[SOLVED] why the contentmode of the uiimageview did not work?

yesterday when i code I am puzzled by a question about contentMode of UIImageView.I want to set UIViewContentModeScaleAspectFill to the UIImageView but the effect of that the image overflow the UIImageView,this is the result:![enter image description here][1]

The red frame is the UIImageView,in the pic we can see the content overflow the UIImageView.Why this happend?

This is the code:![enter image description here][2]

    UIImageView* copySmall = [[UIImageView alloc] init];
    copySmall.layer.borderColor = [UIColor redColor].CGColor;
    copySmall.layer.borderWidth = 1.f;
    [copySmall setContentMode:UIViewContentModeScaleAspectFill];
    [copySmall setFrame:oriRect];
    [copySmall setImage:imgView.image];