iOS CGPoint conversion problem

[chen8002004]

I get “Lvalue required as left operand of assignment” error when compiling the following code. Can anyone help?
Declaration:

@interface myInfo: NSObject
{
    CGPoint startPosition;
}
@property     CGPoint startPosition;
@end

Definition:

@implementation myInfo
@synthesize startPosition;
@end

Use:

myInfo* temp = [[myInfo alloc] init];
int ttt=100;
temp.startPosition.x = (CGFloat)ttt; << Compile error here

 

[Guiyon]

The simple explanation is that the synthesized methods for structs (CGPoint, CGRect, etc) return a *copy* of the structure, not reference to it. Doing something like you are would simply set the value of 'x' on the returned copy and then discard the whole thing. You would need to do something like one of the below snippets:

CGPoint point = temp.startPosition;
point.x = 100;
temp.startPosition = point;

// Assumes that you want the 'y' value to remain constant
temp.startPosition = CGPointMake(100,temp.startPosition.y);