class Peoples {
int id;
String name;
static final Peoples _inst = Peoples._internal();
Peoples._internal();
factory Peoples() {
return _inst;
}
}
我有这个单例课程。这样可以确保只创建一个类的实例。因此,即使有人尝试实例化它,他们也将使用相同的实例。我可以创建和设置值,例如:
Peoples ps1 = Peoples();
Peoples ps2 = Peoples();
ps1.id = 1;
ps1.name = "First";
ps2.id = 2;
ps2.name = "Second";
是否可以实例化和设置以下值:
Peoples ps1 = Peoples(1, "First");
Peoples ps2 = Peoples(2, "Second");
因此,现在“ ps1”和“ ps2”都将具有(2,“ Second”)。
答案 0 :(得分:2)
当然! 您需要将参数传递给factory方法,然后需要使用引用的实例来更新属性。
例如,您拥有
class Peoples {
int id;
String name;
static final Peoples _inst = Peoples._internal();
Peoples._internal();
factory Peoples() {
return _inst;
}
}
如果您应用我的解决方案,那么您有
class Peoples {
int id;
String name;
static final Peoples _inst = Peoples._internal();
Peoples._internal();
factory Peoples({int id, String name}) {
_inst.id = id
_inst.name = name
return _inst;
}
}
对此您的问题应予以回答 有关工厂和参数的更多信息,请访问
https://dart.dev/guides/language/language-tour
工作示例
class Peoples {
int id;
String name;
static final Peoples _inst = Peoples._internal();
Peoples._internal();
factory Peoples(int id, String name) {
_inst.id = id;
_inst.name = name;
return _inst;
}
}
void main() {
print("Instance of = " + Peoples(0, "Dylan").name);
print("Instance of = " + Peoples(1, "Joe").name);
print("Instance of = " + Peoples(2, "Maria").name);
}
答案 1 :(得分:2)
我想回答显示一种通过向其传递参数来创建单例的方法,以及如何在首次创建后“锁定”其值。
class People {
static final People _inst = People._internal();
People._internal();
factory People(int id, String name) {
assert(!_inst._lock, "it's a singleton that can't re-defined");
_inst.id = id;
_inst.name = name;
_inst._lock = true;
return _inst;
}
int id;
String name;
bool _lock = false;
}
void main() {
var people = People(0, 'Dylan');
try{
print('Instance of = ' + People(0, 'Joe').name);
print('Instance of = ' + People(1, 'Maria').name);
print('Instance of = ' + People(2, 'Ete sech').name);
} finally {
print('Instance of = ' + people.name);
}
}