[Classname]() 和 Classname() 之间有什么区别？

Question

I want to know difference between

    var arr = ExamCategory() 
             &
    var arrExamCategories = [ExamCategory]()

Please Why this is declared like this and which should be use for better?

My ExamCategory class is like this.

class ExamCategory: NSObject {

    var CategoryId: Int?
    var CategoryName:String?
    var TotalSection: Int?
    var ImageUrl: String?

    override init() {

    }

    init(dict:[String:Any]) {
        super.init()

        CategoryId = dict["categoryId"] as? Int
        CategoryName = dict["categoryName"] as? String
        TotalSection = dict["totalSection"] as? Int
       ImageUrl = dict[""] as? String
    }
  .....And So On
}

Can anyone describe and differentiate both in details?

Answer 1

Both have different usage, they cannot be compared with each other. When you need to store multiple elements, you should use array but if you need single element you should choose single default initiazer. It depends upon your need. Both are best according to their usage in swift programming.

ExamCategory() is a default initializer for your class which invokes init() for your class when called using classname with round backets () and returns you an instance of your class.

In your example ExamCategory() invokes initializer for class ExamCategory and return you a single instance of the class, which your have stored in var arr

var arr = ExamCategory() 

while...
[ExamCategory]() is an array initializer of type ExamCategory . It (can/must) holds/stores an instance of class ExamCategory or its sub classes.

In your example, [ExamCategory]() is an array for elements of ExamCategory . You can insert/add, above var arr in this array.

var arrExamCategories = [ExamCategory]()
arrExamCategories.append(arr)

Here is apple document for Initialization and array (Collection Types)

Answer 2

var arr = ExamCategory() 

It means that: ExamCategory class has been initialized and reference of this class has been stored in arr variable.

var arrExamCategories = [ExamCategory]()

It means that: You have initialize an array which contains objects of ExamCategory class.

ex: arrExamCategories.append(arr) // var arr = ExamCategory()

For more details please refer apple's swift documentation.