What is android:layout_gravity="clip_vertical" exactly

Question

The property android:layout_gravity="clip_vertical|horizontal" does the following as mentioned in the SDK documentation:

Additional option that can be set to have the top and/or bottom edges of the child clipped to its container's bounds. The clip will be based on the vertical gravity: a top gravity will clip the bottom edge, a bottom gravity will clip the top edge, and neither will clip both edges.

But I can't see anything of this in my applications,

so what is the purpose of this property exactly ?

thanks

Answer 1

Short version:

clip_horizontal and clip_vertical apply to the measurements of the view itself, before any contents (such as the image in a BitmapDrawable) are rendered.

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Long version:

I've run into some similar confusion over clip_horizontal and clip_vertical. (In my case, it was related to android:gravity for a BitmapDrawable, but it's similar enough to be applicable.)

From the documentation I thought that something like android:gravity="top|left|clip_vertical" on a bitmap would cause the image's top left corner to be positioned at the view's top left corner, and that, if the bitmap was taller than the view, it would be "clipped" at the bottom edge of the view. In other words, show only as much of the bitmap that the view is tall enough to reveal; do not stretch the bitmap, but instead only show whatever will fit, letting the rest extend below the bottom edge.

However, the opposite happened: when I set clip_vertical, a large bitmap was squished vertically to fit within the height of the view.

After examining the applyDisplay() method in platform/frameworks/core/java/android/view/Gravity.java, I realized my mistake:

It isn't the bitmap image that was going to be clipped, but the view -- the actual size of the container the image is ultimately rendered into.

Setting clip_vertical in my case didn't mean "clip the image at the bottom edge," it meant "clip the BitmapDrawable's view itself so its height matches the height of its parent container"...which then caused the image to be "squished" as it filled that shorter height.

So, the important thing to remember with android:gravity and android:layout_gravity is that clip_horizontal and clip_vertical apply to the measurements of the view itself, before any contents (such as my BitmapDrawable) are rendered.