merge from original master

README.md

@@ -1180,4 +1180,164 @@ ___`Widget/Image()`___ -Inside-> ___`ClipRRect()`___ -Inside-> ___`Container()`_
         ),
 
 [try in codepen](https://codepen.io/erluxman/pen/abvxvOz)
-![](assets/49circularImage.png)
+![](assets/49circularImage.png)
+
+
+## #Day 50 Use `a is! A` instead of `!(a is A)`
+
+Flutter has special keyword to check if an instance ___`is not a type`___. 
+
+    var name = "Hello World";
+
+    // ✅✅Right way✅✅
+    assert(name is String);
+
+    //❌❌Wrong way❌❌
+    assert(!(name is int));
+
+    // ✅✅Right way✅✅
+    assert( name is! int); 
+
+
+## #Day51 Named constructor.
+
+Have you been using static methods to initialze Objects with name?
+
+Use named constructor :
+
+    class Color {
+        Color({this.r, this.b, this.g});
+        int r = 0, g = 0, b = 0;
+
+        // ❌ static method
+        static Color red() => Color(r: 255,g: 0,b:255);                                      
+        // ✅ named constructor
+        Color.red() {
+            r = 255;
+        }
+
+        // ❌ static method
+        static Color cyan() => Color(r:0, b: 128, g: 128);
+        // ✅ named constructor
+        Color.cyan(): g = 128, b = 128;
+        // ✅ named constructor
+        Color.cyan() {
+            g = 128;
+            b = 128;
+        }
+    }
+
+## #Day52 Imports on Steroids 💉💉
+
+___`as :`___ If we import two or more libraries that have conflicting identifiers, we can use them with `prefix.` given after `as` keyword.
+
+`import 'package:library.dart' as lib;`
+
+
+___`show :`___ Show only certain class and hide everything else from it.
+
+`import 'dart:math' show max,tan;`
+
+
+___`hide :`___ Hide only certain class & show everything else from it.
+
+`import 'dart:core' hide String;`
+
+![](assets/52importonsteroid.png)
+
+## #Day53 final vs const 
+
+`final and const` in dart are confusing to the level we think both of them are same. Let's see their diffrences
+
+| ___`final`___ (global / static / member variables)                                                                                                                                                                 | ___`const`___ (static / global variables)                                                                                                 |
+| ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ | ----------------------------------------------------------------------------------------------------------------------------------------- |
+| Has single value of a `member or static or global variable` from start to end.                                                                                                                                     | Has single value of a `static or global variable` from start to end.                                                                      |
+| Different objects of same type can have different final values in same member varaible.                                                                                                                            | Different objects of same type cannot have different const values in same varaible. (i.e. `const members should be static`)               |
+| Should be initialzed `before constructor is called`.                                                                                                                                                               | Should be `strictly initialized during declaration`.                                                                                      |
+| Only the `final` declared `member/staic/global variable` objects are immutable, their content variables may not. i.e. variables inside final objects can be udpated / reassigned if they are not final themselves. | All `const` declared `Golbal/static` variable objects including all their internal content varibales are immutable and cannot be changed. |
+| Can be `intialized` with `immutable/ mutable / calculated values` determined at  `compile time or runtime`.                                                                                                        | Can be `initialized`  with `only immutable values` with all their immutable internal varaibles, determined at `compile time`.             |
+
+We can take example of various computers and how they can be compared with dart modifiers. 
+![](assets/53finalvsconstant.png)
+
+## #Day54 FutureBuilder
+
+If you want to display data from API backend or any async source, use FutureBuilder.
+
+FutureBuilder will automatically give you Widget with default  value until the data arrives from API/ async Source. 
+
+As soon as the real data arrives, it will rebuild the Widget with actual data. 
+
+Just provide the async function / source that will return the values asynchronously along with initial(default) data.
+
+It works very similar to `StreamBuilder` 
+
+        //Future Builder
+        FutureBuilder<List<Player>>(
+            initialData: [],
+            future: FakePlayersAPI().getPlayers(),
+            builder: (context, snapshot) {
+                if (snapshot.data.isEmpty) return CircularProgressIndicator()
+                else return PlayersListWidget(snapshot.data)
+            }
+        )
+
+        //Fake Backed API.
+        class FakePlayersAPI {
+            Future<List<Player>> getPlayers() async {
+                await Future.delayed(Duration(seconds: 1));
+                return _players;
+            }
+
+            Future<String> getPlayerStory() async {
+                await Future.delayed(Duration(seconds: 1));
+                return playerStoryText;
+            }
+        }
+
+
+[try on codepen](https://codepen.io/erluxman/pen/PoPrgbR)
+
+
+![](assets/54futurebuilder.gif)
+
+
+## #Day55 `Get` the easy Navigation library.
+
+Bored of writing `PageRoute`,`context` and `builder` without actual use of them just to navigate to different Widget? Use `get: ^version` library.
+
+Also this gives us superpower to `navigate/show dialog/ BottomSheet/ Snackbar` without`BuildContext`, there might be cool patterns to be developed with this freedom.
+
+1. Just Replace your MaterialApp with `GetMaterialApp`.
+2. Start navigating like this : 
+
+        //Go to next screen
+        Get.to(NextScreen());
+
+        //Show dialog
+        Get.dialog(MyDialogWidget());
+
+        //Show bottom sheet
+        Get.bottomSheet(MyButtomSheetWidget)
+
+        //Show snackbar 
+        Get.snackbar(title, subTitle);
+
+
+[visit library](https://pub.dev/packages/get) 
+
+[demo](https://gist.github.com/erluxman/2d1723e3395325fb5511809f6f95e21b)
+
+![](assets/55getlib.gif)
+
+## #Day56 `pub outdated`
+
+Maintaining latest versions of pub dependencies is pain. Even worse, every latest versions are compatible.
+
+From dart 2.8 onwards, the command `pub outdated` gives you the overview of your dependencies and possible upgrades in ___**`Resolvable column`**___.
+
+![](assets/56outdated.png) 
+
+🚨🚨Tip: use `flutter pub outdated` if `pub outdated` can't find Flutter SDK. 
+
+