From 98e01e78c91049bd1639e91120d3d0a841035554 Mon Sep 17 00:00:00 2001 From: Joe Fernandez Date: Wed, 27 May 2015 23:42:57 -0700 Subject: docs: M Preview - removing Data Binding doc file from preview section Change-Id: Ib056f31e33828702053ba54700e97d67a1554901 --- docs/html/preview/data-binding/guide.jd | 908 -------------------------------- 1 file changed, 908 deletions(-) delete mode 100644 docs/html/preview/data-binding/guide.jd (limited to 'docs') diff --git a/docs/html/preview/data-binding/guide.jd b/docs/html/preview/data-binding/guide.jd deleted file mode 100644 index 49b690f..0000000 --- a/docs/html/preview/data-binding/guide.jd +++ /dev/null @@ -1,908 +0,0 @@ -page.title=Data Binding Guide - -@jd:body -

Data Binding allows you write declarative layouts and minimize the glue code -that is necessary to bind your application logic and layouts.

- - -

Build Environment

- - -

Setting Up Work Environment:

- -

Data Binding EAP only supports gradle.

- -

To set up your application, unzip the provided bundle to a location. It has 3 -sections

- - - -

Add the following section to the project’s build.gradle file (not the module's -build.gradle) and replace with the absolute path of the bundle that you’ve unzipped in the previous step.

- -
-buildscript {
-   def eapFolder = '<BUNDLE_FOLDER>'
-   def Properties props = new Properties()
-   props.load(new FileInputStream("${eapFolder}/databinding.properties"))
-   props.mavenRepoDir = "${eapFolder}/${props.mavenRepoName}"
-   ext.config = props
-   repositories {
-       jcenter()
-       maven {
-           url config.mavenRepoDir
-       }
-   }
-   dependencies {
-       classpath "com.android.tools.build:gradle:1.1.3"
-       classpath "com.android.databinding:dataBinder:${config.snapshotVersion}"
-   }
-}
-allprojects {
-   repositories {
-       jcenter()
-       maven {
-           url config.mavenRepoDir
-       }
-   }
-}
-
- -

Next, add the following lines to the build.gradle -file of each module that will use data-binding. The application module must -have this, even if only its libraries use data binding.

- -
-apply plugin: 'com.android.databinding'
-dependencies {
-    compile "com.android.databinding:library:${config.snapshotVersion}"
-    compile "com.android.databinding:baseLibrary:${config.snapshotVersion}"
-    compile "com.android.databinding:adapters:${config.snapshotVersion}"
-    provided "com.android.databinding:annotationprocessor:${config.snapshotVersion}"
-}
-
- - -

Data Binding Layout Files

- - -

Writing your first data binding expressions:

- -

Data-binding layout files are slightly different and start with a root tag of -layout followed by a data element and a -view root element. This view element is what your root would -be in a non-binding layout file.A sample file looks like this:

- -
-<?xml version="1.0" encoding="utf-8"?>
-<layout xmlns:android="http://schemas.android.com/apk/res/android">
-   <data>
-       <variable name="user" type="com.example.User"/>
-   </data>
-   <LinearLayout
-       android:orientation="vertical"
-       android:layout_width="match_parent"
-       android:layout_height="match_parent">
-       <TextView android:layout_width="wrap_content"
-           android:layout_height="wrap_content"
-           android:text="@{user.firstName}"/>
-       <TextView android:layout_width="wrap_content"
-           android:layout_height="wrap_content"
-           android:text="@{user.lastName}"/>
-   </LinearLayout>
-</layout>
-
- -

The user variable within data describes a property that may be used within this layout.

- -
-<variable name="user" type="com.example.User"/>
-
- -

Expressions within the layout are written in the attribute properties using the -“@{}” syntax. Here, the TextView’s text is set to the firstName property of user:

-
-<TextView android:layout_width="wrap_content"
-          android:layout_height="wrap_content"
-          android:text="@{user.firstName}"/>
-
- - -

Data Object

- -

Let’s assume for now that you have a plain-old Java object (POJO) for User:

-
-public class User {
-   public final String firstName;
-   public final String lastName;
-   public User(String firstName, String lastName) {
-       this.firstName = firstName;
-       this.lastName = lastName;
-   }
-}
-
- -

This type of object has data that never changes. It is common in applications -to have data that is read once and never changes thereafter. It is also -possible to use a JavaBeans objects:

-
-public class User {
-   private final String firstName;
-   private final String lastName;
-   public User(String firstName, String lastName) {
-       this.firstName = firstName;
-       this.lastName = lastName;
-   }
-   public String getFirstName() {
-       return this.firstName;
-   }
-   public String getLastName() {
-       return this.lastName;
-   }
-}
-
- -

From the perspective of data binding, these two classes are equivalent. The -expression @{user.lastName} used for the TextView’s android:text attribute will access the firstName field in the former class and the getFirstName() method in the latter class. -

Binding Data

- -

By default, a Binding class will be generated based on the name of the layout -file, converting it to Pascal case and suffixing “Binding” to it. The above -layout file was activity_main.xml so the generate class was ActivityMainBinding. This class holds all the bindings from the layout properties (e.g. the user variable) to the layout’s Views and knows how to assign values for the binding -expressions.The easiest means for creating the bindings is to do it while inflating: -

- -
-@Override
-protected void onCreate(Bundle savedInstanceState) {
-   super.onCreate(savedInstanceState);
-   ActivityMainBinding binding = DataBindingUtil.setContentView(this, R.layout.main_activity);
-   User user = new User("Test", "User");
-   binding.setUser(user);
-}
-
- -

You’re done! Run the application and you’ll see Test User in the UI.Alternatively, you can get the view via: -

-MainActivityBinding binding = MainActivityBinding.inflate(getLayoutInflater());
-
- -

If you are using data binding items inside a ListView or RecyclerView adapter, -you may prefer to use: -

-ListItemBinding binding = ListItemBinding.inflate(layoutInflater, viewGroup,
-false);
-//or
-ListItemBinding binding = DataBindingUtil.inflate(layoutInflater, R.layout.list_item, viewGroup, false);
-
- - -

Layout Details

- - -

Imports

- -

Zero or more import elements may be used inside the data element. These allow easy reference to classes inside your layout file, just -like in Java. -

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

Now, View may be used within your binding expression: -

-<TextView
-   android:text="@{user.lastName}"
-   android:layout_width="wrap_content"
-   android:layout_height="wrap_content"
-   android:visibility="@{user.isAdult ? View.VISIBLE : View.GONE}"/>
-
- -

When there are class name conflicts, one of the classes may be renamed to an -“alias:”

-
-<import type="android.view.View"/>
-<import type="com.example.real.estate.View"
-        alias="Vista"/>
-
- -

Now, Vista may be used to reference the com.example.real.estate.View and View may be used to reference android.view.View within the layout file.Imported types may be used as type references in variables and expressions:

-
-<data>
-    <import type="com.example.User"/>
-    <import type="java.util.List"/>
-    <variable name="user" type="User"/>
-    <variable name="userList" type="List<User>"/>
-</data>
-…
-<TextView
-   android:text="@{((User)(user.connection)).lastName}"
-   android:layout_width="wrap_content"
-   android:layout_height="wrap_content"/>
-
- -

Imported types may also be used when referencing static fields and methods in -expressions:

-
-<data>
-    <import type="com.example.MyStringUtils"/>
-    <variable name="user" type="com.example.User"/>
-</data>
-…
-<TextView
-   android:text="@{MyStringUtils.capitalize(user.lastName)}"
-   android:layout_width="wrap_content"
-   android:layout_height="wrap_content"/>
-
- -

Just as in Java, java.lang.* is imported automatically.

-

Variables

- -

Any number of variable elements may be used inside the data element. Each variable element describes a property that may be set on the layout to be used in -binding expressions within the layout file.

-
-<data>
-    <import type="android.graphics.drawable.Drawable"/>
-    <variable name="user"  type="com.example.User"/>
-    <variable name="image" type="Drawable"/>
-    <variable name="note"  type="String"/>
-</data>
-
- -

The variable types are inspected at compile time, so if a variable implements Observable, observable collection, that should be reflected in the type. If the variable is a base class or - interface that does not implement the Observable* interface, the variables will not be observed!

- -

When there are different layout files for various configurations (e.g. -landscape or portrait), the variables will be combined. There must not be -conflicting variable definitions between these layout files.

- -

The generated binding class will have a setter and getter for each of the -described variables. The variables will take the default Java values until the -setter is called — null for reference types, 0 for int, false for boolean, etc.

- -

Custom Binding Class Names

- -

By default, a Binding class is generated based on the name of the layout file, -starting it with upper-case, removing underscores ( _ ) and capitalizing the -following letter and then suffixing “Binding”. This class will be placed in a -databinding package under the module package. For example, the layout file contact_item.xml will generate ContactItemBinding. If the module package is com.example.my.app, then it will be placed in com.example.my.app.databinding.

- -

Binding classes may be renamed or placed in different packages by adjusting the class attribute of the data element. For example:

-
-<data class="ContactItem">
-    ...
-</data>
-
- -

This generates the binding class as ContactItem in the databinding package in the module package. If the class should be -generated in a different package within the module package, it may be prefixed -with “.”:

-
-<data class=".ContactItem">
-    ...
-</data>
-
- -In this case, ContactItem is generated in the module package directly.Any package may be used if the full package is provided: -
-<data class="com.example.ContactItem">
-    ...
-</data>
-
- - -

Includes

- -

Variables may be passed into an included layout's binding from the containing -layout by using the application namespace and the variable name in an -attribute:

-
-<?xml version="1.0" encoding="utf-8"?>
-<layout xmlns:android="http://schemas.android.com/apk/res/android"
-        xmlns:bind="http://schemas.android.com/apk/res-auto">
-   <data>
-       <variable name="user" type="com.example.User"/>
-   </data>
-   <LinearLayout
-       android:orientation="vertical"
-       android:layout_width="match_parent"
-       android:layout_height="match_parent">
-       <include layout="@layout/name"
-           bind:user="@{user}"/>
-       <include layout="@layout/contact"
-           bind:user="@{user}"/>
-   </LinearLayout>
-</layout>
-
- -

Here, there must be a user variable in both the name.xml and contact.xml layout files.

-

Expression Language

- - -

Common Features

- -

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

- -

Examples:

-
-android:text="@{String.valueOf(index + 1)}"
-android:visibility="@{age < 13 ? View.GONE : View.VISIBLE}"
-android:transitionName='@{"image_" + id}'
-
- - -

Missing Operations

- -

A few operations are missing from the expression syntax that you can use in -Java.

- - -

Null Coalescing Operator

- -

The null coalescing operator (??) chooses the left operand if it is not null or the right if it is null.

-
-android:text="@{user.displayName ?? user.lastName}"
-
- -

This is functionally equivalent to:

-
-android:text="@{user.displayName != null ? user.displayName : user.lastName}"
-
- - -

Property Reference

- -

The first was already discussed in the Writing your first data binding expressions above: short form JavaBean references. When an expression references a -property on a class, it uses the same format for fields, getters, and -ObservableFields.

-
-android:text="@{user.lastName}"
-
- - -

Collections

- -

Common collections: arrays, lists, sparse lists, and maps, may be accessed -using the [] operator for convenience.

-
-<data>
-    <import type="android.util.SparseArray"/>
-    <import type="java.util.Map"/>
-    <import type="java.util.List"/>
-    <variable name="list" type="List<String>"/>
-    <variable name="sparse" type="SparseArray<String>"/>
-    <variable name="map" type="Map<String, String>"/>
-    <variable name="index" type="int"/>
-    <variable name="key" type="String"/>
-</data>
-…
-android:text="@{list[index]}"
-…
-android:text="@{sparse[index]}"
-…
-android:text="@{map[key]}"
-
-
- - -

String Literals

- -

When using single quotes around the attribute value, it is easy to use double -quotes in the expression:

-
-android:text='@{map["firstName"]}'
-
- -

It is also possible to use double quotes to surround the attribute value. When -doing so, String literals should either use the " or back quote (`).

-
-android:text="@{map[`firstName`}"
-android:text="@{map["firstName"]}"
-
- - -

Resources

- -

It is possible to access resources as part of expressions using the normal -syntax:

-
-android:padding="@{large? @dimen/largePadding : @dimen/smallPadding}"
-
- -

Format strings and plurals may be evaluated by providing parameters:

-
-android:text="@{@string/nameFormat(firstName, lastName)}"
-android:text="@{@plurals/banana(bananaCount)}"
-
- -

Some resources require explicit type evaluation.

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
TypeNormal ReferenceExpression Reference
-
-String[]
 -@array -@stringArray
-int[] -@array -@intArray
-TypedArray -@array -@typedArray
-Animator -@animator -@animator
-StateListAnimator -@animator -@stateListAnimator
- - -color int -
-@color
 -@color
-ColorStateList -@color -@colorStateList
- - - - -

Data Objects

- - -

Any plain old Java object (POJO) may be used for data binding, but modifying a -POJO will not cause the UI to update. The real power of data binding can be -used by giving your data objects the ability to notify when data changes. There -are three different data change notification mechanisms, Observable objects, ObservableFields, and observable collections.

- -

When one of these observable data object is bound to the UI and a property of -the data object changes, the UI will be updated automatically.

- -

Observable Objects

- - -

A class implementing android.databinding.Observable interface will allow the binding to attach a single listener to a bound object -to listen for changes of all properties on that object.

- -

The Observable interface has a mechanism to add and remove listeners, but notifying is up to -the developer. To make development easier, a base class, BaseObservable, was created to implement the listener registration mechanism. The data class -implementer is still responsible for notifying when the properties change. This -is done by assigning an Bindable annotation to the getter and notifying in the setter.

- -
-private static class User extends BaseObservable {
-   private String firstName;
-   private String lastName;
-   @Bindable
-   public String getFirstName() {
-       return this.firstName;
-   }
-   @Bindable
-   public String getFirstName() {
-       return this.lastName;
-   }
-   public void setFirstName(String firstName) {
-       this.firstName = firstName;
-       notifyPropertyChanged(BR.firstName);
-   }
-   public void setLastName(String lastName) {
-       this.lastName = lastName;
-       notifyPropertyChanged(BR.lastName);
-   }
-}
-
- -

The Bindable annotation generates an entry in the BR class file during compilation. The BR -class file will be generated in the module package.If the base class for data classes cannot be changed, the Observable interface may be implemented using the convenient PropertyChangeRegistry to store and notify listeners efficiently.

- -

ObservableFields

- -

A little work is involved in creating Observable classes, so developers who -want to save time or have few properties may use ObservableFields. -ObservableFields are self-contained observable objects that have a single -field. There are versions for all primitive types and one for reference types. -To use, create a public final field in the data class:

-
-private static class User extends BaseObservable {
-   public final ObservableField<String> firstName =
-       new ObservableField<>();
-   public final ObservableField<String> lastName =
-       new ObservableField<>();
-   public final ObservableInt age = new ObservableInt();
-}
-
- -

That's it! To access the value, use the set and get accessor methods:

-
-user.firstName.set("Google");
-int age = user.age.get();
-
- - -

Observable Collections

- -

Some applications use more dynamic structures to hold data. Observable - collections allow keyed access to these data objects.ObservableArrayMap is useful when the key is a reference type, such as String.

- -
-ObservableArrayMap<String, Object> user = new ObservableArrayMap<>();
-user.put("firstName", "Google");
-user.put("lastName", "Inc.");
-user.put("age", 17);
-
- -In the layout, the map may be accessed through the String keys: -
-<data>
-    <import type="android.databinding.ObservableMap"/>
-    <variable name="user" type="ObservableMap<String, Object>"/>
-</data>
-…
-<TextView
-   android:text='@{user["lastName"]}'
-   android:layout_width="wrap_content"
-   android:layout_height="wrap_content"/>
-<TextView
-   android:text='@{String.valueOf(1 + (Integer)user["age"])}'
-   android:layout_width="wrap_content"
-   android:layout_height="wrap_content"/>
-
- -

ObservableArrayList is useful when the key is an integer:

-
-ObservableArrayList<Object> user = new ObservableArrayList<>();
-user.add("Google");
-user.add("Inc.");
-user.add(17);
-
- -

In the layout, the list may be accessed through the indices:

-
-<data>
-    <import type="android.databinding.ObservableList"/>
-    <import type="com.example.my.app.Fields"/>
-    <variable name="user" type="ObservableList<Object>"/>
-</data>
-…
-<TextView
-   android:text='@{user[Fields.LAST_NAME]}'
-   android:layout_width="wrap_content"
-   android:layout_height="wrap_content"/>
-<TextView
-   android:text='@{String.valueOf(1 + (Integer)user[Fields.AGE])}'
-   android:layout_width="wrap_content"
-   android:layout_height="wrap_content"/>
-
- - -

Generated Binding

- -

The generated binding class links the layout variables with the Views within -the layout. As discussed earlier, the name and package of the Binding may be customized. The Generated binding classes all extend android.databinding.ViewDataBinding.

-

Creating

- -

The binding should be created soon after inflation to ensure that the View -hierarchy is not disturbed prior to binding to the Views with expressions -within the layout. There are a few ways to bind to a layout. The most common is -to use the static methods on the Binding class.The inflate method inflates the View hierarchy and binds to it all it one step. -There are versions that attach the View to its parent and that inflate without -attaching.

-
-MyLayoutBinding binding = MyLayoutBinding.inflate(this);
-MyLayoutBinding binding = MyLayoutBinding.inflate(viewGroup);
-
- -

If the layout was inflated using a different mechanism, it may be bound -separately:

-
-MyLayoutBinding binding = MyLayoutBinding.bind(viewRoot);
-
- -

Sometimes the binding cannot be known in advance. In such cases, the binding -can be created using the DataBindingUtil class:

-
-ViewDataBinding binding = DataBindingUtil.inflate(context, layoutId,
-    parent, attachToParent);
-ViewDataBinding binding = DataBindingUtil.bindTo(viewRoot, layoutId);
-
- - -

Views With IDs

- -

A public final field will be generated for each View with an ID in the layout. -The binding does a single pass on the View hierarchy, extracting the Views with -IDs. This mechanism can be faster than calling findViewById for several Views. For example:

-
-<layout xmlns:android="http://schemas.android.com/apk/res/android">
-   <data>
-       <variable name="user" type="com.example.User"/>
-   </data>
-   <LinearLayout
-       android:orientation="vertical"
-       android:layout_width="match_parent"
-       android:layout_height="match_parent">
-       <TextView android:layout_width="wrap_content"
-           android:layout_height="wrap_content"
-           android:text="@{user.firstName}"
-           android:id="@+id/firstName"/>
-       <TextView android:layout_width="wrap_content"
-           android:layout_height="wrap_content"
-           android:text="@{user.lastName}"           android:id="@+id/lastName"/>
-   </LinearLayout>
-</layout>
-
- -Will generate a binding class with: -
-public final TextView firstName;
-public final TextView lastName;
-
- -

IDs are not nearly as necessary as without data binding, but there are still -some instances where access to Views are still necessary from code.

-

Variables

- -

Each variable will be given a accessor methods.

-
-<data>
-    <import type="android.graphics.drawable.Drawable"/>
-    <variable name="user"  type="com.example.User"/>
-    <variable name="image" type="Drawable"/>
-    <variable name="note"  type="String"/>
-</data>
-
- -

will generate setters and getters in the binding:

-
-public abstract com.example.User getUser();
-public abstract void setUser(com.example.User user);
-public abstract Drawable getImage();
-public abstract void setImage(Drawable image);
-public abstract String getNote();
-public abstract void setNote(String note);
-
- - -

ViewStubs

- -

ViewStubs are a little different from normal Views. They start off invisible -and when they either are made visible or are explicitly told to inflate, they -replace themselves in the layout by inflating another layout.

- -

Because the ViewStub essentially disappears from the View hierarchy, the View -in the binding object must also disappear to allow collection. Because the -Views are final, a ViewStubProxy object takes the place of the ViewStub, giving -the developer access to the ViewStub when it exists and also access to the -inflated View hierarchy when the ViewStub has been inflated.

- -

When inflating another layout, a binding must be established for the new -layout. Therefore, the ViewStubProxy must listen to the ViewStub's -OnInflateListener and establish the binding at that time. Since only one can -exist, the ViewStubProxy allows the developer to set an OnInflateListener on it -that it will call after establishing the binding.

- -

Advanced Binding

- - -

Dynamic Variables

- -

At times, the specific binding class won't be known. For example, a -RecyclerView Adapter operating against arbitrary layouts won't know the -specific binding class. It still must assign the binding value during the -onBindViewHolder.

- -

In this example, all layouts that the RecyclerView binds to have an "item" -variable. The BindingHolder has a getBinding method returning the ViewDataBinding base.

-
-public void onBindViewHolder(BindingHolder holder, int position) {
-   final T item = mItems.get(position);
-   holder.getBinding().setVariable(BR.item, item);
-   holder.getBinding().executePendingBindings();
-}
-
- - -

Immediate Binding

- -

When a variable or observable changes, the binding will be scheduled to change -before the next frame. There are times, however, when binding must be executed -immediately. To force execution, use the executePendingBindings() method.

-

Attribute Setters

- -

Whenever a bound value changes, the generated binding class must call a setter -method on the View with the binding expression. The data binding framework has -ways to customize which method to call to set the value.

-

Automatic Setters

- -For an attribute, data binding tries to find the method setAttribute. The -namespace for the attribute does not matter, only the attribute name itself. - -

For example, an expression associated with TextView's attribute android:text will look for a setText(String). If the expression returns an int, data -binding will search for a setText(int) method. Be careful to have the -expression return the correct type, casting if necessary.Note that data binding will work even if no attribute exists with the given -name. You can then easily "create" attributes for any setter by using data -binding. For example, support DrawerLayout doesn't have any attributes, but -plenty of setters. You can use the automatic setters to use one of these.

-
-<android.support.v4.widget.DrawerLayout
-    android:layout_width="wrap_content"
-    android:layout_height="wrap_content"
-    app:scrimColor="@{@color/scrim}"
-    app:drawerListener="@{fragment.drawerListener}"/>
-
- - -

Renamed Setters

- -

Some attributes have setters that don't match by name. For these methods, an -attribute may be associated with the setter through BindingMethods annotation. -This must be associated with a class and contains BindingMethod annotations, -one for each renamed method. For example, the android:tint attribute is really associated with setImageTintList, not setTint.

-
-@BindingMethods({
-       @BindingMethod(type = "android.widget.ImageView",
-                      attribute = "android:tint",
-                      method = "setImageTintList"),
-})
-
- -

It is unlikely that developers will need to rename setters; the android -framework attributes have already been implemented.

-

Custom Setters

- -

Some attributes need custom binding logic. For example, there is no associated -setter for the android:paddingLeft attribute. Instead, setPadding(left, top, right, bottom) exists. A static -binding adapter method with the BindingAdapter annotation allows the developer -to customize how a setter for an attribute is called.

- -

The android attributes have already had BindingAdapters created. For example, -here is the one for paddingLeft:

-

-@BindingAdapter("android:paddingLeft")
-public static void setPaddingLeft(View view, int padding) {
-   view.setPadding(padding,
-                   view.getPaddingTop(),
-                   view.getPaddingRight(),
-                   view.getPaddingBottom());
-}
-
- -

Binding adapters are useful for other types of customization. For example, a - custom loader can be called off-thread to load an image.

- -

Developer-created binding adapters will override the data binding default -adapters when there is a conflict.

- -

You can also have adapters that receive multiple parameters.

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

This adapter will be called if both imageUrl and error are used for an ImageView and imageUrl is a string and error is a drawable.

- - -
-<ImageView app:imageUrl=“@{venue.imageUrl}”
-app:error=“@{@drawable/venueError}”/>
-
- - -

Converters

- - -

Object Conversions

- -

When an Object is returned from a binding expression, a setter will be chosen -from the automatic, renamed, and custom setters. The Object will be cast to a -parameter type of the chosen setter.

This is a convenience for those using ObservableMaps to hold data. for example:

-
-<TextView
-   android:text='@{userMap["lastName"]}'
-   android:layout_width="wrap_content"
-   android:layout_height="wrap_content"/>
-
- -

The userMap returns an Object and that Object will be automatically cast to -parameter type found in the setter setText(CharSequence). When there may be confusion about the parameter type, the developer will need -to cast in the expression.

-

Custom Conversions

- -

Sometimes conversions should be automatic between specific types. For example, -when setting the background:

-
-<View
-   android:background="@{isError ? @color/red : @color/white}"
-   android:layout_width="wrap_content"
-   android:layout_height="wrap_content"/>
-
- -

Here, the background takes a Drawable, but the color is an integer. Whenever a Drawable is expected and an integer is returned, the int should be converted to a ColorDrawable. This conversion is done using a static method with a BindingConversion -annotation:

-
-@BindingConversion
-public static ColorDrawable convertColorToDrawable(int color) {
-   return new ColorDrawable(color);
-}
-
- -

Note that conversions only happen at the setter level, so it is not allowed to mix types like this:

-
-<View
-   android:background="@{isError ? @drawable/error : @color/white}"
-   android:layout_width="wrap_content"
-   android:layout_height="wrap_content"/>
-
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