小编Sho*_*har的帖子

我设置了一个自定义挂钩，它获取一个ref对象并观察它：

import { useState, useEffect, MutableRefObject } from "react";

const UseOnScreen = (ref: MutableRefObject<undefined>) => {
  const [isIntersecting, setIntersecting] = useState(false);
  useEffect(() => {
    const observer = new IntersectionObserver(([entry]) =>
      setIntersecting(entry.isIntersecting)
    );
    if (ref.current) {
      observer.observe(ref.current);
    }
  });
  return isIntersecting;
};
export default UseOnScreen;

接下来，在我的页面组件中，我声明了一个refusing useRef()：

import { useRef } from "react";
import UseOnScreen from "../hooks/UseOnScreen";
import About from "./about";

export default function Home() {
  const aboutRef = useRef();
  const aboutRefValue = UseOnScreen(aboutRef);

  return ( …

我正在尝试从 API 解析数据。为此，我使用 FutureBuilder 在 ListView 中列出所有解析的数据。

我已经执行了无效检查，snapshot.data但我继续在段中收到此错误snapshot.data.length，它说，The property 'length' can't be unconditionally accessed because the receiver can be 'null'. Try making the access conditional (using '?.') or adding a null check to the target ('!').

我在本节中也有类似的错误snapshot.data[i]，其中写着The method '[]' can't be unconditionally invoked because the receiver can be 'null'. Try making the call conditional (using '?.') or adding a null check to the target ('!').

这是我的代码部分：

 body: Container(
        child: FutureBuilder(
          future: getData('hello'), …