Mobile Application Programing: Android. View Persistence

Transcription

1 Mobile Application Programing: Android Persistence

2 Activities Apps are composed of activities Activities are self-contained tasks made up of one screen-full of information Activities start one another and are destroyed commonly Apps can use activities belonging to another app

3 Creating a Custom Control Create subclass of class Override: ondraw(canvas c) onmeasure(int wmeasure, int hmeasure) Add listener interface and listener property for the interesting events the control generates and call on... methods when events occur

4 Persistence Problem: Rotations rebuild activity oncreate recreates view hierarchy Data model restores state that has been committed, updating UI (more on this in MVC lecture) What about uncommitted UI state? eg. text in text box that has not yet been validated

5 Persistence Problem: Rotations rebuild activity Solution: Implement view-level persistence of transient state Set ID property of custom view Won t save state without one! Override onsaveinstancestate Override onrestoreinstancestate

6 onrestoreinstancestate onsaveinstancestate

7 onsaveinstancestate Create a Parcelable to store state into Use a custom subclass of BaseSaveState or an instance of Bundle Call super.onsaveinstancestate to retrieve super class state and store in Parcelable Store any non-reconstructable state in Parcelable

8 onrestoreinstancestate Cast Parcelable instance to whatever class was used in onsaveinstancestate Use instanceof to ensure class is correct Retrieve super class state and call super.onrestoreinstancestate to restore it Retrieve any non-reconstructable state and restore it to the class instance

9 onsaveinstancestate vs. onpause onsaveinstancestate is meant to save transient activity state Instance state is deleted when activity is finalized Save application state in onpause for all nontransient state onrestoreinstancestate onsaveinstancestate finalize See MVC for details

10 Activity Palette

11 Activity Palette Tap

12 Activity Palette Option 1 overrides its own onclick method In response to click, sets its own selected property Tap

13 Activity Palette Option 1 overrides its own onclick method In response to click, sets its own selected property Tap How does the red view s selected property get unset in this case?

14 Activity Palette Option 2 Palette sets an onclicklistener object for all vies Tap In response to click, palette view sets selected property of tapped view, unsets all others

15 Activity Palette? Tap

16 Activity Option 1 Activity sets onclicklistener, sets Mixing property on Palette Palette Mixing Tap

17 Activity Option 2 Reparent mix button to palette view; palette view sets onclicklistener that sets its mixing property Palette Mixing Tap

18 Activity Palette Mixing Subsequent tap in view the palette view receives in the onclicklistener; Tap

19 Activity Palette Subsequent tap in view the palette view receives in the onclicklistener; The mixing property directs the palette view to calculate the new color, add a view for that color, layout its views, and select the new view

20 Activity ActiveColor Palette

21 Activity ActiveColor Palette Tap

22 Activity ActiveColor Palette?

23 Activity ActiveColor Palette Option 1 Palette has a paint property that allows it to update the activecolor

24 Activity ActiveColor Palette Option 1 Palette has a paint property that allows it to update the activecolor This works, but is messy, and does not allow the palette view and paint view to be used and tested separately!

25 Activity ActiveColor Palette Option 2 Palette defines an oncolorchangedlistener that the Activity sets, calling oncolorchanged when the user taps a view

26 When the paint activity s listener has oncolorchanged called, it sets the paint view s active color Activity ActiveColor Palette Option 2 Palette defines an oncolorchangedlistener that the Activity sets, calling oncolorchanged when the user taps a view

27 Activity Watch the ups and downs ActiveColor Palette

28 Activity Watch the ups and downs ActiveColor Palette Tap

29 Activity Watch the ups and downs ActiveColor Palette onclicklistener

30 Activity Watch the ups and downs ActiveColor Palette onclicklistener set

31 Activity Watch the ups and downs oncolorchangedlistener ActiveColor Palette onclicklistener set

32 Activity Watch the ups and downs setactivecolor oncolorchangedlistener ActiveColor Palette onclicklistener set

33 Activity downs are normal method calls ups are calls on listener methods setactivecolor oncolorchangedlistener ActiveColor Palette onclicklistener set