I want to select all CheckBox from Custom ListView on single Button click .
But when I have more than 9 items in ListView I am getting NullPointerException in below second line of code.
View vi= diffeneceLv.getChildAt(i);
CheckBox cb = (CheckBox) vi.findViewById(R.id.conschkbx);
You are getting it wrong, ListView re-uses your rows, which means number of created rows/layouts in memory are not equal to your items in array.
Typically ListView re-sets the new data to previous row upon scroll.
I would suggest you to study this blog post, here the author is maintaing the Checked state and then setting it accordingly in getView() of adapter.
The author have created an array of bolean like this:
private boolean[] thumbnailsselection;
and storing the state of check or uncheck, and later accessing it from getView(), what you will do is, you will store true for all index and refresh your adapter. It'll select all your rows.
Here is another post.
You should NOT hold references of individual views for this purpose, as they are recycled.
For your convenience, ListView holds a BooleanSparseArray to store what items are checked. This array contains a map of item id (index/position of items in adapter) to a boolean value.
Since ListView does all that for you, its good to avoid re-inventing the wheel and use ListView's capability to hold checked state of its items. All you have to do is to set a choice mode for ListView: setChoiceMode(int choiceMode)
To get any item's state, call isItemChecked(int position) on ListView. Useful, if you are overriding getView() of adapter.
To get all what's checked, call getCheckedItemPositions() on ListView.
To set checked value, call setItemChecked(int position, boolean value) on ListView.
