
                        context.getCacheDir().getPath();

return new File(cachePath + File.separator + uniqueName);
}  

将其用于仿真器,电话时,情况有所不同.即sdCard上的路径访问.

因此,您需要检查在哪种设备上遇到此错误的情况.