自定义列表视图中的复选框问题

Question

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);

Answer 1

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 .

Answer 2

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 .