Brief introduction
Since the Dart is a language, and then the same language as we know, there are basic data types as well as common flow processing grammar, then we come to understand the next.
Dart everything is an object, including numbers, functions, and so on. They are inherited from Object, default is null (including digital), so numbers, strings can call a variety of methods.
Always variables
variable
Var variable declaration used, may impart different types of values; when not initialized, the default value is null; with the final declaration of a variable can only be assigned once
main void () {
// declare a variable a
var a;
Print (a); // value of a print, the display is null
a = 10;
Print (a); // print out the result of 10
a = "Test string ";
Print (a); // print out the results of a test string
a = 30;
Print (a); // print out the result of 30
Final B = 10;
B = 20 is; // this error will , prompted: [DART] 'B', A Final variable, CAN BE SET Once only.
}
constant
Use const declare a constant in dart in; use const declaration must be compile-time constants.
main void () {
const A = 10;
A = 20 is; // also given here: [DART] by Constant Variables CAN BE Not Assigned A value.
}
In the above we can see some of the simple syntax dart. In fact, quite like js and the data type of a variable declaration is just to change them, you do not have a fixed data type (for example: java language). You can not be modified after the second is final and can declare const variables, and declared variables.
Simply put, the difference between here and the next final of const:
final required variable is initialized only once, does not require that the value assigned must be compile-time constants, it can be constant or not. The const requirements initialized when the statement, and the assignment is necessary for the compile-time constant.
Dart built-in type
In Dart several built-in data types: numeric -Number, Boolean -boolean, key-value pair -Map, strings -String, list -List, other types -Runes, Symbols
Numeric
Dart only offers two types:
NUM
. 1, shaping int
2, double float
main void () {
NUM A = 10; // shaping
a = 20.1; // float
int = I 10;
I = 10.1; // this place being given, because an int type data to double type
double d 20.1 =;
D = 20 is; // this place being given, because of the double type to data type int
}
From the above it can see if a variable is declared using num, free conversion type, but if you are using an int or double clear statement, it can not be converted
Numeric operation
Operators: +, -, *, /, - /,%
Common attributes: isNaN, IsEven, IsOdd
Method used: ABS (), round (), floorl (), ceil (), toInt (), toDouble ()
// Since conventional method has in other languages, not repeat the past, the following are some specific
void main () {
int I = 10;
Double D = 20.1;
Print (I / D); // 0.49751243781094523
print (i ~ / d); // 0 this operation is rounding
print (i.isOdd); // Analyzing odd
print (i.isEven); // Analyzing is even
}
Some common conversion
// String -> int
var one = int.parse('1');
assert(one == 1);
// String -> double
var onePointOne = double.parse('1.1');
assert(onePointOne == 1.1);
// int -> String
String oneAsString = 1.toString();
assert(oneAsString == '1');
// double -> String
String piAsString = 3.14159.toStringAsFixed(2);
assert(piAsString == '3.14');
String
I was able to use single or double quotes in the string dart in a statement. Both methods can be.
main void () {
String String = 'single quotes declaration string';
String string1 = "double-quoted statement string";
}
In the case of each double quotes nested single String
void main () {
String STR = "single quotation marks" double quotation marks " ';
String str1 =" double quotes' single quotes' ";
Print (STR);
Print (str1);
String str2 =" single quotes the \ 'single quote \' ';
String Str3 = "double quotes \" double quotation marks \ "";
Print (str2);
Print (Str3);
}
String concatenation way
The following show various operations of the dart in the string concatenation (black magic) listed.
main void () {
// spaces using stitching, a plurality of spaces may
String str1 = 'single quotes space string' splice '' ~ '; // string of single quotes spaces splicing ~
@ line breaks and space
String str2 = 'single quote character string'
'for the trip' plus space 'splice'; // swap single quote character line stitching together the spaces
// single or double quotes space splicing
String str3 = "single or double quotation mark space the string " 'splice'" ~ "; // ~ Mono quoted string space splicing
@ single or double quotation marks and spaces newline
string str4 =" single or double quotes string '
' for the trip 'plus space' splice '; // single or double quotation mark character swap line plus space stitching
String str5 =' ''
to use three single quotes,
see I use it
'' ';
String STR6 = "" "
using three pairs of quotation marks,
see I use it to
"" ";
String str7 = "Well, little or normal" + ", used to splice +";
}
From the above it can be seen dart can use the space to do for the stitching. So we continue to study next.
main void () {
// string concatenation, output: single or double quotation marks blank spaces
String blockStr = 'single quotes' 'space';
String blockStr1 = 'single quotes' 'space';
String blockStr2 = "double quotation marks" " space ";
String blockStr3 =" double quotation marks "" space ";
// error situations like these will
// String blockStr4 = 'single quotes' '' 'space';
// String blockStr5 =" double quotation marks "" "" space ";
intermediate test // add characters
String blockStr6 = 'single quotes' '_' 'space'; // output: single quotes _ space
String blockStr7 =" double quotation marks "" # "" space "; // note can not be used $, $ being given, output: single quote # spaces
// single or double quotation marks mix
String blockStr8 = 'single "" "" quotes'; // output: single "" ""Quotes
String blockStr9 = 'single "" _ "" quotes'; // Output: Single "" _ "" quotes
single or double quotes using mixed //
String blockStr10 = "double' '' 'quotes"; // Output: bis' '''quotation marks
String blockStr11 = "double '' _ '' quotes"; // Output: double '' _ '' quotes
}
Use $ {} of the expression
Similar to the use of the expression in JS ES6 above, the feeling is the same.
main void () {
var = In Flag to false;
var STR = "test String";
Print ( "we authentication string: $ {str}" "Then let our In Flag: $ {} In Flag");
// last output is: we have to verify the string: a test string and then look at our Flag: false
}
Boolean value
assert is a language built-in predicate function, valid only in test mode
during development, unless the condition is true, otherwise it will throw an exception. (Assertion fails, the program is terminated immediately).
// Check whether the empty var the fullName = ''; Assert (fullName.isEmpty); // Check to 0 var Hitpoints = 0; Assert (Hitpoints <= 0); // check whether null. Var Unicorn; Assert (Unicorn null ==); // check whether NaN3. var iMeantToDoThis = 0/0; Assert (iMeantToDoThis.isNaN);
List List
List of the Examples as follows
main void () {
// create configured using
var = new new List List ();
// create a type of int List
List intList = [. 1, 2,. 3];
// create a constant List, can not be changed List
List = const constList [10,. 7, 23 is];
}
Array common method dart
main void () {
// the array can be stored in a plurality of different types of objects
var List = [1, 2,. 3, 'Flutter', to true];
Print (List); // output result of: [1, 2 ,. 3, Flutter, to true]
// modify the array index value of 2
List [2] = 'Dart';
Print (List); // output results: [. 1, 2, Dart, Flutter, to true]
// Get the length of the array of
print (list.length); // output results: 5
// add elements to the array
List.add ( "value");
Print (List); // output result of: [1, 2, Dart, Flutter, to true, value]
// add an element to a specified position in the array
list.insert (. 1, 'element');
Print (List); // output result of: [1, element, 2, Dart, Flutter , to true, value]
// remove elements array
list.remove ( "value");
Print (List); // output result of: [1, element, 2, Dart, Flutter, true]
// remove the specified array element
list.removeAt (. 1);
print (List); // output results: [. 1, 2, Dart, Flutter, to true]
// determines whether there is an element array
print ( list.indexOf ( "element")); // output: -1
// can sort () function to sort, but since we are using different array type definition, can not be used
var intlist = [1, 2, 5, 6, 3];
// The syntax Tip: list.sort ([(int, int) → int Compare]) → void
intlist.sort ((A, B) => a.compareTo (B));
Print (intlist); // output: [1, 2, 3, 5, 6]
}
map collection
Create a Map collection
main void () {
// Create the Map
var = {Language 'the fisrt': 'DART', 'SECOND': 'Java'};
// Create immutable the Map
var constLanguage = const { 'the fisrt': 'DART', 'SECOND': 'Java'};
// created by the constructor
var new new initLanguage the Map = ();
}
Map commonly used method
main void () {
// Create the Map
var = {Map 'the fisrt': 'DART', 'SECOND': 'Java'};
// get the length of
print (map.length); // output: 2
// Analyzing is empty
print (map.isEmpty); // output: false
Print (map.isNotEmpty); // output: to true
// get to all of Key
Print (map.keys); // output: (fisrt , SECOND,)
// get all the values
Print (map.values); // output: (DART, the Java)
// determine whether to include a Key
Print (map.containsKey ( "Key")); // output results: to false
// comprises determining whether a value
Print (map.containsValue ( "Key")); // output: to false
// Add a new element into the
Map [ 'THIRD'] = 'Key';
Print ( map); // output: {fisrt: dart, second: java,third: key}
// 循环打印 代码提示：Map.forEach((String, String) → void f) → void
map.forEach( (key, value) => getMap(key, value) );
}
void getMap(key, value){
print("key:${key}, value:${value}");
}
dynamic keyword
This keyword is defined on a similar case we define a variable in JS. Look at the following code
main void () {
// A can change the data type, the type is dynamic
var A;
A = 10;
A = "DART";
// here we use the dynamic statement
dynamic D = 10;
D = 'DART' ;
}
Original Address: https://blog.csdn.net/qq_18948359/article/details/82749659