如何使用 React 以编程方式填充输入字段值？

Question

I have a modal with some input fields. I can easily pass the data automatically with the user typing an input, using onChange function in the input field, as

<Input onChange={this.props.store.handleCategoryChange} type="text" />

and .. (Using a mobx store, irellevant though)

@observable categoryValue;
@action handleCategoryChange = (e, data) => {
    this.categoryValue = data.value;
    e.preventDefault();
};

However, I want to add a function where the user can pre-fill this with information elsewhere in the application. I have the data to pre-fill the input fields with, but I can't figure out how do actually input it programatically, without the user doing it?

I need to invoke the above handleCategoryChange function. But my variable would be equal to data.value .. Which presents a problem! Invoking this function by myself isn't possible, because I won't have the event e nor a value called data.value as I will "just" pass in a variable by itself.

What's the right way to programatically fill an input field automatically in React, using variables elsewhere? I need to invoke the onChange function somehow, but the input values will be different..

Answer 1

Use controlled component for this situation, define a value property of input element like this:

<Input value={variable_name} ....

Whenever you will update that variable, automatically that value will get populated in input element.

Now you can populate some default value by assigning a value to variable_name and user can update that value by onChange function.

As per DOC :

An input form element whose value is controlled by React in this way is called a "controlled component".

Answer 2

传入value属性进行输入：

<input type="text" value={this.state.value} onChange={(e) => {this.setState({value: e.target.value })}/>

Answer 3

you can use the controlled component and pass the value to it.

<input type="text" value{this.state.value} 
       onChange={()=>  {this.setState({value:e.target.value })}}

Answer 4

Good question. I'm having the same issue, and just found a solution.

The problem is that:

• You can't just use the default state of the modal component to set the initial input value, because the modal renders one time within the parent component (starting off invisible), so the default state of the Modal wont keep up with any changes to the 'pre-filled' info in the store that the inputs within the modal require access to.
• You can't use the value attribute of the input to reference some redux store prop, since this is needed to reference the onChange function so the user can make changes to that pre-filled info.
• And, you can't use the onChange function to set the initial value, because it is required to update the local state with the users changes - not set an initial value. Anyway, this requires the user to click on something, and you want the modal inputs to be pre-populated before the user does anything as soon as the modal opens...

So. What we need is to update these input fields every time the Modal attribute isModalOpen (or whatever you are using) changes.

(ie, pre-populate the fields when the Modal is opened).

Again, note that opening the Modal is not RENDERING the modal, it was already rendered, once, and has sat there being invisible until that isModalOpen attribute changed to true.

The Solution:

Step 1: make a handler function in the Modal component that prefills the inputdata by updating the local state of the Modal component. Mine looks like this :

handlePreFillModalInputsOnOpen = () => {
    this.setState(() => ({
        orthForm: this.props.matchLexUnit['orthForm'],
        orthVar: this.props.matchLexUnit['orthVar'],
        oldOrthForm: this.props.matchLexUnit['oldOrthForm'],
        oldOrthVar: this.props.matchLexUnit['oldOrthVar'],
        source: this.props.matchLexUnit['source'],
        namedEntityCheck: this.props.matchLexUnit['namedEntityCheck'],
        styleMarkingCheck: this.props.matchLexUnit['styleMarkingCheck'],
        artificialCheck: this.props.matchLexUnit['artificialCheck'],
        error: ''
    }));
};

Step 2: Make that function fire ONLY when the isOpen attribute of the modal changes from false to true. (This is the meat of your problem I think). Use the lifecycle method componentDidUpdate . This will execute every time the props of the modal change.

componentDidUpdate(prevProps) {
    if (this.props.isModalOpen === true && prevProps.isModalOpen === false) {
        this.handlePreFillModalInputsOnOpen();
    }
}

Watch out

• make sure that you have a conditional in componentDidUpdate, otherwise you can run into infinite-loop/performance issues
• if you have the possibility of null values icoming in as the prefilled input info, make a null-check so that they will not be passed into the local state.

Hope this helps :)

Answer 5

How to Programmatically Prefill, Fill or Update input fields value in React or useState Hooks?

Firstly - Get and define the data from database

const **yourData** = isDataFromDatabase;

or if the data is stored in Redux, then...

const **yourData** = useSelector(isDataFromDatabase);

Secondly - append it as the default value of a useState hook

const [isDataValue, setIsDataValue] = useState(**yourData**);

Thirdly - create a function to watch and Update the changes made by the user to your data value and set it to the useState hook created above

/** handles Your Data Value */
const handleDataValue = (text) => {
 setIsDataValue(text);
};

Lastly - in your input tag, use the useState State as the "Value" parameter so it can be updated with the onChange function

<input
 className="css"
 id="myDataInput"
 type="text"
 value={isDataValue}
 placeholder={isDataValue}
 onChange={(e) => handleDataValue(e.target.value)}
/>

Now when you load the component, the prefilled value will be shown and can be updated in the HTML Input field.

That's All.