//
// flutter/dart cheatsheet
//
/////////////////////////////////////////////////////////
  flutter changing channels
  
  How to change channels
You can see which channel you're on with the following command:

$ flutter channel
Flutter channels:
* stable
  beta
  dev
  master
To switch channels, run flutter channel [<channel-name>], and then run flutter upgrade to ensure you're on the latest.
///////////////////////////////////////////////////////////
try your flutter / dart code online

https://dartpad.dev/


////////////////////////////////////////////////////////////////
dart inheritance syntax 
class Location {
  num lat, lng; // instance variables
  
  Location(this.lat, this.lng); // generative constructor
}

class ElevatedLocation extends Location { // Extended Location class
  num elevation; // instance variable
  
  ElevatedLocation(num lat, num lng, this.elevation) : super(lat, lng); // call Location(...)
}

main() {
  var location = new ElevatedLocation(21.271488, -157.822806, 20);
  
  print("location=${location.lat},${location.lng},${location.elevation}");
}

////////////////////////////////////////////////////////////////
flutter_blue
Connecting to a device without scan #569

I have done it this way:
protos.BluetoothDevice dev = protos.BluetoothDevice()..remoteId = address;
var _gattClient = BluetoothDevice.fromProto(dev);
var _gattClient.connect(autoConnect: everConnectedDevicesAddresses.contains(address));

Note: be carefull with autoConnect option. I just fixed a big issue on LG phones... 
I could not autoconnect after bluetooth reset. So I made some Set of connected devices, 
that I am clearing when bluetooth is turning off or turned off. autoconnect parameter
should be true only if device was connected at least once after bluetooth or phone reset.

///////////////////////////////////////////////////////////////////
// Provider outside widget tree without buildcontext

typedef Read = T Function<T>();

class Model {
  Model(this._read);
  final Read _read;
  
  void method(){
    final value = _read<Value>>();
  }
}

Provider(
  create: (context) = _read<Value>();
  child: ...,
}
/////////////////////////////////////////////////////////////////
// without cascade

d1.setA(20);
d1.setB(25);
d1.showVal();

// with cascade
d1..setA(20)
  ..setB(25)
  ..showVal();

////////////////////////////////////////////////////////////////////
int mark = 10;
int total = 10;
int amount = 10;
But if you are lazy like me than you can also do these things this way

int mark =10,
  total = 20,
  amount = 30;

//////////////////////////////////////////////////////////
If you want to prevent unwanted widget rebuilds always use const constructor.
In the code below, the instance of BoxDecoration will remain the same even
if the setState is called.

Container(
  width: 250,
  height: 250,
  decoration: const BoxDecoration(
    borderRadius: BorderRadius.only(
    bottomLeft: const Radius.circular(30.0),
    bottomRight: const Radius.circular(30.0))),
  child:.....
);

//////////////////////////////////////////////////////////
vs editor shortcuts/tips

F5 - start debugging
Ctrl + Shift + F5 - restart debugging
Ctrl + F5 - hot restart
Alt + Shift + f - fix indentation and format code, make sure add comma
Ctrl + Tab, hold down Ctrl keep pressing Tab - switch to file/tab
Ctrl + Shift + \ - find bracket pair
Shift + Alt + -> - find firt bracket/paren expand/shrink selection
Ctrl + g - goto line number
Ctrl + space - pop up menu

stanim - create stateful widget with animation controller
stful - create stateful widget and it's subclass
stless - create stateless widget


////////////////////////////////////////////////////////
to test flutter release apk:
start from your project root folder
command -> flutter build apk --split-per-abi
           cd build/app/outputs/apk/release
           python3 -m http.server

on your phone or tablet
go to chrome type in url
  192.168.5.23:8000  // or whatever is the ip of your dev machine
  download the right apk then install
  
  amazon fire tablet 7   - arm 32 bit
  amazon fire tablet 8   - arm 32 bit
  amazon fire tablet 10  - arm 64 bit
  acer chromebook 2 in 1 - arm 32 bit, even though it's an Intel chip
  samsung galaxy s8+     - arm 64 bit
  samsung galaxy s10     - arm 64 bit

//////////////////////////////////////////
when using amazon fire for usb debugging I
get no permissions (user in plugdev group; are your udev rules wrong

solution from stackoverflow
With my Pixel phone plug into the computer, in the notification shade, 
I changed it from USB "Charge this phone" to "PTP" (Picture Transfer Protocol).

I then ran flutter doctor and my Pixel asked me to "Allow USB debugging" for
my computer, I ticked the box to "Always allow from this computer".

/////////////////////////////////////////
hide status bar
import 'package:flutter/services.dart';

void main() {
    SystemChrome.setEnabledSystemUIOverlays([]);
}

///////////////////////////////////////////
lock orientation
import 'package:flutter/services.dart';

void main() async {
  await SystemChrome.setPreferredOrientations([
    DeviceOrientation.portraitUp,
  ]);

  runApp(App());
}

//////////////////////////////////////////////
widget refactor

  constant: -----------------------------------
    Row(children:<Widget>[       // separate file calling container
      container,

    final container = Container( // separate file
      color: ..

  method: ---------------------------------------
    Row(children:<Widget>[     // separate file calling container
      container(),

    Widget container(){       // separate file uses Widget return
      return Container(
        color: ...  

  another method:
    Container container(){    // separate file uses Container return
      return Container(
        color: ...

  widget class: ------------------------------------------
    Row(children:<Widget>[    // separate file calling container
      const MyContainer(),

    class MyContainer extends StatlessWidget { // separate file
      const MyContainer({Key key}):super(key: key);

      @override
      Widget build(BuildContext bc) {
        return Container(
          color: ...
          
          
////////////// another refactor found on stackoverflow

import 'package:flutter/material.dart';

AppBar headerNav({String title}){
  return AppBar(
    title: Text(title),
  );
}

 return Scaffold(
      appBar: headerNav(text:'Home Page'),
      body: Container(
        child: Text('Home'),
      ),
/////////////////////////////////////////
generate list of widgets
child: Column(children:<Widget>[
  for (var widget in widgetList) Text(widget.toString())
    // Text can be any widget, no braces on the for loop, no return keyword

////////////////////////////////////////////
function callback without return value

1st file:

  callBack(){ setState((){});} refresh ui

  Widget1(callBack: callBack);

2nd file:

  final VoidCallback callback;
  Widget1({this.callBack});    // constructor

  @override
  Widget build..
    retrun someWidget ...
      some button on the 2nd file
        onPressed:() => callBack(),  -- function from file 1

/////////////////////////////////////////////////////
function callback with return value

1st file:
  
  Widget1(
    onValueChange:(int val) {
      setState(() => do something with val);

2nd file:

  final Function(int) onValueChange;
  Widget1({this.onValueChange});

  @override
  Widget build ...
    some button on the 2nd file
      onPressed:() { onValueChange(1) }

///////////////////////////////////////////////////////

Screen size - MediaQuery.of(context).size.width and height

hide keyboard - FocusScope.of(context).requestFocus(FocusNode());

b ??= val;
If b is null, assign the value of val to b; otherwise, b stays the same.

a = value ?? 0;
If value is null, set a to 0. Otherwise, set a to value.

a?.b
Conditional access. Equivalent: a == null ? null : a.b