failed to subscribe to PubSub.subscribe for the first time, click back and click publish again, but the subscription was successful twice, and then it was normal after the third time.
but there is no problem with using Subject and Result instead of switch in app.jsx. A lot of advice. Thank you!

app.jsx
    <Switch>
        <Route path="/subject" component={Subject}/>
        <Route path="/result/" component={Result}/>
        <Redirect to="/subject"/>
    </Switch>
subject.jsx    
    handerSubmit = ()=>{
        PubSub.publish("out",outcome);
        this.props.history.push("/result")

    }
result.jsx        
    componentDidMount(){
        let subscr;
        new Promise((resolve,reject)=>{
            subscr = PubSub.subscribe("out",(msg,outcome)=>{
                console.log(1)
                //alert(outcome);
                arr  = [
                    outcome[4]+outcome[9]+outcome[13]+outcome[17]+outcome[23]+outcome[29],
                    outcome[2]+outcome[5]+outcome[12]+outcome[19]+outcome[21]+outcome[28],
                    outcome[1]+outcome[7]+outcome[14]+outcome[16]+outcome[24]+outcome[27],
                    outcome[0]+outcome[6]+outcome[10]+outcome[15]+outcome[20]+outcome[25],
                    outcome[3]+outcome[8]+outcome[11]+outcome[18]+outcome[22]+outcome[26]
                ];
                resolve(arr)
            })
        }).then(
            (result)=> {
                this.showCanvas(result)
            },

        );

    }
    componentWillUnmount(){
        PubSub.unsubscribe(this.subscr);
    }

problem description

the environmental background of the problems and what methods you have tried

related codes

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what result do you expect? What is the error message actually seen?