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Deep Dive Into Android 
State Restoration
TWITTER 
@cyrilmottier 
! 
WEBSITE 
cyrilmottier.com
The story of a newbie 
Android developer
Kevin has just developed his first 
Android app
He discovers an annoying bug: 
Fields are cleared on rotate
3 options
3 options 
Don’t care
3 options 
Don’t care Block orientation
3 options 
Don’t care Block orientation Use configChanges 
Hint: all options are
1 <activity! 
2 android:name=".HomeActivity"! 
3 android:configChanges="orientation">! 
4 ! 
5 <!-- Some sweet IntentFilters. -->! 
6 ! 
7 </activity>
Kevin’s satisfied
Still having issues on…
Still having issues on… 
language changes
1 <activity! 
2 android:name=".HomeActivity"! 
3 android:configChanges="orientation! 
4 ! 
5 <!-- Some annoying IntentFilters. -->! 
6 ! 
7 </activity> 
|locale">
ANGRY! Angry Kevin is
1 <activity! 
2 android:name=".HomeActivity"! 
3 android:configChanges=“orientation|locale|! 
mcc|mnc|touchscreen|keyboard|! 
keyboardHidden|navigation|uiMode|! 
screenLayout|fontScale|screenSize|! 
smallestScreenSize">! 
4 ! 
5 <!-- Some fuc**** IntentFilters. Arrggh! -->! 
6 ! 
7 </activity>
The nightmare continues… 
Still having issues when moving the app to the background
God save the STATE
State restoration 
key components
The container 
Parcel
The container 
Parcel The content 
Primitives types 
Primitives arrays 
Parcelable
The content 
Primitives types 
Primitives arrays 
1 parcel.writeInt(1);! 
2 parcel.writeLong(2L);! 
3 parcel.writeFloat(3F);! 
4 parcel.writeString("Hi!"); 
Parcelable
1 parcel.writeIntArray(new int[]{1, 2, 3});! 
2 parcel.writeLongArray(new long[]{1L, 2L, 3L});! 
3 parcel.writeDoubleArray(new double[]{1, 2, 3});! 
4 parcel.writeStringArray(new String[]{! 
5 "Hi", "Droidcon", "guys!"! 
6 }); 
The content 
Primitives types 
Primitives arrays 
Parcelable
1 public final class Suggestion implements Parcelable {! 
2 ! 
3 public final String id;! 
4 public final String name;! 
5 public final int type;! 
6 ! 
7 public Suggestion(String id, String name, int type) {! 
8 this.id = Objects.requireNonNull(id);! 
9 this.name = Objects.requireNonNull(name);! 
10 this.type = type;! 
11 }! 
12 ! 
13 }
1 @Override! 
2 public int describeContents() {! 
3 return 0;! 
4 }! 
5 ! 
6 @Override! 
7 public void writeToParcel(Parcel dest, int flags) {! 
8 dest.writeString(id);! 
9 dest.writeString(name);! 
10 dest.writeInt(type);! 
11 }! 
12 
13 public static final Parcelable.Creator<Suggestion> CREATOR = ! 
14 new Parcelable.Creator<Suggestion>() {! 
15 public Suggestion createFromParcel(Parcel in) {! 
16 return new Suggestion(in.readString(), // ! 
17 in.readString(), //! 
18 in.readInt());! 
19 }! 
20 ! 
21 public Suggestion[] newArray(int size) {! 
22 return new Suggestion[size];! 
23 }! 
24 };
Parcelable.Creator! 
The base creator interface 
! 
Parcelable.ClassLoaderCreator! 
A creator with the ClassLoader passed on read. 
! 
ParcelableCompat & 
ParcelableCompatCreatorCallbacks! 
Compatibility stuff
Bundle 
A key-value map & type-safe Parcelable
Parcel! 
internally uses reflection 
(required to get the CREATOR instance) 
…i.e. beware Proguard
Activity level 
state restoration
onCreate(null)
onCreate(null)
: non-null Bundle 
onCreate(null) 
onSaveInstanceState( )
onCreate(null) 
onSaveInstanceState( ) 
onCreate( ) 
: non-null Bundle
onCreate(null) 
onSaveInstanceState( ) 
onCreate( ) 
onRestoreInstanceState( ) 
: non-null Bundle
onCreate(null) 
onSaveInstanceState( ) 
onCreate( ) 
onRestoreInstanceState( ) 
: non-null Bundle
onCreate(null) 
onSaveInstanceState( ) 
onCreate( ) 
onRestoreInstanceState( ) 
: non-null Bundle
What to save? 
Non persistent or non reconstructible info
1 public class SearchActivity extends Activity {! 
2 ! 
3 private static final String STATE_OUTWARD = "state:outward";! 
4 ! 
5 private DateComponents mOutward;! 
6 ! 
7 @Override! 
8 protected void onCreate(Bundle inState) {! 
9 super.onCreate(inState);! 
10 ! 
11 if (inState != null) {! 
12 DateComponents components = inState.getParcelable(STATE_OUTWARD);! 
13 if (components != null) {! 
14 setOutward(components);! 
15 }! 
16 }! 
17 }! 
18 ! 
19 @Override! 
20 protected void onSaveInstanceState(Bundle outState) {! 
21 super.onSaveInstanceState(outState);! 
22 outState.putParcelable(STATE_OUTWARD, mOutward);! 
23 }! 
24 }
onSaveInstanceState saves 
Window
onSaveInstanceState saves 
Window Fragments
onSaveInstanceState saves 
Window Fragments Dialogs
Always call the 
SUPER METHODS Android has no guards on save-related methods
android:stateNotNeeded 
For restart-on-crash apps only 
(i.e. launcher app)
Developer options 
Don’t keep activities
Developer options 
Don’t keep activities
View level 
state restoration
Android saves UI state 
AUTOMAGICALLY
Android saves UI state 
AUTOMAGICALLY (aka “It just works!™”)
Android saves UI state 
AUTOMAGICALLY (aka “It just works!™”) 
…except in some cases
Works out-of-the-box if Views 
1. Have an ID 
2. Are “save” enabled 
3. Come from the framework
It always begins with a call to 
saveHierarchyState()
EditText! 
@id/text 
RelativeLayout! 
@id/container 
TextView 
CheckBox! 
@id/check_box
EditText! 
@id/text 
RelativeLayout! 
@id/container 
TextView 
CheckBox! 
@id/check_box 
SparseArray<Parcelable>
RelativeLayout! 
@id/container 
TextView 
CheckBox! 
@id/check_box 
SparseArray<Parcelable> 
S1 
EditText! 
@id/text
SparseArray<Parcelable> 
@id/container 
RelativeLayout! 
@id/container 
TextView 
CheckBox! 
@id/check_box 
S1 
EditText! 
@id/text
EditText! 
@id/text 
RelativeLayout! 
@id/container 
TextView 
CheckBox! 
@id/check_box 
S2 SparseArray<Parcelable> 
@id/container S1
SparseArray<Parcelable> 
@id/container S1 
@id/text 
S2 
RelativeLayout! 
@id/container 
EditText! 
@id/text 
TextView 
CheckBox! 
@id/check_box
RelativeLayout! 
@id/container 
TextView 
CheckBox! 
@id/check_box 
SparseArray<Parcelable> 
@id/container S1 
@id/text 
S2 
S3 
EditText! 
@id/text
SparseArray<Parcelable> 
@id/container 
@id/text 
@id/check_box 
S1 
S2 
S3 
RelativeLayout! 
@id/container 
EditText! 
@id/text 
TextView 
CheckBox! 
@id/check_box
Controlling save 
setSaveEnabled(boolean) 
setSaveFromParentEnabled(boolean)
It always ends with a call to 
restoreHierarchyState()
SparseArray<Parcelable> 
@id/container S1 
@id/text S2 
@id/check_box S3 
RelativeLayout! 
@id/container 
EditText! 
@id/text 
TextView 
CheckBox! 
@id/check_box
SparseArray<Parcelable> 
@id/container S1 
S2 
S3 
@id/text 
@id/check_box 
RelativeLayout! 
@id/container 
EditText! 
@id/text 
TextView 
CheckBox! 
@id/check_box
RelativeLayout! 
@id/container 
TextView 
CheckBox! 
@id/check_box 
SparseArray<Parcelable> 
@id/container S1 
S2 
@id/check_box S3 
S1 
@id/text 
EditText! 
@id/text
SparseArray<Parcelable> 
@id/container S1 
@id/text S2 
@id/check_box S3 
RelativeLayout! 
@id/container 
EditText! 
@id/text 
TextView 
CheckBox! 
@id/check_box
EditText! 
@id/text 
RelativeLayout! 
@id/container 
TextView 
CheckBox! 
@id/check_box 
S2 SparseArray<Parcelable> 
@id/container S1 
@id/text 
S2 
@id/check_box S3
SparseArray<Parcelable> 
@id/container S1 
@id/text S2 
@id/check_box S3 
RelativeLayout! 
@id/container 
EditText! 
@id/text 
TextView 
CheckBox! 
@id/check_box
RelativeLayout! 
@id/container 
TextView 
CheckBox! 
@id/check_box 
@id/container S1 
@id/text S2 
@id/check_box S3 
S3 
SparseArray<Parcelable> 
EditText! 
@id/text
Ensure your Views’ IDs are 
unique & constant
1 static class SavedState extends BaseSavedState {! 
2 int checked;! 
3 ! 
4 SavedState(Parcelable superState) { super(superState); }! 
5 ! 
6 private SavedState(Parcel in) {! 
7 super(in);! 
8 checked = in.readInt();! 
9 }! 
10 ! 
11 @Override! 
12 public void writeToParcel(Parcel out, int flags) {! 
13 super.writeToParcel(out, flags);! 
14 out.writeInt(checked);! 
15 }! 
16 ! 
17 public static final Parcelable.Creator<SavedState> CREATOR = ! 
18 new Parcelable.Creator<SavedState>() {! 
19 public SavedState createFromParcel(Parcel in) {! 
20 return new SavedState(in);! 
21 }! 
22 public SavedState[] newArray(int size) {! 
23 return new SavedState[size];! 
24 }! 
25 };! 
26 }
1 @Override! 
2 public Parcelable onSaveInstanceState() {! 
3 final Parcelable superState = super.onSaveInstanceState();! 
4 SavedState ss = new SavedState(superState);! 
5 ss.checked = isChecked() ? 1 : 0;! 
6 return ss;! 
7 }! 
8 ! 
9 @Override! 
10 public void onRestoreInstanceState(Parcelable state) {! 
11 SavedState ss = (SavedState) state;! 
12 super.onRestoreInstanceState(ss.getSuperState());! 
13 setChecked(ss.checked == 1);! 
14 }
FrameLayout! 
@id/root 
ImageBox! 
@id/container1 
CheckBox! 
@id/check_box 
ImageView! 
@id/image 
ImageBox! 
@id/container2 
CheckBox! 
@id/check_box 
ImageView! 
@id/image
FrameLayout! 
@id/root 
ImageBox! 
@id/container1 
ImageView! 
@id/image 
CheckBox! 
@id/check_box 
ImageBox! 
@id/container2 
ImageView! 
@id/image 
CheckBox! 
@id/check_box 
Custom views with children with same IDs
1 static class SavedState extends BaseSavedState {! 
2 ! 
3 SparseArray childrenStates;! 
4 ! 
5 SavedState(Parcelable superState) { super(superState); }! 
6 ! 
7 private SavedState(Parcel in, ClassLoader loader) {! 
8 super(in);! 
9 childrenStates = in.readSparseArray(loader);! 
10 }! 
11 ! 
12 @Override! 
13 public void writeToParcel(Parcel out, int flags) {! 
14 super.writeToParcel(out, flags);! 
15 out.writeSparseArray(childrenStates);! 
16 }! 
17 ! 
18 public static final Creator<SavedState> CREATOR = ParcelableCompat.! 
19 newCreator(new ParcelableCompatCreatorCallbacks<SavedState>() {! 
20 @Override! 
21 public SavedState createFromParcel(Parcel source, ClassLoader loader) {! 
22 return new SavedState(source, loader);! 
23 }! 
24 @Override! 
25 public SavedState[] newArray(int size) {! 
26 return new SavedState[size];! 
27 }! 
28 });! 
29 }
1 @Override! 
2 public Parcelable onSaveInstanceState() {! 
3 final Parcelable superState = super.onSaveInstanceState();! 
4 SavedState ss = new SavedState(superState);! 
5 ss.childrenStates = new SparseArray<Parcelable>();! 
6 for (int i = 0; i < getChildCount(); i++) {! 
7 getChildAt(i).saveHierarchyState(ss.childrenStates);! 
8 }! 
9 return ss;! 
10 }! 
11 ! 
12 @Override! 
13 public void onRestoreInstanceState(Parcelable state) {! 
14 SavedState ss = (SavedState) state;! 
15 super.onRestoreInstanceState(ss.getSuperState());! 
16 for (int i = 0; i < getChildCount(); i++) {! 
17 getChildAt(i).restoreHierarchyState(ss.childrenStates);! 
18 }! 
19 }
That has solved nothing! 
Still need to block save/restore dispatch
1 @Override! 
2 protected void dispatchSaveInstanceState(SparseArray<Parcelable> container) {! 
3 dispatchFreezeSelfOnly(container);! 
4 }! 
5 ! 
6 @Override! 
7 protected void dispatchRestoreInstanceState(SparseArray<Parcelable> container) {! 
8 dispatchThawSelfOnly(container);! 
9 }
Fragment level 
state restoration
Very similar to Activities 
state restoration lifecycle. 
(Fragments are tied to Activity after all)
Fragment blocks Activity 
save mechanism 
with framework 
setSaveFromParentEnabled(false) 
with support library 
NoSaveStateFrameLayout
2 distinct states 
Fragment + View 
common case 
View only 
detach, addToBackStack, etc.
Leveraging save/restore 
Can to be used to create smooth transitions between 
your Activities: 
! 
- Save the state SA of A 
- Start B with no animations passing SA 
- Apply SA to B 
- Transition between A and B was smooth
Summarizing 
in three rules
Always save the state 
An Android app must survive configuration 
changes & low memory conditions.
Only save essential info 
Only save info that is non persistent 
or can not be reconstructed later.
Use correct levels 
Save instance states at the appropriate 
component level: Activity, Fragment or View.
Thank you! 
@cyrilmottier 
cyrilmottier.com
Resources 
Dressed for Iceland • Cécile Bernard 
Moelwynion, Eryri, Cymru • Marc Poppleton 
Happy, Confused, Wink, Sad, Angry • Megan Sheehan 
Floppy-Disk • Alex Auda Samora 
Fonts 
Source Sans Pro 
Courier

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Deep dive into android restoration - DroidCon Paris 2014

  • 1. Deep Dive Into Android State Restoration
  • 2. TWITTER @cyrilmottier ! WEBSITE cyrilmottier.com
  • 3.
  • 4.
  • 5.
  • 6.
  • 7. The story of a newbie Android developer
  • 8. Kevin has just developed his first Android app
  • 9. He discovers an annoying bug: Fields are cleared on rotate
  • 12. 3 options Don’t care Block orientation
  • 13. 3 options Don’t care Block orientation Use configChanges Hint: all options are
  • 14. 1 <activity! 2 android:name=".HomeActivity"! 3 android:configChanges="orientation">! 4 ! 5 <!-- Some sweet IntentFilters. -->! 6 ! 7 </activity>
  • 17. Still having issues on… language changes
  • 18. 1 <activity! 2 android:name=".HomeActivity"! 3 android:configChanges="orientation! 4 ! 5 <!-- Some annoying IntentFilters. -->! 6 ! 7 </activity> |locale">
  • 20. 1 <activity! 2 android:name=".HomeActivity"! 3 android:configChanges=“orientation|locale|! mcc|mnc|touchscreen|keyboard|! keyboardHidden|navigation|uiMode|! screenLayout|fontScale|screenSize|! smallestScreenSize">! 4 ! 5 <!-- Some fuc**** IntentFilters. Arrggh! -->! 6 ! 7 </activity>
  • 21. The nightmare continues… Still having issues when moving the app to the background
  • 22. God save the STATE
  • 23. State restoration key components
  • 25. The container Parcel The content Primitives types Primitives arrays Parcelable
  • 26. The content Primitives types Primitives arrays 1 parcel.writeInt(1);! 2 parcel.writeLong(2L);! 3 parcel.writeFloat(3F);! 4 parcel.writeString("Hi!"); Parcelable
  • 27. 1 parcel.writeIntArray(new int[]{1, 2, 3});! 2 parcel.writeLongArray(new long[]{1L, 2L, 3L});! 3 parcel.writeDoubleArray(new double[]{1, 2, 3});! 4 parcel.writeStringArray(new String[]{! 5 "Hi", "Droidcon", "guys!"! 6 }); The content Primitives types Primitives arrays Parcelable
  • 28. 1 public final class Suggestion implements Parcelable {! 2 ! 3 public final String id;! 4 public final String name;! 5 public final int type;! 6 ! 7 public Suggestion(String id, String name, int type) {! 8 this.id = Objects.requireNonNull(id);! 9 this.name = Objects.requireNonNull(name);! 10 this.type = type;! 11 }! 12 ! 13 }
  • 29. 1 @Override! 2 public int describeContents() {! 3 return 0;! 4 }! 5 ! 6 @Override! 7 public void writeToParcel(Parcel dest, int flags) {! 8 dest.writeString(id);! 9 dest.writeString(name);! 10 dest.writeInt(type);! 11 }! 12 13 public static final Parcelable.Creator<Suggestion> CREATOR = ! 14 new Parcelable.Creator<Suggestion>() {! 15 public Suggestion createFromParcel(Parcel in) {! 16 return new Suggestion(in.readString(), // ! 17 in.readString(), //! 18 in.readInt());! 19 }! 20 ! 21 public Suggestion[] newArray(int size) {! 22 return new Suggestion[size];! 23 }! 24 };
  • 30. Parcelable.Creator! The base creator interface ! Parcelable.ClassLoaderCreator! A creator with the ClassLoader passed on read. ! ParcelableCompat & ParcelableCompatCreatorCallbacks! Compatibility stuff
  • 31. Bundle A key-value map & type-safe Parcelable
  • 32. Parcel! internally uses reflection (required to get the CREATOR instance) …i.e. beware Proguard
  • 33. Activity level state restoration
  • 36. : non-null Bundle onCreate(null) onSaveInstanceState( )
  • 37. onCreate(null) onSaveInstanceState( ) onCreate( ) : non-null Bundle
  • 38. onCreate(null) onSaveInstanceState( ) onCreate( ) onRestoreInstanceState( ) : non-null Bundle
  • 39. onCreate(null) onSaveInstanceState( ) onCreate( ) onRestoreInstanceState( ) : non-null Bundle
  • 40. onCreate(null) onSaveInstanceState( ) onCreate( ) onRestoreInstanceState( ) : non-null Bundle
  • 41. What to save? Non persistent or non reconstructible info
  • 42. 1 public class SearchActivity extends Activity {! 2 ! 3 private static final String STATE_OUTWARD = "state:outward";! 4 ! 5 private DateComponents mOutward;! 6 ! 7 @Override! 8 protected void onCreate(Bundle inState) {! 9 super.onCreate(inState);! 10 ! 11 if (inState != null) {! 12 DateComponents components = inState.getParcelable(STATE_OUTWARD);! 13 if (components != null) {! 14 setOutward(components);! 15 }! 16 }! 17 }! 18 ! 19 @Override! 20 protected void onSaveInstanceState(Bundle outState) {! 21 super.onSaveInstanceState(outState);! 22 outState.putParcelable(STATE_OUTWARD, mOutward);! 23 }! 24 }
  • 45. onSaveInstanceState saves Window Fragments Dialogs
  • 46. Always call the SUPER METHODS Android has no guards on save-related methods
  • 47. android:stateNotNeeded For restart-on-crash apps only (i.e. launcher app)
  • 48. Developer options Don’t keep activities
  • 49. Developer options Don’t keep activities
  • 50. View level state restoration
  • 51. Android saves UI state AUTOMAGICALLY
  • 52. Android saves UI state AUTOMAGICALLY (aka “It just works!™”)
  • 53. Android saves UI state AUTOMAGICALLY (aka “It just works!™”) …except in some cases
  • 54. Works out-of-the-box if Views 1. Have an ID 2. Are “save” enabled 3. Come from the framework
  • 55. It always begins with a call to saveHierarchyState()
  • 56. EditText! @id/text RelativeLayout! @id/container TextView CheckBox! @id/check_box
  • 57. EditText! @id/text RelativeLayout! @id/container TextView CheckBox! @id/check_box SparseArray<Parcelable>
  • 58. RelativeLayout! @id/container TextView CheckBox! @id/check_box SparseArray<Parcelable> S1 EditText! @id/text
  • 59. SparseArray<Parcelable> @id/container RelativeLayout! @id/container TextView CheckBox! @id/check_box S1 EditText! @id/text
  • 60. EditText! @id/text RelativeLayout! @id/container TextView CheckBox! @id/check_box S2 SparseArray<Parcelable> @id/container S1
  • 61. SparseArray<Parcelable> @id/container S1 @id/text S2 RelativeLayout! @id/container EditText! @id/text TextView CheckBox! @id/check_box
  • 62. RelativeLayout! @id/container TextView CheckBox! @id/check_box SparseArray<Parcelable> @id/container S1 @id/text S2 S3 EditText! @id/text
  • 63. SparseArray<Parcelable> @id/container @id/text @id/check_box S1 S2 S3 RelativeLayout! @id/container EditText! @id/text TextView CheckBox! @id/check_box
  • 64. Controlling save setSaveEnabled(boolean) setSaveFromParentEnabled(boolean)
  • 65. It always ends with a call to restoreHierarchyState()
  • 66. SparseArray<Parcelable> @id/container S1 @id/text S2 @id/check_box S3 RelativeLayout! @id/container EditText! @id/text TextView CheckBox! @id/check_box
  • 67. SparseArray<Parcelable> @id/container S1 S2 S3 @id/text @id/check_box RelativeLayout! @id/container EditText! @id/text TextView CheckBox! @id/check_box
  • 68. RelativeLayout! @id/container TextView CheckBox! @id/check_box SparseArray<Parcelable> @id/container S1 S2 @id/check_box S3 S1 @id/text EditText! @id/text
  • 69. SparseArray<Parcelable> @id/container S1 @id/text S2 @id/check_box S3 RelativeLayout! @id/container EditText! @id/text TextView CheckBox! @id/check_box
  • 70. EditText! @id/text RelativeLayout! @id/container TextView CheckBox! @id/check_box S2 SparseArray<Parcelable> @id/container S1 @id/text S2 @id/check_box S3
  • 71. SparseArray<Parcelable> @id/container S1 @id/text S2 @id/check_box S3 RelativeLayout! @id/container EditText! @id/text TextView CheckBox! @id/check_box
  • 72. RelativeLayout! @id/container TextView CheckBox! @id/check_box @id/container S1 @id/text S2 @id/check_box S3 S3 SparseArray<Parcelable> EditText! @id/text
  • 73. Ensure your Views’ IDs are unique & constant
  • 74. 1 static class SavedState extends BaseSavedState {! 2 int checked;! 3 ! 4 SavedState(Parcelable superState) { super(superState); }! 5 ! 6 private SavedState(Parcel in) {! 7 super(in);! 8 checked = in.readInt();! 9 }! 10 ! 11 @Override! 12 public void writeToParcel(Parcel out, int flags) {! 13 super.writeToParcel(out, flags);! 14 out.writeInt(checked);! 15 }! 16 ! 17 public static final Parcelable.Creator<SavedState> CREATOR = ! 18 new Parcelable.Creator<SavedState>() {! 19 public SavedState createFromParcel(Parcel in) {! 20 return new SavedState(in);! 21 }! 22 public SavedState[] newArray(int size) {! 23 return new SavedState[size];! 24 }! 25 };! 26 }
  • 75. 1 @Override! 2 public Parcelable onSaveInstanceState() {! 3 final Parcelable superState = super.onSaveInstanceState();! 4 SavedState ss = new SavedState(superState);! 5 ss.checked = isChecked() ? 1 : 0;! 6 return ss;! 7 }! 8 ! 9 @Override! 10 public void onRestoreInstanceState(Parcelable state) {! 11 SavedState ss = (SavedState) state;! 12 super.onRestoreInstanceState(ss.getSuperState());! 13 setChecked(ss.checked == 1);! 14 }
  • 76. FrameLayout! @id/root ImageBox! @id/container1 CheckBox! @id/check_box ImageView! @id/image ImageBox! @id/container2 CheckBox! @id/check_box ImageView! @id/image
  • 77. FrameLayout! @id/root ImageBox! @id/container1 ImageView! @id/image CheckBox! @id/check_box ImageBox! @id/container2 ImageView! @id/image CheckBox! @id/check_box Custom views with children with same IDs
  • 78. 1 static class SavedState extends BaseSavedState {! 2 ! 3 SparseArray childrenStates;! 4 ! 5 SavedState(Parcelable superState) { super(superState); }! 6 ! 7 private SavedState(Parcel in, ClassLoader loader) {! 8 super(in);! 9 childrenStates = in.readSparseArray(loader);! 10 }! 11 ! 12 @Override! 13 public void writeToParcel(Parcel out, int flags) {! 14 super.writeToParcel(out, flags);! 15 out.writeSparseArray(childrenStates);! 16 }! 17 ! 18 public static final Creator<SavedState> CREATOR = ParcelableCompat.! 19 newCreator(new ParcelableCompatCreatorCallbacks<SavedState>() {! 20 @Override! 21 public SavedState createFromParcel(Parcel source, ClassLoader loader) {! 22 return new SavedState(source, loader);! 23 }! 24 @Override! 25 public SavedState[] newArray(int size) {! 26 return new SavedState[size];! 27 }! 28 });! 29 }
  • 79. 1 @Override! 2 public Parcelable onSaveInstanceState() {! 3 final Parcelable superState = super.onSaveInstanceState();! 4 SavedState ss = new SavedState(superState);! 5 ss.childrenStates = new SparseArray<Parcelable>();! 6 for (int i = 0; i < getChildCount(); i++) {! 7 getChildAt(i).saveHierarchyState(ss.childrenStates);! 8 }! 9 return ss;! 10 }! 11 ! 12 @Override! 13 public void onRestoreInstanceState(Parcelable state) {! 14 SavedState ss = (SavedState) state;! 15 super.onRestoreInstanceState(ss.getSuperState());! 16 for (int i = 0; i < getChildCount(); i++) {! 17 getChildAt(i).restoreHierarchyState(ss.childrenStates);! 18 }! 19 }
  • 80. That has solved nothing! Still need to block save/restore dispatch
  • 81. 1 @Override! 2 protected void dispatchSaveInstanceState(SparseArray<Parcelable> container) {! 3 dispatchFreezeSelfOnly(container);! 4 }! 5 ! 6 @Override! 7 protected void dispatchRestoreInstanceState(SparseArray<Parcelable> container) {! 8 dispatchThawSelfOnly(container);! 9 }
  • 82. Fragment level state restoration
  • 83. Very similar to Activities state restoration lifecycle. (Fragments are tied to Activity after all)
  • 84. Fragment blocks Activity save mechanism with framework setSaveFromParentEnabled(false) with support library NoSaveStateFrameLayout
  • 85. 2 distinct states Fragment + View common case View only detach, addToBackStack, etc.
  • 86. Leveraging save/restore Can to be used to create smooth transitions between your Activities: ! - Save the state SA of A - Start B with no animations passing SA - Apply SA to B - Transition between A and B was smooth
  • 88. Always save the state An Android app must survive configuration changes & low memory conditions.
  • 89. Only save essential info Only save info that is non persistent or can not be reconstructed later.
  • 90. Use correct levels Save instance states at the appropriate component level: Activity, Fragment or View.
  • 91. Thank you! @cyrilmottier cyrilmottier.com
  • 92. Resources Dressed for Iceland • Cécile Bernard Moelwynion, Eryri, Cymru • Marc Poppleton Happy, Confused, Wink, Sad, Angry • Megan Sheehan Floppy-Disk • Alex Auda Samora Fonts Source Sans Pro Courier