React Native State Management 问题 - useState hook 何时加载？

Question

我有一个 FlatList 项目，旁边有一个 "remove" 按钮。

当我单击删除按钮时，我可以从后端删除该项目，但实际的列表项目并没有从视图中删除。

我正在使用 useState 挂钩，据我了解组件会在 setState 发生后重新呈现。

The setState function is used to update the state. It accepts a new state value and enqueues a re-render of the component. https://reactjs.org/docs/hooks-reference.html

我在状态设置和渲染方面遗漏了什么？

出于各种原因我不想使用 useEffect 侦听器。我希望组件在位置状态更新时重新呈现....我很确定我的其他 setStates 正在发生这种情况....不确定我是否完全错过了 setState 一直在做什么的标记或者是否这是关于 setLocations() 的特定内容。

    const [locations, setLocations] = useState(state.infoData.locations);
    const [locationsNames, setLocationsNames] = useState(state.infoData.names]);

    ...

    const removeLocationItemFromList = (item) => {
      var newLocationsArray = locations;
      var newLocationNameArray = locationsNames;
      for(l in locations){
        if(locations[l].name == item){
          newLocationsArray.splice(l, 1);
          newLocationNameArray.splice(l, 1);
        } else {
          console.log('false');
        }
      }
      setLocationsNames(newLocationNameArray); 
      setLocations(newLocationsArray);
    };

    ...

    <FlatList style={{borderColor: 'black', fontSize: 16}} 
      data={locationNames} 
      renderItem={({ item }) => 
          <LocationItem
            onRemove={() => removeLocationItemFromList(item)}
            title={item}/> } 
      keyExtractor={item => item}/>

更新循环

const removeLocationItemFromList = (item) => {
  var spliceNewLocationArray =locations;
  var spliceNewLocationNameArray = locationsNames;
  for(f in spliceNewLocationArray){
    if(spliceNewLocationArray[f].name == item){
      spliceNewLocationArray.splice(f, 1);
    } else {
      console.log('false');
    }
  }
  for(f in spliceNewLocationNameArray){
    if(spliceNewLocationNameArray[f] == item){
      spliceNewLocationNameArray.splice(f, 1);
    } else {
      console.log('false');
    }
  }
  var thirdTimesACharmName = spliceNewLocationNameArray;
  var thirdTimesACharmLoc = spliceNewLocationArray;
  console.log('thirdTimesACharmName:: ' + thirdTimesACharmName + ', thirdTimesACharmLoc::: ' + JSON.stringify(thirdTimesACharmLoc)); // I can see from this log that the data is correct
  setLocationsNames(thirdTimesACharmName); 
  setLocations(thirdTimesACharmLoc);
};

Answer 1

这归结为改变相同的 locations 数组并再次使用相同的数组调用 setState，这意味着作为纯组件的 FlatList 不会重新渲染因为 locations 的身份没有改变。您可以先将 locations 数组复制到 newLocationsArray（与 newLocationNameArray 类似）以避免这种情况。

      var newLocationsArray = locations.slice();
      var newLocationNameArray = locationsNames.slice();

React Native State Management 问题 - useState hook 何时加载？

React Native State Management Question - when does useState hook load?

react-native

state

react-hooks

react-state-management

react-state