在Android中使用ExpandableListView来渲染子视图到父视图中，可以按照以下步骤进行：

1. 创建一个适配器类，继承自BaseExpandableListAdapter。

public class MyExpandableListAdapter extends BaseExpandableListAdapter {
    private Context context;
    private List parentItems;
    private Map> childItems;

    public MyExpandableListAdapter(Context context, List parentItems, Map> childItems) {
        this.context = context;
        this.parentItems = parentItems;
        this.childItems = childItems;
    }

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

    @Override
    public int getChildrenCount(int groupPosition) {
        String parent = parentItems.get(groupPosition);
        return childItems.get(parent).size();
    }

    @Override
    public Object getGroup(int groupPosition) {
        return parentItems.get(groupPosition);
    }

    @Override
    public Object getChild(int groupPosition, int childPosition) {
        String parent = parentItems.get(groupPosition);
        return childItems.get(parent).get(childPosition);
    }

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

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

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

    @Override
    public View getGroupView(int groupPosition, boolean isExpanded, View convertView, ViewGroup parent) {
        String parentItem = (String) getGroup(groupPosition);

        if (convertView == null) {
            LayoutInflater inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            convertView = inflater.inflate(R.layout.list_item_parent, null);
        }

        TextView parentTextView = convertView.findViewById(R.id.parentTextView);
        parentTextView.setText(parentItem);

        return convertView;
    }

    @Override
    public View getChildView(int groupPosition, int childPosition, boolean isLastChild, View convertView, ViewGroup parent) {
        String childItem = (String) getChild(groupPosition, childPosition);

        if (convertView == null) {
            LayoutInflater inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            convertView = inflater.inflate(R.layout.list_item_child, null);
        }

        TextView childTextView = convertView.findViewById(R.id.childTextView);
        childTextView.setText(childItem);

        return convertView;
    }

    @Override
    public boolean isChildSelectable(int groupPosition, int childPosition) {
        return true;
    }
}

2. 在布局文件中定义ExpandableListView。

3. 在Activity中设置适配器和数据。

public class MainActivity extends AppCompatActivity {
    private ExpandableListView expandableListView;
    private MyExpandableListAdapter expandableListAdapter;
    private List parentItems;
    private Map> childItems;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        expandableListView = findViewById(R.id.expandableListView);

        // 设置父项数据
        parentItems = new ArrayList<>();
        parentItems.add("Parent 1");
        parentItems.add("Parent 2");
        parentItems.add("Parent 3");

        // 设置子项数据
        childItems = new HashMap<>();
        childItems.put("Parent 1", Arrays.asList("Child 1-1", "Child 1-2", "Child 1-3"));
        childItems.put("Parent 2", Arrays.asList("Child 2-1", "Child 2-2", "Child 2-3"));
        childItems.put("Parent 3", Arrays.asList("Child 3-1", "Child 3-2", "Child 3-3"));

        expandableListAdapter = new MyExpandableListAdapter(this, parentItems, childItems);
        expandableListView.setAdapter(expandableListAdapter);
    }
}

在上述代码中，MyExpandableListAdapter类继承自BaseExpandableListAdapter，并根据父项和子项的数据来渲染父视图和子视图。在Activity中创建一个ExpandableListView，并设置