The following GIF diagram shows the layout jump without a picture placeholder:

See the full example in DartPad

If you have cached a picture placeholder in your app, you can use FadeInImage Widgets to display placeholders.If you want to use a widget instead of a picture as a placeholder, you can use Image.frameBuilder Properties.

Image.frameBuilder Attribute is responsible for building a picture widget with four parameters:

• Context: build context
• Child:widget child element
• Frame: A number that codes the frame, if the picture is still loading, for null
• WasSynchronous Loaded : Boolean value, when the picture is loaded true

When implementing a placeholder widget, you first need to pass the WasSynchronous Loaded Check to see if the picture has been loaded, and if the loading is complete, return child . If not, use AnimatedSwitcher Widget to create a placeholder-to-picture gradient animation:

class ImageWidgetPlaceholder extends StatelessWidget {
  const ImageWidgetPlaceholder({
    Key key,
    this.image,
    this.placeholder,
  }) : super(key: key);

  final ImageProvider image;
  final Widget placeholder;

 @override
 Widget build(BuildContext context) {
   return Image(
     image: image,
     frameBuilder: (context, child, frame, wasSynchronousLoaded) {
       if (wasSynchronousLoaded) {
         return child;
       } else {
         return AnimatedSwitcher(
           duration: const Duration(milliseconds: 500),
           child: frame != null ? child : placeholder,
         );
       }
     },
   );
 }
}

With placeholders, the layout never jumps back and forth again, and the pictures have a gradual effect:

See the full example in DartPad

Pre-cached pictures

If your app has a welcome screen before displaying the picture interface, you can call precacheImage Method to pre-cache pictures.

precacheImage(NetworkImage(url), context);

Take a look at the effect:

See the full example in DartPad

Disable navigation transition animation in Flutter web app

Navigation transition animations are commonly used when users switch pages, which is a good way to let users know where they are in a mobile app.However, such interactions are rarely seen on the web.So to improve awareness, you can disable transitional animation between pages.

By default, MaterialApp Different transition animations are used depending on the platform (Android slides up, iOS slides right (left).To override this default behavior, you need to create a custom PageTransitionsTheme Class.You can use the kIsWeb constant to determine if an app is running on the web.If so, by returning child To disable transitional animations:

import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart';

class NoTransitionsOnWeb extends PageTransitionsTheme {
  @override
  Widget buildTransitions<T>(
    route,
    context,
    animation,
    secondaryAnimation,
    child,
  ) {
    if (kIsWeb) {
      return child;
    }
    return super.buildTransitions(
      route,
      context,
      animation,
      secondaryAnimation,
      child,
    );
  }
}
### End

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