如何实现自定义的软键盘

<edit x="c" y="10" w="90%" h="30" focused="true" input_type="custom" text="" />

  <view y="60" x="c" w="90%" h="-60" is_keyboard="true" 
    children_layout="default(r=4,c=4,m=5,s=5)" >
    <button name="key" text="0" />
    <button name="key" text="1" />
    <button name="key" text="2" />
    <button name="key" text="3" />
    <button name="key" text="4" />
    <button name="key" text="5" />
    <button name="key" text="6" />
    <button name="key" text="7" />
    <button name="key" text="8" />
    <button name="key" text="9" />
    <button name="key" text="#" />
    <button name="backspace" text="<=" />
  </view>

static ret_t on_send_key(void* ctx, event_t* e) {
  widget_t* button = WIDGET(e->target);
  char text[2];
  text[0] = (char)button->text.str[0];
  text[1] = '\0';

  input_method_commit_text(input_method(), text);

  return RET_OK;
}

static ret_t on_backspace(void* ctx, event_t* e) {
  input_method_dispatch_key(input_method(), TK_KEY_BACKSPACE);

  return RET_OK;
}