[shutter] dart data type (dynamic data type)

Dart In language dynamic , var , Object ,

3

3

3 Type of data ;

One 、 dynamic data type

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dynamic data type : dynamic yes Drat In language Dynamic data type , adopt dynamic Keyword defined variables , stay The defined data type will not be controlled during compilation , The type of variable is handled only at runtime , Infer the current according to the type of variable assignment dynamic Runtime data type of data type , dynamic Variables only know the data type at run time ;

dynamic Variable definitions :

dynamic  Variable name  =  A variable's value 

dynamic Example of variable code :

  dynamicDemo(){ 
        dynamic d = "CSDN";    //  Print  dynamic  The runtime type of the variable     print(d.runtimeType);    //  Print  dynamic  A variable's value     print(d);  }

Running results :

StringCSDN

Two 、 dynamic Variables cannot be syntax checked

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adopt dynamic Variables can define any data type , At compile time, the Dart The static syntax check of the language is invalid ;

Such as : First, define dynamic Variable , Assigned a string , Then call a method that does not belong to the string object , There must be a mistake here , But the static syntax check can't find out , You can only know the error here when the error is reported in the last run ;

An error occurred while running :

this Flutter There is also an error message in the interface :

3、 ... and 、 dynamic Variable runtime type modification

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dynamic data type The runtime type can be changed , Aforementioned dynamic d The type is initialized to String type , Assign an integer to this variable halfway , At this point, the type of the variable becomes int type ;

Code example : For the first dynamic The variable is assigned a value String Type values “CSDN” , And then to dynamic The variable is assigned a value int Type values 666 ;

  dynamicDemo(){ 
        dynamic d = "CSDN";    //  Print  dynamic  The runtime type of the variable     print(d.runtimeType);    //  Print  dynamic  A variable's value     print(d);    //  call  dynamic  Variable method ,  Static compilation cannot check for errors ,  The runtime will report an error     //d.getName();        //  by  dynamic  Variable assignment  int  data     d = 666;    //  Print  dynamic  The runtime type of the variable     print(d.runtimeType);    //  Print  dynamic  A variable's value     print(d);  }

Running results :

StringCSDNint666

Four 、 Complete code example

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import 'package:flutter/material.dart';class DartType extends StatefulWidget { 
      @override  _DartTypeState createState() => _DartTypeState();}class _DartTypeState extends State<DartType> { 
      @override  Widget build(BuildContext context) { 
        dynamicDemo();    return Container();  }  dynamicDemo(){ 
        dynamic d = "CSDN";    //  Print  dynamic  The runtime type of the variable     print(d.runtimeType);    //  Print  dynamic  A variable's value     print(d);    //  call  dynamic  Variable method ,  Static compilation cannot check for errors ,  The runtime will report an error     //d.getName();    //  by  dynamic  Variable assignment  int  data     d = 666;    //  Print  dynamic  The runtime type of the variable     print(d.runtimeType);    //  Print  dynamic  A variable's value     print(d);  }}

Running results :

StringCSDNint666

5、 ... and 、 Related resources

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Reference material :

• Dart Developer website : https://api.dart.dev/
• Flutter Chinese net ( unofficial , The translation is very good ) : https://flutterchina.club/ , http://flutter.axuer.com/docs/
• Flutter Official website : https://flutter.dev/ ( Quilt wall )
• official GitHub Address : https://github.com/flutter
• Flutter Related issues : https://flutterchina.club/faq/ ( It is recommended to watch it at the introductory stage )

Blog source download :

• GitHub Address : https://github.com/han1202012/flutter_app_hello ( Keep updating with the progress of the blog , There may not be the source code of this blog )

• Blog source snapshot : https://download.csdn.net/download/han1202012/15110705 ( The source code snapshot of this blog , You can find the source code of this blog )