Update State in a Class Component-CodePudding

private readonly maxSizeOfDownloadedFiles: number = 1000000;

state = {
  totalSum: this.maxSizeOfDownloadedFiles
};

handleCallback = () => {
  this.setState({ totalSum: 12 })
  alert('totalSum '   this.state.totalSum);
};

When I run handleCallback method it doesn't update totalSum and gives me the default value, alert show totalSum 1000000 not 12. So why setState doesn't work?

CodePudding user response：

You can use the callback method in setState({} ,() => {}) which gets called immediately after the state update.

private readonly maxSizeOfDownloadedFiles: number = 1000000;

state = {
  totalSum:  this.maxSizeOfDownloadedFiles
}

handleCallback = () => {
  this.setState({ totalSum: 12}, () => {
   alert('totalSum '   this.state.totalSum);
 })
}