Do not mutate state directly, Use setState() react

问题:

<input
  defaultValue={this.props.str.name}
  ref={(input) => { this.state.name = input; }}
  name="name"
  type="text"
  className="form-control"
  onChange={this.handleInputChange}
/> 

handleInputChange(event) {
  this.setState({
    [event.target.name]: event.target.value
  });
}

if(this.state.name.value === "") {
  this.msg.show('Required fields can not be empty', {
    time: 2000,
    type: 'info',
    icon: <img src="img/avatars/info.png" role="presentation"/>
  });
}

I'm trying to set the default value like that and wanted to access it as well. I did like this and accessed the value with this.state.name.value but the thing is its working but showing the warning as

Do not mutate state directly, Use setState() react/no-direct-mutation-state .

回答1:

Getting "Do not mutate state directly, Use setState()", Why?

Because, you are mutating the state value inside ref callback method to store the node ref, Here:

this.state.name = input;

---

Solution:

Don't use state variable to store the reference, You can directly store them in component instance because that will not change with time.

As per DOC:

The state contains data specific to this component that may change over time. The state is user-defined, and it should be a plain JavaScript object.

If you don’t use it in render(), it shouldn’t be in the state. For example, you can put timer IDs directly on the instance.

Since you are using controlled input element, ref is not required. Directly use this.state.name with input element value property and this.state.name to access the value.

Use this:

<input
    value={this.state.name || ''}
    name="name"
    type="text"
    className="form-control"
    onChange={this.handleInputChange} 
/>

If you wanted to use ref then store the ref directly on instance, remove value property and you can remove the onChange event also, Use it like this:

<input
    ref={el => this.el = el}
    defaultValue={this.props.str.name}
    name="name"
    type="text"
    className="form-control"
/> 

Now use this ref to access the value like this:

this.el.value

回答2:

you can instead clone the entire property value inside the with spread operator and then reform or edit the value for example :

state = {Counters: [{id:1,value:1},{id: 2,value: 2},{id: 3,value: 3},{id: 4,value: 4}]}
increment = (Counter) => {

        //This is where the state property value is cloned 

        const Counters = [...this.state.Counters];
        console.log(Counters);
        const index = Counters.indexOf(Counter)
        Counters[index].value++
        this.setState({
            Counters: this.state.Counters
        })
}