An image view displays a single image or an animated sequence of images over a transparent or opaque background. Within an image view, images may be stretched, scaled, sized to fit, or pinned to a specific location. Image views are noninteractive by default.
    图像视图在透明或不透明的背景上显示单个图像或动画图像序列。在一个图像视图中，图像可以被拉伸、缩放、调整到合适的位置，或者固定到特定的位置。默认情况下，图像视图是非交互式的。

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    If possible, make sure all images in an animated sequence are consistently sized. Ideally, images should be prescaled to fit the view so the system doesn’t have to do any scaling. If the system must perform scaling, it’s easiest to achieve the desired results when all images are the same size and shape.
    For developer guidance, see UIImageView.
    如果可能，确保动画序列中的所有图像大小一致。理想情况下，图像应该预先缩放以适应视图，这样系统就不必做任何缩放。如果系统必须进行缩放，那么当所有图像的大小和形状都相同时，最容易达到预期的结果。
    对于开发者的指导，请参阅UIImageView。