鸿蒙开发自定义TabBar，实现tabBar 上中间按钮凸起效果

第一步、定义数据模型

export default class TabItemData{

  defaultIcon: Resource
  selectedIcon: Resource
  title: string
  isMiddle: boolean

  constructor(defaultIcon:Resource, selectedIcon:Resource, title:string, isMiddle: boolean) {
    this.defaultIcon = defaultIcon
    this.selectedIcon = selectedIcon
    this.title = title
    this.isMiddle = isMiddle
  }
}

第二步、定义一个ViewModel， 设置数据源

export class MainViewModel {


  getTabBarImage(): Array<TabItemData>{
    let tabItems: TabItemData[] = [
      new TabItemData($r('app.media.home_normal'), $r('app.media.home_selected'), "首页", false),
      new TabItemData($r('app.media.discover_normal'), $r('app.media.discover_selected'), "", true),
      new TabItemData($r('app.media.mine_normal'), $r('app.media.mine_selected'), "我", false),
    ]
    return tabItems
  }

}

export default new MainViewModel();

第三步、自定义组件，定义一个TabItem，用了两个Column 嵌套，代表两个视图容器，由于鸿蒙没有类似Flutter 中Container 这样的组件，所以选择用Column 代替

@Component
export struct TabBarItem{

  @Prop isSelected: boolean
  itemData: TabItemData

  build(){
    Column(){
      Column(){
        Image(this.isSelected? this.itemData.selectedIcon: this.itemData.defaultIcon)
          .width(this.itemData.isMiddle? '45vp': '25vp')
          .height(this.itemData.isMiddle? '45vp': '25vp')
          .interpolation(ImageInterpolation.High)
        if (!this.itemData.isMiddle){
          Text(this.itemData.title)
            .margin({ top: $r('app.float.mainPage_baseTab_top') })
            .fontSize($r('app.float.main_tab_fontSize'))
            .fontColor(this.isSelected? '#1698CE' : '#6B6B6B')
        }
      }
      .justifyContent(FlexAlign.Center)
      .backgroundColor(this.itemData.isMiddle?Color.White: Color.Transparent)
      .padding(this.itemData.isMiddle?{top:2,left:2, right:2, bottom: 2}: 0)
      .borderRadius('23.5vp')
    }.justifyContent(FlexAlign.Center)
    .height($r('app.float.mainPage_barHeight'))
    .width(Constants.FULL_PARENT)
  }
}

第三步、自定义TabBar 组件

@Component
export struct LMTabBar{

  @Prop tabIdx:number
  tabItemClick:(index)=>void

  build(){
    Flex(){
      ForEach(mainViewModel.getTabBarImage(),(item,index: number)=>{
        TabBarItem({itemData: item, isSelected: this.tabIdx === index })
          .offset({y: item.isMiddle? '-25': '0'})

          .onClick(()=>{
            this.tabIdx = index
            this.tabItemClick(index)
          })
      })
    }
  }
}

第四步、用自定义的TabBar覆盖原来Tabs

@Preview
@Entry
@Component
struct MainPage{
  @State currentIndex: number = 0
  private tabsController: TabsController = new TabsController()

  build(){
    Stack(){
      Tabs({barPosition: BarPosition.End, controller: this.tabsController }){
        TabContent(){
          Home()
        }
        .padding({ left: $r('app.float.mainPage_padding'), right: $r('app.float.mainPage_padding') })
        .backgroundColor($r('app.color.mainPage_backgroundColor'))

        TabContent(){
          Text("发现")
        }
        TabContent(){
          Mine()
        }
        .padding({ left: $r('app.float.mainPage_padding'), right: $r('app.float.mainPage_padding') })
        .backgroundColor($r('app.color.mainPage_backgroundColor'))
      }
      .barHeight(0)
      .onChange((index: number)=>{
        this.currentIndex = index
      })
      LMTabBar({tabIdx: this.currentIndex,tabItemClick: (index)=>{
        this.tabsController.changeIndex(index)
      } })
        .backgroundColor(Color.White)

    }.align(Alignment.Bottom)




  }
}