Flutter Responsive Implementations (v5.9.x / v3.1.x / v1.1.x)

Goal

Implement layout adaptability and responsive UI across varying device screens. This skill provides a decision matrix to choose the right responsiveness package and strict instructions on how to use flutter_screenutil, sizer, and responsive_framework natively.

Instructions

1. Package Decision Matrix

Before writing layout code, strictly evaluate the project's target platforms and design requirements to select the appropriate library:

• Scenario A (Strict Mobile UI Replication): The project targets only iOS/Android, and the designers have provided a strict Figma draft (e.g., 375x812) that must look exactly proportional on all phones (mini to pro max).
• Decision: Use flutter_screenutil. (Math-based density scaling)
• Scenario B (Percentage-based Mobile UI): The project targets mobile, but layout is dictated by percentage of screen real estate rather than fixed Figma pixels.
• Decision: Use sizer. (Percentage-based viewport scaling)
• Scenario C (True Cross-Platform / Web / Desktop): The project spans Mobile, Tablet, Web, and Desktop. UI components must fundamentally change their structure (e.g. BottomNav -> SideRail) based on available space, rather than just zooming in.
• Decision: Use responsive_framework. (Breakpoint-based rendering)

2. Implementing flutter_screenutil

Best for mathematically scaling a fixed design draft across different physical device sizes.

Setup (`main.dart`): Wrap the MaterialApp in ScreenUtilInit and provide the designSize from the design specs (Figma/AdobeXD).

Widget build(BuildContext context) {
  return ScreenUtilInit(
    designSize: const Size(375, 812), // The Figma draft size
    minTextAdapt: true,
    splitScreenMode: true,
    builder: (context, child) {
      return MaterialApp(
        // ...
      );
    },
  );
}

Usage Constraints:

• Width: Use .w (e.g., 100.w)
• Height: Use .h (e.g., 200.h)
• Square dimensions / Radius: Use .r (e.g., Radius.circular(16.r)) or 100.w for both width and height to prevent stretching. Do not use `.h` for width.
• Fonts: Use .sp (e.g., 16.sp). Note: sp changes with system accessibility font sizes.

Container(
  width: 50.w,
  height: 200.h,
  child: Text('Responsive Text', style: TextStyle(fontSize: 14.sp)),
)

3. Implementing sizer

Best for scenarios where defining UI in viewport percentages is easier than absolute dp conversions.

Setup (`main.dart`): Wrap the MaterialApp in Sizer.

Widget build(BuildContext context) {
  return Sizer(
    builder: (context, orientation, screenType) {
      return MaterialApp(
        // ...
      );
    },
  );
}

Usage Constraints:

• Percentages: Use .w and .h as raw screen percentages. 100.w is exactly the full width of the current screen.
• Fonts/Density: Use .dp (Density Pixel) instead of .sp if you want text to scale strictly by physical display density rather than user accessibility settings.
• Crucial Difference: 50.w in sizer means 50% of screen. 50.w in ScreenUtil means 50 logical pixels relative to the 375 Figma draft. Be acutely aware of which package is active.

Container(
  width: 20.w, // Takes exactly 20% of screen width
  height: 30.5.h, // Takes exactly 30.5% of screen height
  child: Text('Sizer Text', style: TextStyle(fontSize: 15.dp)),
)

4. Implementing responsive_framework

Best for Tablet/Desktop/Web where components shift layout structures at specific breakpoints.

Setup (`main.dart`): Wrap the router or MaterialApp builder with ResponsiveBreakpoints.builder(). Do NOT use the deprecated ResponsiveWrapper.

return MaterialApp(
  builder: (context, child) => ResponsiveBreakpoints.builder(
    child: child!,
    breakpoints: [
      const Breakpoint(start: 0, end: 450, name: MOBILE),
      const Breakpoint(start: 451, end: 800, name: TABLET),
      const Breakpoint(start: 801, end: 1920, name: DESKTOP),
      // Custom breakpoint labels can be added here
      const Breakpoint(start: 1921, end: double.infinity, name: '4K'),
    ],
  ),
);

Usage Constraints (Conditionals): Use ResponsiveBreakpoints.of(context) to query the current environment to determine layout structures.

// Check size logic to conditionally render navigation styles
bool showSideNav = ResponsiveBreakpoints.of(context).largerThan(MOBILE);

if (showSideNav) {
  // Render Desktop layout
} else {
  // Render Mobile layout
}

Usage Constraints (Value Scaling): If you need specific padding or constraints to change per breakpoint, use ResponsiveValue.

double padding = ResponsiveValue(
    context, 
    defaultValue: 10.0,
    conditionalValues: [
        Condition.equals(name: MOBILE, value: 10.0),
        Condition.largerThan(name: MOBILE, value: 30.0),
    ]
).value;

Constraints

1. Never Mix Scaling Libraries: Do not use sizer and flutter_screenutil in the same project. They conflict conceptually.
2. Web/Desktop Prohibition: NEVER use flutter_screenutil to blindly scale a mobile UI up to a Desktop screen. A 375-width design scaled to a 1920-width monitor results in cartoonishly massive text and buttons. Use responsive_framework for Desktop/Web.
3. No `MediaQuery` Boilerplate: When utilizing these libraries, do not write raw MediaQuery.of(context).size.width * 0.5. Use the library's native syntax (e.g., 50.w in sizer) to keep code declarative and completely eliminate boilerplate.