Confusion with "smallest width 600 dp" selector

Question

In my application I am supporting phone/tablet form factors and to have individual layouts I use selector "layout" (for phones), "layout-sw600dp" (for tablets).

Following are the details:

http://android-developers.blogspot.in/2011/07/new-tools-for-managing-screen-sizes.html

Typical numbers for screen width dp are:
320: a phone screen (240x320 ldpi, 320x480 mdpi, 480x800 hdpi, etc).
480: a tweener tablet like the Streak (480x800 mdpi).
600: a 7” tablet (600x1024).
720: a 10” tablet (720x1280, 800x1280, etc).

I am having a Nexus 4 mobile, following are its attirbutes

Size:       4.7 inches
Resolution: 768 x 1280 pixels
DPI:        318
dp:         386 
Here is the dp calculation
dp = (px * 160)/dpi
dp = (768 * 160)/318

When I use 768 px in dp calculation formula the dp value comes as 386, but when I pass 1280 px the dp value comes as 644.

With the following understanding I thought for Nexus 4 landscape it would read the layout from sw600dp, but that's not the case.

As the resolution is width X Height, it will be reversed when the device is rotated.

I thought this is the improvisation made with sw selectors compare to pre-3.2 large, xlarge sectors.

Answer 1

As it says in the Android documentation here in bold (scroll down a bit to the "smallestWidth" section of Table 2):

The smallestWidth is a fixed screen size characteristic of the device; the device's smallestWidth does not change when the screen's orientation changes.

Answer 2

The sw figure is always the shorter of the two screen dimensions, regardless of the device orientation. That's where the "smallest" in the name "smallestWidth" comes from. The advantage over Gingerbread-style "large" &c. selectors is only that you get more granularity of control, and it's more predictable what screen sizes you'll actually get, because it doesn't rely on how the manufacturer classes their screen size.

If you want to select a layout based on the width or height of the screen in its current orientation, use a directory called layout-w600dp or layout-h600dp.