Question

我每次运行时都会收到两次此错误。我进行了搜索并尝试在清理函数中取消 onAuthStateChanged() 到 useEffect() 的订阅，但仍然出现相同的错误。此外，uploadAndCreate() 函数运行良好，但 createPlan() 甚至在 createPlan() 完成之前就被调用，因此我得到了 undefined 的 fileUrl。

import React, { useState, useEffect } from "react";
import {
    Image,
    StyleSheet,
    Text,
    TextInput,
    TouchableOpacity,
    View,
} from "react-native";
import firebase from "firebase/app";
import "firebase/auth";
import "firebase/storage";
import { Link, Redirect } from "react-router-native";
import { getDocumentAsync } from "expo-document-picker";
import plus from "../../assets/plus.png";
import cross from "../../assets/cross.png";

const NewPlan = (props) => {
    const [planName, setPlanName] = useState();
    const [categoryName, setCategoryName] = useState();
    const [isPlanCreated, setIsPlanCreated] = useState(false);
    const [currUserId, setCurrUserId] = useState();
    const [uploadProgress, setUploadProgress] = useState(0);
    const [blob, setBlob] = useState({});
    const [isPlanNameValid, setIsPlanNameValid] = useState(true);
    const [ref, setRef] = useState();
    const [fileUrl, setFileUrl] = useState();

    useEffect(() => {
        let mounted = true;

        if (mounted) {
            firebase.auth().onAuthStateChanged((user) => {
                if (user) {
                    setCurrUserId(user.uid);
                }
            });
        }

        return () => {
            mounted = false;
        };
    }, []);

    const validate = () => {
        if (planName) {
            setIsPlanNameValid(true);
            uploadAndCreate();
        } else {
            setIsPlanNameValid(false);
        }
    };

    const uploadAndCreate = async () => {
        if (Object.keys(blob).length !== 0) {
            let task = ref.put(blob);

            await task.on(
                "state_changed",
                (snapshot) => {
                    let progress =
                        (snapshot.bytesTransferred / snapshot.totalBytes) * 100;

                    if (firebase.storage.TaskState.RUNNING)
                        setUploadProgress(progress);
                },
                (error) => {
                    console.log("Error uploading file: " + error);
                },
                () => {
                    task.snapshot.ref.getDownloadURL().then((downloadURL) => {
                        setFileUrl(downloadURL);
                    });
                }
            );
        }

        createPlan();
        setIsPlanCreated(true);
    };

    const createPlan = () => {
        let plansRef = firebase.database().ref().child("plans");
        let newPlanRef = plansRef.push();

        newPlanRef.set({
            plan_id: newPlanRef.key,
            plan_name: planName,
            created_by: currUserId,
            project_id: props.match.params.id,
            status: "active",
            category: categoryName || "uncategorized",
            file_url: fileUrl || "",
        });
    };

    const handlePlanName = (_planName) => setPlanName(_planName);

    return isPlanCreated ? (
        <Redirect to={"/project/" + props.match.params.id} />
    ) : (
        <View style={styles.container}>
            <Link
                to={"/project/" + props.match.params.id}
                style={styles.crossContainer}
            >
                <Image source={cross} style={styles.cross} />
            </Link>
            <View style={styles.topArea}>
                <Image source={plus} style={styles.plus} />
                <Text style={styles.title}>New Plan</Text>
                {!isPlanNameValid ? (
                    <Text style={styles.errorText}>
                        Please enter a valid name.
                    </Text>
                ) : null}
                <TextInput
                    placeholder="Plan Name"
                    style={styles.input}
                    placeholderTextColor="#fff"
                    onChangeText={handlePlanName}
                />
                {uploadProgress > 0 && uploadProgress < 100 ? (
                    <Text>Upload Progress: {uploadProgress.toFixed(0)}%</Text>
                ) : null}
                {uploadProgress === 100 ? <Text>Upload Complete</Text> : null}
                <TouchableOpacity
                    style={styles.button}
                    onPress={() => {
                        getDocumentAsync().then(async (response) => {
                            try {
                                let storageRef = firebase.storage().ref();
                                setRef(
                                    storageRef.child(
                                        response.uri.split("/")[14]
                                    )
                                );

                                let fetchResponse = await fetch(response.uri);
                                let blob = await fetchResponse.blob();

                                setBlob(blob);
                            } catch (error) {
                                console.log(error.message);
                            }
                        });
                    }}
                >
                    <Text style={styles.buttonText}>Upload Plan</Text>
                </TouchableOpacity>
            </View>
            <TouchableOpacity
                style={styles.bottomArea}
                onPress={() => {
                    validate();
                }}
            >
                <Text style={styles.createText}>Create</Text>
            </TouchableOpacity>
        </View>
    );
};

const styles = StyleSheet.create({
    // -- STYLES --
});

export default NewPlan;

Answer 1

您的 mounted 变量没有任何作用。它唯一检查的地方是 useEffect 的开头，这里肯定是 true。

虽然您可以在 onAuthStateChanged 回调中检查它：

        firebase.auth().onAuthStateChanged((user) => {
            if (mounted && user) {
                setCurrUserId(user.uid);
            }
        });

最好使用 firebase 返回的取消订阅功能：

useEffect(() => firebase.auth().onAuthStateChanged((user) => {
    if (user) {
        setCurrUserId(user.uid);
    }
}), []);

或者，脱糖：

useEffect(() => {
    const unsubscribe = firebase.auth().onAuthStateChanged((user) => {
        if (user) {
            setCurrUserId(user.uid);
        }
    });
    return unsubscribe;
}, []);

看起来您有多个异步操作可能会在组件卸载时进行，而这些操作实际上并不容易取消。您可以添加一个 ref 来指示组件当前是否已安装，并在调用任何 setter 函数之前进行检查：

const mountedRef = useRef(true);
useEffect(() => {
    const unsubscribe = firebase.auth().onAuthStateChanged((user) => {
        if (user) {
            setCurrUserId(user.uid);
        }
    });
    return () => {
        mountedRef.current = false;
        unsubscribe();
    }
}, []);

然后，例如，代替

setBlob(blob);

做

if (mountedRef.current) {
    setBlob(blob);
};

并在可能异步运行的 setter 的任何地方遵循相同的模式。

Answer 2

我猜您想使用 onAuthStateChanged 函数的检查返回值。

useEffect(() => {

  const unsubscribe = firebase.auth().onAuthStateChanged((user) => {
    if (user) {
      setCurrUserId(user.uid);
    }
  });

  return unsubscribe;
}, []);

检查来自CertainPerformance的其他答案

收到警告：无法对卸载的组件执行 React 状态更新

2 个答案: