Android Databinding
Denis Kniazhev
About me
Java EE - 8 years
Android - 2 years
Did some Java desktop, Javascript, PHP, Databases, iOS along the way
Currently Development Manager of Mobile project (iOS and Android)
Databinding connects UI and Data Models
What's Databinding?
View
Model
Template
One-Way Binding
Compiles
Template
Model
View
Model is the single source of truth
Compiles
Two-Way Binding
JSP
?
Databinding in Android
- Introduced in Android Marshmallow
- Was initially planned for Lollipop, but Lollipop became too huge
- First prototype was built in late 2014
- Version RC-0 has been presented at Google I/O 2015
- Is a Support Library - works on API 7+
<LinearLayout …>
<TextView android:id="@+id/name"/>
<TextView android:id="@+id/lastName"/>
</LinearLayout>private TextView name
private TextView lastName;
protected void onCreate(Bundle savedInstanceState) {
setContentView(R.layout.activity_main);
name = (TextView) findViewById(R.id.name);
lastName = (TextView) findViewById(R.id.lastName);
}
public void updateUI(User user) {
if (user == null) {
name.setText(null);
lastName.setText(null);
} else {
name.setText(user.getName());
lastName.setText(user.getLastName());
}findViewById
null check
name and lastName need to be set separately
Motivation
@Bind(R.id.name) TextView name
@Bind(R.id.lastName) TextView lastName;
protected void onCreate(Bundle savedInstanceState) {
setContentView(R.layout.activity_main);
ButterKnife.bind(this);
}
public void updateUI(User user) {
if (user == null) {
name.setText(null);
lastName.setText(null);
} else {
name.setText(user.getName());
lastName.setText(user.getLastName());
}
}Libraries like Butterknife can improve it
Databinding
<layout>
<data>
<variable name="user"
type="com.android.example.User"/>
</data>
<LinearLayout …>
<TextView android:text="@{user.name}"/>
<TextView android:text="@{user.lastName}"/>
</LinearLayout>
</layout>private ActivityMainBinding binding;
protected void onCreate(Bundle savedInstanceState) {
binding = DataBindingUtil.setContentView(
this, R.layout.activity_main);
}
public void updateUI(User user) {
binding.setUser(user);
}activity_main.xml:
Expression language
Generated class
Call this instead of activity.setContentView
Declare variable
Databinding Expression language
mostly Java
- Mathematical + - / * %
- String concatenation +
- Logical && ||
- Binary & | ^
- Unary + - ! ~
- Shift >> >>> <<
- Comparison == > < >= <=
- instanceof
- Grouping ()
- Literals - character, String, numeric, null
- Cast
- Method calls
- Field access
- Array access []
- Ternary operator ?:
Missing operators: this, super, new
Resources:
<TextView android:text='@{user.isMale ? @string/male : @string/female}' /><data>
<import type="android.view.View"/>
</data>
...
<TextView android:visibility="@{user.isAdult ? View.VISIBLE : View.GONE}" .../>Imports:
Variables:
<data>
<import type="com.example.User"/>
<import type="java.util.List"/>
<variable name="user" type="User"/>
<variable name="userList" type="List<User>"/>
</data>No NullPointerException
{
"user": {
"name": "John"
}
}if(response != null && response.user != null) {
nameView.setText(response.user.name);
}android:text="@{response.user.name}"Extra functionality
Null coalescing
textView.setText(user.name != null
? user.name : "unknown");android:text='@{user.name ?? "unknown"}'becomes
becomes
Observable Objects
public class User extends BaseObservable {
private String firstName;
@Bindable
public String getFirstName() {
return this.firstName;
}
public void setFirstName(String firstName) {
this.firstName = firstName;
notifyPropertyChanged(BR.firstName);
}
}<TextView android:text="@{user.firstName}" />extend BaseObservable or implement Observable
Annotate fields with @Bindable
Notify of field change
Observable fields
public class User {
public final ObservableField<String> firstName =
new ObservableField<>();
public final ObservableInt age = new ObservableInt();
}
user.firstName.set("John");
int age = user.age.get();<TextView android:text="@{user.firstName}" />
<TextView android:text="@{user.age}" />ObservableFields are implemented for all primitives and for Objects
call get and set
reference the fields in XML
How to set it up?
buildscript {
repositories {
jcenter()
}
dependencies {
classpath 'com.android.tools.build:gradle:1.3.1'
classpath 'com.android.databinding:dataBinder:1.0-rc4'
}
}<LinearLayout …>
<TextView .../>
<TextView .../>
</LinearLayout>activity_main.xml:
<layout>
<data>
...
</data>
<LinearLayout …>
<TextView .../>
<TextView .../>
</LinearLayout>
</layout>MainActivity.java:
ActivityMainBinding binding =
DataBindingUtil.setContentView(
this, R.layout.activity_main);setContentViev(R.layout.activity_main);becomes
becomes
How it works?
All code generation and expression parsing happens at compile time => if an expression has error the project won't compile
No reflection, no runtime overhead
Performance
The compiler needs to traverse the views once - no findViewById needed
textView = (TextView) findViewById(R.id.myTextView);textView = binding.myTextView;Expressions are cached
<TextView android:text='@{"Hello " + user.isMale ? @string/male : @string/female}' />
<TextView android:text='@{"Goodbye " + user.isMale ? @string/male : @string/female}' />UI updates are batched together.
Bindings can be updated on ANY thread.
becomes
Test project
Databinding Summary
- Eliminates SO MUCH boilerplate
- Is in support library
- Compile-time validation
- Performance is fantastic
- Don't need to update views on UI thread
- Models are the Single Source Of Truth
+
-
- IDE integration
- IDE integration
- IDE integration
Links
Yigit Boyar and George Mount: Databinding talk
Official Databinding guide:
Android Developer Backstage podcast: Databinding
http://androidbackstage.blogspot.com/2015/09/episode-35-data-bound.html
Droidcon NYC 2015 - Data Binding Techniques
Thank you!
Questions?
Android Databinding
By Denis Kniazhev
Android Databinding
Android Databinding basics
