png image is not displaying after "reDraw" - ios

Question

I am using custom png images for items of .tabBarItem of my UITabBarController.
But my png images are too big (64x64), so I use the method below to redraw the image in a smaller rect (for example, make the size parameter (25,25) ).
-(UIImage*) getSmallImage:(UIImage*)image inSize: (CGSize)size
{
CGSize originalImageSize = image.size;
CGRect newRect = CGRectMake(0, 0, size.width, size.height);
float ratio = MAX(newRect.size.width/originalImageSize.width,
newRect.size.height/originalImageSize.height);
UIGraphicsBeginImageContextWithOptions(newRect.size, NO, 0.0);
UIBezierPath *path = [UIBezierPath bezierPathWithRoundedRect:newRect cornerRadius:5.0];
[path addClip];
CGRect projectRect;
projectRect.size.width = ratio * originalImageSize.width;
projectRect.size.height = ratio * originalImageSize.height;
//projectRect.origin.x = (newRect.size.width - projectRect.size.width) / 2.0;
//projectRect.origin.y = (newRect.size.height - projectRect.size.height) / 2.0;
// Draw the image on it
[image drawInRect:projectRect];
// Get the image from the image context
UIImage *smallImage = UIGraphicsGetImageFromCurrentImageContext();
// Cleanup image context resources
UIGraphicsEndImageContext();
return smallImage;
}
Every image I use was returned by this method. Everything was fine on simulators, but those images were not displaying when I test them on my iphone.
But if I abandon the method above and import the image directly like this: self.tabBarItem.image = [UIImage imageNamed:#"Input"]; Then the images were correctly shown on my phone, but only too big.
How can I fix this problem?

Answer 1

I'll answer this question by myself.
After hours of debugging, here is the problem:
in the method given above, originproperty of CGRect projectRectwas not set.
After I set both origin.x & origin.y to 0, everything worked out.
Tip: every time you meet a WTF problem, be patient and try to test your code in different ways. 'Cause in 99.9% of this kind of cases, there is something wrong with your code in stead of a bug of Xcode.
Though I still don't know why the code in my question works well in simulators, I'll let it go because I guess someday when I become an expert, this kind of question would be easy as well as silly.