Android Question passing direct reference on assignment

[galimpic]

Suppose I want to keep a reference to one of activity's views in a variable. So, I create a reference variable of the same type as the view. However, if I later change the value of that variable, it changes the original view, as well:

Dim Label1 as Label
Label1.Initialize("")
Label1.Text = "initial value"
Activity.AddView(Label1, 0, 0, 300, 100)

Dim ref as Label

ref = Label1
ref.Text = "ref variable assignment"
ref = null
Label1.Text = "Label1 variable assignment "

This code will produce the "java.lang.RuntimeException: Object should first be initialized (Label)." at the last line. Obviously, changing value of ref also changed the Label1 to point to the same thing (null in this case). Therefore, assignment to a View object produced the direct reference of the assigned View object. However, in the Tutorial "Variables & Objects in Basic4android" (https://www.b4x.com/android/forum/threads/variables-objects-in-basic4android.8385/), Erel said:

All other types, including arrays of primitives types and strings are categorized as non-primitive types.
When you pass a non-primitive to a sub or when you assign it to a different variable, a copy of the reference is passed.
This means that the data itself isn't duplicated.
It is slightly different than passing by reference as you cannot change the reference of the original variable.

This is true if ref object is of type Object and we create a helper object of the appropriate type when we need to access the view's properties:

Dim Label1 as Label
Label1.Initialize("")
Label1.Text = "initial value"
Activity.AddView(Label1, 0, 0, 300, 100)

Dim ref as Object

ref = Label1
Dim helper as Label = ref
helper.Text = "ref variable assignment"
ref = null
Label1.Text = "Label1 variable assignment "

Now, ref holds the COPY of the reference, as it should, and assigning null to it doesn't change the Label1 variable and the error is not produced in the last line.

Finally, the question:

Why are view objects directly referenced on assignment, and other object are passed a reference copy?

 

[Erel]

The answer is that view objects (like many other types) are wrappers over another type. The compiler automatically wraps and unwraps such objects.

This "wrapping" feature makes it easy to build thin wrappers over native types.

In this code:

Dim ref as Label
ref = Label1 'wrapper is assigned
ref.Text = "ref variable assignment"
ref = null
Label1.Text = "Label1 variable assignment "

Both variables point to the same wrapper. When you assign ref to Null you actually set the value of the actual object (the one that is wrapped).

In the second code ref is an object so the compiler unwraps the wrapper and wraps it again with a new wrapper when you set it to 'helper' variable. So there are two different wrappers now.

 

[galimpic]

Thank you for the explanation, now I know I must be careful with handling variables to any type of wrapped object.