UIImageView contentMode不工作

Question

在每一个人中，我都面临着有关UIImageView contentMode的问题。我正在使用以下代码来调整imageView中的图像。

CGSize imageSize=imageView.image.size;
UIInterfaceOrientation orientation=[UIApplication sharedApplication].statusBarOrientation;
if (imageSize.width>imageSize.height) { //land scape image
    if (orientation ==UIInterfaceOrientationLandscapeLeft || orientation==UIInterfaceOrientationLandscapeRight) {  //device in landscape mode
        [imageView setContentMode:UIViewContentModeScaleAspectFill];
    }
    else //device in potriate moded
    {
        [imageView setContentMode:UIViewContentModeScaleAspectFit];
    }
}
else //potrial image
{
    if (orientation ==UIInterfaceOrientationLandscapeLeft || orientation==UIInterfaceOrientationLandscapeRight) {  //device in landscape mode
        [imageView setContentMode:UIViewContentModeScaleAspectFit];
    }
    else //device in potriate moded
    {
        [imageView setContentMode:UIViewContentModeScaleAspectFill];
    }
}

当我在viewDidLoad方法中调用它时，

代码工作正常，但是当我尝试在viewWillAppear方法中调用它时，它无效。我想在viewWillAppear中使用它，所以请告诉我解决方案谢谢。