One way, which is probably the most up to date approach, would be to add 4 auto layout constraints to the containerview in interface builder.
Add the four constraints: x = 0, y = 0, width = 300 & height = 200
Now click on the width constraint in interface builder to highlight it and then control drag it into your .h file and give it a name, like containerWidth.
@property (strong, nonatomic) IBOutlet NSLayoutConstraint *containerWidth;
Repeat with the height.
In your .m file you can adjust the height and width in your drawScreen method by manipulating the contstraints.
self.containerWidth.constant = width; // your calculated new width
self.containerHeight.constant = height; // your calculated new height