在可扩展列表视图的子视图中设置图像时出现空指针异常[关闭]

Question

我在child.bg[i] = bground[0]; 行中得到一个Null Pointer Exception。我正在尝试在子项的ImageView 中设置图像。我在子项布局中有ImageView 和TextView。这是Expandable List View中填充数据的代码。

List<GroupItem> items = new ArrayList<GroupItem>();

    int[] bground ={R.drawable.hawamahal,R.drawable.tajmahal,R.drawable.mysorepalace};
    // Populate our list with groups and it's children
    for(int i = 0; i < 3; i++) {
        GroupItem item = new GroupItem();

        switch(i){

            case 0: item.title = "Western India";
            {
                    ChildItem child = new ChildItem();
                    child.title = getString(R.string.WestDescription);
                   child.bg[i] = bground[0];
                    item.items.add(child);
            }
                break;
            case 1: item.title = "Northern India";
            {
                ChildItem child = new ChildItem();
                child.title = getString(R.string.NorthDescription);
                child.bg[i] = bground[1];

                item.items.add(child);

            }
                break;
            case 2: item.title = "Southern India";
            {
                    ChildItem child = new ChildItem();
                    child.title = getString(R.string.SouthDescription);
                child.bg[i] = bground[2];
                    item.items.add(child);

            }

                break;


        }
        items.add(item);
    }

`

以及Adapter和Holders的代码

private static class GroupItem {
    String title;
    List<ChildItem> items = new ArrayList<ChildItem>();
}

private static class ChildItem {
    String title;
    int[]  bg;

}

private static class ChildHolder {
    TextView title;
    ImageView  childimage;
}

private static class GroupHolder {
    TextView title;

}

/**
 * Adapter for our list of {@link GroupItem}s.
 */
private class ExampleAdapter extends AnimatedExpandableListView.AnimatedExpandableListAdapter {
    private LayoutInflater inflater;

    private List<GroupItem> items;

    public ExampleAdapter(Context context) {
        inflater = LayoutInflater.from(context);
    }

    public void setData(List<GroupItem> items) {
        this.items = items;
    }

    @Override
    public ChildItem getChild(int groupPosition, int childPosition) {
        return items.get(groupPosition).items.get(childPosition);
    }

    @Override
    public long getChildId(int groupPosition, int childPosition) {
        return childPosition;
    }

    @Override
    public View getRealChildView(int groupPosition, int childPosition, boolean isLastChild, View convertView, ViewGroup parent) {
        ChildHolder holder;
        int[] bg={R.drawable.taj};
        ChildItem item = getChild(groupPosition, childPosition);
        if (convertView == null) {
            holder = new ChildHolder();
            convertView = inflater.inflate(R.layout.list_item, parent, false);
            holder.title = (TextView) convertView.findViewById(R.id.textTitle);
            holder.childimage= (ImageView) convertView.findViewById(R.id.ChildImageView);
            convertView.setTag(holder);
        } else {
            holder = (ChildHolder) convertView.getTag();
        }
        holder.title.setText(item.title);
        holder.childimage.setImageResource(bg[groupPosition]);


        return convertView;
    }

    @Override
    public int getRealChildrenCount(int groupPosition) {
        return items.get(groupPosition).items.size();
    }

    @Override
    public GroupItem getGroup(int groupPosition) {
        return items.get(groupPosition);
    }

    @Override
    public int getGroupCount() {
        return items.size();
    }

    @Override
    public long getGroupId(int groupPosition) {
        return groupPosition;
    }

    @Override
    public View getGroupView(int groupPosition, boolean isExpanded, View convertView, ViewGroup parent) {
        GroupHolder holder;
        GroupItem item = getGroup(groupPosition);
        if (convertView == null) {
            holder = new GroupHolder();
            convertView = inflater.inflate(R.layout.group_item, parent, false);
            holder.title = (TextView) convertView.findViewById(R.id.textTitle);
            convertView.setTag(holder);
        } else {
            holder = (GroupHolder) convertView.getTag();
        }
        holder.title.setText(item.title);

        return convertView;
    }

    @Override
    public boolean hasStableIds() {
        return true;
    }

    @Override
    public boolean isChildSelectable(int arg0, int arg1) {
        return true;
    }


}

我是 android 开发的新手，如果您需要更多详细信息，请告诉我。在这里，我试图从 ChildItem 的 ImageView 中的可绘制文件夹中设置图像。如果有任何其他方式这样做，请告诉我。提前致谢。

Answer 1

您未能在 ChildItem 类中初始化 child.bg[] 数组。
更改代码如下：

 ChildItem child = new ChildItem();
 child.title = getString(R.string.WestDescription);
 child.bg[] = new int[3]; // <----- initiliaze bg[] arrays
 child.bg[i] = bground[0];
 item.items.add(child);