setState 没有更新 React Native

Question

I am trying to get state from one component, but somewhy I can't see any changes when I do setState(). Here is my state:

class MyTestComponent extends React.Component {
    constructor(props){
    super(props);

    this.state = {
        check: 'String1'
    }
   this.testOtherFunction = this.testOtherFunction.bind(this);
}

Now, here is the function itself:

   testOtherFunction(){
            this.setState({check: "String2"},
            function(){
               console.log(this.state.check, 'total'); // somewhy is not printed
            });
      return this.state.check;
  }

And here, in another component I call this function:

componentDidMount() {

 console.log("test", MyTestComponent.testOtherFunction()) // returns String1
  }

Why it returning old state from a constructor? And how can I fix that? I know setState is async, but I wonder what is the way out from situations like this.

Answer 1

setState() does not immediately mutate this.state. Accessing this.state after calling this method can potentially return the existing value. That is why you may not see the new value immediately.

you can use setState with callback function.

this.setState({check: "String2"},, function () {
    console.log(this.state.check, 'total');
});