This document provides an overview of Android data binding, including how it works, lambdas, two-way data binding, new features announced at Google IO 2016, best practices and integration with MVVM and TDD. It discusses setting up data binding, using binding expressions and adapters, notifying views of changes, and avoiding common pitfalls like moving business logic to XML. The summary notes that data binding reduces boilerplate code but can introduce compiler errors, and emphasizes its power, official support from Google, and ability to easily integrate with custom views and libraries.

1. Deep dive into
Android Data Binding
+RadoslawPiekarz
@radzio
Radosław Piekarz
Head of Mobile at Tango Agency

2. droidconde2016
talixo.de
10 € discount

3. Basics
How it works?
Lambdas
Two-Way data binding
New stuff announced during Google IO 2016
Dos and don'ts
MVVM & TDD
Summary

4. Basics
How it works?
Lambdas
Two-Way data binding
New stuff announced during Google IO 2016
Dos and don'ts
MVVM & TDD
Summary

5. Setup
// <app-module>/build.gradle
apply plugin: "com.android.application"
android {
dataBinding {
enabled = true
}
}

6. Changes in layout file
<layout
xmlns:android="http://schemas.android.com/apk/res/android">
<TextView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:id="@+id/my_id"/>
</layout>

7. Changes in Activity / Fragment code
@Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
MainActivityBinding binding = DataBindingUtil
.setContentView(this, R.layout.main_activity);
binding.myId.setText("John Doe")
}
Type safe!

8. Binding utils
DataBindingUtil.setContentView(activity, layoutId);
DataBindingUtil.inflate(inflater, layoutId, parent, attachToParrent);
ListItemBinding binding = ListItemBinding.bind(viewRoot);
Use for activities
Use for any view
Bind view that was
already inflated

9. Changes in layout file
<layout
xmlns:android="http://schemas.android.com/apk/res/android">
<data class="CustomClassName">
<variable name="user" type="com.example.User"/>
</data>
<TextView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="@{user.firstName}" />
</layout>

10. Changes in Activity / Fragment Code
@Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
binding = DataBindingUtil
.setContentView(this, R.layout.main_activity);
binding.setUser(new User());
}

11. Binding expression operators
Grouping ()
Literals character, String,
numeric, null
Method calls, field access
Ternary operator ?:
Array access []
Null coalescing operator ??
Mathematical + - / * %
String concatenation +
Logical && ||
Binary & | ^
Unary + - ! ~
Shift >> >>> <<
Comparison == > < >= <=
instanceof, cast

12. Binding expression operators
android:text="@{user.displayName ?? user.lastName}"
android:text="@{user.displayName != null ? user.displayName : user.lastName}"
=

13. Notifying view #1
public class User extends BaseObservable {
private String firstName;
public User(String firstName) {
this.firstName = firstName;
}
public void setFirstName(String firstName) {
this.firstName = firstName;
notifyPropertyChanged(BR.firstName);
}
@Bindable
public String getFirstName() {
return this.firstName;
}
}

14. Notifying view #2
public class User {
public final ObservableField<String> firstName;
public User(String name) {
this.firstName = new ObservableField<>(firstName);
}
public void setName(String firstName) {
this.firstName.set(firstName);
}
}

15. Observable fields & collections
Observable<T>
ObservableBoolean
ObservableByte
ObservableChar
ObservableShort
ObservableInt
ObservableLong
ObservableFloat
ObservableDouble
ObservableParcelable<T>
ObservableList<T>
ObservableArrayList<T>
ObservableMap<K, V>
ObservableArrayMap<K, V>

16. Binding Adapters
<layout>
<ImageView
bind:imageUrl="@{viewModel.someNiceImageUrl}"
bind:error="@{@drawable/defaultImage}"/>
</layout>
@BindingAdapter({"bind:imageUrl", "bind:error"})
public static void loadImage(ImageView view, String url, Drawable error)
{
Picasso.with(view.getContext()).load(url).error(error).into(view);
}

17. Binding Adapters
@BindingAdapter({"bind:imageUrl", "bind:error"})
public static void loadImage(ImageView view, String url, Drawable error)
{
Picasso.with(view.getContext()).load(url).error(error).into(view);
}

18. java.lang.IllegalStateException
Required DataBindingComponent is null. If you don't use an inflation
method taking a DataBindingComponent, use
DataBindingUtil.setDefaultComponent or make all BindingAdapter
methods static.

19. Binding Component
public class MyDataBindingCoponent implements DataBindingComponent
{
public EditTextBindings getEditTextBindings()
{
return new EditTextBindings();
}
}

20. Binding Component
@Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
binding = DataBindingUtil
.setContentView(this,
R.layout.activity_main,
new MyDataBindingCoponent());
binding.setViewModel(new ViewModel());
}

21. Binding Conversions
android:background="@{isError ? @color/red : @color/white}"
@BindingConversion
public static ColorDrawable convertColorToDrawable(int color) {
return new ColorDrawable(color);
}

22. Binding methods
@BindingMethods({
@BindingMethod(type = CircularProgressBar.class,
attribute = "progressText", method = "setProgressMessage")
})
public class ViewBindings
{
}

23. RecyclerView bindings
https://github.com/radzio/android-data-binding-recyclerview

24. Talk is cheap. Show me the code

25. RecyclerView Binding #1
<android.support.v7.widget.RecyclerView
android:id="@+id/activity_users_recycler"
android:scrollbars="vertical"
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_weight="1"
app:items="@{usersViewModel.users}"
app:itemViewBinder="@{view.itemViewBinder}"
/>

26. RecyclerView Binding #2
@Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
usersViewModel = new UsersViewModel();
usersViewModel.users
.add(new SuperUserViewModel(new User("Android", "Dev")));
binding = DataBindingUtil.setContentView(this, R.layout.users_view);
binding.setUsersViewModel(usersViewModel);
binding.setView(this);
}

27. RecyclerView Binding #3
public class UsersViewModel extends BaseObservable
{
@Bindable
public ObservableArrayList<UserViewModel> users;
public UsersViewModel()
{
this.users = new ObservableArrayList<>();
}
public void addUser(String name, String surname)
{
this.users.add(new UserViewModel(new User(name, surname)));
}
}

28. RecyclerView Binding #4
public ItemBinder<UserViewModel> itemViewBinder()
{
return new CompositeItemBinder<UserViewModel>(
new SuperUserBinder(BR.user, R.layout.item_super_user),
new UserBinder(BR.user, R.layout.item_user)
);
}

29. Basics
How it works?
Lambdas
Two-Way data binding
New stuff announced during Google IO 2016
Dos and don'ts
MVVM & TDD
Summary

30. How it works?
Bind ViewModel to
View
Register for
property change
callbacks
Trigger
notifyPropertyChanged
Request rebind
Execute pending
bindings
User input or from
code

31. How it works?
public void setViewModel(TwoWayViewModel viewModel) {
updateRegistration(0, viewModel);
this.mViewModel = viewModel;
synchronized(this) {
mDirtyFlags |= 0x1L;
notifyPropertyChanged(BR.viewModel);
super.requestRebind();
}

32. How it works?
@Override
protected void executeBindings() {
long dirtyFlags = 0;
synchronized(this) {
dirtyFlags = mDirtyFlags;
mDirtyFlags = 0;
}
if ((dirtyFlags & 0x7L) != 0) {
if (viewModel != null) {
colorViewModel = viewModel.getColor();
}
if ((dirtyFlags & 0x7L) != 0) {
ColorPickerViewBindings.setColor(this.colorpicker, colorViewModel);
EditTextBindings.setText(this.mboundView2, colorViewModel);
}
if ((dirtyFlags & 0x4L) != 0) {
ColorPickerViewBindings.setColorListener(this.colorpicker, null, colorpickercolorAttr);
TextViewBindingAdapter.setTextWatcher(this.mboundView2, null, null, null, mboundView2androidTe);
this.mboundView3.setOnClickListener(mCallback2);
}
}

33. Basics
How it works?
Lambdas
Two-Way data binding
New stuff announced during Google IO 2016
Dos and don'ts
MVVM & TDD
Summary

34. Lambdas
<Button
android:onClick="@{() -> viewModel.sendAction()}
/>
public class MainViewModel extends BaseObservable
{
public void sendAction()
{
//code
}
}

35. Method References
<Button
android:onClick="@{viewModel::sendAction}"
/>
public class MainViewModel extends BaseObservable
{
public void sendAction(View view)
{
//code
}
}

36. Basics
How it works?
Lambdas
Two-Way data binding
New stuff announced during Google IO 2016
Dos and don'ts
MVVM & TDD
Summary

37. Two-Way data binding
<layout>
...
<LinearLayout>
<EditText
android:text="@{viewModel.twoWayText}"
/>
</LinearLayout>
</layout>

38. Two-Way data binding
<layout>
...
<LinearLayout>
<EditText
android:text="@={viewModel.twoWayText}"
/>
</LinearLayout>
</layout>

39. Two-Way data binding
classpath 'com.android.tools.build:gradle:2.1.0-alpha3'// or above

40. Views with Two-Way Binding support
• AbsListView -> android:selectedItemPosition
• CalendarView -> android:date
• CompoundButton -> android:checked
• DatePicker -> android:year, android:month, android:day
• NumberPicker -> android:value
• RadioGroup -> android:checkedButton
• RatingBar -> android:rating
• SeekBar -> android:progres
• TabHost -> android:currentTab
• TextView -> android:text
• TimePicker -> android:hour, android:minute

41. What about custom views?

42. NO PROBLEM!

43. Two-Way data binding
@InverseBindingAdapter(attribute = "color", event = "colorAttrChanged")
public static int getColor(ColorPickerView view)
{
return view.getColor();
}
attribute + AttrChanged

44. Activity
@BindingAdapter("colorAttrChanged")
public static void setColorListener(ColorPickerView view,
final InverseBindingListener colorChange)
{
if (colorChange == null)
{
view.setOnColorChangedListener(null);
}
else
{
view.setOnColorChangedListener(new OnColorChangedListener()
{
@Override
public void onColorChanged(int newColor)
{
colorChange.onChange();
}
});
}
}

45. Two-Way data binding
@BindingAdapter("color")
public static void setColor(ColorPickerView view, int color)
{
if (color != view.getColor())
{
view.setColor(color);
}
}
Avoiding cycles

46. Two-Way data binding
public class TwoWayViewModel extends BaseObservable
{
private int color;
public void setColor(int color)
{
this.color = color;
this.notifyPropertyChanged(BR.color);
}
@Bindable
public int getColor()
{
return this.color;
}
}

47. Two-Way data binding
public class TwoWayBindingActivity extends AppCompatActivity
{
private ActivityTwoWayBinding binding;
@Override
protected void onCreate(@Nullable Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
binding = DataBindingUtil.setContentView(this, R.layout.activity_two_way);
binding.setViewModel(new TwoWayViewModel());
}
}

48. Two-Way data binding
<LinearLayout>
<com.github.danielnilsson9.colorpickerview.view.ColorPickerView
bind:color="@={viewModel.color}"
/>
<EditText
android:text="@={viewModel.color}"
/>
<Button
android:text="Set defined color"
android:onClick="@{() -> viewModel.setColor(Color.parseColor(`#C97249`))}"
/>
</LinearLayout>

49. Basics
How it works?
Lambdas
Two-Way data binding
New stuff announced during Google IO 2016
Dos and don'ts
MVVM & TDD
Summary

50. Special Variables
<TextView
android:id="@+id/tv_congrats"
/>
<Button
android:onClick="@{() -> clickHandler.clicked(tvCongrats)}"
/>
<TextView
android:text="@{TextService.load(context, myModel)}"
/>
Context
View IDs

51. Implied Event Updates
<CheckBox
android:id="@+id/cb_show_more"
/>
<TextView
android:visibility="@{cbShowMore.checked ? View.VISIBLE : View.GONE}"
/>

52. Repeated expressions
<TextView
android:id="@+id/tv_congrats"
android:visibility="@{cbShowMore.checked ? View.VISIBLE : View.GONE}"
/>
<TextView
android:visibility="@{cbShowMore.checked ? View.VISIBLE : View.GONE}"
/>
<TextView
android:visibility="@{cbShowMore.checked ? View.VISIBLE : View.GONE}"
/>

53. Repeated expressions
<TextView
android:id="@+id/tv_congrats"
android:visibility="@{cbShowMore.checked ? View.VISIBLE : View.GONE}"
/>
<TextView
android:visibility="@{tvCongrats.visibility}"
/>
<TextView
android:visibility="@{tvCongrats.visibility}"
/>

54. Basics
How it works?
Lambdas
Two-Way data binding
New stuff announced during Google IO 2016
Dos and don'ts
MVVM & TDD
Summary

55. Dos
• From time to time look at generated code
• Learn from already implemented bindings for framework views
• Move view operations to custom bindings as much as possible
• Try to use it together with MVVM design pattern
• Give it a chance!

56. Dos
• Use Data Binding for backward
compatibility!

57. Dos
• Always check if data binging library will work with your other libraries
(squidb won’t work )

58. Don’ts
• Don’t reinvent the wheel, on Github there are many ready to use
bindings
• Don’t forget about unit tests!

60. Don’ts
<EditText
android:layout_height="wrap_content"
android:hint="@string/hint_ticketNumber"
android:inputType="number"
android:layout_width="fill_parent"
android:text="@{viewModel.name == null?
String.format(viewModel.format, viewModel.surname, viewModel.nick) :
viewModel.name + viewModel.city}"
/>
Don’t move your business logic to xml layout
Just don’t!

61. Basics
How it works?
Lambdas
Two-Way data binding
New stuff announced during Google IO 2016
Dos and don'ts
MVVM & TDD
Summary

62. Say hello to
MVVM

63. MVVM & TDD
@Mock
ISendService sendService;
@Test
public void mainViewModel_sendAction_sendService_send()
{
final MainViewModel viewModel = new MainViewModel(sendService);
final String givenText = "my text";
viewModel.setTwoWayText(givenText);
viewModel.sendAction();
verify(sendService).send(givenText);
}

64. Basics
How it works?
Lambdas
Two-Way data binding
New stuff announced during Google IO 2016
Dos and don'ts
MVVM & TDD
Summary

65. Method count
• ~700 methods from databinding library
• n methods from your custom binding adapters, conversions etc.
• k methods from generated code for each layout xml with data binding
enabled

66. Summary
Cons
Compiler errors are sometimes not saying
too much
Still in beta
Documentation is not updated
May break other libraries (for example squidb)
Pros
Easy to start
Less boilerplate code
Code generation during compilation
Easy to integrate with custom views and
libraries
Really powerful
Officialy created and supported by Google
Android Team

67. Q&A
Q&A
https://github.com/radzio/DeepDiveIntoAndroidDataBinding
+RadoslawPiekarz
@radzio
Radosław Piekarz
Head of Mobile at Tango Agency