Making custom back button for navigation bar - iphone

Question

I have made at least 10 buttons for my navigation bar, but it never seems to work right.
The rounded edges get pixelated. I cant have that in an app, so can anyone tell me how to make a good icon that looks like an apple one? Also what is the proper size? The code in the app for the button is
UIButton *backbtn = [UIButton buttonWithType:UIButtonTypeCustom];
backbtn.frame = CGRectMake(0, 0, 55, 30);
[backbtn setBackgroundImage:[UIImage imageNamed:#"button.png"] forState:UIControlStateNormal];
[backbtn addTarget:self action:#selector(goBackOne) forControlEvents:UIControlEventTouchUpInside]; forState:UIControlStateNormal ];
self.navigationItem.leftBarButtonItem = [[UIBarButtonItem alloc] initWithCustomView:backbtn];//set new button
self.navigationItem.hidesBackButton = YES;//hide original back button

Answer 1

Try this code:
UIImage *backButtonImage = [UIImage imageNamed:#"backButton.png"];
UIButton *backButton = [UIButton buttonWithType:UIButtonTypeCustom];
[backButton setImage:backButtonImage forState:UIControlStateNormal];
backButton.frame = CGRectMake(0, 0, backButtonImage.size.width, backButtonImage.size.height);
[backButton addTarget:self action:#selector(back) forControlEvents:UIControlEventTouchUpInside];
UIBarButtonItem *customBackBarItem = [[UIBarButtonItem alloc] initWithCustomView:backButton];
self.navigationItem.leftBarButtonItem = customBackBarItem;
and, the back method:
-(void)back {
[self.navigationController popViewControllerAnimated:YES];
}
The code above just set the image for normal state. You can also set highlighted state for a better appearance. Add some codes Like:
UIImage *backButtonImageHighlighted = [UIImage imageNamed:#"backButtonHighlighted.png"];
[backButton setImage:backButtonImageHighlighted forState:UIControlStateHighlighted];