EditText的返回键监听，删除字符

如下：只需给需要监听返回按键的EditText控件添加该监听即可
editText.setOnKeyListener(new EditKeyListener());

class EditKeyListener implements View.OnKeyListener {
        @Override
        public boolean onKey(View view, int keyCode, KeyEvent event) {
            EditText editText = (EditText) view;
            int index = editText.getSelectionStart();
            Editable editable = editText.getText();
            String editableString = editable.toString();
            if (event.getAction() == KeyEvent.ACTION_DOWN) {
                if (keyCode == KeyEvent.KEYCODE_BACK) {
                    if (editableString.equals("") || index == 0) {
                        Toast.makeText(mContext, R.string.exit_setting, Toast.LENGTH_SHORT).show();
                        return true;
                    } else {
                        editable.delete(index - 1, index);
                        return true;
                    }
                }
            }
            return false;
        }
    }