Hong Mong 5 Development Treasure Case Sharing Waterfall Stream Optimization Real Battle Sharing

Below is an unofficial technical sharing based on the official HarmonyOS waterfall flow optimization case, reinterpreted with practical development experience, and enriched with more scenario analysis and code examples:

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🌟 HarmonyOS Waterfall Flow Performance Optimization in Practice: Say Goodbye to Lag with This Treasure Guide!

Hello everyone! Recently, I discovered a performance optimization treasure trove in the HarmonyOS documentation. It turns out that the official team has already prepared best practices for various scenarios! Today, I'll focus on sharing the solution for "waterfall flow slow loading and dropped frames," complete with full code analysis and lessons learned from real-world pitfalls.

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1. Why Is the Waterfall Flow Prone to Lag?

// Typical problematic code example
WaterFlow() {
  ForEach(this.data, (item) => { // ❌ No lazy loading
    FlowItem() {
      ComplexComponent(item) // Complex subcomponent
    }
    .height('auto') // ❌ Height not fixed
  })
}

Three Major Performance Killers:

1. One-time rendering: ForEach loads all data at once
2. Dynamic height: Image loading triggers re-layout
3. Component reconstruction: Components are repeatedly created and destroyed during scrolling

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2. Four Official Optimization Solutions (with Practical Code)

Solution 1: Lazy Loading + Cache Pool

WaterFlow() {
  LazyForEach(this.dataSource, (item) => {
    FlowItem() {
      ReusableComponent(item) // ✅ Reusable component
    }
    .height(this.calcHeight(item)) // ✅ Fixed height
  }, item => item.id)
}
.columnsTemplate("1fr 1fr")
.cachedCount(5) // ✅ Cache 5 items off-screen

Optimization Principle:

• LazyForEach: Only renders components in the viewport
• cachedCount: Builds a scroll buffer (similar to RecyclerView's cache pool)

Solution 2: Component Reuse (Key!)

@Reusable // ✅ Magic decorator
@Component
struct ReusableComponent {
  build() {
    // Avoid creating temporary components inside
    Column() {
      OptimizedImage() // Optimized image component
      Text(...).lineClamp(2) // Limit text lines
    }
  }
}

Reuse Level Recommendations:

1. Reuse basic blocks like image + text
2. Reuse the entire card (requires fixed height)

Solution 3: Dynamic Preloading

.onScrollIndex((first, last) => {
  if (last >= totalData - 10) { // ✅ Load when 10 items from the bottom
    loadMoreData() 
  }
})

Smoother than **`onReachEnd*`:*

Preload data in advance to avoid the "white screen pause" while users wait

Solution 4: Fixed Height Calculation (Core Technique)

// Pre-calculate image height
private calcHeight(item: ItemData): number {
  const imgRatio = item.imgHeight / item.imgWidth
  const cardWidth = (deviceWidth - gaps) / columns
  return cardWidth * imgRatio + titleHeight + padding
}

Avoid Layout Jitter:

When images load asynchronously, the height won't stretch the container

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3. Performance Comparison Test (500 Data Items)

Optimization Solution	Memory Usage	First Render	Scroll FPS
Unoptimized	485MB	1346ms	45fps
Lazy Loading	122MB	756ms	58fps
+Cache+Reuse	103MB	761ms	59fps
+Fixed Height	98MB	623ms	60fps

💡 Fixed height reduces layout calculation by about 40%

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4. Pitfall Guide (Lessons Learned)

1. Image Optimization:

Image(item.url)
  .objectFit(ImageFit.Contain) // Avoid the calculation overhead of Cover
  .syncLoad(true) // Use synchronous loading for small images

1. Avoid Deep Nesting:

// ❌ Wrong example: 3 layers of Column + 2 layers of Stack
// ✅ Recommended: Flatten layout, use RelativeContainer

1. Special Handling for Video Cards:

.onAppear(() => playVideo())
.onDisappear(() => stopVideo()) // Must release in time!

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Conclusion

I didn't expect so many practical cases to be hidden in the HarmonyOS documentation! After this optimization, our waterfall flow FPS stabilized at 58+, and memory usage dropped by 70%.

What other performance bottlenecks have you encountered? Feel free to discuss and share in the comments below👇