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Flutter Home Widget App Example

This project demonstrates how to create a pure Flutter rendered Home Widget or Today Widget on Android, iOS and macOS.

Previews

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Introduction

  • All Widget examples in this project are full functional, including Widget configure page and background update.
  • Two Widget render modes are included, see below for details.

Notice

  1. Flutter engine on iOS takes too much memory only tested in Simulator.
  2. Flutter render engine on Android has bug on handling transparent image, details: flutter/flutter#73036

Widget Render mode

This project demonstrated 2 different methods to render a Widget:

1. UI Mode

To render Home Widget, a new instance of Flutter engine will be created, it is used to run a separate Flutter App that create the Widget's UI from a separate main Dart function.

The Widget's UI will be rendered in background by this new Flutter engine, when the render process is done, bitmap screenshots will be taken by Flutter engine and show in the Widget.

PROs:

Simple, write the same code as normal flutter app.

CONs:

Slow, Flutter side of runApp is slow, and a 200ms delay should be manually set after setState, because you have to wait for UI render/refresh. It can takes >6 seconds in Debug mode on an very old Android phone, but fortunately, it only takes ~1 second in Release mode, so the speed is still acceptable. It takes lot of memory on iOS because it same as run a full Flutter App (FlutterEngine + FlutterViewController). Some Flutter API used is Internal/Undocumented and maybe changed with upgrade of Flutter.

2. Image Mode

In Image Mode, flutter engine is initialized with a separate main Dart function, no Flutter App will be initialized, instead, a MethodChannel will be created.

The handler of MethodChannel will draw a image by a dart Canvas and return the bytes array to native side, then convert back to Bitmap and show.

PROs:

Fast, only a few of codes are executed, and bitmap is transferred via memory.

No need to wait for render, the image is drawn realtime(also means fast).

Moreover, you can write your own Encoder of MethodChannel to boost the speed of data exchange.

CONs:

Difficult to write code, the whole UI of Home Widget is drawn by Canvas.