Advance DataBinding in Android

In earlier posts we have already seen

Today we will discuss more about Advance DataBinding

Binding Events :

Events will be bound to handler methods directly, like we used to do it with android:onClick. Only change will be we have to take reference of our interface(handler).

public class MyEventListener {
    public void onClickButton1(View view) { ... }
    public void onClickButton2(View view) { ... }
}

public class MyEventListener {

public void onClickButton1(View view) { ... }

public void onClickButton2(View view) { ... }

}

Assign event to a view with binding method

<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android">
   <data>
       <variable name="handler" type="com.androidgig.MyEventListener"/>
   </data>
   <LinearLayout
       android:orientation="vertical"
       android:layout_width="match_parent"
       android:layout_height="match_parent">

       <Button android:layout_width="wrap_content"
           android:layout_height="wrap_content"
           android:text="@{user.firstName}"
           android:onClick="@{handler.onClickButton1}"/>
      
   </LinearLayout>
</layout>

<?xml version="1.0" encoding="utf-8"?>

<data>

</data>

<LinearLayout

android:orientation="vertical"

android:layout_width="match_parent"

android:layout_height="match_parent">

<Button android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:text="@{user.firstName}"

android:onClick="@{handler.onClickButton1}"/>

</LinearLayout>

</layout>

This will not work until you set handler in binding class in your Activity or Fragment.

binding.setHandler(this);

1	binding.setHandler(this);

Passing custom arguments with onClick using lambda expression.

public interface MyClickListener {
    public void onButtonClick1(User user);
}

public interface MyClickListener {

public void onButtonClick1(User user);

}

Pass whole model class from your view onClick.

<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android">

    <data>
        <variable
            name="handler"
            type="com.androidgig.MyClickListener"/>
        <variable
            name="user"
            type="com.androidgig.advancedatabinding.User"/>
    </data>

    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <Button
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:onClick="@{() -> handler.onButtonClick1(user)}" />
    </RelativeLayout>
</layout>

<?xml version="1.0" encoding="utf-8"?>

<data>

<variable

name="handler"

type="com.androidgig.MyClickListener"/>

<variable

name="user"

type="com.androidgig.advancedatabinding.User"/>

</data>

<RelativeLayout

android:layout_width="match_parent"

android:layout_height="match_parent">

<Button

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:onClick="@{() -> handler.onButtonClick1(user)}" />

</RelativeLayout>

</layout>

It will pass whole model class with values to listener method.

Import pre-defined class

<data>
    <import type="android.view.View"/>
</data>

<data>

</data>

use it in your layout to hide/show view

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="@{user.firstName}"
    android:visibility="@{user.firstName.length()>0 ? View.VISIBLE : View.GONE}"/>

<TextView

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:text="@{user.firstName}"

android:visibility="@{user.firstName.length()>0 ? View.VISIBLE : View.GONE}"/>

Expression Language

The expression language looks a lot like a Java expression. These are the same:

Mathematical + – / * %
String concatenation +
Logical && ||
Binary & | ^
Unary + – ! ~
Shift >> >>> <<
Comparison == > < >= <=
instanceof
Grouping ()
Literals – character, String, numeric, null
Cast
Method calls
Field access
Array access [ ]
Ternary operator ? :

you can refer this for more details on this.

Example

android:text="@{`Hello ` + user.firstName}"
android:visibility="@{user.gender==0 ? View.VISIBLE : View.GONE}"
android:text="@{user.age > 18 ? `Adult` : `Child`}"

android:text="@{`Hello ` + user.firstName}"

android:visibility="@{user.gender==0 ? View.VISIBLE : View.GONE}"

android:text="@{user.age > 18 ? `Adult` : `Child`}"

Null Coalescing Operator

android:text="@{user.displayName ?? (user.firstName + ` ` + user.lastName)}"

1	android:text="@{user.displayName ?? (user.firstName + ` ` + user.lastName)}"

If user.displayName is null it will set firstName and lastName as text, else displayName, it is equivalent to

android:text="@{user.displayName != null ? user.displayName : (user.firstName + ` ` + user.lastName)}"

1	android:text="@{user.displayName != null ? user.displayName : (user.firstName + ` ` + user.lastName)}"

Referencing other view’s property

<Button android:id="@+id/btn_submit"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:visibility="@{user.displayName!=null ? View.VISIBLE : View.GONE}"/>

<TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:visibility="@{btnSubmit.visibility}"/>

<Button android:id="@+id/btn_submit"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:visibility="@{user.displayName!=null ? View.VISIBLE : View.GONE}"/>

<TextView

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:visibility="@{btnSubmit.visibility}"/>

Referencing Resources

You can access resources also, it can be anything like string, drawable, dimen…

android:padding="@{user.age > 18 ? @dimen/adultPadding : @dimen/childPadding}"
android:hint="@{@string/firstName}"

1 2	android:padding="@{user.age > 18 ? @dimen/adultPadding : @dimen/childPadding}" android:hint="@{@string/firstName}"

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Ravi Rupareliya

He is author of Android Gig. He loves to explore new technologies and have worked on Android, React Native, Action on Google and Flutter.

Advance DataBinding in Android

Binding Events :

Passing custom arguments with onClick using lambda expression.

Import pre-defined class

Expression Language

Example

Null Coalescing Operator

Referencing other view’s property

Referencing Resources

Ravi Rupareliya

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