Deflating the LayoutInflater

https://droidconin.talkfunnel.com/2016/86-deflating-the-layoutinflater

1. Deflating the LayoutInflater Saket • Uncommon
2. Parts 1. What and how 2. Applications
3. Part 1, What is LayoutInflater
4. Converts View hierarchies written in XML into Java objects XML <TextView android:layout_width="wrap_content" android:layout_height=“wrap_content" /> Java public class TextView extends View { ... }
5. Common Usages
6. Fragments @Override public View onCreateView(LayoutInflater, ViewGroup, Bundle) { return inflater.inflate( R.layout.fragment_layout, container, false ); }
7. ViewHolders @Override public ViewHolder onCreateViewHolder(ViewGroup, int) { return new ViewHolder(inflater.inflate( R.layout.fragment_layout, container, false )); }
8. Activities @Override protected void onCreate(Bundle savedState) { super.onCreate(savedState); setContentView(R.layout.activity_main); }
9. PhoneWindow.java (or AppCompatDelegateImplV7.java) @Override public void setContentView(int layoutRes) { mLayoutInflater.inflate(layoutRes, mParent); }
10. How it works
11. LayoutInflater#inflate() A. XmlPullParser B. AttributeSet C. Creating View objects
12. LayoutInflater#inflate() A. XmlPullParser GSON, Moshi for JSON is the same as XmlPullParser for XML
13. LayoutInflater#inflate() B. AttributeSet <ImageView android:layout_width="100dp" android:layout_height="100dp" android:src="@drawable/ic_done" android:contentDescription="Save" />
14. LayoutInflater#inflate() B. AttributeSet <ImageView android:layout_width="100dp" android:layout_height="100dp" android:src="@drawable/ic_done" android:contentDescription="Save" />
15. LayoutInflater#inflate() B. AttributeSet <ImageView android:layout_width="100dp" android:layout_height="100dp" android:src="@drawable/ic_done" android:contentDescription="Save" />
16. LayoutInflater#inflate() B. AttributeSet <ImageView android:layout_width="100dp" android:layout_height="100dp" android:src="@drawable/ic_done" android:contentDescription="Save" />
17. LayoutInflater#inflate() B. AttributeSet <ImageView android:layout_width="100dp" android:layout_height="100dp" android:src="@drawable/ic_done" android:contentDescription="Save" />
18. LayoutInflater#inflate() B. AttributeSet <ImageView android:layout_width="100dp" android:layout_height="100dp" android:src="@drawable/ic_done" android:contentDescription="Save" />
19. LayoutInflater#inflate() B. AttributeSet <ImageView android:layout_width="@dimen/list_icon" android:layout_height="@dimen/list_icon" android:src="@drawable/ic_done" android:contentDescription="Save" /> res/values/dimens.xml
20. LayoutInflater#inflate() B. AttributeSet Figures precedence of attributes <ImageView style="@style/Button.Save" android:layout_width="100dp" android:layout_height="100dp" android:src=“@drawable/ic_done" />
21. LayoutInflater#inflate() B. AttributeSet Figures precedence of attributes <ImageView style="@style/Button.Save" android:layout_width="100dp" android:layout_height="100dp" android:src=“@drawable/ic_done" />
22. LayoutInflater#inflate() B. AttributeSet Figures precedence of attributes <style name="Button.Save"> <item name="android:layout_width">200dp</item> <item name="android:layout_height">200dp</item> </style>
23. LayoutInflater#inflate() B. AttributeSet Figures precedence of attributes <ImageView style="@style/Button.Save" android:layout_width="100dp" android:layout_height="100dp" android:src=“@drawable/ic_done" />
24. Finding a View’s source Creating the View object using Reflection
 LayoutInflater#inflate() C. Creating View Objects
25. Finding a View’s source Creating the View object using Reflection
 LayoutInflater#inflate() C. Creating View Objects
26. Black magic Slow Reflection?
27. Delegate creation to “Factories” Instantiate View by itself (if #1 fails) Creating View Objects
28. Delegate creation to “Factories” Instantiate View by itself (if #1 fails) context.getClassLoader().loadClass(); Creating View Objects
29. Delegate creation to “Factories” Instantiate View by itself a) Custom View 
 b) Framework View Creating View Objects
30. a) Custom View: <android.support.v7.widget.RecyclerView android:layout_width="match_parent" android:layout_height=“match_parent" /> Creating View Objects
31. a) Custom View: Class<RecyclerView> clazz = ClassLoader#loadClass( "android.support.v7.widget.RecyclerView" ); RecyclerView view = clazz.getConstructor().newInstance(); Creating View Objects
32. a) Framework View: <TextView android:layout_width="match_parent" android:layout_height="match_parent" /> Creating View Objects
33. a) Custom View: Class<TextView> clazz = ClassLoader#loadClass( "TextView" ); Creating View Objects
34. a) Custom View: Class<TextView> clazz = ClassLoader#loadClass( "android.widget.TextView" ); Creating View Objects
35. a) Custom View: Class<TextView> clazz = ClassLoader#loadClass( "android.widget.TextView" ); TextView view = clazz.getConstructor().newInstance(); Creating View Objects
36. Delegate creation to “Factories” Instantiate View by itself Creating View Objects
37. LayoutInflater Factories
38. Installing a Factory @Override protected void onCreate(Bundle savedState) { getLayoutInflater().setFactory2(...); super.onCreate(savedState); }
39. Common Factories a) Activity public class Activity extends ContextThemeWrapper implements LayoutInflater.Factory2 { }
40. Common Factories a) Activity
41. Common Factories a) Activity <LinearLayout> <fragment android:name="is.uncommon.ShinyFragment" android:layout_width="match_parent" android:layout_height="match_parent" /> </LinearLayout>
42. Common Factories a) Activity <LinearLayout> <fragment android:name="is.uncommon.ShinyFragment" android:layout_width="match_parent" android:layout_height="match_parent" /> </LinearLayout>
43. Common Factories b) AppCompat
 Continued in Part 2.
44. Part 2, Hooking into LayoutInflater
45. example, AppCompat How it back-ports material design to pre-Lollipop devices
46. android:theme
47. AppCompat Kitkat
48. AppCompat Kitkat
49. AppCompat <Button android:layout_width="match_parent" android:layout_height="match_parent" android:background="@drawable/custom_btn" /> custom_btn.xml <selector> @drawable/custom_btn_normal @drawable/custom_btn_focussed @drawable/custom_btn_pressed </selector>
50. AppCompat <Button android:layout_width="match_parent" android:layout_height="match_parent" android:theme="@style/CustomButtonTheme" /> styles.xml <style name="CustomButtonTheme"> <item name=“colorButtonNormal”>#09F</item> <item name=“colorControlHighlight">#07F</item> </style>
51. example, AppCompat AppCompatActivity @Override protected void onCreate(Bundle savedState) { installViewFactory(); ... }
52. example, AppCompat AppCompatViewInflater.java implements LayoutInflater.Factory2 { ... }
53. example, AppCompat AppCompatViewInflater.java public View onCreateView(String viewName, ...) { if ("TextView".equals(viewName) { return new AppCompatTextView(); } ... }
54. example, AppCompat
55. example, Calligraphy How it applies custom fonts without using any custom Views. <TextView android:layout_width="wrap_content" android:layout_height="wrap_content" fontPath="fonts/Roboto-Bold.ttf" />
56. example, Calligraphy class CalligraphyLayoutInflater extends LayoutInflater { ... }
57. example, Calligraphy @Override View onCreateView(String name, AttributeSet) { View view = super.onCreateView(...); if (view instanceOf TextView) { applyTypeface((TextView) view); } return view; }
58. example, Calligraphy @Override View onCreateView(String name, AttributeSet) { View view = super.onCreateView(...); if (view instanceOf TextView) { applyTypeface((TextView) view); } return view; }
59. What if… We could do this? <EditText android:layout_width="wrap_content" android:layout_height="wrap_content" formatter="IndianRupees" />
60. What if… We could do this? <EditText android:layout_width="wrap_content" android:layout_height="wrap_content" formatter="IndianRupees" /> 250000
61. What if… We could do this? <EditText android:layout_width="wrap_content" android:layout_height="wrap_content" formatter="IndianRupees" /> Ũ2,50,000
62. What if… Or this? <EditText android:layout_width="wrap_content" android:layout_height="wrap_content" formatter="CreditCardNumber" />
63. What if… Or this? <EditText android:layout_width="wrap_content" android:layout_height="wrap_content" formatter="CreditCardNumber" /> 4652 3700 0055 5032
64. What if… Or this? <EditText android:layout_width="wrap_content" android:layout_height="wrap_content" formatter="CreditCardNumber" /> 3400 123456 000032
65. What if… Or maybe this? <FrameLayout android:layout_width="wrap_content" android:layout_height=“wrap_content" paddings="16dp 20dp" />
66. WHAT IF I TOLD YOU IT’S POSSIBLE TO DO THAT?
67. Introducing, Balloon!
68. Balloon interface BalloonAttributeListener { void onApplyAttribute( View view, int attributeResId, Object attributeValue ); }
69. Application#onCreate() Balloon.config() .registerAttr(R.attr.formatter, FormatterAttrListener) .build();
 Balloon
70. Application#onCreate() Balloon.config() .registerAttr(R.attr.formatter, FormatterAttrListener) .build();
 Balloon
71. Application#onCreate() Balloon.config() .registerAttr(R.attr.formatter, FormatterAttrListener) .build();
 Balloon
72. Balloon class FormatterAttrListener implements BalloonAttributeListener <> { @Override void onApplyAttribute(EditText view, int attrResId, String attrValue) { if ("IndianRupees".equals(attrValue)) { // Add rupee symbol and format digits } } }
73. Pros Composition > Inheritance Can be used for multiple types of Views Quick
74. Cons “Experimental” No layout preview in Android Studio
75. Working class BalloonLayoutInflater extends LayoutInflater { ... }
76. Challenges Activity getLayoutInflater() -> return LayoutInflater
77. Challenges Activity getLayoutInflater() -> return LayoutInflater -> return BalloonLayoutInflater
78. Challenges public class BalloonContext extends Context { ... }
79. Challenges Activity @Override void attachBaseContext(Context base) { super.attachBaseContext(BalloonContext.wrap(base)); }
80. Challenges Activity @Override void attachBaseContext(Context base) { super.attachBaseContext(BalloonContext.wrap(base)); }
81. Challenges BalloonContext @Override Object getSystemService(String name) { if (LAYOUT_INFLATER_SERVICE.equals(name)) { return new BalloonLayoutInflater(); } return super.getSystemService(name); }
82. Challenges BalloonContext @Override Object getSystemService(String name) { if (LAYOUT_INFLATER_SERVICE.equals(name)) { return new BalloonLayoutInflater(); } return super.getSystemService(name); }
83. Challenges Activity getLayoutInflater() -> return BalloonLayoutInflater
84. saket.me/droidcon
85. Learnings Layout inflation is a slow process.
 Complex layouts can affect an Activity’s startup time.
86. Learnings Why non-framework Views require their fully qualified names in XML whereas framework Views don’t. <is.uncommon.FancyCustomView /> vs. <TextView />
87. That’s all folks!
88. Uncommon hello @ uncommon.is
89. Questions?