How can i re-render observable array-data in Mobx? I used observer decorator in this class.

interface IQuiz {
    quizProg: TypeQuizProg;
    qidx: number;
    state: IStateCtx;
    actions: IActionsCtx;
}
@observer
class Comp extends React.Component<IQuiz> {
    private _qtype: common.TypeQuiz = '';
    private _qtime = 60;
    @observable _quizs: common.IQuizData[] = [];

    constructor(props: IQuiz) {
        super(props);
        makeObservable(this);
    };
    public componentWillMount() {
        this._quizs = this.props.actions.getData();
    }
    @action
    public quizSelect(idx: number, v: boolean) {
        this._quizs[idx].selected = true;
        this._quizs.slice();
    }
    public render() {
        const {state, actions, qidx} = this.props;
        let ItemComponent;
        if(this._qtype === 'unscramble') ItemComponent = QuizUnscramble;
        if(this.props.state.prog !== 'quiz') {
            return <QuizList
                state={state}
                quizs={this._quizs}
                quizSelect={(idx: number, v: boolean) => {
                    this.quizSelect(idx, v);
                }}
            />
        } else {
            return (
                <QuizBox
                    view={true}
                    className="t_quiz"
                    quizProg={state.quizProg}
                    qidx={qidx}
                    qtype={this._qtype}
                    qtime={this._qtime}
                    quizs={this._quizs}
                    ItemComponent={ItemComponent}
                    isteacher={false}
                    setQuizProg={actions.setQuizProg}
                />          
            );
        }
    }
}

const Quiz = useTeacher((store: TeacherContext) => (
    <Observer>{() => (
        <Comp 
            quizProg={store.state.quizProg}
            qidx={store.state.qidx}
            state={store.state} 
            actions={store.actions}
        />
    )}</Observer>
));

I use mobx6 and react-typeacript. Comp class dosen't re-rendering when i run quizSelect function. Do not check mobx observable data point of different deeply? @observable.deep is not working too.

How can i fix it?