react-native：将完整的STATE从一个组件发送到另一个组件？

Question

I have a Reminder component comprising of a form where I am storing text and date onClick of a button using AsyncStorage .

Now, I want to display this stored data in Agenda Component .

I am using Agenda component from react-native-calendars library react-native-calendars

this is my reminder component

    class Reminder extends Component {
        constructor(props) {
            super(props);
            this.state = {
                input: '',
                chosenDate: new Date(),
            };
            this.setDate = this.setDate.bind(this);
            this.handleChangeInput = this.handleChangeInput.bind(this);
            this.saveData = this.saveData.bind(this);
        }

        setDate(newDate) {
            this.setState({
                chosenDate: newDate
            });
        }

        handleChangeInput = (text) =>  {
            this.setState({input:text});
        }

        //save the input
        saveData() {
            AsyncStorage.setItem("key", JSON.stringify(this.state));
        }
        render() { 
            return ( 
                <View>
                    <Form style={styles.formContainer}>
                        <View style={styles.formView}>

                                < TextInput
                                placeholder = "Set your reminder"
                                onChangeText={this.handleChangeInput}
                                value={this.state.input}
                                />

                            <DatePicker
                                defaultDate={new Date()}
                                minimumDate={new Date(2018, 1, 1)}
                                maximumDate={new Date(2019, 12, 31)}
                                locale={"en"}
                                timeZoneOffsetInMinutes={undefined}
                                modalTransparent={false}
                                animationType={"fade"}
                                androidMode={"default"}
                                placeHolderText="Select date"
                                textStyle={{ color: "green" }}
                                placeHolderTextStyle={{ color: "#d3d3d3" }}
                                onDateChange={this.setDate}
                            />
                            <Text style={styles.datePicker}>
                                {this.state.chosenDate.toString().substring(0,10)}
                            </Text>
                        </View>
                        <View style={styles.footer}>
                            <Button block success style={styles.saveBtn} 
                            onPress={ () => 
                                {
                                  this.saveData()
                                  console.log('save data',this.state);
                                }
                            } 
                               >
                                <Icon type='MaterialIcons' name='done' />                        
                            </Button>
                        </View>
                    </Form>
                </View> 
            );
        }
    }

export default Reminder;

and this it's screen Reminder screen

import React, { Component } from 'react';
import { View, StatusBar } from 'react-native';
import PropTypes from 'prop-types';

import Reminder from '../components/Reminder';

const ReminderScreen = ({navigation}) => (
    <View >
        <Reminder navigation={navigation} >
            <StatusBar backgroundColor = "#28F1A6" />
         </Reminder >
    </View>
);

Reminder.propTypes = {
    navigation: PropTypes.object.isRequired
}

export default ReminderScreen;

and this is the component I want to display that data Agenda Component

class WeeklyAgenda extends Component {
    constructor(props) {
    super(props);
    this.state = {
      items: {},
      selectedDate: ''
    };
  }

  render() {
    return (
      <View style={{height:600}}>
            <Agenda
              items={this.state.items}
              loadItemsForMonth={this.loadItems.bind(this)}
              selected={this.props.day}
              renderItem={this.renderItem.bind(this)}
              renderEmptyData={this.renderEmptyDate.bind(this)}
              rowHasChanged={this.rowHasChanged.bind(this)}
              onRefresh = {() => { this.setState({refeshing : true})}}
              refreshing = {this.state.refreshing}
              refreshControl = {null}
              pastScrollRange={1}
              futureScrollRange = {3}
              theme = {
                {
                  agendaTodayColor: '#28F1A6',
                  agendaKnobColor: '#28F1A6',
                  dotColor: '#28F1A6',
                  selectedDayBackgroundColor: '#28F1A6',
                  todayTextColor: '#28F1A6',
                }
              }
          />
          <View >
              <Fab
                  active={!this.state.active}
                  direction="up"
                  style={{ backgroundColor: '#28F1A6'}}
                  position = 'bottomRight'
                  onPress={() => this.props.navigation.navigate('Reminder')}>
                  <Icon type='MaterialCommunityIcons' name="reminder" />
              </Fab>
          </View>
      </View>
    );
  }

  //On application loads, this will get the already saved data and set the state true when it's true.
    componentDidMount() {
        AsyncStorage.getItem("key").then((newItems) => {
            this.setState(JSON.parse(newItems));
        });
    }

  loadItems = (day) => {
    console.log('day',day);
    console.log('items', this.state.items);
    const {selectedDate} = this.state;

    setTimeout(() => {
      console.log('selected date', selectedDate);
      this.setState({selectedDate: day});
      console.log('selected date later', day);
      const newItems = {};
      Object.keys(this.state.items).forEach(key => {newItems[key] = this.state.items[key];});
      console.log('new items later', newItems);
      this.setState({
        items: newItems
      });
      console.log('new items later', this.state.newItems);
      console.log('items later', this.state.items);
      this.state.items;
    },1000);

  };

  renderItem(item) {
    return (
      <View style={[styles.item, {height: item.height}]}>
        <TouchableOpacity onPress={() => {this.props.navigation.navigate('Reminder')}}>
          <Text>{item.name}</Text>
        </TouchableOpacity>
      </View>
    );
  }

  renderEmptyDate() {
    return (
      <View style={styles.emptyDate}>
        <TouchableOpacity onPress={() => {this.props.navigation.navigate('Reminder')}}>
          <Text style={styles.emptyTextColor}> No Event or Reminder on this date </Text>
        </TouchableOpacity>
      </View>

    );
  }

  rowHasChanged(r1, r2) {
    return r1.name !== r2.name;
  }

  timeToString(time) {
    const date = new Date(time);
    return date.toISOString().split('T')[0];
  }
}

export default WeeklyAgenda;

and this is it's screen Agenda Screen

import React, { Component } from 'react';
import { View, Text, StatusBar } from 'react-native';
import PropTypes from 'prop-types';

import WeeklyAgenda from '../components/Agenda';
class AgendaScreen extends Component {
    state = {  }
    render() { 
        const {navigation} = this.props;
        const { params } = this.props.navigation.state;
        return (
            <View style={{height: 100}}>     
                <WeeklyAgenda day={params["day"]} navigation={navigation}>
                    <StatusBar backgroundColor="#28F1A6" />
                </WeeklyAgenda >
            </View>
        );
    }
}

WeeklyAgenda.propTypes = {
    navigation: PropTypes.object.isRequired
}

export default AgendaScreen;

I am fairly new to react-native and still trying to figure out how to share data between components and screens.

Answer 1

So basically in react-native data flow between components involves props. In case you need to pass the entire state of one component to another, you can pass props to the second component by stringifying the state and recieve the prop by parsing it to json object again.

If you are using any navigation to navigate between components and screens, you can also use passProps to send state to next screen. Hope this helps.

Answer 2

To do this you want to take your items and map them in your Agenda component. I don't know what props the item object contains so I just made up item.name and item.whatever. I also didn't know how you wanted to display this data. You can display it however you like in the return statement of the map function.

If you want a table just have to render a table in the return statement and dynamically add your item props accordingly. Does this make sense?

Also, the outermost element of your return in your map function must have a key prop that accepts unique keys only.

 state = { 
     items: [], 
     selectedDate: ''
 }
  render() {
      const { items } = this.state; // destructure state, so create a variable called items that is equal to this.state.items essentially takes the items in the state variable items and copies them to a new const variable called items
    return (
      <View style={{height:600}}>
            <Agenda
              items={items} //send those items to Agenda Component via prop
              loadItemsForMonth={this.loadItems.bind(this)}
              selected={this.props.day}
              renderItem={this.renderItem.bind(this)}
              renderEmptyData={this.renderEmptyDate.bind(this)}
              rowHasChanged={this.rowHasChanged.bind(this)}
              onRefresh = {() => { this.setState({refeshing : true})}}
              refreshing = {this.state.refreshing}
              refreshControl = {null}
              pastScrollRange={1}
              futureScrollRange = {3}
              theme = {
                {
                  agendaTodayColor: '#28F1A6',
                  agendaKnobColor: '#28F1A6',
                  dotColor: '#28F1A6',
                  selectedDayBackgroundColor: '#28F1A6',
                  todayTextColor: '#28F1A6',
                }
              }
          />
    );
  }

  //On application loads, this will get the already saved data and set the state true when it's true.

    componentDidMount() {
        AsyncStorage.getItem("key").then((newItems) => {
            //assuming JSON.parse returns an array of JSON objects, if not change
            //items to items: {} the way you had it originally in state
            this.setState({ items: JSON.parse(newItems) }) //add the items or data to state variable called items
        });
    }
}

//let's pretend that this is your Agenda Component

class Agenda extends Component {
    state = { 
        items: this.props.items, //get the items that were passed above using items={item} and assign them to a state variable items here in the Agenda component 
    }

    render() {
        const { items } = this.state; //destructure state
        return(
          <div>
            //put this where you want to render the data in the AgendaComponent you said you were using a Text Component so it would like this
            items.map(item => {
                return (
                  //assuming that item object comes with an id if not you must add a unique key so you can call a func that updates a count variable and returns it
                  <Text key={item.id}>{item.name} {item.date}</Text>
                )
            })
        )
      </div>
    }
}

remember. the map function is almost like a for loop. It will iterate through every element in the array and do what is in the return statement for each element of the array.

Hope this helps.

Update

The previous solution I wrote out had a bug. The Agenda component was setting the state before it actually received props and did not update the state when props updated.

For some reason, componentWillReceiveProps never got any props. However, componentDidUpdate received props after one update. The issue is that you cannot setState in componentDidUpdate() or you will get an infinite loop. So here is a work around. If anyone has a better solution to this please edit my answer or post a new answer with that.

The following is only for your Agenda Component. Nothing else needs updating

1. First, update your state declaration from this:

   state = { items: this.props.items, //get the items that were passed above using items={item} and assign them to a state variable items here in the Agenda component }

to this:

state = {
    items: null, //changed this to null bc the array gave a nested array later on making it more difficult to traverse through
    haveItems: false //this will be used later to check if there are items available in props to update state
  };

2. In your render() function change this

   render() { const { items } = this.state; //destructure state return( //put this where you want to render the data in the AgendaComponent you said you were using a Text Component so it would like this items.map(item => { return ( //assuming that item object comes with an id if not you must add a unique key so you can call a func that updates a count variable and returns it {item.name} {item.date} ) }) ) } }

to this:

const { items, haveItems } = this.state; //destructure state
    if (this.props.items.length === 0) {
      this.setState({ haveItems: false }); //if there aren't any items in props then you have no items so set haveItems to false
    } else {
      //if you already have items then you already handled those items so do nothing
      if (haveItems) {
      } else {
        //handle the items
        this.setState({
          haveItems: true, //set this to true bc now you have items
          items: this.props.items //set items in state to the items in props, you will get one array with all of your objects 
        });
      }
    }
    return (
      <div>
        <div>
          {haveItems
            {* if you have items then map them the question mark means true, if not display nothing, the colon : means false
            ? items.map(item => {
                return (
                  <ul key={item.id}>
                    <li>{item.name}</li>
                    <li>{item.date}</li>
                  </ul>
                );
              })
            : null}
        </div>
      </div>
    );
  }
}

Sorry for a long answer but I hope this is what you needed.