重构反应组分使其更短

Question

我有以下代码，但首先是解释。 我正在使用名为详细信息列表的REACTJS Office UI组件： https://developer.microsoft.com/en-us/fabric#/components/detailslist

我希望我的应用程序能够从任何类型的Sharepoint列表中呈现信息，而不管源有哪些列。为此，我试图实现这样的工厂方法设计模式：

export  interface IListItem {
    [key: string]: any;
    id: string;
    title: string;
    modified: Date;
    created: Date;
    modifiedby: string;
    createdby: string;    
}

import {IListItem} from './IListItem';

export interface  IAnnouncementListItem extends IListItem {
    announcementBody: string;
    expiryDate: Date;  
}

import {IListItem} from './IListItem';

export interface IDirectoryListItem extends IListItem {
        firstName: string;
        lastName: string;
        mobileNumber: string;
        internalNumber: string;  
}


import {IListItem} from './IListItem';

export interface  INewsListItem extends IListItem {
    newsheader: string;
    newsbody: string;
    expiryDate: Date;
}

import { IListItem } from './models/IListItem';
import { SPHttpClient, SPHttpClientResponse } from '@microsoft/sp-http';
export  interface IFactory{
    getItems(requester: SPHttpClient, siteUrl: string, listName: string): IListItem[];
}

import { SPHttpClient, SPHttpClientResponse } from '@microsoft/sp-http';
import { IWebPartContext } from '@microsoft/sp-webpart-base';
import { IListItem} from './models/IListItem';
import { IFactory } from './IFactory';
import { INewsListItem } from './models/INewsListItem';
import { IDirectoryListItem } from './models/IDirectoryListItem';
import { IAnnouncementListItem } from './models/IAnnouncementListItem';

export class ListItemFactory implements IFactory{   
    getItems(requester: SPHttpClient, siteUrl: string, listName: string): IListItem[] {
        switch(listName) {
            case 'List':
                let items: IListItem[];
                requester.get(`${siteUrl}/_api/web/lists/getbytitle('${listName}')/items?$select=Title,Id`,
                SPHttpClient.configurations.v1,
                {
                    headers: {
                    'Accept': 'application/json;odata=nometadata',
                    'odata-version': ''
                    }
                })
                .then((response: SPHttpClientResponse): Promise<{ value: IListItem[] }> => {
                    return response.json();
                })
                .then((response: { value: IListItem[] }): void => {
                    items= response.value;
                });
                return items;
            case 'News':
                let newsitems: INewsListItem[];
                requester.get(`${siteUrl}/_api/web/lists/getbytitle('${listName}')/items?$select=Title,Id`,
                SPHttpClient.configurations.v1,
                {
                    headers: {
                    'Accept': 'application/json;odata=nometadata',
                    'odata-version': ''
                    }
                })
                .then((response: SPHttpClientResponse): Promise<{ value: INewsListItem[] }> => {
                    return response.json();
                })
                .then((response: { value: INewsListItem[] }): void => {
                    newsitems= response.value;
                });
                return newsitems;
            case 'Announcements':
                let announcementitems: IAnnouncementListItem[];
                requester.get(`${siteUrl}/_api/web/lists/getbytitle('${listName}')/items?$select=Title,Id`,
                SPHttpClient.configurations.v1,
                {
                    headers: {
                    'Accept': 'application/json;odata=nometadata',
                    'odata-version': ''
                    }
                })
                .then((response: SPHttpClientResponse): Promise<{ value: IAnnouncementListItem[] }> => {
                    return response.json();
                })
                .then((response: { value: IAnnouncementListItem[] }): void => {
                    announcementitems= response.value;
                });
                return announcementitems;
            case 'Directory':
                let directoryitems: IDirectoryListItem[];
                requester.get(`${siteUrl}/_api/web/lists/getbytitle('${listName}')/items?$select=Title,Id`,
                SPHttpClient.configurations.v1,
                {
                    headers: {
                    'Accept': 'application/json;odata=nometadata',
                    'odata-version': ''
                    }
                })
                .then((response: SPHttpClientResponse): Promise<{ value: IDirectoryListItem[] }> => {
                    return response.json();
                })
                .then((response: { value: IDirectoryListItem[] }): void => {
                    items= response.value;
                });
                return directoryitems;
            default:
                return null;
        }
      }
} 
    /* public getItems(requester: SPHttpClient, siteUrl: string, listName: string): IListItem[] {
        let items: IListItem[];
        requester.get(`${siteUrl}/_api/web/lists/getbytitle('${listName}')/items?$select=Title,Id`,
        SPHttpClient.configurations.v1,
        {
            headers: {
            'Accept': 'application/json;odata=nometadata',
            'odata-version': ''
            }
        })
        .then((response: SPHttpClientResponse): Promise<{ value: IListItem[] }> => {
            return response.json();
        })
        .then((response: { value: IListItem[] }): void => {
            items= response.value;
        });
        return items;
    } */
}

州级：

import { IListItem } from './models/IListItem';
import { INewsListItem } from './models/INewsListItem';
import { IDirectoryListItem } from './models/IDirectoryListItem';
import { IAnnouncementListItem } from './models/IAnnouncementListItem';
import {
  IColumn
} from 'office-ui-fabric-react/lib/DetailsList';

export interface IFactoryMethodState{
  type: string;
  status: string;
  DetailsListItemState: IDetailsListItemState;
  DetailsNewsListItemState: IDetailsNewsListItemState;
  DetailsDirectoryListItemState : IDetailsDirectoryListItemState;
  DetailsAnnouncementListItemState : IDetailsAnnouncementListItemState;
}

export interface IDetailsListItemState {
  columns: IColumn[];
  items: IListItem[];
}

export interface IDetailsNewsListItemState {
  columns: IColumn[];
  items: INewsListItem[];
}

export interface IDetailsDirectoryListItemState {
  columns: IColumn[];
  items: IDirectoryListItem[];
}

export interface IDetailsAnnouncementListItemState {
  columns: IColumn[];
  items: IAnnouncementListItem[];
}

如您所见，我有不同类型的结果，所以我封装了该信息IfactoryMethodState

现在在组件中我使用它：

import * as React from 'react';
import styles from './FactoryMethod.module.scss';
import { IFactoryMethodProps } from './IFactoryMethodProps';
import { 
  IDetailsListItemState,  
  IDetailsNewsListItemState,
  IDetailsDirectoryListItemState,
  IDetailsAnnouncementListItemState,
  IFactoryMethodState
} from './IFactoryMethodState';
import { IListItem } from './models/IListItem';
import { IAnnouncementListItem } from './models/IAnnouncementListItem';
import { INewsListItem } from './models/INewsListItem';
import { IDirectoryListItem } from './models/IDirectoryListItem';

import { escape } from '@microsoft/sp-lodash-subset';
import { SPHttpClient, SPHttpClientResponse } from '@microsoft/sp-http';
import { ListItemFactory} from './ListItemFactory';
import { TextField } from 'office-ui-fabric-react/lib/TextField';
import {
  DetailsList,
  DetailsListLayoutMode,
  Selection,
  IColumn
} from 'office-ui-fabric-react/lib/DetailsList';
import { MarqueeSelection } from 'office-ui-fabric-react/lib/MarqueeSelection';
import { autobind } from 'office-ui-fabric-react/lib/Utilities';

let _columns = [
  {
    key: 'column1',
    name: 'Name',
    fieldName: 'name',
    minWidth: 100,
    maxWidth: 200,
    isResizable: true
  },
  {
    key: 'column2',
    name: 'Value',
    fieldName: 'value',
    minWidth: 100,
    maxWidth: 200,
    isResizable: true
  },
];

export default class FactoryMethod extends React.Component<any, IFactoryMethodState> {
  private listItemEntityTypeName: string = undefined;
  private _selection: Selection;

  constructor(props: IFactoryMethodProps, state: any) {
    super(props);

    //Initialize state
    this.state = {
      type: 'ListItem',
      status: this.listNotConfigured(this.props) ? 'Please configure list in Web Part properties' : 'Ready',
      DetailsListItemState:{
        columns:[],
        items:[]
      },
      DetailsNewsListItemState:{
        columns:[],
        items:[]
      },
      DetailsDirectoryListItemState:{
        columns:[],
        items:[]
      },
      DetailsAnnouncementListItemState:{
        columns:[],
        items:[]
      },
    };
  }

  public componentWillReceiveProps(nextProps: IFactoryMethodProps): void {
    this.listItemEntityTypeName = undefined;
    //Initialize state
    this.state = {
      type: 'ListItem',
      status: this.listNotConfigured(this.props) ? 'Please configure list in Web Part properties' : 'Ready',
      DetailsListItemState:{
        columns:[],
        items:[]
      },
      DetailsNewsListItemState:{
        columns:[],
        items:[]
      },
      DetailsDirectoryListItemState:{
        columns:[],
        items:[]
      },
      DetailsAnnouncementListItemState:{
        columns:[],
        items:[]
      },
    };
  }

  public render(): React.ReactElement<IFactoryMethodProps> {
    let { type, 
      status, 
      DetailsListItemState, 
      DetailsNewsListItemState, 
      DetailsDirectoryListItemState, 
      DetailsAnnouncementListItemState } = this.state;

        switch(this.props.listName)
        {
          case "List":
            return (
              <div>
                <MarqueeSelection selection={ this._selection }>
                  <DetailsList
                    items={ DetailsListItemState.items }
                    columns={ DetailsListItemState.columns }
                    setKey='set'
                    layoutMode={ DetailsListLayoutMode.fixedColumns }
                    selection={ this._selection }
                    selectionPreservedOnEmptyClick={ true }                
                    compact={ true }
                  />
                </MarqueeSelection>
              </div>
            );         
          case "Announcements":
            return (
              <div>
                <MarqueeSelection selection={ this._selection }>
                  <DetailsList
                    items={ DetailsAnnouncementListItemState.items }
                    columns={ DetailsAnnouncementListItemState.columns }
                    setKey='set'
                    layoutMode={ DetailsListLayoutMode.fixedColumns }
                    selection={ this._selection }
                    selectionPreservedOnEmptyClick={ true }                
                    compact={ true }
                  />
                </MarqueeSelection>
              </div>
            );
        case "News":
          return (
            <div>
              <MarqueeSelection selection={ this._selection }>
                <DetailsList
                  items={ DetailsNewsListItemState.items }
                  columns={ DetailsNewsListItemState.columns }
                  setKey='set'
                  layoutMode={ DetailsListLayoutMode.fixedColumns }
                  selection={ this._selection }
                  selectionPreservedOnEmptyClick={ true }                
                  compact={ true }
                />
              </MarqueeSelection>
            </div>
          );
        case "Directory":
          return (
            <div>
              <MarqueeSelection selection={ this._selection }>
                <DetailsList
                  items={ DetailsDirectoryListItemState.items }
                  columns={ DetailsDirectoryListItemState.columns }
                  setKey='set'
                  layoutMode={ DetailsListLayoutMode.fixedColumns }
                  selection={ this._selection }
                  selectionPreservedOnEmptyClick={ true }                
                  compact={ true }
                />
              </MarqueeSelection>
            </div>
          );
        default : 
          break;
      }
  }

  private readItems(): void {
    this.setState({
      status: 'Loading all items...'
    });
    let factory = new  ListItemFactory();

    //Here its where we actually use the pattern to make our coding easier.
    switch(this.props.listName)
    {
      case "List":
        let listItems  = factory.getItems(this.props.spHttpClient, this.props.siteUrl, this.props.listName);  
        this.setState({
          status: `Successfully loaded ${listItems.length} items`,
          DetailsListItemState : {
            items: listItems,
            columns: [
            ]
          }
        });      
        break;
      case "Announcements":
        let announcementlistItems  = factory.getItems(this.props.spHttpClient, this.props.siteUrl, this.props.listName) as IAnnouncementListItem[];  
        this.setState({
          status: `Successfully loaded ${listItems.length} items`,
          DetailsAnnouncementListItemState : {
            items: announcementlistItems,
            columns: []
          }
        });          
        break;
      case "News":
        let newsListItems  = factory.getItems(this.props.spHttpClient, this.props.siteUrl, this.props.listName) as INewsListItem[];  
        this.setState({
          status: `Successfully loaded ${listItems.length} items`,
          DetailsNewsListItemState : {
            items: newsListItems,
            columns: []
          }
        });      
        break;
      case "Directory":
        let directoryListItems  = factory.getItems(this.props.spHttpClient, this.props.siteUrl, this.props.listName) as IDirectoryListItem[];  
        this.setState({
          status: `Successfully loaded ${listItems.length} items`,
          DetailsDirectoryListItemState : {
            items: directoryListItems,
            columns: []
          }
        });   
        break;
      default : 
        break;
    }    
  }

  private _getSelectionDetails(): string {
    let selectionCount = this._selection.getSelectedCount();

    switch (selectionCount) {
      case 0:
        return 'No items selected';
      case 1:
        return '1 item selected: ' + (this._selection.getSelection()[0] as any).name;
      default:
        return `${selectionCount} items selected`;
    }
  }

  private listNotConfigured(props: IFactoryMethodProps): boolean {
    return props.listName === undefined ||
      props.listName === null ||
      props.listName.length === 0;
  }


}

我不喜欢这段代码：

1. switch语句，是否可以重写它并使其缩短，可能没有SWITCH？

2. 国家实施，我对此并不十分确信。

更新1： 在做出改变之后，我发现了一些不正确的事情：

错误1：

public ListMarqueeSelection =（itemState：{fixedColumns：number，columns：{} []，items：{} []}）=＆gt; （                                compact = {true}＆gt;                         ）;

  

输入＆＃39; {items：{} [];列： {}[]; setKey：＆＃34; set＆＃34 ;; layoutMode：   DetailsListLayoutMode.fixedColumns;塞莱...＆＃39;不能分配给类型   ＆＃39; IntrinsicAttributes＆amp; IntrinsicClassAttributes＆amp;   Readonly＆lt; {children？：ReactNode; }＆GT; ...＆＃39 ;.输入＆＃39; {items：{} [];   列： {}[]; setKey：＆＃34; set＆＃34 ;; layoutMode：   DetailsListLayoutMode.fixedColumns;塞莱...＆＃39;不能分配给类型   ＆＃39;只读＆＃39 ;.       财产类型＆＃39;列＆＃39;是不相容的。         输入＆＃39; {} []＆＃39;不能分配给类型＆＃39; IColumn []＆＃39;。 [ts]输入＆＃39; {items：{} [];列： {}[]; setKey：＆＃34; set＆＃34 ;; layoutMode：   DetailsListLayoutMode.fixedColumns;塞莱...＆＃39;不能分配给类型   ＆＃39; IntrinsicAttributes＆amp; IntrinsicClassAttributes＆amp;   Readonly＆lt; {children？：ReactNode; }＆GT; ...＆＃39 ;.输入＆＃39; {items：{} [];   列： {}[]; setKey：＆＃34; set＆＃34 ;; layoutMode：   DetailsListLayoutMode.fixedColumns;塞莱...＆＃39;不能分配给类型   ＆＃39;只读＆＃39 ;.       财产类型＆＃39;列＆＃39;是不相容的。         输入＆＃39; {} []＆＃39;不能分配给类型＆＃39; IColumn []＆＃39;。           输入＆＃39; {}＆＃39;不能分配给类型＆＃39; IColumn＆＃39;。             物业＆＃39;关键＆＃39;在＆＃39; {}＆＃39;中缺少。 （参数）itemState：{       fixedColumns：number;       列： {}[];       items：{} []; }

错误2：

public render() {
    let { type, 
      status, 
      DetailsListItemState, 
      DetailsNewsListItemState, 
      DetailsDirectoryListItemState, 
      DetailsAnnouncementListItemState } = this.state;

      switch(this.props.listName)
      {
          case "List":
            return <ListMarqueeSelection itemState={this.state.DetailsListItemState}/>;
          case "News":
            return <ListMarqueeSelection itemState={this.state.DetailsNewsListItemState}/>;
          case "Announcements":
            return <ListMarqueeSelection itemState={this.state.DetailsAnnouncementListItemState}/>;
          case "Directory":
            return <ListMarqueeSelection itemState={this.state.DetailsDirectoryListItemState}/>;
          default:
            return undefined;
      }  
  }

  

找不到名称＆＃39; ListMarqueeSelection＆＃39;。你的意思是实例吗？   member＆＃39; this.ListMarqueeSelection＆＃39;？

Answer 1

你是对的，它太长了，但那是因为它的因素很少。幸运的是，它可以以简单的方式进行改进

首先，在setState的所有案例中，*ListItemState的所有来电都是相同的，但所使用的readItems除外。我们应该提取一个函数并调用它，删除重复。

首先从方法readItems开始

  private readItems() {
    this.setState({
      status: 'Loading all items...'
    });
    let factory = new ListItemFactory();

    //Here its where we actually use the pattern to make our coding easier.
    switch(this.props.listName)
    {
      case "List":
        this.setState({
          status: `Successfully loaded ${listItems.length} items`,
          DetailsListItemState : {
            items: announcementlistItems,
            columns: []
          }
        });          
        break;

        break;
      case "Announcements":
        let announcementlistItems  = factory.getItems(this.props.spHttpClient, this.props.siteUrl, this.props.listName) as IAnnouncementListItem[];  
        this.setState({
          status: `Successfully loaded ${listItems.length} items`,
          DetailsAnnouncementListItemState : {
            items: announcementlistItems,
            columns: []
          }
        });          
        break;
      case "News":
        let newsListItems  = factory.getItems(this.props.spHttpClient, this.props.siteUrl, this.props.listName) as INewsListItem[];  
        this.setState({
          status: `Successfully loaded ${listItems.length} items`,
          DetailsNewsListItemState : {
            items: newsListItems,
            columns: []
          }
        });      
        break;
      case "Directory":
        let directoryListItems  = factory.getItems(this.props.spHttpClient, this.props.siteUrl, this.props.listName) as IDirectoryListItem[];  
        this.setState<keyof {}>({
          status: `Successfully loaded ${listItems.length} items`,
          DetailsDirectoryListItemState : {
            items: directoryListItems,
            columns: []
          }
        });   
        break;
      default : 
        break;
    }    
  }

所以让我们提取一个共享方法

  setStateWithList() {
    const factory = new ListItemFactory();
    const items  = factory.getItems(this.props.spHttpClient,
    this.props.siteUrl, this.props.listName); 
    const keyPart = this.props.listName === 'Items' ? '' : this.props.listName;    
    this.setState({
        status: `Successfully loaded ${items.length} items`,
        ['Details' + keyPart + 'ListItemState' as keyof IFactoryMethodProps] : {
          items,
          columns: [
          ]
        }
      });      
    }

这导致我们

  private readItems() {
    this.setState({
      status: 'Loading all items...'
    });

    //Here its where we actually use the pattern to make our coding easier.
    if (this.props.listName) {
      this.setStateWithList();
    }   
  }

这显然是多余的，所以我们可以用

替换它

  private readItems() {
    this.setState({
      status: 'Loading all items...'
    });

    if (this.props.listName) {
      this.setStateWithList();
    }  
  }

现在，转到render

我们拥有什么

  public render() {
    let { type, 
      status, 
      DetailsListItemState, 
      DetailsNewsListItemState, 
      DetailsDirectoryListItemState, 
      DetailsAnnouncementListItemState } = this.state;

        switch(this.props.listName)
        {
          case "List":
            return (
              <div>
                <MarqueeSelection selection={ this._selection }>
                  <DetailsList
                    items={ DetailsListItemState.items }
                    columns={ DetailsListItemState.columns }
                    setKey='set'
                    layoutMode={ DetailsListLayoutMode.fixedColumns }
                    selection={ this._selection }
                    selectionPreservedOnEmptyClick={ true }                
                    compact={ true }
                  />
                </MarqueeSelection>
              </div>
            );         
          case "Announcements":
            return (
              <div>
                <MarqueeSelection selection={ this._selection }>
                  <DetailsList
                    items={ DetailsAnnouncementListItemState.items }
                    columns={ DetailsAnnouncementListItemState.columns }
                    setKey='set'
                    layoutMode={ DetailsListLayoutMode.fixedColumns }
                    selection={ this._selection }
                    selectionPreservedOnEmptyClick={ true }                
                    compact={ true }
                  />
                </MarqueeSelection>
              </div>
            );
        case "News":
          return (
            <div>
              <MarqueeSelection selection={ this._selection }>
                <DetailsList
                  items={ DetailsNewsListItemState.items }
                  columns={ DetailsNewsListItemState.columns }
                  setKey='set'
                  layoutMode={ DetailsListLayoutMode.fixedColumns }
                  selection={ this._selection }
                  selectionPreservedOnEmptyClick={ true }                
                  compact={ true }
                />
              </MarqueeSelection>
            </div>
          );
        case "Directory":
          return (
            <div>
              <MarqueeSelection selection={ this._selection }>
                <DetailsList
                  items={ DetailsDirectoryListItemState.items }
                  columns={ DetailsDirectoryListItemState.columns }
                  setKey='set'
                  layoutMode={ DetailsListLayoutMode.fixedColumns }
                  selection={ this._selection }
                  selectionPreservedOnEmptyClick={ true }                
                  compact={ true }
                />
              </MarqueeSelection>
            </div>
          );
        default : 
          break;
      }
    }     

我们将应用与之前相同的方法并应用参数化

  ListMarqueeSelection(itemState: {fixedColumns: number, colums: IColumn[], items: IListItem[] }) => (
       <div>
         <MarqueeSelection selection={ this._selection }>
           <DetailsList
             items={ itemState.items }
             columns={ itemState.columns }
             setKey='set'
             layoutMode={ DetailsListLayoutMode.fixedColumns }
             selection={ this._selection }
             selectionPreservedOnEmptyClick={ true }                
             compact={ true }>
           </DetailsList
         </MarqueeSelection>
     </div>
    );  

引导我们

  render() {
    switch(this.props.listName)
    {
        case "List":
          return <this.ListMarqueeSelection
            itemState={this.state.DetailsListItemState}/>;
        case "News":
          return <this.ListMarqueeSelection
            itemState={this.state.DetailsNewsListItemState}/>;
        case "Announcements":
          return (<this.ListMarqueeSelection
            itemState={this.state.DetailsAnnouncementsListItemState}/>;
        case "Directory":
          return <this.ListMarqueeSelection
            itemState={this.state.DetailsDirectoryListItemState}/>;
        default:
          return undefined;
    }
  }

最后，让我们通过提取共享方法来清除constructor和componentWillReceiveProps之间的重复逻辑。

Out State组件最终看起来像

export default class FactoryMethod extends React.Component<any, IFactoryMethodState> {
  listItemEntityTypeName?: string;
  _selection: Selection;

  constructor(props: IFactoryMethodProps, state: any) {
    super(props);
    setInitialState();
  }

  componentWillReceiveProps(nextProps: IFactoryMethodProps) {
    this.listItemEntityTypeName = undefined;
    setInitialState();
  }    


  render() {
    switch(this.props.listName)
    {
        case "List":
          return <this.ListMarqueeSelection
            itemState={this.state.DetailsListItemState}/>;
        case "News":
          return <this.ListMarqueeSelection
            itemState={this.state.DetailsNewsListItemState}/>;
        case "Announcements":
          return (<this.ListMarqueeSelection
            itemState={this.state.DetailsAnnouncementsListItemState}/>;
        case "Directory":
          return <this.ListMarqueeSelection
            itemState={this.state.DetailsDirectoryListItemState}/>;
        default:
          return undefined;
    }
  }

  readItems() {
    this.setState({
      status: 'Loading all items...'
    });


    if (this.props.listName) {
        this.setStateWithList();
    }    
  }

  setInitialState() {
    this.state = {
      type: 'ListItem',
      status: this.listNotConfigured(this.props)
        ? 'Please configure list in Web Part properties'
        : 'Ready',
      DetailsListItemState:{
        columns:[],
        items:[]
      },
      DetailsNewsListItemState:{
        columns:[],
        items:[]
      },
      DetailsDirectoryListItemState:{
        columns:[],
        items:[]
      },
      DetailsAnnouncementListItemState:{
        columns:[],
        items:[]
      },
    };
  }

  ListMarqueeSelection = (itemState: {fixedColumns: number, colums: {}[], items: {}[] }) => (
   <div>
     <MarqueeSelection selection={ this._selection }>
       <DetailsList
         items={ itemState.items }
         columns={ itemState.columns }
         setKey='set'
         layoutMode={ DetailsListLayoutMode.fixedColumns }
         selection={ this._selection }
         selectionPreservedOnEmptyClick={ true }                
         compact={ true }>
       </DetailsList
     </MarqueeSelection>
   </div>
  );

  setStateWithList() {
    const factory = new ListItemFactory();
    const items  = factory.getItems(this.props.spHttpClient,
    this.props.siteUrl, this.props.listName);  
    const keyPart = this.props.listName === 'Items' ? '' : this.props.listName;    

    // the explicit specification of the type argument `keyof {}` is bad and
    // it should not be required.
    this.setState<keyof {}>({
        status: `Successfully loaded ${items.length} items`,
        ['Details' + keyPart + 'ListItemState'] : {
          items,
          columns: [
          ]
        }
      });      
  }

  _getSelectionDetails() {
    const selectionCount = this._selection.getSelectedCount();

    switch (selectionCount) {
      case 0:
        return 'No items selected';
      case 1:
        return `1 item selected: ${this._selection.getSelection()[0]).name}`;
      default:
        return `${selectionCount} items selected`;
    }
  }

  listNotConfigured(props: IFactoryMethodProps) {
    return !props.listNane || props.listName.length === 0;
  }
}

当然，我们可以用另一种机制取代开关并改进更多，但这是一项重大改进。

我们可以看到问题不是转换，而是重复并丢失了临时子类型的机会