Question

I want to draw a check mark for the image view I click on and uncheck the imageview I clicked on before using the following code snip. I store last checked position in mDeviceAdapter. When I try to uncheck old position, the image view always gives null even for the partial visible image view. I am really confused because I thought only invisible one is recycled… Newbie in Android and any comment is appreciated.

    public void CheckableImageView#setChecked(boolean checked) {
    if (mChecked != checked) {
        mChecked = checked;
        invalidate();
    }
}

    mDeviceGallery.setOnItemClickListener(new AdapterView.OnItemClickListener() {

                @Override
                public void onItemClick(AdapterView<?> parent, View view,
                        int position, long id) {

                    CheckableImageView viewToCheck = (CheckableImageView) view;
                    if (!viewToCheck.isChecked()) {
                        int oldCheckedPosition = mDeviceAdapter
                                .getCheckedPosition();
                        mDeviceAdapter.setCheckedPosition(position);
                        View checkedView = mDeviceGallery
                                .getChildAt(oldCheckedPosition);
                        Log.d(TAG, "old position="+oldCheckedPosition + "old view="+checkedView);
                        if (checkedView != null) {
                            ((CheckableImageView) checkedView)
                                    .setChecked(false);
                            Log.d(TAG, "uncheck position="
                                    + oldCheckedPosition);
                        }
                        viewToCheck.setChecked(true);

Answer 1

That’s not the right approach.
You need to add to your data type a boolean field (i.e mIsChecked).
On the onItemClick method set the value of that variable to true and keep its INDEX as a member of the adapter. When another item is clicked set the value of that item to true and set the value of the saved one to false (change the value of the datatype in you ArrayList in the INDEX you stored in the previous click).

Now, in the getView() method, you must have if/else statement. Something like:

if (item.isChecked())
{
    checkedView.setChecked(true);
}
else
{
    checkedView.setChecked(false);
}

Example to the onClick method: (just a general direction)

if (item.isChecked())
    {
        checkedView.setChecked(false);
        yourList.get(position).setChecked(true);
        yourList.get(mLastCheckedIndex).setChecked(false);
        mLastCheckedIndex = position;
        notifyDataSetChanged();
    }
    else
    {
        //same but opposite.
    }

Hope this helps!