CODEWITHSUNDEEP
javascriptreact-native
kapkong
kapkong

Reputation: 117

Promise Calls in React Native

New to React Native, and Javascript in general. Currently, I am trying to enact a Promise to handle an undefined error while using the react-native-sqlite-storage package.

I was following this previous post here, but have not succeeded in implementing the Promise properly from what I can tell.

Here my current function:

nextPackage (q_id: number) {
    return new Promise((resolve, reject) =>
        db.transaction(tx => { 
            tx.executeSql(
                'SELECT * FROM Questions INNER JOIN Choices on Choices.q_id = Questions.global_id WHERE Questions.global_id = ?', [q_id], (tx, results) => {
                    for (let i = 0; i < results.rows.length; i++) {
                        console.log('item:', i);
                        console.log('row:', results.rows.item(i));
                        this.pack.push(results.rows.item(i));
                    }
                    resolve(this.pack);
                }, function (tx, error) {
                    reject(error);
            });
        })
    )
}

And the Screen that calls it:

this.pack = this.wrapper.nextPackage(this.session.data_next.qID)
        .then(data => { 
            console.log("Retrieved data: ", data);
        })
        .catch(error => {
            console.error(error);
        })

    this.pkHelp = new PackageHelper(this.pack);

However, when I then try to access this.pack[0] I receive an undefined is not an object (evaluating 'this.pack[0].choiceType'). console.log() has shown that the database rows are indeed being read in, and that choiceType is indeed the proper column name.

Thanks in advance for any assistance!

Upvotes: 2

Views: 3781

Answers (1)

invisal
invisal

Reputation: 11171

You can't assign the value to your pack like this. The returned value is in the then part. You can do something like this

this.wrapper.nextPackage(this.session.data_next.qID).then(data => {
   this.pkHelp = new PackageHelper(this.pack);
}).catch(error => {
   console.error(error);
});

Or you can use await. But you have to use it in the async function

try {
   this.pkHelp = await this.wrapper.nextPackage(this.session.data_next.qID);
   this.pkHelp = new PackageHelper(this.pack);
} catch(error) {
   console.error(error);
}

Upvotes: 2

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