Android Supporting various screen resolutions

Android categorises devices using two property. screen size and screen density.

There are four general sizes: small, medium, large, extra large. 

there are four general screen densities: low(ldli), medium(mdpi), high (hdpi), extra high (xhdpi) 

Application can provide different layout files so that the resources are taken accordingly. the naming is such that layout- 

for example, a extra large screen would have the layout directory name as res/layout-xlarge 

Android automatically scales the layout in order to fit the screen. Due to this layout for different screen sizes doesn't need to worry about the 

absolute size of the UI elements but instead focus on the layout structure that affects the user experience. 

A project that includes a default layout and an alternate layout for extra large screen will have resource folder something like below 

res/layout/main.xml 

res/layout-large/main.xml

If want to provide a different layout xml for landscape as well, below is the format

res/layout/main.xml

res/layout-land/main.xml

res/layout-large/main.xml

res/layout-large-land/main.xml 

When creating the bit map resources, we need to keep in mind the density of the pixels on screen 

xhdpi  is 2.0 dpi , hdpi is 1.5dpi, mdpi is 1.0 dpi, ldpi is 0.75 dpi. 

This means that a image needs to be 200x200 for xhdpi, 150x150 for hdpi, 100x100 for mdpi and 75x75 for ldpi. 

Once the image is made like above, one needs to place these under the folder in the following structure 

res/drwable-xhdpi/myimage.png

res/drawable-hdpi/myimage.png

res/drawable-mdpi/myimage.png

res/drawable-ldpi/myimage.png

System selects the bitmap according to the running device density. 

as a note ldpi image resources are not necessary. If provided hdpi images, the system scales it down by 1/2 to fit the ldpi screens.