The Singleton pattern is a frequently used pattern in object-oriented programming languages. It is one of the most frequently used programming patterns.
In this post I will show you when the Singleton Pattern is useful for you and how you can integrate it into your Flutter project.
The purpose
The Singleton pattern makes it in object-oriented programming languages possible to use an object of a class in different contexts, without passing it on with function calls constantly. Inversely said it prevents the creation of several objects of a class. The Singleton Pattern is used to control the object creation and usage of a class dynamically at runtime. It is mostly used when tasks are used frequently and in different parts of an application.
The implementation
Following the Singleton pattern, a class ‘MySingletonClass’ should manage an object ‘_instance’ and return this object instance when it is created. This is implemented as follows:
class MySingletonClass {
static final MySingletonClass _instance =
MySingletonClass ._internal();
// passes the instantiation to the _instance object
factory MySingletonClass() => _instance;
}
The _internal method can be used to initialize variables:
class MySingletonClass {
[...]
//initialize variables in here
MySingletonClass._internal() {
//_myVariable has to be defined before
_myVariable = 0;
}
}
The singleton-class is now finished and can be implemented. To use it in an existing widget, we get the instance object of the class just as we would create a new instance. This is usually done within a ‘State<>’ object:
class _MyHomePageState extends State<MyHomePage> {
MySingletonClass _mySingletonClass = MySingletonClass();
[...]
}
Comments
Even if the Singleton pattern seems to be useful, it should not be applied everywhere, otherwise the program code can become dirty and become more like procedurally generated code.
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