adding control programmatically

[johnmmcparland]

am trying to add controls (e.g. radio buttons, group boxes) to a
windows form in a method which I call from the constructor.

However, when I do things like;

RadioButton rb= new RadioButton();
....
rb.Location.X= 67;

this.Controls.Add(rb); // this is the Windows Form instance

I am told that;

"Cannot modify the return value of
'System.Window.Forms.Control.Locatoin' because it is not a variable"

I have tried to use CreateControl() but it doesn't seem to have any
effect.

If anyone knows how to do this please help asap

John

 

[Nicholas Paldino [.NET/C# MVP]]

John,

The reason that this doesn't work is because Location is of type Point,
which is a value type. When you return value types from properties or
methods (through the return value, not ref parameters), a copy is made and
returned to you.

That being said, when you do this:

rb.Location.X= 67;

You are setting the X property/field on a copy returned to you. To
perform this operation, you would need to do this:

// Store the location.
Point temp = rb.Location;

// Set the X value.
temp.X = 67;

// Set the location back.
rb.Location = temp;

Hope this helps.

 

[Ignacio Machin \( .NET/ C# MVP \)]

Hi,


Additionaly to Nicholas comment you can use Left to set a new position.

cheers,

 

[Jon]

The Location property is of type System.Drawing.Point (a struct). This
means that accessing the button's Location property returns a copy of
the struct, and since this is not assigned to a variable it cannot be
modified. (Even if the compiler let this through you would still have
been modifying a temporary variable, and it would have no effect on the
button).

Instead, use

rb.Location = new Point(x, y);

Jon.

 

[johnmmcparland]

[reply to all]

thanks all for your help. I went for the option Nicholas posted. It's
got past the compiler and it's now up to me to make sure my algorithm
is right.

Thanks again all

John