Question

我是编码和java的新手并且遇到了问题并且无法修复它。奇怪的是，错误只发生在android 5上。

以下是错误消息

java.lang.NullPointerException: Attempt to invoke virtual method 'void com.nostra13.universalimageloader.core.ImageLoader.displayImage(java.lang.String, android.widget.ImageView, com.nostra13.universalimageloader.core.DisplayImageOptions)' on a null object reference
at com.fragments.activity.StoreActivity$1.OnMGArrayAdapterCreated(StoreActivity.java:143)
at com.adapters.MGArrayAdapter.getView(MGArrayAdapter.java:82)

StoreActivity.java

public void OnMGArrayAdapterCreated (MGArrayAdapter adapter, View v,
int position, ViewGroup viewGroup, Object obj){
    // TODO Auto-generated method stub

    final Store store = arrayData.get(position);

    Photo p = q.getPhotoByStoreId(store.getStore_id());

    MGImageView imgViewPhoto = (MGImageView) v.findViewById(R.id.imgViewPhoto);
    imgViewPhoto.setCornerRadius(0.0f);
    imgViewPhoto.setBorderWidth(UIConfig.BORDER_WIDTH);
    imgViewPhoto.setBorderColor(getResources().getColor(UIConfig.THEME_BLACK_COLOR));
    imgViewPhoto.setOnClickListener(new OnClickListener() {

        @Override
        public void onClick(View arg0) {
            // TODO Auto-generated method stub
            Intent i = new Intent(StoreActivity.this, DetailActivity.class);
            i.putExtra("store", store);
            StoreActivity.this.startActivity(i);
        }
    });

    if (p != null) {
        MainActivity.getImageLoader().displayImage(p.getPhoto_url(), imgViewPhoto, options);
    }
    else {
        imgViewPhoto.setImageResource(UIConfig.SLIDER_PLACEHOLDER);
    }
}

MGArrayAdapter.java

public class MGArrayAdapter extends BaseAdapter {

    private Context c;
    private int resId;
    private OnMGArrayAdapterListener mCallback;
    public List<Object> objects;

    public interface OnMGArrayAdapterListener {
        public void OnMGArrayAdapterCreated(MGArrayAdapter adapter, View v, int position, ViewGroup viewGroup, Object obj);
    }

    public void setOnMGArrayAdapterListener(OnMGArrayAdapterListener listener) {
        try {
            mCallback = (OnMGArrayAdapterListener) listener;
        }
        catch (ClassCastException e) {
            throw new ClassCastException(this.toString() + " must implement OnMGArrayAdapterListener");
        }
    }

    public MGArrayAdapter(Context c, ArrayList<Object> objects, int resId) {
        this.c = c;
        this.objects = objects;
        this.resId = resId;
    }

    @Override
    public int getCount() {
        // TODO Auto-generated method stub
        return objects.size();
    }

    @Override
    public Object getItem(int pos) {
        // TODO Auto-generated method stub
        return objects.get(pos);
    }

    @Override
    public long getItemId(int pos) {
        // TODO Auto-generated method stub
        return pos;
    }

    @Override
    public View getView(int pos, View v, ViewGroup viewGroup) {
        // TODO Auto-generated method stub

        ViewHolder viewHolder = null;

        if (v == null) {
            LayoutInflater li = (LayoutInflater) c.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            v = li.inflate(resId, null);

            viewHolder = new ViewHolder();
            viewHolder.view = v;
            v.setTag(viewHolder);
        }
        else {
            viewHolder = (ViewHolder) v.getTag();
            Log.w("MGListAdapter Class", "View being reused.");
        }

        if (mCallback != null)
            mCallback.OnMGArrayAdapterCreated(this, viewHolder.view, pos, viewGroup, objects.get(pos));

        return v;
    }

    public class ViewHolder {
        public View view;
    }

    public void add(Object obj) {
        if (objects == null)
            objects = new ArrayList<Object>();

        objects.add(obj);
    }

    public void clearAll() {
        if (objects == null)
            objects = new ArrayList<Object>();

        objects.clear();
    }
}

Answer 1

为什么不尝试：

public void add(Object obj) {

    if(objects == null)
        objects = new ArrayList<Object>();

    objects.add(obj);
}

public void clearAll(Object obj) {

    if(objects == null)
        objects = new ArrayList<Object>();

    objects.clear();
}

Answer 2

在StoreActivity.java中，行MainActivity.getImageLoader()以某种方式返回null，然后在其上面调用dispalyImage，这会导致空指针异常。请检查静态方法getImageLoader的代码，以了解其返回null的原因或在此处发布代码，以便我们可以帮助您找出答案。

java新手 - 尝试调用虚方法＆＃39; void

2 个答案: