react render method is called Twice, changing url - reactjs

Question

I am newbie in react. I read this question , but didn't solve my problem. I think I'm wrong with componentWillReceiveProps comprehension . My component and it's parent are like this:
the parent:
import React from 'react';
import { Router, Route, Link } from 'react-router';
export default class App extends React.Component {
items = [
{id: 1086, title: 'MENU1'},
{id: 1083, title: 'MENU2'},
{id: 1093, title: 'MENU3'}]
renderItems = ()=> {
return this.items.map((item, index)=> {
let url = 'content/' + item.id;
return (<li key={index}><Link to={url} activeClassName="active">{item.title}</Link></li>);
});
}
render() {
return (
<div>
<h1 style={{textAlign:'center'}}>My First React App</h1>
<ul className="nav nav-pills nav-justified">{this.renderItems()}</ul>
{this.props.children}
</div>
);
}
}
the child:
import React, { Component } from 'react';
import UmContent from './UmContent'
import $ from 'jquery';
import ProgressBar from 'progressbar.js';
export default class UmContentContainer extends Component {
state = {
data: ''
}
firstInitial = true;
componentDidMount() {
if (this.firstInitial) {
let props = this.props;
this.sendRequestToServer(props);
this.firstInitial = false;
}
}
sendRequestToServer = (props)=> {
if (!props || !props.params || !props.params.id) {
return;
}
let itemId = props.params.id;
let that = this;
this.setState({data: itemId});
}
componentWillReceiveProps(props, states) {
this.sendRequestToServer(props);
console.log(props.params.id);
}
render() {
return (
<div className="col-md-12">
<h1>{this.state.data}</h1>
</div>);
}
}
and index.js :
import React from 'react'
import { render } from 'react-dom'
import { Router, Route, Link,hashHistory } from 'react-router'
import App from './App';
import UmContentContainer from './Umbreco/UmContentContainer';
render((
<Router history={hashHistory}>
<Route path="/" component={App}>
<Route path="/content/:id" component={UmContentContainer} />
</Route>
</Router>
), document.getElementById('root'))
after first mounting , console writes "id" twice. I can't understand why?

Answer 1

I found my answer HERE , I was wrong , actually it was about the hashHistory and pushing new url . not componentWillReceiveProps.