None ：The content preserves its original size.
保持原始尺寸。
Supported by Silverlight for Windows Phone
Fill： The content is resized to fill the destination dimensions. The aspect ratio is not preserved.
缩放到目标尺寸，宽高比不会保留。
Supported by Silverlight for Windows Phone
Uniform：The content is resized to fit in the destination dimensions while it preserves its native aspect ratio.
缩放到目标尺寸之内，并保持原始宽高比。
Supported by Silverlight for Windows Phone
UniformToFill：The content is resized to fill the destination dimensions while it preserves its native aspect ratio. If the aspect ratio of the destination rectangle differs from the source, the source content is clipped to fit in the destination dimensions.
保持原始宽高比进行缩放，以填充。如果两者的宽高比不同，源会被剪切掉多余的部分。