react-native – 为什么AsyncStorage getItem返回null？

export const USER_KEY = "isLoggedIn";

export const phoneVerified = () => AsyncStorage.setItem(USER_KEY,1);
export const userInfoVerified = () => AsyncStorage.setItem(USER_KEY,2);

我已经使用上面的函数来存储值,而使用下面的函数来获取值.

export const isSignedIn = () => {
  return new Promise((resolve,reject) => {
    AsyncStorage.getItem(USER_KEY)
      .then(res => {
          console.log("from isSignedIn : "+res); //res is showing null.
        if (res !== null) {
          resolve(res);
        } else {
          resolve(0);
        }
      })
      .catch(err => reject(err));
  });
};

为什么这总是返回null？我正在尝试async / await但仍然是null.我想某种方式数据不存储.