鴻蒙HarmonyOS實戰-ArkTS語言（渲染控制）

蜀道山QAQ發表於2024-03-21
鴻蒙

🚀前言

程式語言中都有自己基本的控制結構，它們在程式設計中起到了非常重要的作用。以下是幾個原因：

分支控制： 在程式執行過程中，有時需要根據不同的條件分支來執行不同的程式碼邏輯。if/else結構透過判斷條件來決定程式如何執行，實現了程式的分支控制。

資料迭代： 在程式中，需要對一些資料進行遍歷、操作或者計算。ForEach和LazyForEach提供了一種便捷的方法，可以針對資料集合進行遍歷，並對其中的每個元素執行特定操作。

**惰性計算： **在某些情況下，程式中需要對大量的資料進行遍歷或計算。LazyForEach可以實現惰性計算，只在需要時才計算相應的結果，避免了程式在執行時不必要的計算，從而提高程式效率。

🚀一、ArkTS語言渲染控制

ArkTS是一種基於TypeScript的程式語言，支援對渲染過程進行控制和調整。以下是ArkTS語言中實現渲染控制的三個關鍵元件：

  1. if/else：if/else結構可以用於根據條件控制是否渲染某些元素。例如，可以透過if/else語句來實現某些物體在特定場景或條件下的顯示或隱藏。

  2. ForEach：ForEach是一個迭代方法，能夠遍歷陣列、物件等資料結構中的元素，並在渲染過程中對它們進行控制。例如，可以使用ForEach在場景中定位並控制多個物體的位置、尺寸、顏色等屬性。

  3. LazyForEach：與普通ForEach不同，LazyForEach是一個惰性迭代方法，它只在需要迭代資料時才進行計算。這使得LazyForEach在處理大型資料集時更加高效，可以減少渲染時間和資源佔用。

透過這些關鍵元件，ArkTS語言可以實現靈活、高效的渲染控制，幫助開發人員實現各種複雜的渲染效果和場景呈現。

🔎1.if/else：條件渲染

🦋1.1 變化規則

If/else是一種在程式中用於控制流程的結構。它包括一個if語句和一個可選的else語句。if語句表示如果條件成立，那麼就執行一段程式碼，否則跳過該程式碼；else語句表示如果條件不成立，那麼就執行另一段程式碼。這種結構允許程式根據不同的條件執行不同的操作，從而實現更靈活的程式控制。

🦋1.2 使用場景

☀️1.2.1 使用if進行條件渲染
@Entry
@Component
struct ViewA {
  @State count: number = 0;

  build() {
    Column() {
      Text(`count=${this.count}`)

      if (this.count > 0) {
        Text(`count is positive`)
          .fontColor(Color.Green)
      }

      Button('increase count')
        .onClick(() => {
          this.count++;
        })
      Button('decrease count')
        .onClick(() => {
          this.count--;
        })
    }
  }
}
☀️1.2.2 使用if/else進行條件渲染
@Component
struct CounterView {
  @Link counter: number;
  label: string = 'unknown';

  build() {
    Row() {
      Text(`${this.label}`)
      Button(`counter ${this.counter} +1`)
        .onClick(() => {
          this.counter += 1;
        })
    }
  }
}
@Entry
@Component
struct MainView {
  @State toggle: boolean = true;
  @State counter: number = 0;
  build() {
    Column() {
      if (this.toggle) {
        CounterView({ counter: $counter, label: 'CounterView #positive' })
      } else {
        CounterView({ counter: $counter, label: 'CounterView #negative' })
      }
      Button(`toggle ${this.toggle}`)
        .onClick(() => {
          this.toggle = !this.toggle;
        })
    }
  }
}
☀️1.2.3 巢狀if語句
@Entry
@Component
struct CompA {
  @State toggle: boolean = false;
  @State toggleColor: boolean = false;

  build() {
    Column() {
      Text('Before')
        .fontSize(15)
      if (this.toggle) {
        Text('Top True, positive 1 top')
          .backgroundColor('#aaffaa').fontSize(20)
        // 內部if語句
        if (this.toggleColor) {
          Text('Top True, Nested True, positive COLOR  Nested ')
            .backgroundColor('#00aaaa').fontSize(15)
        } else {
          Text('Top True, Nested False, Negative COLOR  Nested ')
            .backgroundColor('#aaaaff').fontSize(15)
        }
      } else {
        Text('Top false, negative top level').fontSize(20)
          .backgroundColor('#ffaaaa')
        if (this.toggleColor) {
          Text('positive COLOR  Nested ')
            .backgroundColor('#00aaaa').fontSize(15)
        } else {
          Text('Negative COLOR  Nested ')
            .backgroundColor('#aaaaff').fontSize(15)
        }
      }
      Text('After')
        .fontSize(15)
      Button('Toggle Outer')
        .onClick(() => {
          this.toggle = !this.toggle;
        })
      Button('Toggle Inner')
        .onClick(() => {
          this.toggleColor = !this.toggleColor;
        })
    }
  }
}

🔎2.ForEach：迴圈渲染

🦋2.1 變化規則

ForEach是一個陣列方法，用於執行一些操作，例如對陣列中的每個元素執行一些程式碼，或者將每個元素轉換為新的陣列。它可以接收一個回撥函式作為引數，該函式將在陣列的每個元素上執行一次。在每次呼叫回撥函式時，都會向其傳遞當前元素的值、索引和整個陣列。該方法不會更改原始陣列，而是返回一個新的、由回撥函式返回的陣列。

ForEach介面描述：

ForEach(
  arr: Array,
  itemGenerator: (item: Array, index?: number) => void,
  keyGenerator?: (item: Array, index?: number): string => string
)

注意點keyGenerator為鍵值生成函式，可以達到去重的效果：
image

@Entry
@Component
struct Parent {
  @State simpleList: Array<string> = ['one', 'two', 'two', 'three'];

  build() {
    Row() {
      Column() {
        ForEach(this.simpleList, (item: string) => {
          ChildItem({ item: item })
        }, (item: string) => item)
      }
      .width('100%')
      .height('100%')
    }
    .height('100%')
    .backgroundColor(0xF1F3F5)
  }
}
@Component
struct ChildItem {
  @Prop item: string;
  build() {
    Text(this.item)
      .fontSize(50)
  }
}

執行結果
image

🦋2.2 使用場景

☀️2.2.1 資料來源不變
@Entry
@Component
struct ArticleList {
  @State simpleList: Array<number> = [1, 2, 3, 4, 5];

  build() {
    Column() {
      ForEach(this.simpleList, (item: string) => {
        ArticleSkeletonView()
          .margin({ top: 20 })
      }, (item: string) => item)
    }
    .padding(20)
    .width('100%')
    .height('100%')
  }
}
@Builder
function textArea(width: number | Resource | string = '100%', height: number | Resource | string = '100%') {
  Row()
    .width(width)
    .height(height)
    .backgroundColor('#FFF2F3F4')
}
@Component
struct ArticleSkeletonView {
  build() {
    Row() {
      Column() {
        textArea(80, 80)
      }
      .margin({ right: 20 })
      Column() {
        textArea('60%', 20)
        textArea('50%', 20)
      }
      .alignItems(HorizontalAlign.Start)
      .justifyContent(FlexAlign.SpaceAround)
      .height('100%')
    }
    .padding(20)
    .borderRadius(12)
    .backgroundColor('#FFECECEC')
    .height(120)
    .width('100%')
    .justifyContent(FlexAlign.SpaceBetween)
  }
}

執行效果：
image

☀️2.2.2 資料來源陣列項發生變化
@Entry
@Component
struct ArticleListView {
  @State isListReachEnd: boolean = false;
  @State articleList: Array<Article> = [
    new Article('001', '第1篇文章', '文章簡介內容'),
    new Article('002', '第2篇文章', '文章簡介內容'),
    new Article('003', '第3篇文章', '文章簡介內容'),
    new Article('004', '第4篇文章', '文章簡介內容'),
    new Article('005', '第5篇文章', '文章簡介內容'),
    new Article('006', '第6篇文章', '文章簡介內容')
  ]

  loadMoreArticles() {
    this.articleList.push(new Article('007', '載入的新文章', '文章簡介內容'));
  }

  build() {
    Column({ space: 5 }) {
      List() {
        ForEach(this.articleList, (item: Article) => {
          ListItem() {
            ArticleCard({ article: item })
              .margin({ top: 20 })
          }
        }, (item: Article) => item.id)
      }
      .onReachEnd(() => {
        this.isListReachEnd = true;
      })
      .parallelGesture(
        PanGesture({ direction: PanDirection.Up, distance: 80 })
          .onActionStart(() => {
            if (this.isListReachEnd) {
              this.loadMoreArticles();
              this.isListReachEnd = false;
            }
          })
      )
      .padding(20)
      .scrollBar(BarState.Off)
    }
    .width('100%')
    .height('100%')
    .backgroundColor(0xF1F3F5)
  }
}
@Component
struct ArticleCard {
  @Prop article: Article;
  build() {
    Row() {
      Image($r('app.media.icon'))
        .width(80)
        .height(80)
        .margin({ right: 20 })
      Column() {
        Text(this.article.title)
          .fontSize(20)
          .margin({ bottom: 8 })
        Text(this.article.brief)
          .fontSize(16)
          .fontColor(Color.Gray)
          .margin({ bottom: 8 })
      }
      .alignItems(HorizontalAlign.Start)
      .width('80%')
      .height('100%')
    }
    .padding(20)
    .borderRadius(12)
    .backgroundColor('#FFECECEC')
    .height(120)
    .width('100%')
    .justifyContent(FlexAlign.SpaceBetween)
  }
}

當列表滾動到底部時，如果手勢滑動距離超過指定的80，將觸發loadMoreArticle()函式。此函式會在articleList資料來源的尾部新增一個新的資料項，從而增加資料來源的長度。

執行效果：

image

☀️2.2.3 資料來源陣列項子屬性變化
@Entry
@Component
struct ArticleListView {
  @State articleList: Array<Article> = [
    new Article('001', '第0篇文章', '文章簡介內容', false, 100),
    new Article('002', '第1篇文章', '文章簡介內容', false, 100),
    new Article('003', '第2篇文章', '文章簡介內容', false, 100),
    new Article('004', '第4篇文章', '文章簡介內容', false, 100),
    new Article('005', '第5篇文章', '文章簡介內容', false, 100),
    new Article('006', '第6篇文章', '文章簡介內容', false, 100),
  ];

  build() {
    List() {
      ForEach(this.articleList, (item: Article) => {
        ListItem() {
          ArticleCard({
            article: item
          })
            .margin({ top: 20 })
        }
      }, (item: Article) => item.id)
    }
    .padding(20)
    .scrollBar(BarState.Off)
    .backgroundColor(0xF1F3F5)
  }
}
@Component
struct ArticleCard {
  @ObjectLink article: Article;
  handleLiked() {
    this.article.isLiked = !this.article.isLiked;
    this.article.likesCount = this.article.isLiked ? this.article.likesCount + 1 : this.article.likesCount - 1;
  }
  build() {
    Row() {
      Image($r('app.media.icon'))
        .width(80)
        .height(80)
        .margin({ right: 20 })
      Column() {
        Text(this.article.title)
          .fontSize(20)
          .margin({ bottom: 8 })
        Text(this.article.brief)
          .fontSize(16)
          .fontColor(Color.Gray)
          .margin({ bottom: 8 })
        Row() {
          Image(this.article.isLiked ? $r('app.media.iconLiked') : $r('app.media.iconUnLiked'))
            .width(24)
            .height(24)
            .margin({ right: 8 })
          Text(this.article.likesCount.toString())
            .fontSize(16)
        }
        .onClick(() => this.handleLiked())
        .justifyContent(FlexAlign.Center)
      }
      .alignItems(HorizontalAlign.Start)
      .width('80%')
      .height('100%')
    }
    .padding(20)
    .borderRadius(12)
    .backgroundColor('#FFECECEC')
    .height(120)
    .width('100%')
    .justifyContent(FlexAlign.SpaceBetween)
  }
}

執行結果：

image

== 注意：開發者在使用ForEach時應特別重視keyGenerator為鍵值生成函式，會根據鍵值生成函式確定替換的值。==

🔎3.LazyForEach：資料懶載入

🦋3.1 變化規則

LazyForEach是一種延遲執行的迭代方法，它可以幫助我們更高效地遍歷和運算元組。與常規的ForEach方法不同，LazyForEach方法不會立即執行回撥函式，而是在需要訪問陣列元素時才將回撥函式應用於該元素。這種延遲執行的方式可以大大減少不必要的計算，提高程式碼效能。LazyForEach在處理大型陣列或頻繁進行迭代時特別有用。

LazyForEach介面描述：

LazyForEach(
    dataSource: IDataSource,             // 需要進行資料迭代的資料來源
    itemGenerator: (item: any, index?: number) => void,  // 子元件生成函式
    keyGenerator?: (item: any, index?: number) => string // 鍵值生成函式
): void

IDataSource介面描述：

interface IDataSource {
    totalCount(): number; // 獲得資料總數
    getData(index: number): Object; // 獲取索引值對應的資料
    registerDataChangeListener(listener: DataChangeListener): void; // 註冊資料改變的監聽器
    unregisterDataChangeListener(listener: DataChangeListener): void; // 登出資料改變的監聽器
}

DataChangeListener介面描述：

interface DataChangeListener {
    onDataReloaded(): void; // 重新載入資料時呼叫
    onDataAdded(index: number): void; // 新增資料時呼叫
    onDataMoved(from: number, to: number): void; // 資料移動起始位置與資料移動目標位置交換時呼叫
    onDataDeleted(index: number): void; // 刪除資料時呼叫
    onDataChanged(index: number): void; // 改變資料時呼叫
    onDataAdd(index: number): void; // 新增資料時呼叫
    onDataMove(from: number, to: number): void; // 資料移動起始位置與資料移動目標位置交換時呼叫
    onDataDelete(index: number): void; // 刪除資料時呼叫
    onDataChange(index: number): void; // 改變資料時呼叫
}

🦋3.2 使用場景

☀️3.2.1 首次渲染
🌈3.2.1.1 生成不同鍵值

1、正常渲染

// Basic implementation of IDataSource to handle data listener
class BasicDataSource implements IDataSource {
  private listeners: DataChangeListener[] = [];
  private originDataArray: string[] = [];

  public totalCount(): number {
    return 0;
  }

  public getData(index: number): string {
    return this.originDataArray[index];
  }

  // 該方法為框架側呼叫，為LazyForEach元件向其資料來源處新增listener監聽
  registerDataChangeListener(listener: DataChangeListener): void {
    if (this.listeners.indexOf(listener) < 0) {
      console.info('add listener');
      this.listeners.push(listener);
    }
  }

  // 該方法為框架側呼叫，為對應的LazyForEach元件在資料來源處去除listener監聽
  unregisterDataChangeListener(listener: DataChangeListener): void {
    const pos = this.listeners.indexOf(listener);
    if (pos >= 0) {
      console.info('remove listener');
      this.listeners.splice(pos, 1);
    }
  }

  // 通知LazyForEach元件需要過載所有子元件
  notifyDataReload(): void {
    this.listeners.forEach(listener => {
      listener.onDataReloaded();
    })
  }

  // 通知LazyForEach元件需要在index對應索引處新增子元件
  notifyDataAdd(index: number): void {
    this.listeners.forEach(listener => {
      listener.onDataAdd(index);
    })
  }

  // 通知LazyForEach元件在index對應索引處資料有變化，需要重建該子元件
  notifyDataChange(index: number): void {
    this.listeners.forEach(listener => {
      listener.onDataChange(index);
    })
  }

  // 通知LazyForEach元件需要在index對應索引處刪除該子元件
  notifyDataDelete(index: number): void {
    this.listeners.forEach(listener => {
      listener.onDataDelete(index);
    })
  }
}

class MyDataSource extends BasicDataSource {
  private dataArray: string[] = [];

  public totalCount(): number {
    return this.dataArray.length;
  }

  public getData(index: number): string {
    return this.dataArray[index];
  }

  public addData(index: number, data: string): void {
    this.dataArray.splice(index, 0, data);
    this.notifyDataAdd(index);
  }

  public pushData(data: string): void {
    this.dataArray.push(data);
    this.notifyDataAdd(this.dataArray.length - 1);
  }
}

@Entry
@Component
struct MyComponent {
  private data: MyDataSource = new MyDataSource();
   
  aboutToAppear() {
    for (let i = 0; i <= 20; i++) {
      this.data.pushData(`Hello ${i}`)
    }
  }

  build() {
    List({ space: 3 }) {
      LazyForEach(this.data, (item: string) => {
        ListItem() {
          Row() {
            Text(item).fontSize(50)
              .onAppear(() => {
                console.info("appear:" + item)
              })
          }.margin({ left: 10, right: 10 })
        }
      }, (item: string) => item)
    }.cachedCount(5)
  }
}

2、鍵值相同時錯誤渲染

class BasicDataSource implements IDataSource {
 private listeners: DataChangeListener[] = [];
 private originDataArray: string[] = [];

 public totalCount(): number {
   return 0;
 }

 public getData(index: number): string {
   return this.originDataArray[index];
 }

 registerDataChangeListener(listener: DataChangeListener): void {
   if (this.listeners.indexOf(listener) < 0) {
     console.info('add listener');
     this.listeners.push(listener);
   }
 }

 unregisterDataChangeListener(listener: DataChangeListener): void {
   const pos = this.listeners.indexOf(listener);
   if (pos >= 0) {
     console.info('remove listener');
     this.listeners.splice(pos, 1);
   }
 }

 notifyDataReload(): void {
   this.listeners.forEach(listener => {
     listener.onDataReloaded();
   })
 }

 notifyDataAdd(index: number): void {
   this.listeners.forEach(listener => {
     listener.onDataAdd(index);
   })
 }

 notifyDataChange(index: number): void {
   this.listeners.forEach(listener => {
     listener.onDataChange(index);
   })
 }

 notifyDataDelete(index: number): void {
   this.listeners.forEach(listener => {
     listener.onDataDelete(index);
   })
 }
}

class MyDataSource extends BasicDataSource {
 private dataArray: string[] = [];

 public totalCount(): number {
   return this.dataArray.length;
 }

 public getData(index: number): string {
   return this.dataArray[index];
 }

 public addData(index: number, data: string): void {
   this.dataArray.splice(index, 0, data);
   this.notifyDataAdd(index);
 }

 public pushData(data: string): void {
   this.dataArray.push(data);
   this.notifyDataAdd(this.dataArray.length - 1);
 }
}

@Entry
@Component
struct MyComponent {
 private data: MyDataSource = new MyDataSource();

 aboutToAppear() {
   for (let i = 0; i <= 20; i++) {
     this.data.pushData(`Hello ${i}`)
   }
 }

 build() {
   List({ space: 3 }) {
     LazyForEach(this.data, (item: string) => {
       ListItem() {
         Row() {
           Text(item).fontSize(50)
             .onAppear(() => {
               console.info("appear:" + item)
             })
         }.margin({ left: 10, right: 10 })
       }
     }, (item: string) => 'same key')
   }.cachedCount(5)
 }
}
☀️3.2.2 非首次渲染
🌈3.2.2.1 新增資料
class BasicDataSource implements IDataSource {
  private listeners: DataChangeListener[] = [];
  private originDataArray: string[] = [];

  public totalCount(): number {
    return 0;
  }

  public getData(index: number): string {
    return this.originDataArray[index];
  }

  registerDataChangeListener(listener: DataChangeListener): void {
    if (this.listeners.indexOf(listener) < 0) {
      console.info('add listener');
      this.listeners.push(listener);
    }
  }

  unregisterDataChangeListener(listener: DataChangeListener): void {
    const pos = this.listeners.indexOf(listener);
    if (pos >= 0) {
      console.info('remove listener');
      this.listeners.splice(pos, 1);
    }
  }

  notifyDataReload(): void {
    this.listeners.forEach(listener => {
      listener.onDataReloaded();
    })
  }

  notifyDataAdd(index: number): void {
    this.listeners.forEach(listener => {
      listener.onDataAdd(index);
    })
  }

  notifyDataChange(index: number): void {
    this.listeners.forEach(listener => {
      listener.onDataChange(index);
    })
  }

  notifyDataDelete(index: number): void {
    this.listeners.forEach(listener => {
      listener.onDataDelete(index);
    })
  }
}

class MyDataSource extends BasicDataSource {
  private dataArray: string[] = [];

  public totalCount(): number {
    return this.dataArray.length;
  }

  public getData(index: number): string {
    return this.dataArray[index];
  }

  public addData(index: number, data: string): void {
    this.dataArray.splice(index, 0, data);
    this.notifyDataAdd(index);
  }

  public pushData(data: string): void {
    this.dataArray.push(data);
    this.notifyDataAdd(this.dataArray.length - 1);
  }
}

@Entry
@Component
struct MyComponent {
  private data: MyDataSource = new MyDataSource();

  aboutToAppear() {
    for (let i = 0; i <= 20; i++) {
      this.data.pushData(`Hello ${i}`)
    }
  }

  build() {
    List({ space: 3 }) {
      LazyForEach(this.data, (item: string) => {
        ListItem() {
          Row() {
            Text(item).fontSize(50)
              .onAppear(() => {
                console.info("appear:" + item)
              })
          }.margin({ left: 10, right: 10 })
        }
        .onClick(() => {
          // 點選追加子元件
          this.data.pushData(`Hello ${this.data.totalCount()}`);
        })
      }, (item: string) => item)
    }.cachedCount(5)
  }
}
🌈3.2.2.2 刪除資料
class BasicDataSource implements IDataSource {
  private listeners: DataChangeListener[] = [];
  private originDataArray: string[] = [];

  public totalCount(): number {
    return 0;
  }

  public getData(index: number): string {
    return this.originDataArray[index];
  }

  registerDataChangeListener(listener: DataChangeListener): void {
    if (this.listeners.indexOf(listener) < 0) {
      console.info('add listener');
      this.listeners.push(listener);
    }
  }

  unregisterDataChangeListener(listener: DataChangeListener): void {
    const pos = this.listeners.indexOf(listener);
    if (pos >= 0) {
      console.info('remove listener');
      this.listeners.splice(pos, 1);
    }
  }

  notifyDataReload(): void {
    this.listeners.forEach(listener => {
      listener.onDataReloaded();
    })
  }

  notifyDataAdd(index: number): void {
    this.listeners.forEach(listener => {
      listener.onDataAdd(index);
    })
  }

  notifyDataChange(index: number): void {
    this.listeners.forEach(listener => {
      listener.onDataChange(index);
    })
  }

  notifyDataDelete(index: number): void {
    this.listeners.forEach(listener => {
      listener.onDataDelete(index);
    })
  }
}

class MyDataSource extends BasicDataSource {
  dataArray: string[] = [];

  public totalCount(): number {
    return this.dataArray.length;
  }

  public getData(index: number): string {
    return this.dataArray[index];
  }

  public addData(index: number, data: string): void {
    this.dataArray.splice(index, 0, data);
    this.notifyDataAdd(index);
  }

  public pushData(data: string): void {
    this.dataArray.push(data);
    this.notifyDataAdd(this.dataArray.length - 1);
  }
  
  public deleteData(index: number): void {
    this.dataArray.splice(index, 1);
    this.notifyDataDelete(index);
  }
}

@Entry
@Component
struct MyComponent {
  private data: MyDataSource = new MyDataSource();

  aboutToAppear() {
    for (let i = 0; i <= 20; i++) {
      this.data.pushData(`Hello ${i}`)
    }
  }

  build() {
    List({ space: 3 }) {
      LazyForEach(this.data, (item: string, index: number) => {
        ListItem() {
          Row() {
            Text(item).fontSize(50)
              .onAppear(() => {
                console.info("appear:" + item)
              })
          }.margin({ left: 10, right: 10 })
        }
        .onClick(() => {
          // 點選刪除子元件
          this.data.deleteData(this.data.dataArray.indexOf(item));
        })
      }, (item: string) => item)
    }.cachedCount(5)
  }
}

🌈3.2.2.3 改變單個資料

class BasicDataSource implements IDataSource {
  private listeners: DataChangeListener[] = [];
  private originDataArray: string[] = [];

  public totalCount(): number {
    return 0;
  }

  public getData(index: number): string {
    return this.originDataArray[index];
  }

  registerDataChangeListener(listener: DataChangeListener): void {
    if (this.listeners.indexOf(listener) < 0) {
      console.info('add listener');
      this.listeners.push(listener);
    }
  }

  unregisterDataChangeListener(listener: DataChangeListener): void {
    const pos = this.listeners.indexOf(listener);
    if (pos >= 0) {
      console.info('remove listener');
      this.listeners.splice(pos, 1);
    }
  }

  notifyDataReload(): void {
    this.listeners.forEach(listener => {
      listener.onDataReloaded();
    })
  }

  notifyDataAdd(index: number): void {
    this.listeners.forEach(listener => {
      listener.onDataAdd(index);
    })
  }

  notifyDataChange(index: number): void {
    this.listeners.forEach(listener => {
      listener.onDataChange(index);
    })
  }

  notifyDataDelete(index: number): void {
    this.listeners.forEach(listener => {
      listener.onDataDelete(index);
    })
  }
}

class MyDataSource extends BasicDataSource {
  private dataArray: string[] = [];

  public totalCount(): number {
    return this.dataArray.length;
  }

  public getData(index: number): string {
    return this.dataArray[index];
  }

  public addData(index: number, data: string): void {
    this.dataArray.splice(index, 0, data);
    this.notifyDataAdd(index);
  }

  public pushData(data: string): void {
    this.dataArray.push(data);
    this.notifyDataAdd(this.dataArray.length - 1);
  }
  
  public deleteData(index: number): void {
    this.dataArray.splice(index, 1);
    this.notifyDataDelete(index);
  }
  
  public changeData(index: number, data: string): void {
    this.dataArray.splice(index, 0, data);
    this.notifyDataChange(index);
  }
}

@Entry
@Component
struct MyComponent {
  private moved: number[] = [];
  private data: MyDataSource = new MyDataSource();

  aboutToAppear() {
    for (let i = 0; i <= 20; i++) {
      this.data.pushData(`Hello ${i}`)
    }
  }
  build() {
    List({ space: 3 }) {
      LazyForEach(this.data, (item: string, index: number) => {
        ListItem() {
          Row() {
            Text(item).fontSize(50)
              .onAppear(() => {
                console.info("appear:" + item)
              })
          }.margin({ left: 10, right: 10 })
        }
        .onClick(() => {
          this.data.changeData(index, item + '00');
        })
      }, (item: string) => item)
    }.cachedCount(5)
  }
}
🌈3.2.2.4 改變多個資料
class BasicDataSource implements IDataSource {
  private listeners: DataChangeListener[] = [];
  private originDataArray: string[] = [];

  public totalCount(): number {
    return 0;
  }

  public getData(index: number): string {
    return this.originDataArray[index];
  }

  registerDataChangeListener(listener: DataChangeListener): void {
    if (this.listeners.indexOf(listener) < 0) {
      console.info('add listener');
      this.listeners.push(listener);
    }
  }

  unregisterDataChangeListener(listener: DataChangeListener): void {
    const pos = this.listeners.indexOf(listener);
    if (pos >= 0) {
      console.info('remove listener');
      this.listeners.splice(pos, 1);
    }
  }

  notifyDataReload(): void {
    this.listeners.forEach(listener => {
      listener.onDataReloaded();
    })
  }

  notifyDataAdd(index: number): void {
    this.listeners.forEach(listener => {
      listener.onDataAdd(index);
    })
  }

  notifyDataChange(index: number): void {
    this.listeners.forEach(listener => {
      listener.onDataChange(index);
    })
  }

  notifyDataDelete(index: number): void {
    this.listeners.forEach(listener => {
      listener.onDataDelete(index);
    })
  }
}

class MyDataSource extends BasicDataSource {
  private dataArray: string[] = [];

  public totalCount(): number {
    return this.dataArray.length;
  }

  public getData(index: number): string {
    return this.dataArray[index];
  }

  public addData(index: number, data: string): void {
    this.dataArray.splice(index, 0, data);
    this.notifyDataAdd(index);
  }

  public pushData(data: string): void {
    this.dataArray.push(data);
    this.notifyDataAdd(this.dataArray.length - 1);
  }
  
  public deleteData(index: number): void {
    this.dataArray.splice(index, 1);
    this.notifyDataDelete(index);
  }
  
  public changeData(index: number): void {
    this.notifyDataChange(index);
  }
    
  public reloadData(): void {
    this.notifyDataReload();
  }
    
  public modifyAllData(): void {
    this.dataArray = this.dataArray.map((item: string) => {
        return item + '0';
    })
  }
}

@Entry
@Component
struct MyComponent {
  private moved: number[] = [];
  private data: MyDataSource = new MyDataSource();

  aboutToAppear() {
    for (let i = 0; i <= 20; i++) {
      this.data.pushData(`Hello ${i}`)
    }
  }

  build() {
    List({ space: 3 }) {
      LazyForEach(this.data, (item: string, index: number) => {
        ListItem() {
          Row() {
            Text(item).fontSize(50)
              .onAppear(() => {
                console.info("appear:" + item)
              })
          }.margin({ left: 10, right: 10 })
        }
        .onClick(() => {
          this.data.modifyAllData();
          this.data.reloadData();
        })
      }, (item: string) => item)
    }.cachedCount(5)
  }
}

🌈3.2.2.5 改變資料子屬性

class BasicDataSource implements IDataSource {
  private listeners: DataChangeListener[] = [];
  private originDataArray: StringData[] = [];

  public totalCount(): number {
    return 0;
  }

  public getData(index: number): StringData {
    return this.originDataArray[index];
  }

  registerDataChangeListener(listener: DataChangeListener): void {
    if (this.listeners.indexOf(listener) < 0) {
      console.info('add listener');
      this.listeners.push(listener);
    }
  }

  unregisterDataChangeListener(listener: DataChangeListener): void {
    const pos = this.listeners.indexOf(listener);
    if (pos >= 0) {
      console.info('remove listener');
      this.listeners.splice(pos, 1);
    }
  }

  notifyDataReload(): void {
    this.listeners.forEach(listener => {
      listener.onDataReloaded();
    })
  }

  notifyDataAdd(index: number): void {
    this.listeners.forEach(listener => {
      listener.onDataAdd(index);
    })
  }

  notifyDataChange(index: number): void {
    this.listeners.forEach(listener => {
      listener.onDataChange(index);
    })
  }

  notifyDataDelete(index: number): void {
    this.listeners.forEach(listener => {
      listener.onDataDelete(index);
    })
  }
}

class MyDataSource extends BasicDataSource {
  private dataArray: StringData[] = [];

  public totalCount(): number {
    return this.dataArray.length;
  }

  public getData(index: number): StringData {
    return this.dataArray[index];
  }

  public addData(index: number, data: StringData): void {
    this.dataArray.splice(index, 0, data);
    this.notifyDataAdd(index);
  }

  public pushData(data: StringData): void {
    this.dataArray.push(data);
    this.notifyDataAdd(this.dataArray.length - 1);
  }
}

@Observed
class StringData {
  message: string;
  constructor(message: string) {
    this.message = message;
  }  
}

@Entry
@Component
struct MyComponent {
  private moved: number[] = [];
  @State data: MyDataSource = new MyDataSource();

  aboutToAppear() {
    for (let i = 0; i <= 20; i++) {
      this.data.pushData(new StringData(`Hello ${i}`));
    }
  }

  build() {
    List({ space: 3 }) {
      LazyForEach(this.data, (item: StringData, index: number) => {
        ListItem() {
          ChildComponent({data: item})
        }
        .onClick(() => {
          item.message += '0';
        })
      }, (item: StringData, index: number) => index.toString())
    }.cachedCount(5)
  }
}
@Component
struct ChildComponent {
  @ObjectLink data: StringData
  build() {
    Row() {
      Text(this.data.message).fontSize(50)
        .onAppear(() => {
          console.info("appear:" + this.data.message)
        })
    }.margin({ left: 10, right: 10 })
  }
}
☀️3.2.3 問題點
🌈3.2.3.1 索引重置
class BasicDataSource implements IDataSource {
  private listeners: DataChangeListener[] = [];
  private originDataArray: string[] = [];

  public totalCount(): number {
    return 0;
  }

  public getData(index: number): string {
    return this.originDataArray[index];
  }

  registerDataChangeListener(listener: DataChangeListener): void {
    if (this.listeners.indexOf(listener) < 0) {
      console.info('add listener');
      this.listeners.push(listener);
    }
  }

  unregisterDataChangeListener(listener: DataChangeListener): void {
    const pos = this.listeners.indexOf(listener);
    if (pos >= 0) {
      console.info('remove listener');
      this.listeners.splice(pos, 1);
    }
  }

  notifyDataReload(): void {
    this.listeners.forEach(listener => {
      listener.onDataReloaded();
    })
  }

  notifyDataAdd(index: number): void {
    this.listeners.forEach(listener => {
      listener.onDataAdd(index);
    })
  }

  notifyDataChange(index: number): void {
    this.listeners.forEach(listener => {
      listener.onDataChange(index);
    })
  }

  notifyDataDelete(index: number): void {
    this.listeners.forEach(listener => {
      listener.onDataDelete(index);
    })
  }
}

class MyDataSource extends BasicDataSource {
  private dataArray: string[] = [];

  public totalCount(): number {
    return this.dataArray.length;
  }

  public getData(index: number): string {
    return this.dataArray[index];
  }

  public addData(index: number, data: string): void {
    this.dataArray.splice(index, 0, data);
    this.notifyDataAdd(index);
  }

  public pushData(data: string): void {
    this.dataArray.push(data);
    this.notifyDataAdd(this.dataArray.length - 1);
  }
  
  public deleteData(index: number): void {
    this.dataArray.splice(index, 1);
    this.notifyDataDelete(index);
  }
    
  public reloadData(): void {
    this.notifyDataReload();
  }
}

@Entry
@Component
struct MyComponent {
  private data: MyDataSource = new MyDataSource();

  aboutToAppear() {
    for (let i = 0; i <= 20; i++) {
      this.data.pushData(`Hello ${i}`)
    }
  }

  build() {
    List({ space: 3 }) {
      LazyForEach(this.data, (item: string, index: number) => {
        ListItem() {
          Row() {
            Text(item).fontSize(50)
              .onAppear(() => {
                console.info("appear:" + item)
              })
          }.margin({ left: 10, right: 10 })
        }
        .onClick(() => {
          // 點選刪除子元件
          this.data.deleteData(index);
          // 重置所有子元件的index索引
          this.data.reloadData();
        })
      }, (item: string, index: number) => item + index.toString())
    }.cachedCount(5)
  }
}
🌈3.2.3.2 圖片閃爍
class BasicDataSource implements IDataSource {
  private listeners: DataChangeListener[] = [];
  private originDataArray: StringData[] = [];

  public totalCount(): number {
    return 0;
  }

  public getData(index: number): StringData {
    return this.originDataArray[index];
  }

  registerDataChangeListener(listener: DataChangeListener): void {
    if (this.listeners.indexOf(listener) < 0) {
      console.info('add listener');
      this.listeners.push(listener);
    }
  }

  unregisterDataChangeListener(listener: DataChangeListener): void {
    const pos = this.listeners.indexOf(listener);
    if (pos >= 0) {
      console.info('remove listener');
      this.listeners.splice(pos, 1);
    }
  }

  notifyDataReload(): void {
    this.listeners.forEach(listener => {
      listener.onDataReloaded();
    })
  }

  notifyDataAdd(index: number): void {
    this.listeners.forEach(listener => {
      listener.onDataAdd(index);
    })
  }

  notifyDataChange(index: number): void {
    this.listeners.forEach(listener => {
      listener.onDataChange(index);
    })
  }

  notifyDataDelete(index: number): void {
    this.listeners.forEach(listener => {
      listener.onDataDelete(index);
    })
  }
}

class MyDataSource extends BasicDataSource {
  private dataArray: StringData[] = [];

  public totalCount(): number {
    return this.dataArray.length;
  }

  public getData(index: number): StringData {
    return this.dataArray[index];
  }

  public addData(index: number, data: StringData): void {
    this.dataArray.splice(index, 0, data);
    this.notifyDataAdd(index);
  }

  public pushData(data: StringData): void {
    this.dataArray.push(data);
    this.notifyDataAdd(this.dataArray.length - 1);
  }
}

@Observed
class StringData {
  message: string;
  imgSrc: Resource;
  constructor(message: string, imgSrc: Resource) {
    this.message = message;
      this.imgSrc = imgSrc;
  }  
}

@Entry
@Component
struct MyComponent {
  @State data: MyDataSource = new MyDataSource();

  aboutToAppear() {
    for (let i = 0; i <= 20; i++) {
      this.data.pushData(new StringData(`Hello ${i}`, $r('app.media.img')));
    }
  }

  build() {
    List({ space: 3 }) {
      LazyForEach(this.data, (item: StringData, index: number) => {
        ListItem() {
          ChildComponent({data: item})
        }
        .onClick(() => {
          item.message += '0';
        })
      }, (item: StringData, index: number) => index.toString())
    }.cachedCount(5)
  }
}
@Component
struct ChildComponent {
  @ObjectLink data: StringData
  build() {
    Column() {
      Text(this.data.message).fontSize(50)
        .onAppear(() => {
          console.info("appear:" + this.data.message)
        })
      Image(this.data.imgSrc)
        .width(500)
        .height(200)
    }.margin({ left: 10, right: 10 })
  }
}
🌈3.2.3.3 ObjectLink屬性變化後UI更新
class BasicDataSource implements IDataSource {
  private listeners: DataChangeListener[] = [];
  private originDataArray: StringData[] = [];

  public totalCount(): number {
    return 0;
  }

  public getData(index: number): StringData {
    return this.originDataArray[index];
  }

  registerDataChangeListener(listener: DataChangeListener): void {
    if (this.listeners.indexOf(listener) < 0) {
      console.info('add listener');
      this.listeners.push(listener);
    }
  }

  unregisterDataChangeListener(listener: DataChangeListener): void {
    const pos = this.listeners.indexOf(listener);
    if (pos >= 0) {
      console.info('remove listener');
      this.listeners.splice(pos, 1);
    }
  }

  notifyDataReload(): void {
    this.listeners.forEach(listener => {
      listener.onDataReloaded();
    })
  }

  notifyDataAdd(index: number): void {
    this.listeners.forEach(listener => {
      listener.onDataAdd(index);
    })
  }

  notifyDataChange(index: number): void {
    this.listeners.forEach(listener => {
      listener.onDataChange(index);
    })
  }

  notifyDataDelete(index: number): void {
    this.listeners.forEach(listener => {
      listener.onDataDelete(index);
    })
  }
}

class MyDataSource extends BasicDataSource {
  private dataArray: StringData[] = [];

  public totalCount(): number {
    return this.dataArray.length;
  }

  public getData(index: number): StringData {
    return this.dataArray[index];
  }

  public addData(index: number, data: StringData): void {
    this.dataArray.splice(index, 0, data);
    this.notifyDataAdd(index);
  }

  public pushData(data: StringData): void {
    this.dataArray.push(data);
    this.notifyDataAdd(this.dataArray.length - 1);
  }
}

@Observed
class StringData {
  message: NestedString;
  constructor(message: NestedString) {
    this.message = message;
  }  
}

@Observed
class NestedString {
  message: string;
  constructor(message: string) {
    this.message = message;
  }  
}

@Entry
@Component
struct MyComponent {
  private moved: number[] = [];
  @State data: MyDataSource = new MyDataSource();

  aboutToAppear() {
    for (let i = 0; i <= 20; i++) {
      this.data.pushData(new StringData(new NestedString(`Hello ${i}`)));
    }
  }

  build() {
    List({ space: 3 }) {
      LazyForEach(this.data, (item: StringData, index: number) => {
        ListItem() {
          ChildComponent({data: item})
        }
        .onClick(() => {
          item.message = new NestedString(item.message.message + '0');
        })
      }, (item: StringData, index: number) => item.toString() + index.toString())
    }.cachedCount(5)
  }
}
@Component
struct ChildComponent {
  @ObjectLink data: StringData
  build() {
    Row() {
      Text(this.data.message.message).fontSize(50)
        .onAppear(() => {
          console.info("appear:" + this.data.message.message)
        })
    }.margin({ left: 10, right: 10 })
  }
}

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