I want to randomly display some of the news from a google rss news feed using the url and the package react-native-url-preview. Im doing a fetch call on it:
const [rssFeed, setRssFeed] = useState([]);
const [shouldFetch, setShouldFetch] = useState(true);
var feed = [];
if (shouldFetch) {
console.log("shouldFetch");
getFeed();
setShouldFetch(false);
}
function getFeed() {
console.log("getFeed: " + shouldFetch);
fetch(
"https://news.google.com/rss/search?q=cars&hl=en-GB&gl=GB&ceid=GB%3Aen"
)
.then((response) => response.text())
.then((responseData) => rssParser.parse(responseData))
.then((rss) => {
console.log(typeof rss.items);
let feedItems = rss.items;
feed = feedItems;
// #ts-ignore
setRssFeed(rss.items);
});
}
if (!shouldFetch) {
console.log(rssFeed);
var randomArr = [];
while (randomArr.length < 4) {
var r = Math.floor(Math.random() * 100);
if (randomArr.indexOf(r) === -1) randomArr.push(r);
// #ts-ignore
console.log(r + " " + rssFeed[r].links[0].url);
}
}
This only works sometimes!
50% of the times I get the error: undefined is not an object (evaluating 'rssFeed[r].links'.
I thought this is beacause of the reloading in react-native and this is why i put the if check. But it has not solved it. Any ideas?
You can use optional chaining like rss?.items.
which means if rss is present check for rss.item.
rssFeed?.[r]?.links
Sometimes you get an Undefined Error because the UI gets rendered before the actual data is present.
Related
I'm trying to get data from API
but. I'm getting this error Error Image.
Here is my code.
const [datas, setDatas] = useState(" ");
const res = async () => {
const response = await axios.get("http://hasanadiguzel.com.tr/api/kurgetir");
setDatas(response.data.TCMB_AnlikKurBilgileri);
};
datas.map((item) => {
return (
<KurCard
title={item.Isim}
alis={item.BanknoteBuying}
satis={item.BanknoteSelling}
/>
);
});
How can I solve this?
I'm trying to map() datas, because I need it
Hi #n00b,
The data that datas is initially being set to an empty string, which does not have a map method. First, you need an empty array instead of an empty stringuseState([]). Now you can map.
const [datas, setDatas] = useState([]);
const res = async () => {
const response = await axios.get('http://hasanadiguzel.com.tr/api/kurgetir');
setDatas(response.data.TCMB_AnlikKurBilgileri);
};
{datas.length > 0 &&
datas.map((item) => {
return <KurCard title={item.Isim} alis={item.BanknoteBuying} satis={item.BanknoteSelling}/>
})
}
make sure you data. it has a length greater than 0 before trying to map over it.
Assuming your API request is valid, you would need to actually return something from the component itself and not just the array:
return datas.map((item) => {return <KurCard title={item.Isim} alis={item.BanknoteBuying} satis={item.BanknoteSelling}/>})
const [Datalist,setDatalist] = useState([]);
useEffect(() => {
axios.get( 'http://0.0.0.0:8000/api/v1/questions/history/1')
.then(response => {
const questions = response.data;
const datalist = [];
for (let i = 0; i < questions.length - 1; i++) {
const data = new Object();
data.isExpanded = false;
data.question_id = questions[i].id;
data.question = questions[i].content;
data.type = questions[i].type;
data.commentType = questions[i].comment_type;
data.answer = [];
datalist.push(data);
}
setDatalist(datalist);
});
},[]);
I have three questions in my database currently. The for loop should be iterating through 0 to 2, however, it is only iterating twice.
And I'm also having problems putting the data into Datalist.
Anybody know where the issue is??
Thanks in advance!!
Change your for loop to this:
for (let i = 0; i < questions.length; i++)
Since you are iterating over each question you receive, you could use the map-method (if your environment supports ES6-Syntax - but since you're using react, it most likely dooes).
From the MDN Docs:
The map() method creates a new array populated with the results of calling a provided function on every element in the calling array.
With map, your code could look like this:
(Also note the removal of const data = new Object();. you can initialize an object and assign its properties/values at the same time)
const [Datalist,setDatalist] = useState([]);
useEffect(() => {
axios.get( 'http://0.0.0.0:8000/api/v1/questions/history/1')
.then(response => {
const questions = response.data;
const datalist = questions.map(question => {
return {
isExpanded: false;
question_id: question.id;
question: question.content;
type: question.type;
commentType: question.comment_type;
answer: [];
};
});
setDatalist(datalist);
});
},[]);
Trying to learn react native here and want to reuse a variable between two "buttons" to perform tasks.
Take for example a simple workflow:
When the user presses Start a random number is generated and a
message is displayed
When the user presses Check I do some checking and display a
message according to the results.
This is my approach:
state = {
statusText: "Press Start to begin",
randNum: 0,
};
generateRandNum = () => {
var rand = Math.floor(Math.random() * 100);
return rand;
};
pressStart = () => {
this.setState({
randNum: this.generateRandNum(),
statusText: "started; " + randNum, //display randnum for simple check-debug
});
};
pressCheck = () => {
this.setState({
statusText: "checked; ",
});
};
Above, when pressStart is pressed, returns an error saying randNum is not found.
This, however, does work, but now can't access the variable elsewhere
pressStart = () => {
this.setState({
statusText: "started; " + this.generateRandNum(), //display randnum for simple check-debug
});
};
How can I properly update randNum to the generated number so that I can access it globally?
==== While the answer below works this is what I ended up using, which seems to work just the same.
pressCheck = () => {
this.setState({
statusText: "checked; " + this.state.randNum,
});
};
You never initialize randNum anywhere, so in order to use it in both places, you should give it a value before the setState.
Try this :
pressStart = () => {
const randNum = this.generateRandNum()
this.setState({
randNum: randNum,
statusText: "started; " + randNum, //display randnum for simple check-debug
});
};
pressCheck = () => {
this.setState(oldState => ({
...oldState,
statusText: "checked; " + oldState.randNum,
}));
};
I am making a call to an API and the response is somehow what I expect. However, I want to count the number of elements returned and I can not do it. This is what I think is important from the code.
Call in Vue component
data(){
return {
messages: {}
}
},
loadMessages(){
axios.get("api/messagesmenu")
.then((data) => { this.messages = data.data})
}
Api controller
public function index(){
$messages = Message::all()->where('read_at', NULL);
if(isset($messages)){
foreach($messages as $message){
$from = User::find($message->from_id);
$message->fromPrenom = $from->first_name;
$message->fromNom = $from->last_name;
$message->fromImage = $from->user_image;
}
}else{
$messages = [];
}
return $messages;
}
Type of response from the API
{"3":{"id":560,"from_id":2,"to_id":1,"content":"tgr","created_at":"2019-07-15 16:59:03","read_at":null,"fromPrenom":"abdel1","fromNom":"Hidalgo","fromImage":"user2-160x160.png"}}
I want to count the number of objects I obtain. if (in vue component) I do
this.messages.length
it returns undefined
Try this:
const messages = {"3":{"id":560,"from_id":2,"to_id":1,"content":"tgr","created_at":"2019-07-15 16:59:03","read_at":null,"fromPrenom":"abdel1","fromNom":"Hidalgo","fromImage":"user2-160x160.png"}}
console.log(Object.keys(messages).length) // 1
Or in your code:
...
.then((data) => {
this.messages = data.data
console.log(Object.keys(this.messages).length)
})
I'm trying to get information (true/false) from AsyncStorage in a function and create a string which is importent to fetch data in the next step. My problem is, the function is not finished until the string is required.
I tried many solutions from the internet like async function and await getItem or .done() or .then(), but none worked out for me.
//_getFetchData()
AsyncStorage.getAllKeys().then((result) => { //get all stored Keys
valuelength = result.length;
if (valuelength !== 0) {
for (let i = 0; i < valuelength; i++) {
if (result[i].includes("not") == false) { //get Keys without not
AsyncStorage.getItem(result[i]).then((resultvalue) => {
if (resultvalue === 'true') {
if (this.state.firstValue) {
this.state.channels = this.state.channels + "channel_id" + result[i];
console.log("channel: " + this.state.channels);
}
else {
this.state.channels = this.state.channels + "channel" + result[i];
}
}
});
}
return this.state.channels;
_fetchData() {
var channel = this._getFetchData();
console.log("channel required: " + channel);
}
The current behaviour is that the console displays first "channel required: " than "channel: channel_id0".
Aspects in your question are unclear:
You don't say when this.state.firstValue is set, and how that relates to what you are trying to accomplish.
You have a for-loop where you could be setting the same value multiple times.
You mutate the state rather than set it. This is not good, see this SO question for more on that.
There are somethings we can do to make your code easier to understand. Below I will show a possible refactor. Explaining what I am doing at each step. I am using async/await because it can lead to much tidier and easier to read code, rather than using promises where you can get lost in callbacks.
Get all the keys from AsyncStorage
Make sure that there is a value for all the keys.
Filter the keys so that we only include the ones that do not contain the string 'not'.
Use a Promise.all, this part is important as it basically gets all the values for each of the keys that we just found and puts them into an array called items
Each object in the items array has a key and a value property.
We then filter the items so that only the ones with a item.value === 'true' remain.
We then filter the items so that only the ones with a item.value !== 'true' remain. (this may be optional it is really dependent on what you want to do)
What do we return? You need to add that part.
Here is the refactor:
_getFetchData = async () => {
let allKeys = await AsyncStorage.getAllKeys(); // 1
if (allKeys.length) { // 2
let filteredKeys = allKeys.filter(key => !key.includes('not')); // 3
let items = await Promise.all(filteredKeys.map(async key => { // 4
let value = await AsyncStorage.getItem(key);
return { key, value }; // 5
}))
let filteredTrueItems = items.filter(item => items.value === 'true'); // 6
let filteredFalseItems = items.filter(item => items.value !== 'true'); // 7
// now you have two arrays one with the items that have the true values
// and one with the items that have the false values
// at this points you can decide what to return as it is not
// that clear from your question
// return the value that your want // 8
} else {
// return your default value if there are no keys // 8
}
}
You would call this function as follows:
_fetchData = async () => {
let channel = await this._getFetchData();
console.log("channel required: " + channel);
}
Although the above will work, it will not currently return a value as you haven't made it clear which value you wish to return. I would suggest you build upon the code that I have written here and update it so that it returns the values that you want.
Further reading
For further reading I would suggest these awesome articles by Michael Chan that discuss state
https://medium.learnreact.com/setstate-is-asynchronous-52ead919a3f0
https://medium.learnreact.com/setstate-takes-a-callback-1f71ad5d2296
https://medium.learnreact.com/setstate-takes-a-function-56eb940f84b6
I would also suggest taking some time to read up about async/await and promises
https://medium.com/#bluepnume/learn-about-promises-before-you-start-using-async-await-eb148164a9c8
And finally this article and SO question on Promise.all are quite good
https://www.taniarascia.com/promise-all-with-async-await/
Using async/await with a forEach loop
Try this instead. Async functions and Promises can be tricky to get right and can be difficult to debug but you're on the right track.
async _getFetchData() {
let channels = "";
let results = await AsyncStorage.getAllKeys();
results.forEach((result) => {
if (result.includes("not") === false) {
let item = await AsyncStorage.getItem(result);
if (item === 'true') {
console.log(`channel: ${result}`)
channels = `channel_id ${result}`;
}
}
});
return channels;
}
_fetchData() {
this._getFetchData().then((channels) => {
console.log(`channel required: ${channel}`);
});
}
what if you wrap the _getFetchData() in a Promise? This would enable you to use
var channel = this._getFetchData().then(console.log("channel required: " + channel));
Otherwise the console.log won't wait for the execution of the _getFetchData().
This is what the console.log is telling you. it just logs the string. the variable is added after the async operation is done.
UPDATE
I would try this:
//_getFetchData()
AsyncStorage.getAllKeys().then((result) => { //get all stored Keys
valuelength = result.length;
if (valuelength !== 0) {
for (let i = 0; i < valuelength; i++) {
if (result[i].includes("not") == false) { //get Keys without not
AsyncStorage.getItem(result[i]).then((resultvalue) => {
if (resultvalue === 'true') {
if (this.state.firstValue) {
this.state.channels = this.state.channels + "channel_id" + result[i];
console.log("channel: " + this.state.channels);
}
else {
this.state.channels = this.state.channels + "channel" + result[i];
}
}
});
}
return new Promise((resolve, reject) => {
this.state.channels !=== undefined ? resolve(this.state.channels) : reject(Error('error '));
}
_fetchData() {
var channel = this._getFetchData().then(console.log("channel required: " + channel));
}
maybe you must change the this.state.channels !=== undefined to an expression that's matches the default value of this.state.channels.