ReactNative / Switch Component: onValueChange - react-native

I've trying to set up a change event if someone modifies a switch component. The approach is to design a view that contains multiple switches and allows the user to set the state per each notification that will end up in a POST api-call. Futher, I'd like to load the initial values from a api-call.
How can I access the state (weather it's checked / unchecked) in my onChangeFunction? And how can I get an element using their ID or name? (same as in HTML/CSS with #mySwitch.setValue(true)?
Given code:
class Settings extends Component {
onChangeFunction(type, props) {
Alert.alert("changed", "==> " + props.state)
}
render() {
return (
<View style={styles.container}>
<Switch onValueChange={this.onChangeFunction.bind(this, "TASK_CREATED", this.props)} value={this.state} />
</View>
);
}
}

You have a mess there between the propsand the state concept. You can do:
class Settings extends Component {
state = {
taskCreated: false,
};
onChangeFunction(newState) {
this.setState(newState, () => Alert.alert("Changed", "==> " + this.state));
}
render() {
return (
<View style={styles.container}>
<Switch onValueChange={(value) => this.onChangeFunction({taskCreated: value})}
value={this.state.taskCreated}
/>
</View>
);
}
}
Notice that this.setState is asynchronous so you can safely read its value using the callback that the method provides.

Related

React Native components seem to be sharing a state

I'm having an issue with React-native where I have a component TouchTimer which uses an AnimatedTimer component. This timer is supposed to start and stop when it is tapped, which it does, however all of the TouchTimer components I add to a page will start and stop whenever any of them are tapped, rather than only affecting the tapped component.
Below is a snippet of my component:
TouchTimer.tsx
export class TouchTimer extends React.Component<TouchTimerProps> {
state: {
...
paused: boolean,
}
constructor(props) {
super(props);
...
this.state = {
...
paused: true,
}
}
startStop() {
this.setState({paused: !this.state.paused});
}
render() {
const { time } = this.props;
return (
<TouchableHighlight onPress={() => this.startStop()}>
<View>
<AnimatedTimer
...
time={time}
pause={this.state.paused}
/>
<View style={styles.timeContainer}>
<Text style={styles.time}>{this.state.remaining}</Text>
</View>
</View>
</TouchableHighlight>
)
}
}
And here is a snippet of the screen containing these components:
Details.tsx
import { TouchTimer } from '../components/TouchTimer';
...
export class RecipeDetailsScreen extends React.Component<NavigationInjectedProps> {
...
{this.state.steps.map(step => (
<List.Item
key={step.id}
title={"Step " + step.index}
style={styles.step}
description={step.short_desc}
right={() => (step.time > 0 &&
<TouchTimer
time={step.time * 60000}
/>
)}
/>
)
}
I have tried wrapping the TouchTimer components in a View and changing the paused boolean to a prop, to no avail.
I have also tested to see if this issue appears when the components are not siblings, and when they are not produced as the result of a callback, and the issue still persists in both these cases.
If anybody has any advice or answers on how to make these timers independent I would very much appreciate it!
Curiously that component seems to be implemented with a global pauseFlag that applies to all component instances. See https://github.com/dalisalvador/react-native-animated-timer/blob/master/src/Components/AnimatedTimer.js#L34
So I don't think you're doing anything wrong here, this is a limitation of the library code that is coupling all instances of your timer to the same pauseFlag value.

How to reload flat list in React-Native?

I am switching from android to react native. Complete naive.
I wanted to implement something like recyclerview in react native and found out about FLATLIST
Now the problem is initially my data variable is empty and later on i am adding data into that variable. Now how do i notify the flat list that the data has changed and it should now re render itself.
Like in recyclerview we use adapter.notifyDataSetChanged(); to inform the recycler view about the change that it should re-render itself now
The code i am using is
export default class Convo extends Component{
constructor(props){
super(props);
this.state = {
loggedIn: 'false',
title: 'Login/SignUp',
messages: []
};
this.downloadConversation = this.downloadConversation.bind(this);
}
componentDidMount(){
this.downloadConversation();
}
downloadConversation(){
this.setState(
{message: [
{
key: "HIHI",
name: "lets this bullshit",
message: "I i i"
},
{
key: "HIHI2",
name: "lets change bullshit",
message: "I i i"
},
{
key: "HIHI3",
name: "lets change this ",
message: "I i i"
}
]}
);
//After updating the messages object, i want to notify flat list about
//the change, basically i will be updating this object asynchronously
// in background which will take time. for now i am updating directly
//to show you
}
renderFlatListItem(item) {
return (
<View key={item.key} style={styles1.flatviewItem}>
<Text>User1</Text>
<Text style={styles1.name}>{item.name}</Text>
<Text style={styles1.messageStyle}>{item.message}</Text>
</View>
)
}
render(){
return(
<View style={styles1.container}>
<View style={styles1.header}>
<Text style={styles1.h2style}>Conversation List</Text>
</View>
<FlatList
style={styles1.flatview}
extraData={this.state}
keyExtractor={item=>item.key}
showsVerticalScrollIndicator={true}
data={this.state.messages}
renderItem={({item}) => this.renderFlatListItem(item)}
/>
</View>
);
}
}
Your component should automatically re-render when the component state changes (if anything in your render method references the changed piece of state). I think you just need to change 'message' to 'messages' when you setState in your downloadConversation() method. Your FlatList is looking for this.state.messages, not this.state.message and this.state.messages is never changed. Just fix that typo & hopefully that fixes it.

Getting the Id of a react-native element in event handler

How to get the Id of the element in onPress event handler.
I am adding elements dynamically and wants to know in the event handler of onPress of these elements to store in the state which elements are clicked.
Here is the code i have
export default class App extends Component {
constructor(props){
super(props);
this.getElements= this.getElements.bind(this);
this.selectElement = this.selectElement.bind(this);
}
componentWillMount(){
this.state = {
noOfElements :10
}
}
selectElement(e,key){
console.log('selectElement() : key=',key);
}
getElements(){
let elements =[];
for(let index=0;index<this.state.noOfElements;index++){
elements.push(
<View key={'View_'+index} style={{flex:1}}>
<Button
key={'View_'+index}
id={index}
onPress={(e,index) => {this.selectElement(e,index)}}
title={'Button-'+index}
/>
</View>
);
}
return elements;
}
render(){
let elements = this.getElements();
return(
<View style={styles.container}>
<Text>Test</Text>
{elements}
</View>
);
}
}
I tried just passing the key like
onPress={(index) => {this.selectElement(index)}}
with no success..
Not sure what i am doing wrong.
The way you have it, i think index would come up undefined, just remove index as an argument in your onPress so it grabs index from the for loop. Also you can prob refactor it using map.
onPress={(e) => this.selectElement(e,index)}
Changed the event handler as below and it is working fine now.
onPress={this.selectElement.bind(this,index)}
and the function now just accepts the index
selectElement(key){
console.log('selectElement() : Index=',key);
}

Listview blanks when using navigator pop

I am facing two problems & can not resolve this. Can anyone explain why this is happening? Or can anyone give me the solution?
Problem NO 1:
There are two components 1) Home 2) Inner
In the Home there are list of data & when I click any one of them it route to Inner. There are also a back button with using navigator pop. There is the issue sometime reproduce - When I click on back, it routes to Home but there is no data(listview element) but when I touch on the screen the data shows properly.
Problem NO 2:
In the home component within the list data, there also some repeated data within the single row.
I have used map function for this. Sometimes ( Most of the time it shows correctly ) it is also not shown in list view, the row is showing properly but the repeated data are missing.
<ListView onEndReached={this.props.reloadArticles} onEndReachedThreshold={10} dataSource={this.props.dataSource} renderRow={this.renderPost} enableEmptySections={true} refreshControl={ <RefreshControl refreshing={this.props.isRefreshing} onRefresh={this.props._onRefresh} /> } />
NO 1:
Sounds like this: https://github.com/facebook/react-native/issues/8607
If you use rn 0.4.0 setting initialListSize={0} could help
NO 2:
Could you please post your renderRow / dataSource code
#SnowMax Sorry for late reply & thanks for help.
Due to confedential project I could not share all code but I can share u the code structure:
renderPost = (list, sectionID, rowID) => {
if(list && list.is_shared_post == true){
return (
<WallShared list={list} rowID={rowID} />
);
}
}
class WallShared extends Component {
constructor(props) {
super(props);
}
render() {
if( this.props.list.is_shared_post == true){
switch(this.props.list.TblPostsComments.post_type){
case 'T':
return (<ShareText list={this.props.list} />);
default:
return (<ShareDefault list={this.props.list} rowID={this.props.rowID} />);
break;
}
} else {
return (
<View>something</View>
)
}
}
}
export default WallShared;
class ShareText extends Component {
constructor(props) {
super(props);
this.state ={
isLoggedIn:false,
}
}
componentDidMount(){
}
render() {
var ShareBlock = this.props.list.TblPostsComments.shared_contents.map(function(cont, ind) {
return (
<View style={[styles.feedItem, styles.SfeedItem]} key={ind}> </View>
);
},this);
return(
<View style={styles.feedItem}>
<View style={styles.sharedWrap}>
{ ShareBlock }
</View>
</View>
);
}
}
export default ShareText;

React Native: Updating state in onLayout gives "Warning: setState(...): Cannot update during an existing state transition"

I have a component in React Native which updates it's state once it knows what size it is.
Example:
class MyComponent extends Component {
...
render() {
...
return (
<View onLayout={this.onLayout.bind(this)}>
<Image source={this.state.imageSource} />
</View>
);
}
onLayout(event) {
...
this.setState({
imageSource: newImageSource
});
}
...
}
This gives the following error:
Warning: setState(...): Cannot update during an existing state transition (such as within render or another component's constructor). Render methods should be a pure function of props and state; constructor side-effects are an anti-pattern, but can be moved to componentWillMount.
I guess the onLayout function is called while still rendering (which can be good, the sooner the update, the better). What is the correct way to solve this problem?
Thanks in advance!
We got around this by using the measure function, you will have to wait until the scene is fully complete before measuring to prevent incorrect values (i.e. in componentDidMount/componentDidUpdate). Here's an example:
measureComponent = () => {
if (this.refs.exampleRef) {
this.refs.exampleRef.measure(this._logLargestSize);
}
}
_logLargestSize = (ox, oy, width, height, px, py) => {
if (height > this.state.measureState) {
this.setState({measureState:height});
}
}
render() {
return (
<View ref = 'exampleRef' style = {{minHeight: this.props.minFeedbackSize}}/>
);
}
Here is a solution from documentation for such cases
class MyComponent extends Component {
...
render() {
...
return (
<View>
<Image ref="image" source={this.state.imageSource} />
</View>
);
}
componentDidMount() {
//Now you can get your component from this.refs.image
}
...
}
But for my opinion it's better to do such things onload