[fluent] dart data type string type (string definition | string splicing | string API call)

I . String definition

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Use single quotes ’ ’ and Double quotes " " You can define strings ;

// String definition  :  You can use either single quotation marks  ,  You can also use double quotes String str_1 = ' Single quotation marks define the string ';String str_2 = " Double quotation marks define the string ";

I . String splicing

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1 . Use “$” String splicing : In a single quotation mark or double quotation mark string , Use $ Variable name The way , You can splice the contents represented by the variable name into a string ;

String str_3 = "str_1 : $str_1 str_2 : $str_2";// Use  $  String concatenation  : str_1 :  Single quotation marks define the string  str_2 :  Double quotation marks define the string print(" Use  \$  String concatenation  : " + str_3);

2 . Use “+” Operator : Use + Operator You can concatenate strings , This method is similar to Java similar ;

String str_4 = "str_1 : " + str_1 + " , str_2 : " + str_2;//  Print the results  :  Use  +  String concatenation  : str_1 :  Single quotation marks define the string  , str_2 :  Double quotation marks define the string print(" Use  +  String concatenation  : " + str_4);

3 . Use ${ expression } The way :${ expression } , Can be expression The content is spliced into a string ;

String add = "1 + 2 = ${1 + 2}";//  Print the results  :  Use  ${}  String concatenation  : 1 + 2 = 3print(" Use  \${}  String concatenation  : " + add);

III . character string API call

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1 . String character string API file : https://api.dart.dev/stable/2.7.1/dart-core/String-class.html

2 . String interception : Start position needs to be specified ( contain ) And end position ( It doesn't contain ) , from 0 Start counting ; If only the starting position , Then it will be intercepted directly to the end ;

String str_substring = str_1.substring(3, 6);// Print the results  :  String interception  :  Definition words print(" String interception  : " + str_substring);

3 . Get string index :

//  Pass in the substring in the parameter  ,  Or regular expressions int index = str_1.indexOf(" set ");// Print the results  : index : 3print("index : $index");

IV . character string Demo Example

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1 . Code example :

import 'package:flutter/material.dart';class DartType_String extends StatefulWidget { 
      @override  _DartType_StringState createState() => _DartType_StringState();}class _DartType_StringState extends State<DartType_String> { 
      @override  Widget build(BuildContext context) { 
        stringDemo();    return Container(child: Text(' String type '));  }  // String type   Example   stringDemo(){ 
        // I .  String definition     // String definition  :  You can use either single quotation marks  ,  You can also use double quotes     String str_1 = ' Single quotation marks define the string ';    String str_2 = " Double quotation marks define the string ";    // II .  String splicing     // 1 .  String splicing  1 : $  String splicing  :  In a single quotation mark or double quotation mark string  ,  Use  $ Variable name   The way  ,    //  You can splice the contents represented by the variable name into a string     String str_3 = "str_1 : $str_1 str_2 : $str_2";    // Use  $  String concatenation  : str_1 :  Single quotation marks define the string  str_2 :  Double quotation marks define the string     print(" Use  \$  String concatenation  : " + str_3);    // 2 .  String splicing  2 :  Use  "+"  Operator  ,  You can concatenate strings  ,  This method is similar to  Java  similar     String str_4 = "str_1 : " + str_1 + " , str_2 : " + str_2;    //  Print the results  :  Use  +  String concatenation  : str_1 :  Single quotation marks define the string  , str_2 :  Double quotation marks define the string     print(" Use  +  String concatenation  : " + str_4);    // 3 .  String splicing  3 :  Use  ${ expression } ,  You can splice the contents of an expression into a string     String add = "1 + 2 = ${1 + 2}";    //  Print the results  :  Use  ${}  String concatenation  : 1 + 2 = 3    print(" Use  \${}  String concatenation  : " + add);    // III .  Commonly used strings  API    // 1 .  String interception     //  Start position needs to be specified ( contain )  And end position ( It doesn't contain ) ,  from  0  Start counting     //  If only the starting position  ,  Then it will be intercepted directly to the end     String str_substring = str_1.substring(3, 6);    // Print the results  :  String interception  :  Definition words     print(" String interception  : " + str_substring);    // 2 .  Get string index     //  Pass in the substring in the parameter  ,  Or regular expressions     int index = str_1.indexOf(" set ");    // Print the results  : index : 3    print("index : $index");  }}

2 . Execution results :

 Use  $  String concatenation  : str_1 :  Single quotation marks define the string  str_2 :  Double quotation marks define the string use  +  String concatenation  : str_1 :  Single quotation marks define the string  , str_2 :  Double quotation marks define the string use  ${ 
    }  String concatenation  : 1 + 2 = 3 String interception  :  Definition words index : 3