{
  "id": 1709766,
  "title": "Flutter Streaming UI: How the Typewriter Experience of AI Replies Is Built",
  "url": "https://urgent.news/2026/08/18/flutter-streaming-ui-how-the-typewriter-experience-of-ai-replies-is",
  "topic": "tech",
  "section": "Tech",
  "published": "2026-08-18T12:44:59.000Z",
  "source": {
    "name": "Dev.to",
    "slug": "dev-to",
    "url": "https://dev.to/yuelinghuashu/flutter-streaming-ui-how-the-typewriter-experience-of-ai-replies-is-built-371l"
  },
  "original_language": "en",
  "account": "The \"typewriter effect\" in AI-generated responses appears simple at first glance, with characters appearing one by one. However, there is a complex set of engineering decisions that enable this effect without performance regression. The implementation in this article is based on Flutter/Dart, but the core decisions are framework-agnostic and apply to Web EventSource and native/RN SSE clients.\n\nThe article begins with a prologue about the challenges faced when creating a \"skip typewriter\" button in an AI narrative app. The button allows users to see the full AI reply immediately instead of waiting for the text to appear character by character. The button went through three versions in the development cycle:\n\nV1: Clicking the button does nothing.\nV2: Clicking truncates the content, resulting in an incomplete reply.\nV3: Clicking reveals the partial text immediately, while the LLM continues generating the full reply in the background.\n\nThere are three common pitfalls in streaming UI when implementing this effect:\n\n1. From SSE to screen: The streaming rendering pipeline\nThe LLM sends the reply in chunks via HTTP SSE. Each chunk is a small piece of the complete response, with a delay between chunks determined by the model's generation speed. The characters appear one by one, creating the typewriter animation. However, updating the UI on every chunk can cause performance issues. To address this, chunks are buffered and committed together using a Timer and a 50ms batching window. This reduces the number of UI notifications and improves performance.\n\n2. The correct semantics of \"skip animation\": Silent accumulation vs. aborting generation\nThe most subtle point in the streaming experience is understanding the correct semantics of the \"skip animation\" button. Initially, the implementation only skipped the UI batching window, committing all buffered chunks immediately to the UI. However, this doesn't solve the user's problem, as the LLM still spends time generating the full reply. The correct approach is to silently accumulate the chunks and let the LLM finish generating the full response in the background. When the generation is complete, the entire reply is written into the message list all at once. This ensures that the user only skips the animation, not the generation process.\n\nIn summary, the \"typewriter effect\" in AI-generated responses involves a complex set of engineering decisions to ensure a smooth and performant experience. By understanding the common pitfalls and the correct semantics of the \"skip animation\" button, developers can create an effective and user-friendly implementation.",
  "summary": "The typewriter effect looks simple: characters appear one by one. But behind \"skip animation\", \"no truncation\", and \"no performance regression\" lies a whole set of engineering decisions. The implementation in this article is Flutter/Dart based, but the core semantic decisions — \"skip ≠ abort\" and \"buffer and batch\" — are framework-agnostic : Web's EventSource, and native/RN SSE clients, face the…",
  "key_points": [
    "Typewriter effect in AI responses involves complex engineering decisions",
    "Three versions of skip typewriter button developed during implementation",
    "Correct semantics of skip animation button involves silent chunk accumulation"
  ],
  "editors_take": null,
  "illustration": null,
  "coverage": {
    "outlets": 1,
    "also_reported_by": []
  },
  "ai_generated": true,
  "disclaimer": "Summaries, key points and the editor’s take are written by software from other outlets’ reporting and may contain errors — always check the linked original."
}