question: private void initKeyboardButtons ( KeyboardView view ) { mButtons = new ArrayList < > ( ) ; mButtons . add ( ( KeyboardButtonView ) view . findViewById ( R . id . pin_code_button_0 ) ) ; mButtons . add ( ( KeyboardButtonView ) view . findViewById ( R . id . pin_code_button_1 ) ) ; mButtons . add ( ( KeyboardButtonView ) view . findViewById ( R . id . pin_code_button_2 ) ) ; mButtons . add ( ( KeyboardButtonView ) view . findViewById ( R . id . pin_code_button_3 ) ) ; mButtons . add ( ( KeyboardButtonView ) view . findViewById ( R . id . pin_code_button_4 ) ) ; mButtons . add ( ( KeyboardButtonView ) view . findViewById ( R . id . pin_code_button_5 ) ) ; mButtons . add ( ( KeyboardButtonView ) view . findViewById ( R . id . pin_code_button_6 ) ) ; mButtons . add ( ( KeyboardButtonView ) view . findViewById ( R . id . pin_code_button_7 ) ) ; mButtons . add ( ( KeyboardButtonView ) view . findViewById ( R . id . pin_code_button_8 ) ) ; mButtons . add ( ( KeyboardButtonView ) view . findViewById ( R . id . pin_code_button_9 ) ) ; mButtons . add ( ( KeyboardButtonView ) view . findViewById ( R . id . pin_code_button_clear ) ) ; for ( View button : mButtons ) { button . setOnClickListener ( this ) ; } }
target:  Init the keyboard buttons (onClickListener)