I'm trying to create an ExpandableListView in my app. It has 2 groups: the first is colours, and the second is symbols. The first group clicked on works fine. The second group, however, shows the rows from the first group (if the second group has more items in it, then the 'extra' ones will be correct).
Eg let's say the 'colours' are white, black, red and blue, and the symbols are '/' and '.'.
If I start the activity and click on colours, then they appear correctly. If I then click on 'symbols', I see white and black.
If I click 'symbols' first, then I see '/' and '.', but when I then click on colours I see '/', '.', red, blue.
I searched online and have established that I need to use ViewHolders to avoid it reusing the same view when I change groups. I haven't been able to implement it though. At first it didn't make any difference, and the current version is crashing out when I click the second group. I think part of the issue is that I have a different child layout for each group (ie the symbols are shown differently from the colours).
Currently here's what I have (I've shown what I think are the relevant bits; if I've left out anything important, I can add it in):
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;
}
}
Layout for the parent (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>
Layout for the colour rows (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>
and for the symbol rows (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>
If I click the 'colour' group first, and then the 'symbol' group, it crashes out on the line: symbolviewholder = (SymbolViewHolder) row.getTag().
Since you have 2 different child layouts, you need to override getChildTypeCount() and getChildType() so the adapter will receive the proper view type to reuse. Otherwise, in some cases you will get a ClassCastException when trying to retrieve your ViewHolder.
@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;
}
For more info, see HeterogeneousExpandableList documentation.