Using ListView Built-in Item ChoiceMode for Item Selection
ListVIew Item Selection
Q: Should we need to track/untrack item state by ourself?
A: NO. You don't need to do this. Let ListView(or GridView) built-in ChoiceMode help you to do this. If we want to mark some item(s) been selected, we don't need to add an extra property (maybe named checked or something...) to track. Just setChoiceMode
mListView.setChoiceMode(AbsListView.CHOICE_MODE_SINGLE);
When we done this, the mListView object will track the selected item (or position), you could call the follwing realted APIs to get the information.
mListView.getCheckedItemCount() //get the count of selected items
mListView.getCheckedItemIds() //get the ids of selected items
mListView.getCheckedItemPosition() //get the selected item
mListView.getCheckedItemPositions() //get the all the selected items
Q: What if we want to mark the selected item on UI?
A: In the past, I'm not familiar with ListView, I usually implement this feature like this way
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
view.setSelected(true);
}
, and the view object applied with an selector drawable resource with a condition android:state_selected="true".
Nevertheless, we don't need to implement like this way.
Reference to Android AbsListView source, an AbsListView will update all checked items as activated, or update as checked when the view is an instance of Checkable. So, just create a drawable selector like this
<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">
<!-- pressed -->
<item android:drawable="@color/material_blue_grey_800" android:state_pressed="true" />
<!-- focused -->
<item android:drawable="@color/material_blue_grey_800" android:state_activated="true" />
<!-- default -->
<item android:drawable="@color/background_floating_material_light" />
</selector>
and apply this selector to you item layout.
Recursive State Activated
When a parent layout is set as state_activated, all the children are set as state_activated. Therefore, you don't need to handle the change of state for each child, jsut create a selector resource and apply it to children you want to do some UI viration when the state is set as activated.
OnItemClickListener
Basically, if you implement ListView/GridView with ChoiceMode, you already could select item(s) which been touched without need to setup an OnItemClickListener to track/untrack state of clicked items. We only do this when we really want to handle some things while item is clicked.
when you using some Checkable view in item layout and want to set it as checked, you have to handle this by yourself with OnItemClickListener.
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
ViewGroup vp = (ViewGroup) view;
final int count = vp.getChildCount();
for(int i = 0; i < count; i++) {
final View child = vp.getChildAt(i);
if(child instanceof Checkable) {
((Checkable) child).setChecked(true);
}
}
mCount.setText(String.format(getResources().getString(R.string.item_count), getListView().getCheckedItemCount()));
}