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【每日学点鸿蒙知识】线程创建、构造函数中创建变量仍报错、List上下拖拽，调用JS代码、无法选择本地csr文件问题

article 2024/12/27 21:23:36

1、HarmonyOS 如何创建一个单线程？

请问 worker 是单线程还是多线程？
如果 worker 不是单线程，如何创建一个单线程呢？

ArkTS是单线程模型，所以worker也是单线程，他是在宿主线程上创建的一个子线程：https://developer.huawei.com/consumer/cn/doc/harmonyos-guides-V5/worker-introduction-V5

2、HarmonyOS 已经在构造函数中创建了变量，还是提示错误？

![[【每日学点鸿蒙知识】24.10.29.png]]

参考代码：

cat1?:Cat
constructor() {
  super();
  this.cat1 = new Cat()
}
//或者：
cat1:Cat = new Cat()
constructor() {
  super();
  //this.cat1 = new Cat()
}
//或者：
cat1!:Cat
constructor() {
  super();
  this.cat1 = new Cat()
}

3、HarmonyOS List列表如何支持item的上下拖拽排序？

参考以下demo：

import curves from '@ohos.curves';
import Curves from '@ohos.curves' // xxx.ets

@Entry
@Component
struct ListDemo {
  @State private arr: number[] = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
  @State dragItem: number = -1
  @State scaleItem: number = -1
  @State neighborItem: number = -1
  @State neighborScale: number = -1
  private dragRefOffset: number = 0
  @State offsetX: number = 0
  @State offsetY: number = 0
  private ITEM_INTV: number = 120

  scaleSelect(item: number): number {
    if (this.scaleItem == item) {
      return 1.05
    }
    else if (this.neighborItem == item) {
      return this.neighborScale
    } else {
      return 1
    }
  }

  itemMove(index: number, newIndex: number): void {
    let tmp = this.arr.splice(index, 1)
    this.arr.splice(newIndex, 0, tmp[0])
  }

  build() {
    Stack() {
      List({ space: 20, initialIndex: 0 }) {
        ForEach(this.arr, (item: number) => {
          ListItem() {
            Text('' + item)
              .width('100%')
              .height(100)
              .fontSize(16)
              .textAlign(TextAlign.Center)
              .borderRadius(10)
              .backgroundColor(0xFFFFFF)
              .shadow(this.scaleItem == item ? { radius: 70, color: '#15000000', offsetX: 0, offsetY: 0 } : {
                radius: 0,
                color: '#15000000',
                offsetX: 0,
                offsetY: 0
              })
              .animation({ curve: Curve.Sharp, duration: 300 })
          }
          .margin({ left: 12, right: 12 })
          .scale({ x: this.scaleSelect(item), y: this.scaleSelect(item) })
          .zIndex(this.dragItem == item ? 1 : 0)
          .translate(this.dragItem == item ? { y: this.offsetY } : { y: 0 })
          .gesture(
            // 以下组合手势为顺序识别，当长按手势事件未正常触发时则不会触发拖动手势事件
            GestureGroup(GestureMode.Sequence, LongPressGesture({ repeat: true })
              .onAction((event?: GestureEvent) => {
                animateTo({ curve: Curve.Friction, duration: 300 }, () => {
                  this.scaleItem = item
                })
              })
              .onActionEnd(() => {
                animateTo({
                  curve: Curve.Friction, duration: 300
                }, () => {
                  this.scaleItem = -1
                })
              }),
              PanGesture({ fingers: 1, direction: null, distance: 0 })
                .onActionStart(() => {
                  this.dragItem = item
                  this.dragRefOffset = 0
                })
                .onActionUpdate((event: GestureEvent) => {
                  this.offsetY = event.offsetY - this.dragRefOffset
                  // console.log('Y:' + this.offsetY.toString())
                  this.neighborItem = -1
                  let index = this.arr.indexOf(item)
                  let curveValue = Curves.initCurve(Curve.Sharp)
                  let value: number = 0 //根据位移计算相邻项的缩放
                  if (this.offsetY < 0) {
                    value = curveValue.interpolate(-this.offsetY / this.ITEM_INTV)
                    this.neighborItem = this.arr[index-1]
                    this.neighborScale = 1 - value / 20;
                    console.log('neighborScale:' + this.neighborScale.toString())
                  } else if (this.offsetY > 0) {
                    value = curveValue.interpolate(this.offsetY / this.ITEM_INTV)
                    this.neighborItem = this.arr[index+1]
                    this.neighborScale = 1 - value / 20;
                  } //根据位移交换排序
                  if (this.offsetY > this.ITEM_INTV / 2) {
                    animateTo({ curve: curves.interpolatingSpring(0, 1, 400, 38) }, () => {
                      this.offsetY -= this.ITEM_INTV
                      this.dragRefOffset += this.ITEM_INTV
                      this.itemMove(index, index + 1)
                    })
                  }
                  else if (
                    this.offsetY < -this.ITEM_INTV / 2) {
                    animateTo({ curve: curves.interpolatingSpring(0, 1, 400, 38) }, () => {
                      this.offsetY += this.ITEM_INTV
                      this.dragRefOffset -= this.ITEM_INTV
                      this.itemMove(index, index - 1)
                    })
                  }
                })
                .onActionEnd((event: GestureEvent) => {
                  animateTo({ curve: curves.interpolatingSpring(0, 1, 400, 38) }, () => {
                    this.dragItem = -1
                    this.neighborItem = -1
                  })
                  animateTo({ curve: curves.interpolatingSpring(14, 1, 170, 17), delay: 150 }, () => {
                    this.scaleItem = -1
                  })
                }))
              .onCancel(() => {
                animateTo({ curve: curves.interpolatingSpring(0, 1, 400, 38) }, () => {
                  this.dragItem = -1
                  this.neighborItem = -1
                })
                animateTo({ curve: curves.interpolatingSpring(14, 1, 170, 17), delay: 150 }, () => {
                  this.scaleItem = -1
                })
              }))
        }, (item: number) => item.toString())
      }
    }
    .width('100%')
    .height('100%')
    .backgroundColor(0xDCDCDC)
    .padding({ top: 5 })
  }
}

4、HarmonyOS 如何调用js代码？

应用侧可以通过runJavaScript()方法调用前端页面的JavaScript相关函数，参考文档：https://developer.huawei.com/consumer/cn/doc/harmonyos-guides-V5/web-in-app-frontend-page-function-invoking-V5