Question

我正在尝试在片段中创建网格视图。我已经实现了适配器类和相应的overriden方法。但是在运行它时会抛出异常：

gridView.setOnItemClickListener (this);

声明gridView对象是一个NULL指针。

这是我的代码（非常类似于Google Sample）：

public static class OcrOverrideFragment extends Fragment implements AdapterView.OnItemClickListener {

    // The Adaptor Class for the grid view
    public class ImageAdaptor extends BaseAdapter{

        private Context mContext;

        public ImageAdaptor (Context c)
        {
            mContext = c;

        }

        public long getItemId(int position) {
            return (long) position;
        }

        public Object getItem(int position) {
            return null;
        }

        public int getCount (){

            try
            {
                String[] f = mContext.getAssets().list("OcrSampleImages");
                return f.length;
            }
            catch (IOException e)
            {
                LogUtil.d (TAG,"OCR_OVERRIDE gave " + e);
            }
            return 0;
        }

        // For each of the items in the grid, this method will be called
        public View getView(int position, View convertView, ViewGroup parent) {

            ImageView imageView = null;

            try
            {
                String[] f = mContext.getAssets().list("OcrSampleImages");

                if (convertView == null) {
                    imageView = new ImageView(getContext());
                    imageView.setLayoutParams(new GridView.LayoutParams(85, 85));
                    imageView.setScaleType(ImageView.ScaleType.CENTER_CROP);
                    imageView.setPadding(8, 8, 8, 8);
                }
                else {
                    imageView = (ImageView) convertView;
                }

                // Setting the appropriate image for each gird item
                imageView.setImageBitmap(getBitmapFromAsset("OcrSampleImages"+System.getProperty("file.separator")+f[position]));

            }
            catch (IOException e)
            {
                LogUtil.d (TAG,"OCR_OVERRIDE gave " + e);
            }

            return imageView;
        }
    } // End Of ImageAdaptor Class

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {

        View v = inflater.inflate(R.layout.ocr_override, container, false);

            GridView gridView = (GridView) (getActivity().findViewById(R.id.ocrgridview));
            gridView.setAdapter(new ImageAdaptor(v.getContext()));
            gridView.setOnItemClickListener (this);

        return v;
    }

    @Override
    public void onItemClick (AdapterView<?> adaptorView,View v,int i,long l)
    {
        // Implementation details unncessary

    }

Answer 1

更改此行

GridView gridView = (GridView) (getActivity().findViewById(R.id.ocrgridview));

要

GridView gridView = (GridView) v.findViewById(R.id.ocrgridview); //Note "v" not activity

Answer 2

getActivity（）

返回此片段当前与之关联的活动。

但是

查看v

在布局文件中获取 v 的引用。

这就是为什么我们称第二种方法而不是第一种方法。您可以访问以下以获得更好的答案

<强> Difference between getActivity() and view in Fragment

在Fragment中创建图像的GridView

2 个答案: