《PRE_andevcon_mastering-the-android-touch-system》.pdf

Sample Code: hps:///devunwired/custom-touch-examples Mastering the Android Touch System Dave Smith @devunwired Who Is This Guy? • Android developer since 2009 – ROM customizaon for Embedded applicaons • Recovering Spark Chaser – Embedded M2M Monitoring systems – P2P Radio Links • Co-Author of Android Recipes from Apress Topics Covered • Touch System Overview • Touch Event Framework • Custom Touch Handling • System Provided Touch Handlers • System Provided Gesture Handlers How Android Handles Touches • Each user touch event is wrapped up as a MoonEvent • Describes users current acon – ACTION_DOWN – ACTION_UP – ACTION_MOVE – ACTION_POINTER_DOWN – ACTION_POINTER_UP – ACTION_CANCEL • Event metadata included – Touch locaon – Number of pointers (fingers) – Event me • A “gesture” is defined as beginning with ACTION_DOWN and ending with ACTION_UP. How Android Handles Touches • Events start at the Acvity with dispatchTouchEvent() • Events flow top down through views – Parents (ViewGroups) dispatch events to their children – Can intercept events at any me • Events flow down the chain (and back up) unl consumed – Views must declare interest by consuming ACTION_DOWN – Further events not delivered for efficiency • Any unconsumed events end at the Acvity with onTouchEvent() • Oponal External OnTouchListener can intercept touches on any View/ViewGroup How Android Handles Touches • Acvity.dispatchTouchEvent() – Always first to be called – Sends event to root view aached to Window – onTouchEvent() • Called if no views consume the event • Always last to be called