React context Unusual Behaviour-CodePudding

I have been working on an form editor Component and I'm updating all the input state in context. I can see that context behavior is unusual. Eg: When I try to update the input value in the context on the blur event I can see that context is lagging. when trying to update the context the data is not getting updated and the focus event, blur event are being prevented(Not working when I update the context in that event)

I'm expecting the context to update properly. But the context is not updating the state properly. Please provide me some suggestion on this issue.

CodePudding user response：

It sounds like you may be running into some issues with React's event handling and updating state in a context provider. It is generally not recommended to update state directly within an event handler, as this can cause unexpected behavior.

One approach you could try is to use the useState hook within your form editor component to manage the local state of your inputs, and then pass the values from this local state up to your context provider using a callback function. This way, you can update the local state of your inputs within your event handlers, and then pass the updated values to your context provider using the callback.

Here is an example of how this could work:

function FormEditor() {
  const [inputValues, setInputValues] = useState({});
  const { updateInputValues } = useContext(FormEditorContext);

  const handleInputChange = (event) => {
    // Update the local state of the input
    setInputValues({
      ...inputValues,
      [event.target.name]: event.target.value,
    });
  }

  const handleInputBlur = (event) => {
    // Update the context provider with the updated input value
    updateInputValues({
      ...inputValues,
      [event.target.name]: event.target.value,
    });
  }

  return (
    <form>
      <input type="text" name="firstName" onChange={handleInputChange} onBlur={handleInputBlur} />
      <input type="text" name="lastName" onChange={handleInputChange} onBlur={handleInputBlur} />
    </form>
  );
}

In this example, we are using the useState hook to manage the local state of our inputs within the FormEditor component. Then, we are passing the updated input values to our context provider using the updateInputValues callback whenever an input value changes or loses focus. This allows us to update the context provider with the latest input values, while still maintaining a local state within our component.

CodePudding user response：

There are a few potential reasons why this might be happening.

First, it's important to remember that the React context API is designed to be used for sharing data that is considered "global" or "application-level" within your application. This means that data stored in the context should be considered read-only by most of your application, and should only be updated by a small number of components that are responsible for managing that data.

If you're trying to update the context from multiple components, or from event handlers like the focus and blur events, this can cause unexpected behavior because the context is not designed to be updated in this way. Instead, you should only update the context from a small number of components that are specifically designed to manage the global state of your application.

Another potential reason for the unexpected behavior that you're seeing is that the context API uses reference equality to determine when to re-render components that are subscribed to the context. This means that if you update the context by modifying an existing object, the components that are subscribed to the context will not re-render because the reference to the object in the context has not changed.

To fix this, you can either create a new object and assign it to the context, or you can use the setState() method provided by the context API to update the context in a way that will trigger a re-render of the subscribed components.

Here's an example of how you might update the context using the setState() method:

const { state, setState } = useContext(MyContext);

// Update the value of the "input" property in the context
setState(prevState => ({
  ...prevState,
  input: 'new value',
}));