[移动开发]Flutter——Dart语言特征优化体会

一、初始代码

根据 java 或者 OC 的代码习惯，定义代码如下

void main() {

  ShoppingCart sc = ShoppingCart('购物车');
  sc.items = [Item('苹果',10.0), Item('鸭梨',20.0)];
  print(sc.getInfo());
  
}


//商品Item
class Item {
  double? price;
  String? name;
  Item(name,price) {
    this.name = name;
    this.price = price;
  }
}


//定义购物车类
class ShoppingCart {
  String? name;
  List<Item>? items;
  ShoppingCart(this.name)
  price() {
    double sum = 0.0;    
    for(Item i in items??[]) {      
      sum += i.price??0.toDouble();
    }    
    return sum;
  }
  
  getInfo() {   
    return '===' + name.toString() + '===' + price().toString();  
  }
}
  

二、初始化函数优化

Dart语言特性，优化初始化函数

void main() {

  ShoppingCart sc = ShoppingCart('购物车');
  sc.items = [Item('苹果',10.0), Item('鸭梨',20.0)];
  print(sc.getInfo());
  
}


//商品Item
class Item {
  double? price;
  String? name;
  Item(this.name,this.price);
}


//定义购物车类
class ShoppingCart {
  String? name;
  List<Item>? items;
  ShoppingCart(this.name);
  price() {
    double sum = 0.0;    
    for(Item i in items??[]) {      
      sum += i.price??0.toDouble();
    }    
    return sum;
  }
  
  getInfo() {   
    return '===' + name.toString() + '===' + price().toString();  
  }
}
  

三、提取公共类

由于两个类都有price和name 了两个属性，因此提出公共类，并让两个类都继承公共类

void main() {

  ShoppingCart sc = ShoppingCart('购物车');
  sc.items = [Item('苹果',10.0), Item('鸭梨',20.0)];
  print(sc.getInfo());
  
}

class Meta { 
  double price;
  String name;
  Meta(this.name, this.price);
}

//商品Item
class Item extends Meta{
  Item(name, price) : super(name, price);
}


//定义购物车类
class ShoppingCart extends Meta{
  List<Item>? items;
  ShoppingCart(name,) : super(name, 0);
  double get price {
    double sum = 0.0;    
    for(Item i in items??[]) {      
      sum += i.price;
    }    
    return sum;
  }
  
  getInfo() {   
    return '===' + name.toString() + '===' + price.toString();  
  }
}
  

四、优化逻辑函数

重载了+运算符，合并商品为套餐商品，然后把迭代求和改写为归纳合并

void main() {

  ShoppingCart sc = ShoppingCart('购物车');
  sc.items = [Item('苹果',10.0), Item('鸭梨',20.0)];
  print(sc.getInfo());
  
}

class Meta { 
  double price;
  String name;
  Meta(this.name, this.price);
}

//商品Item
class Item extends Meta{
  Item(name, price) : super(name, price);
  //重载了+运算符，合并商品为套餐商品 
  Item operator+(Item item) => Item(name + item.name, price + item.price);
}


//定义购物车类
class ShoppingCart extends Meta{
  List<Item> items;
  ShoppingCart(name) : items = [], super(name, 0);
  //把迭代求和改写为归纳合并 
  double get price => items.reduce((value, element) => value + element).price; 
  
  getInfo() {   
    return '===' + name.toString() + '===' + price.toString();  
  }
}
  

五、调用优化

声明抽象类，提供打印的函数

abstract class PrintHelper { 
  printInfo() => print(getInfo()); 
  getInfo();
}

让ShoppingCart mixin PrintHelper

//定义购物车类
class ShoppingCart extends Meta with PrintHelper{
  List<Item> items;
  ShoppingCart(name) : items = [], super(name, 0);
  //把迭代求和改写为归纳合并 
  double get price => items.reduce((value, element) => value + element).price; 
  
  getInfo() {   
    return 'name' + name.toString() + '价格' + price.toString();  
  }
}

优化调用方式，使用…来减少中间变量的声明定义

  ShoppingCart('购物车')
  ..items = [Item('苹果',10.0), Item('鸭梨',20.0)]
  ..printInfo();

最终代码

void main() {

  ShoppingCart('购物车')
  ..items = [Item('苹果',10.0), Item('鸭梨',20.0)]
  ..printInfo();
  
}

abstract class PrintHelper { 
  printInfo() => print(getInfo()); 
  getInfo();
}

class Meta { 
  double price;
  String name;
  Meta(this.name, this.price);
}

//商品Item
class Item extends Meta{
  Item(name, price) : super(name, price);
  //重载了+运算符，合并商品为套餐商品 
  Item operator+(Item item) => Item(name + item.name, price + item.price);
}


//定义购物车类
class ShoppingCart extends Meta with PrintHelper{
  List<Item> items;
  ShoppingCart(name) : items = [], super(name, 0);
  //把迭代求和改写为归纳合并 
  double get price => items.reduce((value, element) => value + element).price; 
  
  getInfo() {   
    return 'name' + name.toString() + '价格' + price.toString();  
  }
}