How to call constructor for each object in arraylist?

Question

denkai · Answer

1. The error you are getting is because objMyClass is not defined in the scope of the first loop and cannot be re-used in the second loop. Your variable scope (or lifetime) is defined by the { } characters. You need to declare the variable again in the second loop if you wish to use it: MyClass objMyClass = (MyClass) lstCells[i]; 2. You should indeed cast the return value from the ArrayList indexer to MyClass to get the intellisense to recognize its type. MyClass objMyClass = (Myclass) lstCells[i]; regards Dom

amit_gupta14 · Answer

Dominique 1. I have added now MyClass objMyClass = new MyClass ( ); in the 1st for loop now constructor is called for each object. But when I run the application there is following compilation error: The name 'objMyClass' does not exist in the class or namespace 'arraylist.Class1' Why this error? 2. Moreover if I treat objMyClass equal to lstCells[i]. then lstCells[i]. is not able to access any method/member of class. It works only when we append ( MyClass ) i.e. ( MyClass ) lstCells [ i ] Now what's the equivalent of ( MyClass ) lstCells [ i ] in terms of objMyClass

denkai · Answer

In your example all instances of MyClass are the same because you created it outside of the loop. ArrayList lstCells = new ArrayList ( ); MyClass objMyClass = new MyClass ( ); for ( int i = 0; i < 10; i++ )//1st for loop { //adds the same instance of my class 10 times in the array. lstCells.Add ( objMyClass ); } Versus.... ArrayList lstCells = new ArrayList ( ); for ( int i = 0; i < 10; i++ )//1st for loop { MyClass objMyClass = new MyClass ( ); //adds a new instance of my class 10 times in the array. lstCells.Add ( objMyClass ); } In the second loop if you set the objMyClass variable to be lstCells [ 3 ] you can just continue using the objMyClass variable it will point to that entry in the array. so if you do for ( int i = 0; i < 10; i++ ) //2nd for loop { objMyClass = ( MyClass ) lstCells [ i ]; //from now on objMyClass is equal to lstCells[i]. } regards Dom

amit_gupta14 · Answer

Hi Dominique it's working but I want in a different way. class MyClass { public MyClass ( ) { } public String SayHello ( ) { return Hello!; } } ArrayList lstCells = new ArrayList ( ); MyClass objMyClass = new MyClass ( ); for ( int i = 0; i < 10; i++ )//1st for loop { lstCells.Add ( objMyClass ); } now to read the values... for ( int i = 0; i < 10; i++ ) //2nd for loop { objMyClass = ( MyClass ) lstCells [ i ]; Console.Write ( objMyClass.SayHello ( ) ); } This is the sample code. Here I want to call constructor for each object objMyClass in the 1st for loop. i.e. instead of writing myArrayList.Add(new MyClass()) (as you mentioned above in example) I would use lstCells.Add ( objMyClass );. I know both are the same thing. In 2nd for loop how I am sure that which object is in use. e.g. If I want to print something related to object no. 4 how will I use . I mean will I have to use ( MyClass ) lstCells [ 3] everytime to access 4th object or I can use the same with objMyClass.

denkai · Answer

The constuctor for an object is called when your object is initialized and cannot be called again. The only way to do what you want is to reset the entry in the arrayList to a new object. ArrayList myArrayList = new ArrayList(); myArrayList.Add(new MyClass()); myArrayList.Add(new MyClass()); myArrayList[0] = new MyClass(); regards Dom