uiimage缩放图片大小和属性UIViewContentModeScaleAspectFit

 UIImageView *tmp = [[UIImageView alloc]initWithFrame:CGRectMake(5.0f, 5.0f, 40.0f, 40.0f)];
                    tmp.image = self.friendRecord.appIcon;
                    [tmp setContentMode:UIViewContentModeScaleAspectFit];

按照一定比例缩放图片后需要注意使用UIViewContentModeScaleAspectFit才可以正常显示否则总是铺满全屏显示的