对reactjs生命周期感到困惑

Question

我有以下Sharepoint Framework webpart，它基本上根据具有列表名称的下拉属性呈现网格。

import * as React from "react";
import * as ReactDom from "react-dom";
import { Version } from "@microsoft/sp-core-library";
import {
  BaseClientSideWebPart,
  IPropertyPaneConfiguration,
  PropertyPaneTextField,
  PropertyPaneDropdown,
  IPropertyPaneDropdownOption,
  IPropertyPaneField,
  PropertyPaneLabel
} from "@microsoft/sp-webpart-base";

import * as strings from "FactoryMethodWebPartStrings";
import FactoryMethod from "./components/FactoryMethod";
import { IFactoryMethodProps } from "./components/IFactoryMethodProps";
import { IFactoryMethodWebPartProps } from "./IFactoryMethodWebPartProps";
import * as lodash from "@microsoft/sp-lodash-subset";
import List from "./components/models/List";
import { Environment, EnvironmentType } from "@microsoft/sp-core-library";
import IDataProvider from "./components/dataproviders/IDataProvider";
import MockDataProvider from "./test/MockDataProvider";
import SharePointDataProvider from "./components/dataproviders/SharepointDataProvider";

export default class FactoryMethodWebPart extends BaseClientSideWebPart<IFactoryMethodWebPartProps> {
  private _dropdownOptions: IPropertyPaneDropdownOption[];
  private _selectedList: List;
  private _disableDropdown: boolean;
  private _dataProvider: IDataProvider;
  private _factorymethodContainerComponent: FactoryMethod;

  protected onInit(): Promise<void> {
    this.context.statusRenderer.displayLoadingIndicator(this.domElement, "Todo");

    /*
    Create the appropriate data provider depending on where the web part is running.
    The DEBUG flag will ensure the mock data provider is not bundled with the web part when you package the
     solution for distribution, that is, using the --ship flag with the package-solution gulp command.
    */
    if (DEBUG && Environment.type === EnvironmentType.Local) {
      this._dataProvider = new MockDataProvider();
    } else {
      this._dataProvider = new SharePointDataProvider();
      this._dataProvider.webPartContext = this.context;
    }

    this.openPropertyPane = this.openPropertyPane.bind(this);

    /*
    Get the list of tasks lists from the current site and populate the property pane dropdown field with the values.
    */
    this.loadLists()
      .then(() => {
        /*
         If a list is already selected, then we would have stored the list Id in the associated web part property.
         So, check to see if we do have a selected list for the web part. If we do, then we set that as the selected list
         in the property pane dropdown field.
        */
        if (this.properties.spListIndex) {
          this.setSelectedList(this.properties.spListIndex.toString());
          this.context.statusRenderer.clearLoadingIndicator(this.domElement);
        }
      });

    return super.onInit();
  }

  // render method of the webpart, actually calls Component
  public render(): void {
    const element: React.ReactElement<IFactoryMethodProps > = React.createElement(
      FactoryMethod,
      {
        spHttpClient: this.context.spHttpClient,
        siteUrl: this.context.pageContext.web.absoluteUrl,
        listName: this._dataProvider.selectedList === undefined ? "GenericList" : this._dataProvider.selectedList.Title,
        dataProvider: this._dataProvider,
        configureStartCallback: this.openPropertyPane
      }
    );

    // reactDom.render(element, this.domElement);
    this._factorymethodContainerComponent = <FactoryMethod>ReactDom.render(element, this.domElement);

  }

  // loads lists from the site and fill the dropdown.
  private loadLists(): Promise<any> {
    return this._dataProvider.getLists()
      .then((lists: List[]) => {
        // disable dropdown field if there are no results from the server.
        this._disableDropdown = lists.length === 0;
        if (lists.length !== 0) {
          this._dropdownOptions = lists.map((list: List) => {
            return {
              key: list.Id,
              text: list.Title
            };
          });
        }
      });
  }

  protected get dataVersion(): Version {
    return Version.parse("1.0");
  }

  protected onPropertyPaneFieldChanged(propertyPath: string, oldValue: any, newValue: any): void {
    /*
    Check the property path to see which property pane feld changed. If the property path matches the dropdown, then we set that list
    as the selected list for the web part.
    */
    if (propertyPath === "spListIndex") {
      this.setSelectedList(newValue);
    }

    /*
    Finally, tell property pane to re-render the web part.
    This is valid for reactive property pane.
    */
    super.onPropertyPaneFieldChanged(propertyPath, oldValue, newValue);
  }

  // sets the selected list based on the selection from the dropdownlist
  private setSelectedList(value: string): void {
    const selectedIndex: number = lodash.findIndex(this._dropdownOptions,
      (item: IPropertyPaneDropdownOption) => item.key === value
    );

    const selectedDropDownOption: IPropertyPaneDropdownOption = this._dropdownOptions[selectedIndex];

    if (selectedDropDownOption) {
      this._selectedList = {
        Title: selectedDropDownOption.text,
        Id: selectedDropDownOption.key.toString()
      };

      this._dataProvider.selectedList = this._selectedList;
    }
  }


  // we add fields dynamically to the property pane, in this case its only the list field which we will render
  private getGroupFields(): IPropertyPaneField<any>[] {
    const fields: IPropertyPaneField<any>[] = [];

    // we add the options from the dropdownoptions variable that was populated during init to the dropdown here.
    fields.push(PropertyPaneDropdown("spListIndex", {
      label: "Select a list",
      disabled: this._disableDropdown,
      options: this._dropdownOptions
    }));

    /*
    When we do not have any lists returned from the server, we disable the dropdown. If that is the case,
    we also add a label field displaying the appropriate message.
    */
    if (this._disableDropdown) {
      fields.push(PropertyPaneLabel(null, {
        text: "Could not find tasks lists in your site. Create one or more tasks list and then try using the web part."
      }));
    }

    return fields;
  }

  private openPropertyPane(): void {
    this.context.propertyPane.open();
  }

  protected getPropertyPaneConfiguration(): IPropertyPaneConfiguration {
    return {
      pages: [
        {
          header: {
            description: strings.PropertyPaneDescription
          },
          groups: [
            {
              groupName: strings.BasicGroupName,
              /*
              Instead of creating the fields here, we call a method that will return the set of property fields to render.
              */
              groupFields: this.getGroupFields()
            }
          ]
        }
      ]
    };
  }
}

my component.tsx

//#region Imports
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,
  buildColumns,
  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";
import PropTypes from "prop-types";
//#endregion


export default class FactoryMethod extends React.Component<IFactoryMethodProps, IFactoryMethodState> {
  constructor(props: IFactoryMethodProps, state: any) {
    super(props);
    this.setInitialState();
  }

  // lifecycle help here: https://staminaloops.github.io/undefinedisnotafunction/understanding-react/

  //#region Mouting events lifecycle

  // the data returned from render is neither a string nor a DOM node.
  // it's a lightweight description of what the DOM should look like.
  // inspects this.state and this.props and create the markup.
  // when your data changes, the render method is called again.
  // react diff the return value from the previous call to render with
  // the new one, and generate a minimal set of changes to be applied to the DOM.
  public render(): React.ReactElement<IFactoryMethodProps> {
    switch(this.props.listName) {
        case "GenericList":
          // tslint:disable-next-line:max-line-length
          return <this.ListMarqueeSelection items={this.state.DetailsListItemState.items} columns={this.state.columns} />;
        case "News":
          // tslint:disable-next-line:max-line-length
          return <this.ListMarqueeSelection items={this.state.DetailsNewsListItemState.items} columns={this.state.columns}/>;
        case "Announcements":
          // tslint:disable-next-line:max-line-length
          return <this.ListMarqueeSelection items={this.state.DetailsAnnouncementListItemState.items} columns={this.state.columns}/>;
        case "Directory":
          // tslint:disable-next-line:max-line-length
          return <this.ListMarqueeSelection items={this.state.DetailsDirectoryListItemState.items} columns={this.state.columns}/>;
        default:
          return null;
    }
  }

   // invoked once, only on the client (not on the server), immediately AFTER the initial rendering occurs.
   public componentDidMount(): void {
    // you can access any refs to your children
    // (e.g., to access the underlying DOM representation - ReactDOM.findDOMNode).
    // the componentDidMount() method of child components is invoked before that of parent components.
    // if you want to integrate with other JavaScript frameworks,
    // set timers using setTimeout or setInterval,
    // or send AJAX requests, perform those operations in this method.
    this._configureWebPart = this._configureWebPart.bind(this);
    this.readItemsAndSetStatus("");
  }

  //#endregion

  //#region Props changes lifecycle events (after a property changes from parent component)
  public componentWillReceiveProps(nextProps: IFactoryMethodProps): void {
    if(nextProps.listName !== this.props.listName) {
      this.readItemsAndSetStatus(nextProps.listName);
    }
  }

  //#endregion

  //#region private methods
  private _configureWebPart(): void {
    this.props.configureStartCallback();
  }

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

  // reusable inline component
  private ListMarqueeSelection = (itemState: {columns: IColumn[], items: IListItem[] }) => (
      <div>
          <DetailsList
            items={ itemState.items }
            columns={ itemState.columns }
            setKey="set"
            layoutMode={ DetailsListLayoutMode.fixedColumns }
            selectionPreservedOnEmptyClick={ true }
            compact={ true }>
          </DetailsList>
      </div>
  )

  // read items using factory method pattern and sets state accordingly
  private readItemsAndSetStatus(nextListName: string): void {
    this.setState({
      status: "Loading all items..."
    });

    const factory: ListItemFactory = new ListItemFactory();
    factory.getItems(this.props.spHttpClient, this.props.siteUrl, nextListName)
    .then((items: any[]) => {
      const keyPart: string = this.props.listName === "GenericList" ? "" : nextListName;
        // 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: buildColumns(items)
        });
    });
  }

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

  //#endregion
}

和我的工厂对象

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 {
    private _listItems: IListItem[];
    public getItems(requester: SPHttpClient, siteUrl: string, listName: string): Promise<IListItem[]> {
        if(listName === ""){
            listName = "GenericList";
        }
        switch(listName) {
            case "GenericList":
                let items: IListItem[];
                // tslint:disable-next-line:max-line-length
                return requester.get(`${siteUrl}/_api/web/lists/getbytitle('${listName}')/items?$select=Title,Id,Modified,Created,Author/Title,Editor/Title&$expand=Author,Editor`,
                SPHttpClient.configurations.v1,
                {
                    headers: {
                        "Accept": "application/json;odata=nometadata",
                        "odata-version": ""
                    }
                })
                .then((response: SPHttpClientResponse): Promise<{ value: IListItem[] }> => {
                    return response.json(); 
                })
                .then((json: { value: IListItem[] }) => {
                    console.log(JSON.stringify(json.value));
                    return items=json.value.map((v,i)=>(
                        { 
                            //key: v.id,
                            id: v.Id,
                            title: v.Title,
                            created: v.Created,
                            createdby: v.Author.Title,
                            modified: v.Modified,
                            modifiedby: v.Editor.Title                        
                        }
                    ));
                });  
            case "News":
                let newsitems: INewsListItem[];
                // tslint:disable-next-line:max-line-length
                return requester.get(`${siteUrl}/_api/web/lists/getbytitle('${listName}')/items?$select=Title,Id,Modified,Created,Created By,Modified By,newsheader,newsbody,expiryDate`,
                SPHttpClient.configurations.v1,
                {
                    headers: {
                        "Accept": "application/json;odata=nometadata",
                        "odata-version": ""
                    }
                })
                .then((response: SPHttpClientResponse): Promise<{ value: INewsListItem[] }> => {
                    return response.json();
                })
                .then((json: { value: INewsListItem[] }) => {
                    return items=json.value.map((v,i)=>(
                        { 
                            id: v.Id,
                            title: v.Title,
                            created: v.Created,
                            createdby: v.Author.Title,
                            modified: v.Modified,
                            modifiedby: v.Editor.Title,
                            newsheader: v.newsheader,
                            newsbody: v.newsbody,
                            expiryDate: v.expiryDate
                        }
                    ));
                });
            case "Announcements":
                let announcementitems: IAnnouncementListItem[];
                return requester.get(`${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((json: { value: IAnnouncementListItem[] }) => {
                    return items=json.value.map((v,i)=>(
                        { 
                            id: v.Id,
                            title: v.Title,
                            created: v.Created,
                            createdby: v.Author.Title,
                            modified: v.Modified,
                            modifiedby: v.Editor.Title,
                            announcementBody: v.announcementBody,
                            expiryDate: v.expiryDate
                        }
                    ));
                });
            case "Directory":
                let directoryitems: IDirectoryListItem[];
                return requester.get(`${siteUrl}/_api/web/lists/getbytitle('${listName}')/items?$select=Title,Id`,
                SPHttpClient.configurations.v1,
                {
                    headers: {
                        "Accept": "application/json;odata=nometadata",
                        "odata-version": ""
                    }
                })
                .then((response: SPHttpClientResponse): Promise<{ value: IDirectoryListItem[] }> => {
                    return response.json();
                })
                .then((json: { value: IDirectoryListItem[] }) => {
                    return items=json.value.map((v,i)=>(
                        { 
                            id: v.Id,
                            title: v.Title,
                            created: v.Created,
                            createdby: v.Author.Title,
                            modified: v.Modified,
                            modifiedby: v.Editor.Title,
                            firstName: v.firstName,
                            lastName: v.lastName,
                            mobileNumber: v.mobileNumber,
                            internalNumber: v.internalNumber
                        }
                    ));
                });
            default:
            // tslint:disable-next-line:max-line-length
                return requester.get(`${siteUrl}/_api/web/lists/getbytitle('${listName}')/items?$select=Title,Id,Modified,Created,Author/Title,Editor/Title&$expand=Author,Editor`,
                SPHttpClient.configurations.v1,
                {
                    headers: {
                        "Accept": "application/json;odata=nometadata",
                        "odata-version": ""
                    }
                })
                .then((response: SPHttpClientResponse): Promise<{ value: IListItem[] }> => {
                    return response.json(); 
                })
                .then((json: { value: IListItem[] }) => {
                    console.log(JSON.stringify(json.value));
                    return items=json.value.map((v,i)=>(
                        { 
                            //key: v.id,
                            id: v.Id,
                            title: v.Title,
                            created: v.Created,
                            createdby: v.Author.Title,
                            modified: v.Modified,
                            modifiedby: v.Editor.Title                        
                        }
                    ));
                }); 
            }
      }
}

问题是它第一次渲染时，listname是未定义的，所以它从GenericList中读取数据，我可以看到呈现的网格是期望的行为

但每当我选择另一个列表时，我会在getlistitems参数中获得一个空字符串作为参数，它不会采用公告，新闻等

我在这里缺少什么？

Answer 1

请注意：我不使用SharePoint框架。

我认为您的问题在于SharePoint框架WebPart和React之间的集成。在下拉列表选择后，您看不到React应用程序中的更改，因为React应用程序从未收到其属性的更改。

有两种选择：

1）当FactoryMethodWebPart.render()期间下拉列表发生变化时，请手动呼叫setSelectedList()。由于我不使用SharePoint框架，我不知道这是否是最佳做法。我知道这会重新构建React应用程序并再次将其插入DOM而不是触发重新渲染。

2）使用更高阶的组件，允许您将新的道具传递给已经构建的React应用程序。此解决方案基于this article。想法是构建一个返回Component周围包装的函数。此函数接受要渲染的Component和subscribe函数，该函数接受可用于将新道具传递给组件的函数。创建组件时，它会调用subscribe()方法，只需将组件传递给它。

HOC：

const connect = (Component, subscribe) => class extends React.Component {
  constructor(props) {
    super(props);

    const rerender = props => this.setState(props);
    subscribe(rerender);
  }

  render() {
    const props = { ...this.props, ...this.state };
    return <Component {...props} />;
  }
}

用例：

export default class FactoryMethodWebPart extends BaseClientSideWebPart<IFactoryMethodWebPartProps> {
  // other private fields
  private _factoryMethodComponent;
  private _setFactoryMethodProps;

  protected onInit(): Promise<void> {
    // ...
    this._factoryMethodComponent = connect(FactoryMethod, rerender => this._setFactoryMethodProps = rerender);
  }

  public render(): void {
    const element = React.createElement(
      this._factoryMethodComponent, // use the connected component instead of FactoryMethod
      { ... }
  ]  );

    this._factorymethodContainerComponent = ReactDom.render(element, this.domElement);
  }

  private setSelectedList(value: string): void {
    // ...

    this._setFactoryMethodProps({ listName: selectedDropDownOption ? selectedDropDownOption.text : 'GenericList' });
  }
}