将限定词添加到布局或值中时会发生什么？

Question

Something that has been bothering me in android is when I create a layout I have an option to add qualifier. For instance, when I add a layout I have the option to put in the qualifier of orientation and landscape or portrait.

1) What confuses me is how does android exactly knows which layouts files to use simply by adding a qualifier?

2) What code keeps track of this resource and called when appropriate because a resource can't just simply determine which files to be drawn from but rather there has to be a code saying which resource to load much like setContentView().

Answer 1

When a layout is inflated those properties are read and used. No one keeps track of them other the developer.

Answer 2

Android chooses the appropriate layout file based on (a) the physical characteristics of the device, eg screen density, and (b) the state of the device, eg orientation.

For example, if your phone is high-density, the layout in res/layout-hdpi will be used (if it exists).

Or if your phone is in landscape mode, the layout in res/layout-land will be used (if it exists).

For more info see: https://developer.android.com/guide/practices/screens_support.html