flutter - 错误：尝试添加初始化表达式，或在此构造函数中添加字段初始化，或将其标记为“延迟”

Question

void main() {
  Car c1 = new Car('E1001');
}

class Car {
  String engine;
  Car(String engine) {
    this.engine = engine;
    print("The engine is : ${engine}");
  }
}

标签： flutterdartconstructor

Answer 1

在飞镖零安全功能中，

1. 要么使引擎变量可以为空?，

   class Car {
     String? engine;
     Car(String engine){
        this.engine = engine;
        print("The engine is : ${engine}");
     }
   }
   

2. 或者添加late关键字来懒惰地初始化它，

   class Car {
     late String engine;
     Car(String engine){
        this.engine = engine;
        print("The engine is : ${engine}");
     }
   }
   

3. 或在构造函数的初始化块中初始化变量。

   class Car {
     String engine;
     Car(String engine) : engine = engine {
        print("The engine is : ${engine}");
     }
   }