AsyncStorage.getItem returns undefined : React Native

问题

Codeflow is-

I am checking if an entry called listobject exists in the AsyncStorage.

If it doesn't exist, then, I create an object, add few attributes and set the store. I get the store to obj as I have to compare in the next if condition.
If the listobject entry already exists(2nd time), then, it directly comes to the 2nd block, and compares. (The reason I get values to obj in 1st step is because I can have a common obj.data.isdirty condition.

Here is my code-

AsyncStorage.getItem('listobject').then((obj) => {
    if(obj == undefined)
    {
        var obj1 ={};
        obj1.data ={};
        obj1.data.isdirty = true;
        console.log("obj1 = "+ JSON.stringify(obj1));
        AsyncStorage.setItem('listobject',obj1);
        obj = AsyncStorage.getItem('listobject');
        console.log("obj = "+ JSON.stringify(obj));
    }
    if(obj.data.isdirty)
    {
        obj.data.isdirty = false;
        AsyncStorage.setItem('listobject',JSON.stringify(obj));
        return AsyncStorage.getItem('listobject');
    }
}).done();

I have 2 questions which are the outcome of the same issue-

Logs. I am setting obj1 and getting the same value for obj (so that I can compare the next if condition). Why am I not able to get the same value that I have set?

12-03 00:27:56.281 32598-487/com.abc D/ReactNativeJS: 'obj1 = {"data":{"isdirty":true}}'

12-03 00:27:56.286 32598-487/com.abc D/ReactNativeJS: 'obj = {"_37":0,"_12":null,"_59":[]}'

This is the end result of the above logs. I am getting that list.data.isdirty is undefined. I guess that because the JSON format I am accessing does not exist in obj i.e., obj.data.isdirty doesn't exist. So, how do I overcome this?

undefined is not an object (evaluating 'list.data.isdirty');

Please tell me what am I doing wrong?

回答1:

I actually copied the object from one to another. It worked.

AsyncStorage.getItem('listobject').then((obj) => {
    if(obj == undefined)
    {
        var obj1 ={};
        obj1.data ={};
        obj1.data.isdirty = true;
        console.log("obj1 = "+ JSON.stringify(obj1));
        AsyncStorage.setItem('listobject',obj1);
        obj = obj1; //THIS IS WHAT I DID!
        console.log("obj = "+ JSON.stringify(obj));
    }
    if(obj.data.isdirty)
    {
        obj.data.isdirty = false;
        AsyncStorage.setItem('listobject',JSON.stringify(obj));
        return AsyncStorage.getItem('listobject');
    }
}).done();

回答2:

I'm not quite following the entire question I do however see an issue with the use AsyncStorage. Going by the name, Async implies that the operations are asynchronous. So when you do getItem(key), you should either pass in a callback or use the Promise object it returns as you are doing in the first line of code.

obj = AsyncStorage.getItem('listobject'); console.log("obj = "+ JSON.stringify(obj));

obj is going to be the Promise in this case.

Then if you check on obj for the presence of a data and isDirty child property, they will not exist on the Promise.

来源：https://stackoverflow.com/questions/34051216/asyncstorage-getitem-returns-undefined-react-native

标签

reactjs

undefined

react-native