React component doesn't re-render on updating state

Question

I think u know better solution for this: I have file with array of objects with my cats:

var categories = [
  {
    "id": 1,
    "name" : "Faktury",
    "selected" : false
  },
  {
    "id": 2,
    "name" : "Telefony",
    "selected" : false
  },
  {
    "id": 3,
    "name" : "Komputery",
    "selected" : false
  },
  {
    "id": 4,
    "name" : "Rachunkowośc",
    "selected" : false
  },
  {
    "id": 5,
    "name" : "Finanse",
    "selected" : false
  }
];

and i have:

<ul className="category">
  {this.state.categories.map((item,index) =>
    <li onClick={()=>this.filterCategory(item,index)} key={item.id} className={item.selected? 'active' : ''}>{item.name}</li>
  )}
</ul>

and my filterCategory:

filterCategory(item,index) {
  this.state.categories[index].selected = !this.state.categories[index].selected;
  this.forceUpdate();
}

Do u know how i can make it without forceUpdate() ? I have read on stack i should avoid use this.forceUpdate()

Answer 1

Using setState automatically triggers a rerender, so instead of directly mutating the state use setState to update the state.

filterCategory(item,index){
   var categories = [...this.state.categories];
   categories[index].selected = !categories[index].selected;
   this.setState({categories})
}

According to the DOCS:

NEVER mutate this.state directly, as calling setState() afterwards may replace the mutation you made. Treat this.state as if it were immutable.

Answer 2

Do Not Modify State Directly

Use setState method for state changes.