click method
void
click()
Implementation
void click() {
final bool state = !_open;
// 判断是否禁用
if (widget.disabled) return;
// checked为bool时候表示是受控组件
if (widget.checked == null) {
_open = state;
toggleChecked();
}
// onChange
if (widget.onChange is Function) widget.onChange!(state);
}