CODEWITHSUNDEEP
reactjsreact-native
dsdsa
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Reputation: 77

react native checking previous state

I cant check a value of a previous state in render

my code is

    this.setState(previousState => ({
  if(name!=previousState.name){

                 name:name,
                uri:uri,
                fbid:fbid,


 }           
        }));

Upvotes: 1

Views: 10797

Answers (5)

M_droid
M_droid

Reputation: 2788

I think we can answer this in a more detailed and recent way:

const MyVideoPlayer = () => {
  const [isPlaying, setIsPlaying] = useState(false);

  return (
    <View>
      <!--...my video player...-->
      <TouchableOpacity onPress={() => setIsPlaying(prevState => !prevState)}>
        <!-- My setIsPlaying is returning me the previous state in "prevState"
         and me in turn returning it's negation. So every time the user klicks the
         button it will change from play to pause -->
        {isPlaying ? <PauseButton /> : <PlayButton />}
      </TouchableOpacity>
    </View>
  );
};

Upvotes: 0

kamalesh biswas
kamalesh biswas

Reputation: 1013

handelFilterVisibility -> this is a custom method which will invoke when someone clicks a button & prevState -> is the previous state, so in this method, we take the previous state and change it's property 'isFilterVisible'

Upvotes: 0

kamalesh biswas
kamalesh biswas

Reputation: 1013

handelFilterVisibility = () => {
  this.setState(prevState => ({
    isFilterVisible: !prevState.isFilterVisible
  }));
}

Upvotes: 2

th3g3ntl3m3n
th3g3ntl3m3n

Reputation: 151

react-native do have a lifecycle method for this which contains your previous state as well as new state you can compare both of them into this LC method. you can read about lifecycle methods over here https://reactjs.org/docs/react-component.html

Upvotes: 0

Arslan Tariq
Arslan Tariq

Reputation: 2528

There is a component lifecycle method,componentWillUpdate by which you can check the current and the new state. It is always called when the props or state changes. For example:

componentWillUpdate(nextProps, nextState) {
  console.log(nextState); //will show the new state
  console.log(this.state); //will show the previous state
}

For reference, visit: componentWillUpdate

Upvotes: 5

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