Câu hỏi phỏng vấn React Native
Câu hỏi

What is State in react native?

Câu trả lời

State in React Native is a fundamental concept used to manage data that can change over time within a component. It is similar to state management in React for web applications. Here are the key points to understand about state in React Native:

Definition and Purpose

  • State is a built-in object that allows components to create and manage their own data that can change over time. This data is local to the component and is not accessible to other components unless passed down as props.
  • State is used to store information that a component needs to render and update dynamically. For example, user inputs, fetched data, or any other dynamic data that affects the component's rendering.

Initialization and Usage

  • State is typically initialized in the constructor of a class component or by using the useState hook in a functional component.
  • In a class component, state is initialized like this:
    javascript Copy
    class MyComponent extends React.Component {
      constructor(props) {
        super(props);
        this.state = { count: 0 };
      }
    }
  • In a functional component, state is initialized using the useState hook:
    javascript Copy
    import React, { useState } from 'react';
    
    function MyComponent() {
      const [count, setCount] = useState(0);
    }

Updating State

  • State should not be modified directly. Instead, the setState method (in class components) or the state updater function (in functional components) should be used to update state.
  • Example in a class component:
    javascript Copy
    this.setState({ count: this.state.count + 1 });
  • Example in a functional component:
    javascript Copy
    setCount(count + 1);

Re-rendering

  • When state changes, React Native re-renders the component to reflect the new state. This ensures that the UI is always in sync with the current state of the component.
  • For example, if a state variable message is updated, the component will re-render to display the new message:
    javascript Copy
    const [message, setMessage] = useState("");
    return (
      <SafeAreaView>
        <TextInput
          placeholder="Enter message ...
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