android - 如何将 Viewholder 与 ExpandableListView 一起使用？

Question

我正在尝试在我的应用程序中创建一个 ExpandableListView。它有两组:第一组是颜色，第二组是符号。第一组点击效果很好。然而，第二组显示第一组中的行(如果第二组中有更多项目，则“额外”的项目将是正确的)。

例如，假设“颜色”是白色、黑色、红色和蓝色，符号是“/”和“.”。

如果我开始 Activity 并点击颜色，它们就会正确显示。如果我随后点击“符号”，我会看到白色和黑色。

如果我先单击“符号”，然后我会看到“/”和“.”，但是当我随后单击颜色时，我会看到“/”、“.”、红色、蓝色。

我在网上搜索并确定我需要使用 ViewHolders 以避免它在我更改组时重复使用相同的 View 。虽然我没能实现它。一开始没什么区别，点第二组的时候当前版本就闪退了。我认为部分问题是我为每个组设置了不同的子布局(即符号与颜色的显示方式不同)。

目前这是我所拥有的(我已经展示了我认为相关的部分；如果我遗漏了任何重要的内容，我可以添加它):

public class ColourSymbolKeyAdapter extends BaseExpandableListAdapter {

    private Context context;
    private HashMap<String, List<KeyItem>> childDataSource;
    private List<String> parentDataSource;

    public ColourSymbolKeyAdapter(Context context,
                                  List<String> childParent,
                                  HashMap<String, List<KeyItem>> child) {

        this.context = context;
        this.parentDataSource = childParent;
        this.childDataSource = child;
    }

... Left out various override functions ...

    @Override
    public View getGroupView(int groupPosition, boolean isExpanded, View convertView, ViewGroup parent) {

        View v = convertView;
        GroupViewHolder holder;

        if(v == null) {
            LayoutInflater inflater =
                    (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            v = inflater.inflate(R.layout.expandablelist_parent, parent, false);
            holder = new GroupViewHolder();

            holder.mGroupName = (TextView) v.findViewById(R.id.textViewParent);
            v.setTag(holder);
        }else {
            holder = (GroupViewHolder) v.getTag();
        }

        String parentHeader = (String) getGroup(groupPosition);
        holder.mGroupName.setText(parentHeader);
        return v;
    }

    @Override
    public View getChildView(int groupPosition, int childPosition, boolean isLastChild, View convertView, ViewGroup parent) {

        View row = convertView;
        KeyItem childItem = (KeyItem) getChild(groupPosition, childPosition);
        ColourViewHolder colourviewholder;
        SymbolViewHolder symbolviewholder;

        LayoutInflater inflater =
                (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);

        if(childItem.getPatternColour() == null) { // This is a symbol row

            if(row == null) {
                symbolviewholder = new SymbolViewHolder();
                row = inflater.inflate(R.layout.expandablelist_child_symbol, parent, false);
                symbolviewholder.mChildName = (TextView) row.findViewById(R.id.symbol_desc);
                symbolviewholder.mSymbolCell = (SymbolCell) row.findViewById(R.id.symbol_cell);
                row.setTag(symbolviewholder);
            }else {
                symbolviewholder = (SymbolViewHolder) row.getTag();
            }

            String drawableName = childItem.getPatternSymbol().getDrawable();
            final int resourceId = context.getResources().getIdentifier(drawableName, "drawable", context.getPackageName());
            Drawable drawable;
            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
                drawable = context.getResources().getDrawable(resourceId, context.getTheme());
            } else {
                drawable = context.getResources().getDrawable(resourceId);
            }

            symbolviewholder.mSymbolCell.setDrawable(drawable);
            symbolviewholder.mChildName.setText(childItem.getPatternSymbol().getSymbolDescription());

        }else { // This is a colour row
            if(row == null) {
                colourviewholder = new ColourViewHolder();
                row = inflater.inflate(R.layout.expandablelist_child_colour, parent, false);
                colourviewholder.mChildName = (TextView) row.findViewById(R.id.colour_name);
                colourviewholder.mChildDesc = (TextView) row.findViewById(R.id.colour_desc);
                colourviewholder.mColourCell = (ColourCell) row.findViewById(R.id.colour_cell);
                row.setTag(colourviewholder);
            }else {
                colourviewholder = (ColourViewHolder) row.getTag();
            }

            colourviewholder.mColourCell.setColour(childItem.getPatternColour());
            colourviewholder.mChildName.setText(childItem.getPatternColour().getName());
            colourviewholder.mChildDesc.setText(childItem.getPatternColour().getDescription());
        }

        return row;
    }

    public final class GroupViewHolder {

        TextView mGroupName;
    }

    public final class ColourViewHolder {

        ColourCell mColourCell;
        TextView mChildName, mChildDesc;
    }

    public final class SymbolViewHolder {

        SymbolCell mSymbolCell;
        TextView mChildName;
    }
}

父布局(expandablelist_parent.xml):

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:id="@+id/parentView">

    <TextView xmlns:android="http://schemas.android.com/apk/res/android"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:id="@+id/textViewParent"
        android:textColor="#000000"
        android:textAppearance="@style/ParagraphBold">
    </TextView>

</LinearLayout>

颜色行的布局 (expandablelist_child_colour.xml):

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:padding="@dimen/small_padding"
    android:id="@+id/childViewColour"
    android:orientation="horizontal">

    <com.myname.appname.ColourCell xmlns:android="http://schemas.android.com/apk/res/android"
        android:layout_width="@dimen/grid_cell_column_width"
        android:layout_height="@dimen/grid_cell_column_width"
        android:id="@+id/colour_cell"
        android:layout_marginRight="@dimen/small_padding" />

    <LinearLayout
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:orientation="vertical">

        <TextView xmlns:android="http://schemas.android.com/apk/res/android"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:textAppearance="@style/ParagraphBold"
            android:textColor="@color/colorPrimaryDark"
            android:id="@+id/colour_name">
        </TextView>

        <TextView xmlns:android="http://schemas.android.com/apk/res/android"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:textAppearance="@style/Paragraph"
            android:textColor="@color/colorPrimaryDark"
            android:id="@+id/colour_desc">
        </TextView>

    </LinearLayout>

</LinearLayout>

对于符号行 (expandablelist_child_symbol.xml):

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:id="@+id/childViewSymbol"
    android:padding="@dimen/small_padding">

    <com.myname.appname.SymbolCell xmlns:android="http://schemas.android.com/apk/res/android"
        android:layout_width="@dimen/grid_cell_column_width"
        android:layout_height="@dimen/grid_cell_column_width"
        android:textAppearance="@style/Paragraph"
        android:id="@+id/symbol_cell"
        android:layout_marginRight="@dimen/small_padding" />

    <TextView xmlns:android="http://schemas.android.com/apk/res/android"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:textColor="@color/colorPrimaryDark"
        android:id="@+id/symbol_desc">
    </TextView>

</LinearLayout>

如果我先点击“颜色”组，然后点击“符号”组，它就会崩溃:symbolviewholder = (SymbolViewHolder) row.getTag()。

Answer 1

由于您有 2 个不同的子布局，您需要重写 getChildTypeCount() 和 getChildType() 以便适配器将接收正确的 View 类型以供重用。否则，在某些情况下，您将在尝试检索 ViewHolder 时收到 ClassCastException。

@Override
public int getChildTypeCount() {
    return 2;
}

@Override
public int getChildType(int groupPosition, int childPosition) {
    KeyItem childItem = (KeyItem) getChild(groupPosition, childPosition);
    return (childItem.getPatternColour() == null) ? 0 : 1;
}

有关详细信息，请参阅 HeterogeneousExpandableList文档。