Question

我正在尝试使用react native设置redux，但是商店更新时它并没有更新我的组件。

class Dinner extends React.Component {

    componentDidUpdate() {
        console.log('does not get called when store update');
    }

    setSelected = (meal) => {
        var index = this.props.selectedDinner.indexOf(meal);

        if (index === -1) {
            console.log('Adding meal to selected: '+meal.name);
            if (this.props.selectedDinner[0] === null) {
                var tempArr = this.props.selectedDinner;
                tempArr[0] = meal;
                this.props.setSelectedDinner(tempArr);

            } else if(this.props.selectedDinner[1] === null)  {
                var tempArr = this.props.selectedDinner;
                tempArr[1] = meal;
                this.props.setSelectedDinner(tempArr);
            } else if(this.props.selectedDinner[2] === null)  {
                var tempArr = this.props.selectedDinner;
                tempArr[2] = meal;
                this.props.setSelectedDinner(tempArr);
            }
        } else {
            console.log("removing meal from selected: "+meal.name)
            var tempArr = this.props.selectedDinner;
            tempArr[index] = null;
            this.props.setSelectedDinner(tempArr);
        }
        LayoutAnimation.configureNext(LayoutAnimation.Presets.easeInEaseOut);
        this.forceUpdate()
    };

    render() {
        return (
          <View style={{flex: 1, width: 360, justifyContent: 'center', alignItems: 'center', paddingBottom: 20}}>
            <View style={{width: 340, backgroundColor: 'white', justifyContent: 'flex-start', alignItems: 'center'}}>
              <Text style={{height: 50, fontSize: 20, fontWeight: 'bold', flex: 1, justifyContent: 'center', alignItems: 'center'}}>Dinner</Text>
              {
                this.props.dinnerFeed.map((prop, key) => 
                  prop === null ?
                    <TouchableOpacity style={{width: 320, height: 120, backgroundColor: 'lightgrey', flex: 1, justifyContent: 'center', alignItems: 'center', zIndex: 1, marginBottom: 10, flexShrink: 0}} key={key}><LoadingMealTile /></TouchableOpacity>
                    :
                    (prop === 'none' ? 
                      <TouchableOpacity style={{width: 320, height: 120, backgroundColor: 'lightgrey', flex: 1, justifyContent: 'center', alignItems: 'center', zIndex: 1, marginBottom: 10, flexShrink: 0}} key={key}><BlankMealTile /></TouchableOpacity>
                      :
                      this.props.selectedDinner === null || this.props.selectedDinner.indexOf(prop) === null ?
                        <TouchableOpacity onPress={this.setSelected.bind(this, prop)} style={{width: 320, height: 120, backgroundColor: 'lightgrey', flex: 1, justifyContent: 'center', alignItems: 'center', zIndex: 1, marginBottom: 10, flexShrink: 0}} key={key}><MealTile selected={-1} name={prop.name} id={prop.id} url={prop.url} key={key}/></TouchableOpacity>
                        :
                        <TouchableOpacity onPress={this.setSelected.bind(this, prop)} style={{width: 320, height: 120, backgroundColor: 'lightgrey', flex: 1, justifyContent: 'center', alignItems: 'center', zIndex: 1, marginBottom: 10, flexShrink: 0}} key={key}><MealTile selected={this.props.selectedDinner.indexOf(prop)} name={prop.name} id={prop.id} url={prop.url} key={key}/></TouchableOpacity>
                    )
                )  
              }

              <TouchableOpacity onPress={this.props.loadFeedMeals} style={{width: 320, height: 50, backgroundColor: 'lightgrey', flex: 1, justifyContent: 'center', alignItems: 'center', zIndex: 1, marginBottom: 10}}><Text style={{fontSize: 15, }}>Load More Meals</Text></TouchableOpacity>
            </View>
          </View>
        );
      }
    }


    function mapStateToProps(state) { 
      return {
           dinnerFeed: state.dinnerFeed,
           selectedDinner: state.selectedDinner,
      }
    };

    function mapDispatchToProps(dispatch) {
      return {
        setDinnerMeals: (dinnerMeals) => dispatch(setDinnerMeals(dinnerMeals)),
        setSelectedDinner: (selectedDinner) => dispatch(setSelectedDinner(selectedDinner)),

      }
    };

    export default connect(mapStateToProps, mapDispatchToProps)(Dinner);

函数setSelectedDinner可以正确更改redux存储，但是组件未调用其componentDidUpdate函数

编辑：这是减速器代码


    export default (state, action) => {
        console.log(action);
        switch (action.type) {
            case "SET-SELECTED-DINNER":
                return {
                        ...state,
                        selectedDinner: action.selectedDinner
                  };
            default:
                return state;
        }
    };

我相信这段代码不应该直接改变状态，因为我已经在reactjs项目上使用了reduce来实现redux

Answer 1

Redux状态被更新但连接的组件未更新的最常见原因是减速器内的突变状态。一个非常相似的常见问题是没有意识到Redux connect HoC进行的浅表比较。

这是因为Redux通过使用对象相等性检查更改。（如果===比较返回true，则认为该对象未更改。）

考虑以下不正确 reducer：

function todoApp(state = initialState, action) {
  switch (action.type) {
    case SET_VISIBILITY_FILTER:
      return state.visibilityFilter = action.filter;
    default:
      return state
  }
}

由于上述reducer改变了状态，因此不会触发任何更新。

正确的示例（取自Redux documentation）如下所示：

function todoApp(state = initialState, action) {
  switch (action.type) {
    case SET_VISIBILITY_FILTER:
      return Object.assign({}, state, {
        visibilityFilter: action.filter
      })
    default:
      return state
  }
}

浅比较

除了上述不改变状态而是始终为发生变化的内容始终返回新状态的最佳实践一样，重要的是要记住Redux connect对mapStateToProps返回的所有对象都使用了这种浅表比较。 / p>

请考虑简化您的mapStateToProps函数的版本：

function mapStateToProps(state) { 
    return {
        selectedDinner: state.selectedDinner,
    }
};

现在考虑您如何将选择的晚餐传递给setSelectedDinner操作（再次简化）：

setSelected = (meal) => {
    var index = this.props.selectedDinner.indexOf(meal);

    // when index === -1 we need to add this meal
    if (index === -1) {     
        // there is no meal at index 0 so we add it                    
        if (this.props.selectedDinner[0] === null) {
            // NOTICE - the line below still references selected dinner in state!
            var tempArr = this.props.selectedDinner;
            tempArr[0] = meal;

            // NOTICE - we are calling setSelectedDinner with the same object
            // that comes from state! 
            this.props.setSelectedDinner(tempArr);
        }
    }
}

问题是，在化简函数中，您很容易用自身替换selectedDinner对象，因此Redux看不到任何更新。

解决您问题的最快方法是修改reducer函数以使其读取（切片调用会克隆您的数组）：

export default (state, action) => {
    switch (action.type) {
        case "SET-SELECTED-DINNER":
            return {
                    ...state,
                    selectedDinner: action.selectedDinner.slice()
              };
        default:
            return state;
    }
};

还有许多其他小的更改，这些更改将使此代码更易于使用，并且不易出现此类错误。两个简单的是：

将修改您的selectedDinner数组的逻辑移出组件，然后将其放置在reducer中。
介绍选择器

Answer 2

我认为您在更新Redux中的默认状态时应该尝试传递当前时间戳。这会改变当前状态，并且您在课堂上的回答也会改变。

反应本机redux不更新组件

2 个答案:

浅比较