最近几年来，地理信息系统无论是在理论上还是应用上都处在一个飞速发展的阶段。 GIS被应用于多个领域的建模和决策支持，如城市管理、区划、环境整治等等，地理信息成为信息时代重要的组成部分之一； “数字地球”概念的提出，更进一步推动了作为其技术支撑的GIS的发展。 与此同时，一些学者致力于相关的理论研究，如空间感知、空间数据误差、空间关系的形式化等等。 这恰好说明了地理信息系统作为应用技术和学科的两个方面，并且这两个方面构成了相互促进的发展过程。
getDerivedStateFromProps() the format of the method is as follows:
static getDerivedStateFromProps(props, state) getDerivedStateFromProps will be called render method, that is, before rendering the DOM element, and during the initial mount and subsequent updates.
state at all times depends on props .
getDerivedStateFromProps exists for only one purpose: to make the component in the props update when Chan state .
This method returns an object for updating state if you return null nothing is updated.
The following example favoritesite the initial value of the runoob , but getDerivedStateFromProps() methods pass through favsite properties have been updated favoritesite walue of: 3.14.1. Example ¶
classHeaderextendsReact.Component{constructor(props){super(props);this.state={favoritesite:"runoob"};}staticgetDerivedStateFromProps(props,state){return{favoritesite:props.favsite};}render(){return(<h1>My favorite website is{this.state.favoritesite}h1>);}}ReactDOM.render(<Headerfavsite="Google"/>,document.getElementById('root'));
3.14.2. Example ¶
classHeaderextendsReact.Component{constructor(props){super(props);this.state={favoritesite:"runoob"};}staticgetDerivedStateFromProps(props,state){return{favoritesite:props.favsite};}changeSite=()=>{this.setState({favoritesite:"google"});}render(){return(<div> <h1>My favorite website is{this.state.favoritesite}h1> <buttontype="button"onClick={this.changeSite}>Change website namebutton> div>);}}ReactDOM.render(<Headerfavcol="taobao"/>,document.getElementById('root'));