反应原生 redux 不更新组件

Question

我正在尝试使用 react native 设置 redux，但它不会在商店更新时更新我的​​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);

setSelectedDinner 函数正确更改了 redux 存储，但组件没有调用其 componentDidUpdate 函数

edit:这里是reducer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，因为我在 reactjs 项目中使用了这个 reducer 来进行 redux

Answer 1

Redux 状态被更新但连接的组件没有更新的最常见原因是 reducer 中的状态变化。一个非常相似的常见问题是没有认识到 Redux connect HoC 执行的是浅层比较。

这是因为 Redux 通过使用对象相等来检查更改。 （如果 === 比较返回 true，则认为对象没有改变。）

考虑以下不正确的减速器：

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

由于上面的reducer改变了状态，所以没有触发更新。

一个正确的例子（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但总是为任何变化返回一个新状态的最佳实践之外，重要的是要记住 Redux connect 对mapStateToProps 返回的所有对象使用这种浅层比较。

考虑您的mapStateToProps 函数的简化版本：

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

现在考虑如何将选定的晚餐传递给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);
        }
    }
}

所以问题是，在你的 reducer 函数中，你只是简单地将 selectedDinner 对象替换为自身，因此 Redux 看不到任何更新。

将解决您的问题的最快更改是修改 reducer 函数以读取（切片调用克隆您的数组）：

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可以使此代码更易于使用且不易出现此类错误。两个简单的是：

1. 将修改 selectedDinner 数组的逻辑移出组件，并将其放在 reducer 中。

2. 介绍选择器

Answer 2

我认为当您在 redux 中更新默认状态时，您应该尝试传递当前时间戳。这将使当前状态发生一些变化，并且您在课堂上的反应也会发生变化。