I am trying to create a button that changes the text when clicked and it saves a value to an array. I then need to save the state of the button and the array to the device using AsyncStorage.
I have the first part done (please see Snack link here) but I am struggling to get the AsyncStorage to work properly. If the button had been clicked once, I would expect that the array has the "item 1" value in it and the button would say clicked. Even if the app is closed and reopened, those values should still remain until the button is clicked again.
I have not found any solutions so far. Is there anyone that has some ideas?
This is the workflow that you should follow:
create an object in state (in this.state = {} for classes, or setState() with hooks) for your button's text value
initialize the above value with the value from AsyncStorage (make sure to add some conditional that if it's empty it returns [])
also take note of how Asyncstorage is async, meaning you'll have to add 'await' when you're assigning the value
add some conditional for the text value of your button, whereas it will show a loading icon, (or nothing, doesn't matter) while AsyncStorage is retrieving the initial data
onPress on your button will change the state value AND the AsyncStorage value (or you can only update the AsyncStorage value when you're closing the page with componentWillUnMount, or useEffect(() => return(--do it here--))
If you're using functional components, it would look something like this:
const [textValues, setTextValues] = useState([])
const setInitialValues = async () => {
const info = await AsyncStorage.getItem('myValues')
setTextValues(info)
}
useEffect(() => {
setInitialValues()
return(
AsyncStorage.setItem('myValues', textValues)
)
}, [])
return(
<View>
<Button onPress={() => setTextValues(textValues + 1) title={textValues.length === 0 ? '' : textValues[textValues.length - 1]}}
</View>
)
Related
I am rendering a component for every item in a flatList. Each component has a label, and when the component is rendered, I have a useEffect that fetches the updated label name for that specific label.
For some reason, it seems to only be running for the last item in the flatList. The last item is the only item with the updated name, while all other still contain the outdated information.
Assuming there is an updated name for each label, why could my useEffect only be running on the last item?
<FlatList
data={labels}
keyExtractor={keyExtractor}
renderItem={renderItem}
/>
Label.js - I would think this would run for every label component rendered. Could there be a possible issue with what I have here? Or must it be somewhere else in my code?
let name = label.name;
useEffect(() => {
updateLabel()
name = label.name
}, [label]);
return (
<>
{name}
</>
)
I see several possible issues. Some important code is missing, so I'll answer what I can.
You're not using state to hold your label name in the Label component (name = label.name), so React will never know to re-render the component when it changes. It's rare to need to use a let variable in React. To hold properties that the component needs to change, use the useState hook.
However, you shouldn't do that here, because of the next point.
It looks like you are updating the label somewhere else, and also locally (name = label.name). Don't do this, it's too easy for the two to get out of sync and cause bugs. If the name is coming from somewhere else, show it and set it from props.
I'm not sure what updateLabel() does or where it comes from (how does the function know what to update the label to?), but if you need it, it should come from props.
If label.name is a string, you can't render it in a fragment. You must render it in a Text component. <Text>{label.name}</Text>
The object that FlatList passes in to the renderItem callback does not have a property called label, you are looking for item - this is the object from the data prop.
function renderLabel({ item }) { // item, not label
return <Label label={item} onPress={() => onPressLead(item)}/>;
}
const Label = ({ label, updateLabel }) => {
// no local label variable
useEffect(() => {
updateLabel(); // what is this supposed to do?
}, []); // no dependencies, if you only want to update the label once on mount
return <Text>{label.name}</Text>; // if label.name is a string
};
// your FlatList is fine as written
Your use effect probably needs the label as a dependency.
useEffect(() => {
updateLabelName()
}, [label]);
If I change text of TextInput then I change useState named name and setName.
const [name, setName] = useState("")
<TextInput
defaultValue={meData?.me?.name}
onChangeText={(text) => setNameValue(text)}
/>
And I want to change disableConfirm state from true to first, if I change just one word in this TextInput with useEffect.
const [disableConfirm, setDisableConfirm] = useState(true);
useEffect(() => {
setDisableConfirm(false)
}, [nameValue]);
The problem is when screen is first rendered, this useEffect is executed.
So disableConfirm state becomes false even though I don't change any word in TextInput.
How to prevent first rendering here? how to detect only change of TextInput?
Another way to achieve this would be using the TextInput as a controlled component.
First, create a state with a default value.
Look for changes in that state variable, if it changes from what it was originally, then enable the submit button.
Snack Implementation for the same is here
Approach:
Declare a state variable with a default value
const [name, setName] = React.useState(SOME_DEFAULT_VALUE);
Now for the TextInput, what you can do is
<TextInput placeholder="Enter Name" onChangeText={setName} value={name} />
What this does is, it updates the field with the name variable every time you type something in it.
Now, to look for the changes, what you can do is,
useEffect(() => {
if (name !== SOME_DEFAULT_VALUE) {
setDisableConfirm(false);
} else {
/*
You can disable the button here
If you want user to change the textinput value
atleast once from what it was originally,
for that set disableConfirm to false here
*/
}
}, [name]);
I have a table that has items in it. When I click a specific item's edit button. It goes to edit page but when I submit an edit of that item. It goes back to main table page but the table page won't be updated. So, I think I need to trigger the useeffect function. To do that I need to update the state in main table page from another screen that is edit page screen.
my apps are not class-based. all of them functional. Here are my codes.
Main Table Page:
//I created a state to update
const [reload,
setReloader] = useState('');
I try to send the state to change it in edit item screen.
<TouchableOpacity onPress={() => navigation.navigate('addProduct', [reload])}>
Edit Item Page:
const [reload,
setReloader] = useState(route.params.reload); //I tried to pass state but it didn't work like that.
Pass a function through navigation
Pass the function in which you will be updating the state. i.e. setReloader
<TouchableOpacity onPress={() => navigation.navigate('addProduct', {setReloader})}>
On addProduct screen get the function by
const setReloader = route.params.setReloader;
once you have edited simply call the setReloader function on the edit page and then go back to the main screen
Using the navigation lifecycle method.
On the main screen, you can add a focus lister
const focusListner = navigation.addListener('focus', () => {
//call the API to fetch the updated data from the server
});
Focus listener is called whenever the return to that screen
You can do something like:
//I created a state to update
const [reload, setReloader] = useState('');
const updateState = (value) => {
setReloader(value);
}
Send `setReloader` as callback to update on edit screen
<TouchableOpacity onPress={() => navigation.navigate('addProduct', {callback: updateState})}>
Edit Item Page:
const callback = route.params.callback;
// call `callback` which will update view on parent screen
import { useIsFocused } from "#react-navigation/native";
const isFocused = useIsFocused();
Well it is worked for me. To trigger.
useEffect not called in React Native when back to screen
I need to get the current cursor position, the current text value and the pressed key of a TextInput when the text value changes, either in onKeyPress or in onChangeText.
For example, typing "A" should result in the following:
keyboardKey: 'A'
text: 'A'
cursorPosition: 1
Then, typing "B" should result in:
keyboardKey: 'B'
text: 'AB'
cursorPosition: 2
I tried to achieve that by listening to onKeyPress, onChangeText and onSelectionChange (getting start and end from nativeEvent.selection) but without any success as the events are probably happening asynchronously so using useState() or useRef() didn't help in order to get the latest values of the three in any of the eents.
<TextInput
onChangeText={onChangeText}
onKeyPress={onKeyPress}
onSelectionChange={onSelectionChange}
/>
I also tried getting the text value from a reference of the TextInput in onKeyPress but this didn't work either.
Finally, tried with setting all three values as states and listening for their changes in useEffect but this wouldn't work because the function will get executed if any of the values change and I want this to be called only once per key press. In addition, I'm not getting the latest values of cursorPosition and text for some reason.
useEffect(() => {
console.log('useEffect', keyboardKey, cursorPosition, text)
}, [keyboardKey, cursorPosition, text]);
I don't think there is a way you can get the cursor position value from the TextInput itself. You would have to implement it on your own. You can use the onKeyPress prop to check what key is pressed and increment a counter that should be in the state like so:
const [cursorPosition, setCursorPosition] = useState(0);
const [text, setText] = useState("");
const onKeyPress = ({ nativeEvent: { key: string } }) => {
// Logic to check what key is pressed if needed
// Here I put +1 for this simple example, but you can put whatever value you want here
setCursorPosition(cursorPosition + 1);
};
const onChangeText = (newText: string) => {
setText(newText);
}
<TextInput onKeyPress={onKeyPress} onChangeText={onChangeText} />
You can then use the setCursorPosition function to update your cursor position and then read it from cursorPosition. Same goes for text.
I'm developing a react-native / redux app with a bottom-tab-navigator similar to the example at https://reactnavigation.org/docs/en/tab-based-navigation.html#customizing-the-appearance. My screens all connect to a Redux store and display shared data, however I'd like at least one of these screens to ignore the current data in the store and instead re-initialize this data each time it's navigated to (instead of continuing to display the data in whatever state it was last left in).
The screen has a method to do this, but I can't figure out how to call it after the first time the screen is rendered (e.g. from the constructor or componentDidMount() method). I can't call it from the render() method as this causes a "Cannot update during an existing state transition" error.
I need my navigator to somehow cause my HomeScreen.initializeData() method to be invoked each time the Home icon is pressed, but how do I do this?
HomeScreen.js:
initializeData() {
this.props.resetData(initialValue);
}
const initialValue = ...
(resetData() is a dispatch function that re-initializes the Redux store).
Updating state from render() would create an infinite loop. Also, you don’t want to run your state update every time the component re-render, only when the tab button is pressed. This tells me that the proper place to make your state update is some onPress function on the tab button.
So the question now relies on how to implement some onPress function on a tab button. I believe this answer this question:
Is there an onPress for TabNavigator tab in react-navigation?
So I found an answer, it's a little more complicated than might be expected: As Vinicius has pointed out I need to use the tabBarOnPress navigation option, but I also need to make my dispatch function available to this navigation option.
To do this I found I need to pass a reference to my dispatch function (which is available as a property of my screen) into the navigation option, so I've used navigation params to do this and here's what I've ended up with:
HomeScreen.js:
componentDidMount() {
initializeData(this.props);
this.props.navigation.setParams({ homeProps: this.props });
}
export const initializeData = (homeProps) => {
homeProps.resetData(initialValue);
};
const initialValue = ...
AppNavigator.js:
tabBarOnPress: ({navigation, defaultHandler}) => {
const routeName = navigation.state.routeName;
if (navigation.state.params === undefined) {
// no params available
} else if (routeName === 'Home') {
let homeProps = navigation.getParam('homeProps', null);
initializeData(homeProps);
} else if (routeName === ...
...
}
defaultHandler();
}
Notes:
I'm passing props as a navigation param rather than my dispatch function (which also works) as it's more flexible (e.g. it makes all of my dispatch functions available).
initializeData() is called both during construction of HomeScreen (for the first time the screen is displayed) and from the navigation icon (for subsequent displays of the screen).
It's necessary to check that params is defined within the navigation option as it'll be undefined the first time the screen is displayed (as screen construction has yet to occur). This also makes it necessary to call initializeData() during screen construction.