Accessing a rectangle's value?

myObject.rect.X = 100

myObject has a property called rect (which is a Rectangle). During runtime I will want to chage the X position of such rectangle, but I am given this error:

Expression is a value and therefore cannot be the target of an ass开发者_开发百科ignment.

Then, how am I supposed to change such values?

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I assume you are talking about System.Drawing.Rectangle here. Rectangle is a value type (Structure in VB.NET), so when you access it via the myObject.rect property, you get a copy of it locally. Since you have a copy of the values instead of a reference to the instance, you cannot update it.

If you want to change myObject's Rectangle property, you can update myObject to refer to a newly constructed Rectangle with values you desire. For example:

    Dim myObject As MyObject = New MyObject()

    ' Prints 0
    Console.WriteLine(myObject.rect.X)

    ' Refer to a new rectangle with X=100 and all other values kept the same
    myObject.rect = New Rectangle(
        100,
        myObject.rect.Y,
        myObject.rect.Width,
        myObject.rect.Height
    )

    ' Prints 100
    Console.WriteLine(myObject.rect.X)