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ImageView.ScaleType

將圖片邊界縮放到所在view邊界時的縮放選項。
Options for scaling the bounds of an image to the bounds of this view.

不同選項含義

CENTER

居中，不縮放。

Center the image in the view, but perform no scaling.

CENTER_CROP

居中，如果圖片寬或高比view小，就等比放大使得寬和高都大于等于view，計算時view大小減去對應padding值。
比如view是100x100，圖片是120x50，view的padding為10，那么就放大至(100 - 2*10) / 50 = 1.6倍。
圖片寬高都大于等于view時無需任何縮放。

Scale the image uniformly (maintain the image's aspect ratio) so that both dimensions (width and height) of the image will be equal to or larger than the corresponding dimension of the view (minus padding).

CENTER_INSIDE

居中，如果圖片寬或高比view大，就等比縮小使得寬或高都小于等于view，計算時view大小減去對應padding值。
比如view是100x100，圖片是120x50，view的padding為10，那么就縮小至(100 - 2*10) / 120 = 2/3倍。
圖片寬高都小于等于view時無需任何縮放。

Scale the image uniformly (maintain the image's aspect ratio) so that both dimensions (width and height) of the image will be equal to or less than the corresponding dimension of the view (minus padding).

FIT_CENTER

居中，填充，等比縮放使得寬高都小于等于view，其中寬或高至少一個和view相等。
和CENTER_INSIDE的不同是總是保證至少寬或高中一個和view相等。

Compute a scale that will maintain the original src aspect ratio, but will also ensure that src fits entirely inside dst. At least one axis (X or Y) will fit exactly. The result is entered inside dst.

FIT_END

右下對齊，填充，等比縮放使得寬高都小于等于view，其中寬或高至少一個和view相等。

Compute a scale that will maintain the original src aspect ratio, but will also ensure that src fits entirely inside dst. At least one axis (X or Y) will fit exactly. END aligns the result to the right and bottom edges of dst.

FIT_START

左上對齊，填充，等比縮放使得寬高都小于等于view，其中寬或高至少一個和view相等。

Compute a scale that will maintain the original src aspect ratio, but will also ensure that src fits entirely inside dst. At least one axis (X or Y) will fit exactly. START aligns the result to the left and top edges of dst.