Android Programming: The Big Nerd Ranch Guide, 2nd Edition

Challenge: Efficient Thumbnail Load

In this chapter, you had to use a crude estimate of the size you should scale down to. This is not ideal, but it works and is quick to implement.

With the out-of-the-box APIs you can use a tool called ViewTreeObserver. ViewTreeObserver is an object that you can get from any view in your Activity’s hierarchy:

V​i​e​w​T​r​e​e​O​b​s​e​r​v​e​r​ ​o​b​s​e​r​v​e​r​ ​=​ ​m​I​m​a​g​e​V​i​e​w​.​g​e​t​V​i​e​w​T​r​e​e​O​b​s​e​r​v​e​r​(​)​;​

You can register a variety of listeners on a ViewTreeObserver, including OnGlobalLayoutListener. This listener fires an event whenever a layout pass happens.

For this challenge, adjust your code so that it uses the dimensions of mPhotoView when they are valid, and waits ...