如何正确实现notifydatasetchanged（）

Question

如何在我的示例中正确使用notifydatasetchanged ImageAdapter我想在函数中使用它来获取图像的高度

 public class ImageAdapter extends Activity {

    private Context mContext;
    private int mItemHeight = 0;
    private int mNumColumns = 0;
    private int mActionBarHeight = 0;
    private GridView.LayoutParams mImageViewLayoutParams;

    public ImageAdapter(Context context) {
 //      super();

        mContext = context;
        mImageViewLayoutParams = new GridView.LayoutParams(
                LayoutParams.MATCH_PARENT, LayoutParams.MATCH_PARENT);
        // Calculate ActionBar height
        TypedValue tv = new TypedValue();
        if (context.getTheme().resolveAttribute(
                android.R.attr.actionBarSize, tv, true)) {
            mActionBarHeight = TypedValue.complexToDimensionPixelSize(
                    tv.data, context.getResources().getDisplayMetrics());
        }
    }

    public int getCount() {
        // Size + number of columns for top empty row
        return mThumbIds.length + mNumColumns;
    }

    public Object getItem(int position) {
        return position < mNumColumns ?
                null : mThumbIds[position - mNumColumns];
    }

    public long getItemId(int position) {
        return position < mNumColumns ? 0 : position - mNumColumns;
    }

    public int getViewTypeCount() {
        // Two types of views, the normal ImageView and the top row of empty views
        return 2;
    }

    public int getItemViewType(int position) {
        return (position < mNumColumns) ? 1 : 0;
    }

    public boolean hasStableIds() {
        return true;
    }

    public View getView(int position, View convertView, ViewGroup container) {
        // First check if this is the top row
        if (position < mNumColumns) {
            if (convertView == null) {
                convertView = new View(mContext);
            }
            // Set empty view with height of ActionBar
            convertView.setLayoutParams(new AbsListView.LayoutParams(
                    ViewGroup.LayoutParams.MATCH_PARENT, mActionBarHeight));
            return convertView;
        }

        // Now handle the main ImageView thumbnails
        ImageView imageView;
        if (convertView == null) { // if it's not recycled, instantiate and initialize
            imageView = new ImageView(mContext);
            imageView.setScaleType(ImageView.ScaleType.CENTER_CROP);
            imageView.setLayoutParams(mImageViewLayoutParams);
        } else { // Otherwise re-use the converted view
            imageView = (ImageView) convertView;
        }

        // Check the height matches our calculated column width
        if (imageView.getLayoutParams().height != mItemHeight) {
            imageView.setLayoutParams(mImageViewLayoutParams);
        }

        // Finally load the image asynchronously into the ImageView, this also takes care of
        // setting a placeholder image while the background thread runs
        imageView.setImageResource(mThumbIds[position]);
        return imageView;
       // mImageFetcher.loadImage(Images.imageThumbUrls[position - mNumColumns], imageView);
     //   return imageView;
    }

    /**
     * Sets the item height. Useful for when we know the column width so the height can be set
     * to match.
     *
     * @param height
     */
    public void setItemHeight(int height) {
        if (height == mItemHeight) {
            return;
        }
        mItemHeight = height;
        mImageViewLayoutParams =
                new GridView.LayoutParams(LayoutParams.MATCH_PARENT, mItemHeight);
     //   mImageFetcher.setImageSize(height);
        notifyDataSetChanged();
    }

    public void setNumColumns(int numColumns) {
        mNumColumns = numColumns;
    }

    public int getNumColumns() {
        return mNumColumns;
    }

    // references to our images that each can be a wallpaper
    public final static Integer[] mThumbIds = {
        R.drawable.img,
        R.drawable.img1,
        R.drawable.img2,
        R.drawable.img3,
        R.drawable.img4,
        R.drawable.img5,
        R.drawable.img6,
        R.drawable.img7,
        R.drawable.img8,
        R.drawable.img9,
        R.drawable.img10,
        R.drawable.img11,
        R.drawable.img12,
        R.drawable.img13,
        R.drawable.img14,
        R.drawable.img15,
        R.drawable.img16,
        R.drawable.img17,
        R.drawable.img18,




    };

}

在当前的代码中它没有正常工作是否有

的变量