React Native: how to simulate onBlur and onFocus event for View - react-native

In React Native, only TextInput has onFocus and onBlur event listener. However, we would like to simulate this effect on a View.
Here is what we try to achieve. There is a View on the screen. It gains "focus" when user taps on it and is hightlighted. We want to detect that user taps outside the View, so that we can "blur" the View, that is, remove the highlight.
I know we can use focus method (https://facebook.github.io/react-native/docs/nativemethodsmixin.html#focus) to request focus for the View. The problem is that I don't know how to detect that user presses outside the View.

I think the easiest is to set a state variable instead so you can play with that one such as:
class MyView extends Component {
constructor(props) {
super(props);
this.state = {
activeView: null,
}
this.views = [
(<View style={{ padding: 20 }}><Text>View 1</Text></View>),
(<View style={{ padding: 20 }}><Text>View 2</Text></View>),
(<View style={{ padding: 20 }}><Text>View 3</Text></View>),
(<View style={{ padding: 20 }}><Text>View 4</Text></View>),
(<View style={{ padding: 20 }}><Text>View 5</Text></View>),
];
}
_setActive( index ) {
return () => {
this.setState({ activeView: index })
}
}
render() {
return (
<View style={{flex: 1, alignItems: 'center', justifyContent: 'center'}}>
{this.views.map( (view, index) => {
let containerStyle = [];
if ( index === this.state.activeView ) {
containerStyle.push({ borderWidth: 10 })
}
return (
<TouchableOpacity onPress={this._setActive(index)} style={containerStyle}>
{view}
</TouchableOpacity>
);
})}
</View>
);
}
}
You can use MyView where requried as <MyView /> also every item on the array views can have any style required and configure each if is active just by access to this.state.activeView.
Let me know if you have any question.

In situations like this, I add onPress() to the the element that is outside of the View in question.
<View onPress(removeHighlight)></View>
<View onPress(addHighlight)></View>

Related

How to display a button at the bottom of a Webview in react-native?

Inside my component (PrivacyPolicy.js), i have a header view, a webview, and a footer view. the webview, depending on the size, gets scrollable. my issue is that the footer view is displayed at the bottom of the screen like if its style was "position: 'absolute'" so it keeps displayed while scrolling. I need to have it after all webview is displayed.
<View style={styles.main_container}>
<View style={styles.header_container}>
...
</View>
<WebView originWhitelist={['*']} source={{ html: privacyPolicyContent }}/>
<View style={styles.footer_container}>
<CheckBox
disabled={false}
value={this.state.isChecked}
onValueChange={(newValue) => this.setState({
isChecked: newValue
})}
style={styles.checkbox}
tintColors={{ true: '#157dfa' }}
/>
<Text style={styles.checkbox_text}>I have read and accept the Privacy Polic</Text>
</View>
</View>
My styles:
const styles = StyleSheet.create({
main_container: {
flex: 1,
paddingHorizontal:'5%'
},
header_container: {
height: scale(90),
flexDirection: 'row',
marginLeft: 10
},
checkbox_container: {
flexDirection: 'row'
},
checkbox: {
marginLeft: -5,
},
checkbox_text: {
marginTop: 8,
fontSize: 10
}
})
I can see few suggestions:
Since your button is a React Native Button => You can show/hide based on the scrollY positions. For that, you need to communicate over the Bridge to dispatch an event accordingly.
As an alternative solution => You can create the button on the Webview its self to have the same functionality.

Component only reachable by scrolling regardless of window size

I'm trying to make a layout so that the later parts of the view are only reachable by scrolling.
Currently I'm using Dimensions to generate Views with the correct height. Is there a better way of doing so? My current solution doesn't seem too correct.
export default function MyApp() {
const height = Dimensions.get('window').height;
return (
<View style={styles.container}>
<ScrollView>
<View style={{backgroundColor: 'green', height:height}}/>
<View style={{backgroundColor: 'red', height:40}}/>
</ScrollView>
</View>
);
}
const styles = StyleSheet.create({
container:{
backgroundColor: 'white',
flex: 1
}
});
You can use VirtualizedList component, for example as
<VirtualizedList
data={['body']}
renderItem={({ item }) => (
<View style={styles.screen}>
{/* Put more content for body */}
</View>
)}
keyExtractor={(item, index) => index.toString()}
getItemCount={() => {
return 1;
}}
getItem={(data, index) => {
return data[index];
}}>
</VirtualizedList>
Your solution work, but not good and it have downside, when you change your phone orientation to landscape there will be bug. I dont like using Dimensions in my code unless there is no other way or use Dimensions addEventListener to listen window size and update component whenever window size change. I will suggest you a better way.
First, create a component called LayoutSizeAwareView, after this view rendered, we will catch it size from onLayout props and use them to render it children.
const LayoutSizeAwareView = (props) => {
const [size, setSize] = React.useState({width: 0, height: 0});
return (
<View
...props,
onLayout={(e) => {
setSize({
width: e.nativeEvent.layout.width,
height: e.nativeEvent.layout.height,
})
props.onLayout(e)
}}
>
{props.children(size)}
</View>
)
}
And then, in your case, use it like this
export default function MyApp() {
return (
<LayoutSizeAwareView style={styles.container}>
{({width, height}) => {
return (
<ScrollView>
<View style={{backgroundColor: 'green', height: height}}/>
<View style={{backgroundColor: 'red', height: 40}}/>
</ScrollView>
)
}}
</View>
);
}
const styles = StyleSheet.create({
container:{
backgroundColor: 'white',
flex: 1
}
});
This way your code look even cooler, there will be some typo in my code since I dont have IDE here, but you might get the idea.

how to stop images from rendering on setState

I have images associated with a counter and based on this increment or decrement in counter, a calculation is done and displayed in a text at the bottom.
The problem is that when I render, the images get rendered again and are loaded again and again and again. which I dont want.
If I dont render, the text will not update with the calculated amount.
For the counter I am using react-native-counter.
I have already tried with shouldcomponentupdate, but I want to stop only image rendering, the rest should work.
Please advise.
export default class App extends Component {
constructor(props) {
super(props);
}
render() {
return (
<div>
<Header
backgroundColor="#25D366"
leftComponent={
<Icon
name="menu"
size={40}
color={"#fff000"}
onPress={() => this.props.navigation.openDrawer()}
/>
}
centerComponent={{
text: "Veg & Fruits",
style: {
color: "#ffffff",
fontSize: 25,
fontWeight: "bold",
},
}}
rightComponent={<Icon name="home" color={"#ff0000"} />}
></Header>
/// this is searchbar component,
<SearchBar
fontColor="#ffffff"
fontWeight="bold"
fontSize={20}
iconColor="#c6c6c6"
shadowColor="#ffffff"
cancelIconColor="#c6c6c6"
backgroundColor="#25D366"
placeholder="Search here"
onChangeText={(text) => {
this.setState({ photos: [] });
this.state.search = text;
this.filterList(this.state.search);
console.log("text changed");
}}
onPressCancel={(text) => {
text = "";
//this.filterList(text);
}}
onPress={(text) => {
console.log("rendering");
console.log("now text is: ", this.state.search);
}}
/>
/// in this view images are displayed using functions
<View>
<ScrollView
style={{
height: Dimensions.get("window").height - 200,
}}
>
<View
key={Date.now()}
style={{
flex: 1,
flexDirection: "column",
flexWrap: "wrap",
}}
>
{this.filterList(this.state.search)}
{this._renderImages()}
</View>
</ScrollView>
<CalcText tt={total_num} />
</View>
</div>
);
}
}
class CalcText extends Component {
constructor(props) {
super(props);
this.state = {
ta: 0,
};
}
shouldComponentUpdate(nextProps) {
console.log(nextProps.tt);
if (this.props.tt !== nextProps.tt) {
console.log("changed");
return true;
} else {
console.log("Not changed");
return false;
}
}
render() {
return (
<View style={{ height: 40, backgroundcolor: "ff0000" }}>
<Text style={{ fontSize: 26, fontWeight: "bold" }}>
Total : {this.props.tt}
</Text>
</View>
);
}
}
You can create a TextBox component and split it from ImageComponent. In this way the images will not be bound to the state of the component rendering text, and you can safely change TextBox state and text preventing ImageComponent to re-render.
Edit:
Okei, now i get it. I think you have no possibility to do it like this.
Let's formalize the problem:
<Parent>
<Images calc={functionToCalc} />
<CalcText totalAmount={this.state.totalAmount}/>
</Parent>
functionToCalc is defined in in <Parent> and update parent state, something like:
const funcToCalc = () => {
// when condition occurs
this.setState({
totalAmount : computedAmount
})
}
The state of <Parent> has:
this.state : {
totalAmount: none
}
Whenever condition (buttonClick?) occurs in <Images/> you run functionToCalc update <Parent> state and rerender <CalcText>. Problem here is that also <Images> will be rerender again as all the parent component will be rerender.
this is one of the way to pass info from siblings in React.
You only have a possibility if you want to prevent <Images> rerendering.
Redux or similar libraries for centralize state
You will move the computed calculation in a Store and <CalcText/> will read that from there. <Images/> component will trigger an action modifying that state but won't listen to that so not being rerender.

React Native FlatList rendering a few items at a time

I have a list of chat messages in my app to which new items are added to the bottom. I used some code from another SO question to make the FlatList stick to the bottom when new items are added, as below
<FlatList
data={messages}
renderItem={({item}) => <ChatMessage message={item}></ChatMessage>}
keyExtractor={(item, index) => index.toString()}
initialNumToRender={messages.length}
initialScrollIndex={messages.length-1}
ref={ref => this.flatList = ref}
onContentSizeChange={(contentWidth, contentHeight)=>{
this.flatList.scrollToEnd();
}}
/>
The problem is that when the initial list renders (only 35 items, hardcoded in an array for now) it seems to render just a few items, then scroll down a bit, then render a few more, then scroll down a bit until it finally completes the rendering and sticks to the bottom. It's choppy and slow, despite adding initialNumToRender={messages.length} and rendering an incredibly simple node for each result.
Ideally I guess I need to wait for it to fully render before displaying anything to the user but (A) they'd have to wait a couple of seconds to start using the chat room and (B) I don't think that's how Flatlist works, I assume the elements have to be viewable before it is rendered.
Is there just a better way to do this? (Testing on Android by the way)
EDIT: Adding ChatMessage component for completeness
// Chat Message
import React, { Component } from 'react'
import {
StyleSheet,
ImageBackground,
Text,
View
} from 'react-native'
class ChatMessage extends Component {
constructor(props) {
super(props)
this.state = { }
}
render() {
return (
<View style={styles.chatMessage}>
<View style={styles.chatMessage_layout}>
<View style={styles.chatMessage_pic}>
<View style={styles.chatMessage_pic_image}>
<ImageBackground
source={require('./assets/images/profile-pics/example-profilr.png')}
style={styles.chatMessage_pic_image_background}
imageStyle={{ borderRadius: 40/2 }}
resizeMode="cover"
>
</ImageBackground>
</View>
</View>
<View style={styles.chatMessage_details}>
<View style={styles.chatMessage_name}>
<Text style={styles.chatMessage_name_text}>
{this.props.message.name}
<Text style={styles.chatMessage_name_time}> 24h</Text>
</Text>
</View>
<View style={styles.chatMessage_message}>
<Text style={styles.chatMessage_message_text}>{this.props.message.text}</Text>
</View>
</View>
</View>
</View>
)
}
}
export default ChatMessage;
const styles = StyleSheet.create({
chatMessage: {
paddingVertical: 10,
paddingHorizontal: 24
},
chatMessage_layout: {
flexDirection: 'row'
},
chatMessage_pic: {
width: 40,
height: 40,
marginRight: 12
},
chatMessage_pic_image: {
width: 40,
height: 40
},
chatMessage_pic_image_background: {
width: 40,
height: 40
},
chatMessage_details: {
flex: 1
},
chatMessage_name_text: {
color: '#FFF',
fontSize: 14,
fontWeight: 'bold'
},
chatMessage_name_time: {
fontSize: 11,
color: 'rgba(255,255,255,0.6)'
},
chatMessage_message: {
flexDirection: 'row',
alignItems: 'center'
},
chatMessage_message_text: {
color: '#FFF',
fontSize: 12
}
})
If you have less number of items and want to render all items at once then you should use ScrollView as mentioned in the docs
ScrollView: Renders all elements at once, but slow if there are large number of elements.
FlatList: Renders items in a lazy mode, when they are about to appear and removes them when they leave the visible display to save memory that makes it usable for performance on large lists.
For Flatlist optimization you need to use PureComponent whenever you render the child so that it only shallow compares the props.
Also in the keyExtractor use a unique id for your item and do not depend upon the index, since when the item updates the index is not reliable and may change

setNativeProps Change Value for Text Component React Native Direct Manipulation

I want to directly update the value of a component due to performance reasons.
render(){
<View>
<Text style={styles.welcome} ref={component => this._text = component}>
Some Text
</Text>
<TouchableHighlight underlayColor='#88D4F5'
style={styles.button}>
<View>
<Text style={styles.buttonText}
onPress={this.useNativePropsToUpdate.bind(this)}>
Iam the Child
</Text>
</View>
</TouchableHighlight>
</View>
}
This is the method I use to update the text component. I dont know if I am setting the right attribute/ how to figure out which attribute to set:
useNativePropsToUpdate(){
this._text.setNativeProps({text: 'Updated using native props'});
}
Essentially trying to follow the same approach from this example:
https://rnplay.org/plays/pOI9bA
Edit:
When I attempt to explicitly assign the updated value:
this._text.props.children = "updated";
( I know this this the proper way of doing things in RN ). I get the error "Cannot assign to read only property 'children' of object'#'"
So maybe this is why it cant be updated in RN for some reason ?
Instead of attempting to change the content of <Text> component. I just replaced with <TextInput editable={false} defaultValue={this.state.initValue} /> and kept the rest of the code the same. If anyone know how you can change the value of <Text> using setNativeProps OR other method of direct manipulations. Post the answer and ill review and accept.
The text tag doesn't have a text prop, so
this._text.setNativeProps({ text: 'XXXX' })
doesn't work.
But the text tag has a style prop, so
this._text.setNativeProps({ style: { color: 'red' } })
works.
We can't use setNativeProps on the Text component, instead, we can workaround and achieve the same result by using TextInput in place of Text.
By putting pointerEvent='none' on the enclosing View we are disabling click and hence we can't edit the TextInput (You can also set editable={false} in TextInput to disbale editing)
Demo - Timer (Count changes after every 1 second)
import React, {Component} from 'react';
import {TextInput, StyleSheet, View} from 'react-native';
class Demo extends Component {
componentDidMount() {
let count = 0;
setInterval(() => {
count++;
if (this.ref) {
this.ref.setNativeProps({text: count.toString()});
}
}, 1000);
}
render() {
return (
<View style={styles.container} pointerEvents={'none'}>
<TextInput
ref={ref => (this.ref = ref)}
defaultValue={'0'}
// editable={false}
style={styles.textInput}
/>
</View>
);
}
}
const styles = StyleSheet.create({
container: {
flex: 0.7,
justifyContent: 'center',
alignItems: 'center',
},
textInput: {
fontSize: 60,
width: '50%',
borderColor: 'grey',
borderWidth: 1,
aspectRatio: 1,
borderRadius: 8,
padding: 5,
textAlign: 'center',
},
});
export default Demo;
As setNativeProps not solving the purpose to alter the content of <Text />, I have used below approach and is working good. Create Simple React Component like below...
var Txt = React.createClass({
getInitialState:function(){
return {text:this.props.children};
},setText:function(txt){
this.setState({text:txt});
}
,
render:function(){
return <Text {...this.props}>{this.state.text}</Text>
}
});