Android的GridView控件getChildAt（0）.findViewById（）返回nu

我有一个GridView一些项目，我用它扩展自定义适配器BaseAdapter 。每行显示一个可下载的项目，每一行都有显示下载进度的图标。

所以，我需要更新此图标。

对于此更新，我知道我可以更改数据和调用notifyDataChanged()和视图将得到更新，但这种方法费用我了很大的变化，我不希望这样做。

所以，我试图从获得一个特定的孩子gridview ，找到这个图标，更改图标，但返回的视图中为空。

View v = mGridView.getChildAt(0);
if(v != null)
{
    ImageButton mDownloadButton = (ImageButton)v.findViewById(R.id.download_icon_button);
    if(mDownloadButton != null)
        updateDownloadIcon(mDownloadButton, intent.getIntExtra(DATA.EXTRA_DOWNLOAD_PROGRESS, 0));
    else
        Log.e(TAG, "null image button");
}

v不为空，但mDownloadButton为空。

任何帮助，将不胜感激。

更新：

@Override
    public View getView(int position, View convertView, ViewGroup parent)
    {
        if(convertView == null)
        {
            LayoutInflater mInflater = (LayoutInflater) mContext.getSystemService(Activity.LAYOUT_INFLATER_SERVICE);
            convertView = mInflater.inflate(R.layout.all_book_frag_item_layout, null);
        }

        mBookCoverImageView = (ImageView)convertView.findViewById(R.id.bookCoverID);
        mBookNameTextView = (TextView)convertView.findViewById(R.id.bookNameID);
        mBookWriterTextView = (TextView)convertView.findViewById(R.id.bookWriterID);
        mBookOtherInfoTextView = (TextView)convertView.findViewById(R.id.bookInfoID);
        mAudioImageView = (ImageView)convertView.findViewById(R.id.audio_image);
        mVideoImageView = (ImageView)convertView.findViewById(R.id.video_image);
        mDownloadButton = (ImageButton)convertView.findViewById(R.id.download_icon_button);
        mBookSize = (TextView)convertView.findViewById(R.id.download_size);
        mBookNameInCover = (TextView)convertView.findViewById(R.id.bookNameInCover);

        sectionRow = getSectionRow(position);

        if(!mHeaderInfo.get(sectionRow[0][0]).getmBooksInCat().get(sectionRow[1][0]).getmBookCover().equals(""))
        {
            imageLoader.DisplayImage(mHeaderInfo.get(sectionRow[0][0]).getmBooksInCat().get(sectionRow[1][0]).getmBookCover(), mBookCoverImageView);
            mBookNameInCover.setText("");
        }
        else
        {
            mBookCoverImageView.setImageResource(R.drawable.trans_icon);
            mBookNameInCover.setText(mHeaderInfo.get(sectionRow[0][0]).getmBooksInCat().get(sectionRow[1][0]).getmPostTitle());
        }

        mBookNameTextView.setText(mHeaderInfo.get(sectionRow[0][0]).getmBooksInCat().get(sectionRow[1][0]).getmPostTitle());
        mBookWriterTextView.setText(mHeaderInfo.get(sectionRow[0][0]).getmBooksInCat().get(sectionRow[1][0]).getmAuthorName());
        mBookOtherInfoTextView.setText(mHeaderInfo.get(sectionRow[0][0]).getmBooksInCat().get(sectionRow[1][0]).getCatString());
        mBookSize.setText(mHeaderInfo.get(sectionRow[0][0]).getmBooksInCat().get(sectionRow[1][0]).getmEpubSize());

        if(isBookDownloaded(mHeaderInfo.get(sectionRow[0][0]).getmBooksInCat().get(sectionRow[1][0]).getmPostId()))
        {
            mDownloadButton.setImageResource(R.drawable.download_icon_90_100);
        }
        else
        {
            mDownloadButton.setImageResource(R.drawable.download_icon);
        }

        if(mHeaderInfo.get(sectionRow[0][0]).getmBooksInCat().get(sectionRow[1][0]).ismSound())
        {
            mAudioImageView.setVisibility(View.VISIBLE);
        }
        else
        {
            mAudioImageView.setVisibility(View.INVISIBLE);
        }

        if(mHeaderInfo.get(sectionRow[0][0]).getmBooksInCat().get(sectionRow[1][0]).ismVideo())
        {
            mVideoImageView.setVisibility(View.VISIBLE);
        }
        else
        {
            mVideoImageView.setVisibility(View.INVISIBLE);
        }

        if(mSelectsItems[sectionRow[0][0]][sectionRow[1][0]])
        {
            convertView.findViewById(R.id.allBookBaseLayout).setBackgroundResource(R.color.selection_color);
        }
        else
        {
            convertView.findViewById(R.id.allBookBaseLayout).setBackgroundResource(R.drawable.book_view_one_column_item_background);
        }

        mDownloadButton.setOnClickListener(new DownloadClickListener(mDownloadButton, mHeaderInfo.get(sectionRow[0][0]).getmBooksInCat().get(sectionRow[1][0]), position));

        return convertView;
    }

更新2：

我的适配器实现StickyGridHeadersBaseAdapter有时这让我重复ID错误，所以我设置mGridView.setId(-1);

Answer 1:

您可以使用getItemIdAtPosition到ID比较对标头的ID。如果不是头应该包含你的东西的看法。

long id = mGridView.getItemIdAtPosition(i);
if (id != StickyGridHeadersBaseAdapterWrapper.ID_HEADER) {
    // you now know that this item is not a header.
    View v = mGridView.getChildAt(i);
    if(v != null)
    {
        ImageButton mDownloadButton = (ImageButton)v.findViewById(R.id.download_icon_button);
        if(mDownloadButton != null)
            updateDownloadIcon(mDownloadButton, intent.getIntExtra(DATA.EXTRA_DOWNLOAD_PROGRESS, 0));
        else
            Log.e(TAG, "null image button");
    }
}

他们这样做是在源 StickyGridHeadersGridView的找头，所以应该努力找到究竟是不是头也。

Answer 2:

好像你使用了错误的ID，你肯定R.id.download_icon_button在视图中？如果没有，你必须添加它。