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无法读取undefined with promises的属性“then”

async-await promise react-native reactjs javascript

-1

BRDroid · 技术社区 · 6 年前

嗨,我有一个函数,它从共享的首选项中返回一个值,但最初它返回null/undefined是因为承诺或从共享首选项返回的数据,因为它最初没有任何内容。

export function getSharedPreferenceValue( key ) {
    SInfo.getItem(key, {
        sharedPreferencesName: sharedPreferenceName,
                keychainService: keyChainServiceName}).then(value => {
                    consoleLog('getSharedPreferenceValue - ' + key + ' - ' + value) //value 1
                    if( typeof value === 'undefined'){
                        return 'true';
                    }else{
                        return value;                    
                    }                    
                });
}

   whereShoulINavigateTo = async () => {
        const returned = await getSharedPreferenceValue( globals.SHARED_PREFERENCES_KEY_FIRST_LAUNCH).then ((isFirstLaunch) => {
            consoleLog('isFirstLaunch - ' + isFirstLaunch); 
            consoleLog('isFirstLaunch - ' + typeof isFirstLaunch); 
            //do something based on the value
        });
    }

错误是

TypeError: Cannot read property 'then' of undefined TypeError: Cannot read property 'then' of undefined

我在这里哪里做错了

1 回复 | 直到 6 年前

Francisco 6 年前

export function getSharedPreferenceValue(key) {
    dataObj = {
        sharedPreferenceName: sharedPreferenceName,
        keychainService: keyChainServiceName
    };

    return new Promise((res, rej) => {
        SInfo.getItem(key, dataObj).then(value => {
            console.log(`{key} {value}`);
            if (typeof value === 'undefined') {
                res('true');
            } else {
                rej(value)
            }
        });
    });
}

然后相应地修改第二个函数。

whereShoulINavigateTo = async () => {
    getSharedPreferenceValue(globals.SHARED_PREFERENCES_KEY_FIRST_LAUNCH).then((isFirstLaunch) => {
        console.log(`{isFirstLaunch}`);
    }).catch((value) => {
        console.log('Failed');
    });
}

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