expo-chat-ui

Overview

This skill covers building a performant chat UI in Expo with:

• Smooth keyboard animations with interactive dismissal
• High-performance recycling list for messages
• Safe area and inset management
• Platform-specific implementations (native SwiftUI / web HTML)
• Image attachments and speech recognition

Required Dependencies

npx expo install react-native-reanimated react-native-safe-area-context react-native-keyboard-controller @legendapp/list @react-native-masked-view/masked-view expo-haptics expo-speech-recognition expo-glass-effect @expo/ui

Architecture

components/
├── keyboard-scroll-view.tsx    # ChatView wrapper with keyboard handling
├── measure-node.tsx            # Height measurement context
├── composer/
│   ├── composer.tsx            # Native implementation
│   ├── composer.web.tsx        # Web implementation
│   ├── composer-text-input.tsx # Text input with keyboard integration
│   ├── send-button.tsx         # Send/Mic/Stop button states
│   ├── multi-button.tsx        # Context menu for attachments
│   └── selected-media-context.tsx # Image attachment state
└── lib/
    ├── haptic.ts               # Native haptics
    └── haptic.web.ts           # Web haptics (no-op)

Core Components

1. ChatView Wrapper

The ChatView component provides context for measuring toolbar height and coordinating keyboard animations.

import { MeasureNode } from "./measure-node";

export function ChatView(props: { children?: React.ReactNode }) {
  return <MeasureNode>{props.children}</MeasureNode>;
}

// Sub-components attached to ChatView
ChatView.Toolbar = ChatViewToolbar;
ChatView.ScrollView = ChatScrollView;

2. MeasureNode Context

Tracks dynamic heights using shared values for smooth animations:

import { SharedValue, useSharedValue } from "react-native-reanimated";
import { View } from "react-native";

const MeasureNodeContext = React.createContext<{
  uiHeight: SharedValue<number>;
} | null>(null);

export function MeasureNode(props: { children?: React.ReactNode }) {
  const uiHeight = useSharedValue(0);
  return (
    <MeasureNodeContext value={{ uiHeight }}>
      {props.children}
    </MeasureNodeContext>
  );
}

MeasureNode.Trigger = function Trigger(props: { children?: React.ReactNode }) {
  const ref = useRef<View>(null);
  const { uiHeight } = React.use(MeasureNodeContext);

  useLayoutEffect(() => {
    if (!ref.current) return;
    const rect = ref.current.getBoundingClientRect();
    uiHeight.value = rect.height;
  }, [ref, uiHeight]);

  const onLayout = ({ nativeEvent: { layout } }) => {
    uiHeight.set(layout.height);
  };

  return <View {...props} ref={ref} onLayout={onLayout} />;
};

MeasureNode.useHeightSharedValue = function useFrame() {
  const context = React.use(MeasureNodeContext);
  return context.uiHeight;
};

Keyboard Handling

useKeyboardAnimation Hook

Handles all keyboard lifecycle events for smooth animations:

import {
  useReanimatedKeyboardAnimation,
  useKeyboardHandler,
} from "react-native-keyboard-controller";
import {
  useSharedValue,
  useAnimatedScrollHandler,
} from "react-native-reanimated";
import { useSafeAreaInsets } from "react-native-safe-area-context";

const useKeyboardAnimation = () => {
  const progress = useSharedValue(0);
  const height = useSharedValue(0);
  const inset = useSharedValue(0);
  const offset = useSharedValue(0);
  const scroll = useSharedValue(0);
  const shouldUseOnMoveHandler = useSharedValue(false);
  const { bottom } = useSafeAreaInsets();

  useKeyboardHandler({
    onStart: (e) => {
      "worklet";
      // Handle interactive gesture detection
      if (progress.value !== 1 && progress.value !== 0 && e.height !== 0) {
        shouldUseOnMoveHandler.value = true;
        return;
      }
      progress.value = e.progress;
      height.value = e.height;
      inset.value = Math.max(bottom, height.value);
      offset.value = Math.max(Math.max(height.value, bottom) + scroll.value, 0);
    },
    onInteractive: (e) => {
      "worklet";
      progress.value = e.progress;
      height.value = e.height;
    },
    onMove: (e) => {
      "worklet";
      if (shouldUseOnMoveHandler.value) {
        progress.value = e.progress;
        height.value = e.height;
      }
    },
    onEnd: (e) => {
      "worklet";
      height.value = e.height;
      progress.value = e.progress;
      shouldUseOnMoveHandler.value = false;
    },
  });

  const isCloseToEnd = useSharedValue(true);

  const onScroll = useAnimatedScrollHandler(
    {
      onScroll: (e) => {
        scroll.value = e.contentOffset.y - inset.value;
      },
    },
    []
  );

  return { height, onScroll, inset, offset, scroll, isCloseToEnd };
};

Toolbar Positioning

Position the composer toolbar above the keyboard:

function ChatViewToolbarPadding(
  props: React.ComponentProps<typeof Animated.View>
) {
  const { bottom: paddingBottom } = useSafeAreaInsets();
  const { height, progress } = useReanimatedKeyboardAnimation();
  const keyboard = useAnimatedKeyboard();
  const toolbarHeightSharedValue = MeasureNode.useHeightSharedValue();

  const bottomStyle = useAnimatedStyle(() => {
    const absMax =
      progress.value === 1
        ? Math.max(Math.abs(height.value), keyboard.height.value)
        : Math.abs(height.value);
    return {
      bottom: Math.max(paddingBottom, absMax),
    };
  }, [paddingBottom, toolbarHeightSharedValue, height, keyboard, progress]);

  return (
    <Animated.View
      {...props}
      style={[{ position: "absolute" }, bottomStyle, props.style]}
      pointerEvents="box-none"
    />
  );
}

ChatView.Toolbar = function ChatViewToolbar({
  children,
  ...props
}: React.ComponentProps<typeof Animated.View>) {
  return (
    <ChatViewToolbarPadding {...props}>
      <MeasureNode.Trigger>{children}</MeasureNode.Trigger>
    </ChatViewToolbarPadding>
  );
};

Recycling List

ChatScrollView with Legend List

High-performance list using @legendapp/list:

import { LegendList, LegendListProps, LegendListRef } from "@legendapp/list";

const AnimatedLegendListComponent =
  Animated.createAnimatedComponent(LegendList);

export type ChatScrollViewRef = AnimatedRef<LegendListRef>;
export type ChatScrollViewProps<T = any> = LegendListProps<T> & {
  ref: ChatScrollViewRef;
};

function ChatScrollView<T>({
  children,
  ref,
  ...props
}: ChatScrollViewProps<T>) {
  const toolbarHeightSharedValue = MeasureNode.useHeightSharedValue();
  const scrollViewContentHeight = useSharedValue(0);
  const { height } = useReanimatedKeyboardAnimation();
  const { bottom } = useSafeAreaInsets();
  const isTouching = useSharedValue(false);
  const scrollViewHeight = useSharedValue(0);
  const controllerProps = useKeyboardAnimation();

  // Custom ref with requestScrollToEnd
  useImperativeHandle(
    ref,
    () => ({
      ...ref?.current,
      requestScrollToEnd: (animated: boolean) => {
        if (isTouching.value) return; // Skip if user is touching
        ref.current?.scrollToEnd({ animated });
      },
    }),
    [ref]
  );

  // Scroll indicator insets
  const scrollIndicatorInsets = useDerivedValue(
    () => ({
      top: 56, // composer header height
      bottom:
        Math.max(0, Math.abs(height.value) - bottom) +
        toolbarHeightSharedValue.value,
    }),
    [toolbarHeightSharedValue, bottom, height]
  );

  // Animated content insets
  const animatedProps = useAnimatedProps(() => ({
    contentInset: {
      bottom:
        Math.abs(controllerProps.inset.value) + toolbarHeightSharedValue.value,
    },
    contentOffset: {
      x: 0,
      y: controllerProps.offset.value,
    },
  }));

  return (
    <AnimatedLegendListComponent
      {...props}
      ref={ref}
      animatedProps={animatedProps}
      scrollIndicatorInsets={scrollIndicatorInsets}
      scrollEventThrottle={16}
      onScrollBeginDrag={(e) => {
        isTouching.value = true;
        props.onScrollBeginDrag?.(e);
      }}
      onScrollEndDrag={(e) => {
        isTouching.value = false;
        props.onScrollEndDrag?.(e);
      }}
      onScroll={controllerProps.onScroll}
      keyboardDismissMode="interactive"
      contentInsetAdjustmentBehavior="never"
      onContentSizeChange={(width: number, height: number) => {
        scrollViewContentHeight.value = height;
        props.onContentSizeChange?.(width, height);
      }}
      onLayout={(e) => {
        scrollViewHeight.value = e.nativeEvent.layout.height;
        props.onLayout?.(e);
      }}
    />
  );
}

Usage

<ChatView.ScrollView<MessageType>
  ref={scrollViewRef}
  keyboardShouldPersistTaps="handled"
  contentContainerStyle={{
    gap: 16,
    paddingTop: 72,
    alignItems: "stretch",
  }}
  maintainScrollAtEnd={isThinking}
  maintainVisibleContentPosition={isThinking}
  estimatedItemSize={32}
  initialScrollIndex={messages.length - 1}
  keyExtractor={(item) => item?.id}
  recycleItems={true}
  data={messages}
  renderItem={({ item }) => <Message key={item.id} message={item} />}
  ListFooterComponent={() =>
    error ? <ChatErrorMessage error={error} /> : null
  }
/>

Composer Text Input

Native Implementation with SwiftUI

import * as SUI from "@expo/ui/swift-ui";
import * as mod from "@expo/ui/swift-ui/modifiers";
import { ChatView } from "@/components/keyboard-scroll-view";

export function ComposerTextInput({
  authenticated,
  canSend,
  scrollViewRef,
  textInputRef,
  onSend,
  onChangeText,
  setTextInput,
}: Props) {
  return (
    <ChatView.Toolbar style={{ width: "100%" }}>
      <Host
        style={{ minWidth: "100%", maxWidth: "100%" }}
        matchContents={{ vertical: true }}
      >
        <SUI.GlassEffectContainer
          spacing={4}
          modifiers={[
            mod.disabled(!authenticated),
            frame({ idealWidth: 11111 }),
            ignoreSafeArea({ regions: "all", edges: "all" }),
          ]}
        >
          <SUI.HStack spacing={6} alignment="bottom">
            <MultiButton disabled={!authenticated} />

            <SUI.ZStack
              modifiers={[
                glassEffectId("composer", "container"),
                glassEffect({
                  glass: { variant: "regular", interactive: authenticated },
                  shape: "roundedRectangle",
                  cornerRadius: 24,
                }),
              ]}
              alignment="bottom"
            >
              <SUI.TextField
                multiline
                placeholder="Generate code..."
                allowNewlines={false}
                numberOfLines={6}
                ref={textInputRef}
                onChangeFocus={(focus) => {
                  if (focus) {
                    scrollViewRef?.current?.scrollToOffset({
                      offset: Number.MAX_SAFE_INTEGER - 1,
                      animated: true,
                    });
                  }
                }}
                onChangeText={onChangeText}
                onSubmit={onSend}
                autoFocus={authenticated}
                modifiers={[
                  mod.disabled(!authenticated),
                  mod.padding({ leading: 12, top: 8, bottom: 8, trailing: 48 }),
                  mod.frame({
                    minHeight: 44,
                    maxHeight: 200,
                    idealWidth: 10000,
                  }),
                  mod.clipShape("roundedRectangle"),
                ]}
              />
              <SendButton canSend={canSend} onSend={onSend} />
            </SUI.ZStack>
          </SUI.HStack>
        </SUI.GlassEffectContainer>
      </Host>
    </ChatView.Toolbar>
  );
}

Send Button with Speech Recognition

Three-state button: recording, ready to send, or thinking:

import {
  ExpoSpeechRecognitionModule,
  useSpeechRecognitionEvent,
} from "expo-speech-recognition";
import { haptics } from "@/lib/haptic";

export function SendButton({
  disabled,
  canSend,
  onSend,
  setTextInput,
  textInputText,
}) {
  const isThinking = useIsAgentThinking();
  const { stop } = useAgentActions();
  const [isRecording, setIsRecording] = useState(false);

  useSpeechRecognitionEvent("start", () => setIsRecording(true));
  useSpeechRecognitionEvent("end", () => {
    setIsRecording(false);
    const text = textInputText?.current?.trim();
    if (text) {
      haptics.success();
      setTextInput(text, true);
    }
  });
  useSpeechRecognitionEvent("result", (event) => {
    const text = event.results[0]?.transcript || "";
    if (text) setTextInput(text, false);
  });

  // Stop button when AI is thinking
  if (isThinking) {
    return (
      <SUI.Button variant="borderedProminent" onPress={stop}>
        <SUI.Image systemName="stop.fill" />
      </SUI.Button>
    );
  }

  // Mic button when no text / recording
  if (isRecording || !canSend) {
    return (
      <SUI.Button
        variant="borderedProminent"
        color={isRecording ? AC.systemRed : AC.label}
        onPress={async () => {
          if (isRecording) {
            ExpoSpeechRecognitionModule.stop();
            return;
          }
          haptics.impact("medium");
          const permission =
            await ExpoSpeechRecognitionModule.requestSpeechRecognizerPermissionsAsync();
          if (permission.status === "denied") {
            alert("Permission denied. Enable in App Settings.");
            return;
          }
          ExpoSpeechRecognitionModule.start({
            interimResults: true,
            continuous: false,
            addsPunctuation: true,
          });
        }}
      >
        <SUI.Image systemName={isRecording ? "stop.fill" : "mic.fill"} />
      </SUI.Button>
    );
  }

  // Send button
  return (
    <SUI.Button
      variant="borderedProminent"
      onPress={() => onSend(textInputText?.current)}
    >
      <SUI.Image systemName="arrow.up" />
    </SUI.Button>
  );
}

Image Attachments

SelectedMediaContext

interface SelectedImage {
  url: string;
}

const SelectedMediaContext =
  createContext<SelectedMediaContextValue>(undefined);

export function SelectedMediaProvider({ children }) {
  const [selectedImages, setSelectedImages] = useState<SelectedImage[]>([]);

  const addImages = (images: SelectedImage[]) => {
    setSelectedImages((current) => {
      const combined = [...current, ...images];
      const unique = Array.from(
        new Map(combined.map((item) => [item.url, item])).values()
      );
      return unique.slice(-3); // Keep only last 3
    });
  };

  const removeImage = (index: number) => {
    setSelectedImages((current) => current.filter((_, i) => i !== index));
  };

  return (
    <SelectedMediaContext
      value={{ selectedImages, addImages, removeImage, clearImages, setImages }}
    >
      {children}
    </SelectedMediaContext>
  );
}

Image Preview

function ImagePreviewSection() {
  const { selectedImages, removeImage } = useSelectedMedia();

  return (
    <AnimatedFlatList
      horizontal
      entering={FadeIn}
      exiting={FadeOut}
      itemLayoutAnimation={LinearTransition}
      keyboardShouldPersistTaps="handled"
      contentContainerClassName="pt-2 px-3 gap-2"
      data={selectedImages}
      renderItem={({ item, index }) => (
        <AnimatedView entering={FadeIn} exiting={FadeOut}>
          <Image source={{ uri: item.url }} className="w-15 h-15 rounded-lg" />
          <Pressable
            onPress={() => removeImage(index)}
            className="absolute -top-1 -right-1 w-6 h-6 rounded-full bg-black/80"
          >
            <SFIcon name="xmark" className="text-white" />
          </Pressable>
        </AnimatedView>
      )}
    />
  );
}

Haptic Feedback

Native (haptic.ts)

import * as Haptics from "expo-haptics";

export const haptics = {
  impact(
    type:
      | "success"
      | "warning"
      | "error"
      | "select"
      | "light"
      | "medium"
      | "heavy"
  ) {
    if (type === "success" || type === "warning" || type === "error") {
      return Haptics.notificationAsync(type);
    }
    if (type === "select") {
      return Haptics.selectionAsync();
    }
    return Haptics.impactAsync(type);
  },
  success: () =>
    Haptics.notificationAsync(Haptics.NotificationFeedbackType.Success),
  warning: () =>
    Haptics.notificationAsync(Haptics.NotificationFeedbackType.Warning),
  error: () =>
    Haptics.notificationAsync(Haptics.NotificationFeedbackType.Error),
};

Web (haptic.web.ts)

export const haptics = {
  impact: () => {},
  success: () => {},
  warning: () => {},
  error: () => {},
};

Full Composer Usage

export function FullComposer() {
  return (
    <SelectedMediaProvider>
      <View className="flex-1">
        <ComposerModalBackdrop />
        <Composer />
      </View>
    </SelectedMediaProvider>
  );
}

function Composer() {
  const { sendMessageAsync } = useAgentActions();
  const { messages, error } = useAgentState();
  const isThinking = useIsAgentThinking();
  const textInputRef = useRef<SUI.TextFieldRef>(null);
  const scrollViewRef = useRef<ChatScrollViewRef>(null);
  const { selectedImages, clearImages } = useSelectedMedia();

  const sendMessageWrapper = async (text: string) => {
    if (!text.trim()) return;

    textInputRef.current?.setText("");
    clearImages();

    sendMessageAsync({
      text,
      images: selectedImages.length ? selectedImages : undefined,
    });
  };

  return (
    <View className="flex-1">
      <ComposerHeader />

      <ChatView>
        <MaskedView
          style={{ flex: 1 }}
          maskElement={
            <View
              style={{
                flex: 1,
                experimental_backgroundImage:
                  "linear-gradient(180deg,rgba(0,0,0,0) 0%, rgba(0,0,0,1) 80px)",
              }}
            />
          }
        >
          <ChatView.ScrollView
            ref={scrollViewRef}
            keyboardShouldPersistTaps="handled"
            maintainScrollAtEnd={isThinking}
            maintainVisibleContentPosition={isThinking}
            estimatedItemSize={32}
            recycleItems={true}
            data={messages}
            renderItem={({ item }) => <Message message={item} />}
          />
        </MaskedView>

        <ComposerTextInput
          scrollViewRef={scrollViewRef}
          textInputRef={textInputRef}
          onSend={sendMessageWrapper}
        />
      </ChatView>
    </View>
  );
}

Key Props Reference

ChatView.ScrollView Props

Keyboard Animation Shared Values

Platform-Specific Files

Use file suffixes for platform-specific implementations:

• composer.tsx - Native implementation with SwiftUI
• composer.web.tsx - Web implementation with HTML/radix
• multi-button.tsx - Native context menu
• multi-button.web.tsx - Web dropdown menu
• haptic.ts - Native haptics
• haptic.web.ts - Web haptics (no-op)

Tips

1. Always use keyboardShouldPersistTaps="handled" to allow button interactions while keyboard is open
2. Track isTouching state to prevent auto-scroll while user is manually scrolling
3. Use useImperativeHandle to extend refs with custom methods like requestScrollToEnd
4. Worklet functions must include the "worklet" directive for keyboard handlers
5. Use useDerivedValue for computed animations that depend on multiple shared values
6. Set estimatedItemSize based on your average message height for optimal recycling