使用 if 语句反应组件未在 .map 内呈现 [英] React component not rendering inside .map with if statement

问题描述

请帮忙.如果 list.display = true，我有一个要加载的组件.我可以做一个控制台日志来确认何时应该显示列表并且它工作正常.但是，组件不会加载.如果我将组件从 .map 循环中取出，它会完美运行.

Please help. I have a component that I am trying to load if list.display = true. I am able to do a console log confirming when the list should be displayed and it works properly. However, the component does not load. If I take the component out of the .map loop it works perfectly.

谢谢

return (
        <div className="container"> 
            <h1>To Do App</h1>
            <p>Create a list:</p>
            <form>
                <label htmlFor="list">
                    <input type="text" name="list" id="list" onChange={e => setInputListName(e.target.value)}/>
                    <button onClick={addList}>Create List</button>
                </label>
            </form>

            <div className="listsContainer">
                {
                    lists.map( (list: listInterface, index:number) => 
                        (<button onClick={() => loadList(index)}>{list.listName}</button>)
                    )
                }
                {
                    lists.map( (list: listInterface, index:number) => {
                        if (list.display == true) {
                            <ToDoApp list={lists[0]} /> 
                            console.log("List " + list.listName + " ordered");
                        }
                    })
                }
            </div>
        </div>
    );

推荐答案

我认为你完全错过了 javascript 的 array::map 函数的目的，它应该为每个元素返回一个值 它被调用.它返回一个与迭代的数组长度相同的数组.你实际上是在过滤你的结果.

I think you completely miss the purpose of javascript's array::map function, it should return a value for every element it is called on. It returns an array that is the same length as the array it iterated over. You are actually filtering your results a bit.

Filter/Map - 过滤数组结果然后映射到响应 JSX

Filter/Map - Filter array results then map to react JSX

{
  lists
    .filter((list: listInterface) => list.display) // exploit truthy/falsey display value
    .map((list: listInterface) => (
    <ToDoApp list={lists[0]} />
  ))
}

Reduce - 允许将结果直接过滤"到 React JSX 中

Reduce - Allows to "filter" results directly into react JSX

{
  lists.reduce((filteredLists: listsInterface, list: listInterface) => {
    if (list.display) {
      filteredLists.push(<ToDoApp list={lists[0]} />);
    }
    return filteredLists
  }, [])
}

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