DataBindingのコードを読む - DroidKaigi 2018

DataBindingのコードを読む
DroidKaigi 2018

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About me
• Kenji Abe
• Android/iOS Developer
• Twitter: STAR_ZERO
• GitHub: STAR-ZERO

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コントリビュートしました
• https://android.googlesource.com/platform/frameworks/data-
binding/+log/studio-master-dev

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話すこと
• DataBindingのコードから仕組みを解説
• Gradle Plugin
• Annotation Processor
• コード生成・実行
※Android Gradle Plugin 3.0を対象してます

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DataBindingのコード取得とデバッグ
• ブログにまとめておきました
• https://goo.gl/o68Ekt

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Gradle Plugin

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Gradle Plugin
• https://android.googlesource.com/platform/
tools/base/+/gradle_3.0.0
• build-system/gradle
• build-system/gradle-api
• build-system/gradle-core

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Gradle Plugin
• 依存ライブラリの追加
• タスク追加
• レイアウトファイルのパース

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依存ライブラリの追加
• com.android.databinding:library
• com.android.databinding:baseLibrary
• com.android.databinding:adapters
• com.android.databinding:compiler

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com.android.databinding:library
• DataBindingUtil
• BaseObservable
• ObservableField
https://android.googlesource.com/platform/frameworks/
data-binding/+/gradle_3.0.0/extensions/library/

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com.android.databinding:baseLibrary
• @Bindable
• @BindingAdapter
• @InverseBindingAdapter
data-binding/+/gradle_3.0.0/baseLibrary/

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com.android.databinding:adapters
• ViewBindingAdapter
• TextViewBindingAdapter
• CompoundButtonBindingAdapter
data-binding/+/gradle_3.0.0/extensions/baseAdapters/

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com.android.databinding:compiler
• Annotation Processor
• コード生成
data-binding/+/gradle_3.0.0/compiler/

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• https://android.googlesource.com/platform/tools/base/+/gradle_3.0.0/build-system/gradle-
core/src/main/java/com/android/build/gradle/internal/TaskManager.java
依存ライブラリの追加
public abstract class TaskManager {
// ...
public void addDataBindingDependenciesIfNecessary(DataBindingOptions options) {
if (!options.isEnabled()) {
return;
}
String version = MoreObjects.firstNonNull(options.getVersion(),
dataBindingBuilder.getCompilerVersion());
project.getDependencies()
.add(
"api",
SdkConstants.DATA_BINDING_LIB_ARTIFACT
+ ":"
+ dataBindingBuilder.getLibraryVersion(version));
.add(
"api",
SdkConstants.DATA_BINDING_BASELIB_ARTIFACT
+ ":"
+ dataBindingBuilder.getBaseLibraryVersion(version));
.add(
"annotationProcessor",
SdkConstants.DATA_BINDING_ANNOTATION_PROCESSOR_ARTIFACT + ":" + version);
if (options.isEnabledForTests() || this instanceof LibraryTaskManager) {
project.getDependencies().add("androidTestAnnotationProcessor",

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Gradle Plugin
• タスク追加

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タスク追加
• dataBindingExportBuildInfoタスクが追加
• DataBindingInfo.javaを生成する

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DataBindingInfo
• 空のクラス
• ここの@BindingBuildInfoが 
Annotation Processorで処理される
@BindingBuildInfo(buildId="8c129f13-798b-4137-8327-f76a34f6a51f")
public class DataBindingInfo {}

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タスク追加
• https://android.googlesource.com/platform/tools/base/+/gradle_3.0.0/build-system/gradle-
core/src/main/java/com/android/build/gradle/internal/TaskManager.java
public abstract class TaskManager {
// ...
protected void createDataBindingTasksIfNecessary(@NonNull TaskFactory tasks,
@NonNull VariantScope scope) {
if (!extension.getDataBinding().isEnabled()) {
return;
}
VariantType type = scope.getVariantData().getType();
boolean isTest = type == VariantType.ANDROID_TEST || type == VariantType.UNIT_TEST;
if (isTest && !extension.getDataBinding().isEnabledForTests()) {
BaseVariantData testedVariantData = scope.getTestedVariantData();
if (testedVariantData.getType() != LIBRARY) {
return;
}
}
dataBindingBuilder.setDebugLogEnabled(getLogger().isDebugEnabled());
AndroidTask exportBuildInfo = androidTasks
.create(tasks, new DataBindingExportBuildInfoTask.ConfigAction(scope));
exportBuildInfo.dependsOn(tasks, scope.getMergeResourcesTask());
exportBuildInfo.dependsOn(tasks, scope.getSourceGenTask());
scope.setDataBindingExportBuildInfoTask(exportBuildInfo);
}
}

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タスク追加
• https://android.googlesource.com/platform/frameworks/data-binding/+/gradle_3.0.0/
compilerCommon/src/main/java/android/databinding/tool/LayoutXmlProcessor.java
public class LayoutXmlProcessor {
// ...
public void writeEmptyInfoClass() {
final Class annotation = BindingBuildInfo.class;
String classString = "package " + RESOURCE_BUNDLE_PACKAGE + ";\n\n" +
"import " + annotation.getCanonicalName() + ";\n\n" +
"@" + annotation.getSimpleName() + "(buildId=\"" + mBuildId + "\")\n" +
"public class " + CLASS_NAME + " {}\n";
mFileWriter.writeToFile(RESOURCE_BUNDLE_PACKAGE + "." + CLASS_NAME, classString);
}
}

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Gradle Plugin
• タスク追加

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レイアウトファイルのパース
• mergeDebugResourceタスクで実行される
• レイアウトファイルのタグあるもの
をパースして、新しくXMLファイルを生成する

xmlns:app="http://schemas.android.com/apk/res-auto">

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directory="layout"
isMerge="false"
layout="activity_main" modulePackage="com.star_zero.debugdatabinding">

false

変数
View
式
Two-way binding

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compilerCommon/src/main/java/android/databinding/tool/store/LayoutFileParser.java
public class LayoutFileParser {
// ...
private void parseExpressions(String newTag, final XMLParser.ElementContext rootView,
final boolean isMerge, ResourceBundle.LayoutFileBundle bundle) {
// ...
for (XMLParser.ElementContext parent : bindingElements) {
// ...
for (XMLParser.AttributeContext attr : XmlEditor.expressionAttributes(parent)) {
String value = escapeQuotes(attr.attrValue.getText(), true);
final boolean isOneWay = value.startsWith("@{");
final boolean isTwoWay = value.startsWith("@={");
if (isOneWay || isTwoWay) {
if (value.charAt(value.length() - 1) != '}') {
L.e("Expecting '}' in expression '%s'", attr.attrValue.getText());
}
final int startIndex = isTwoWay ? 3 : 2;
final int endIndex = value.length() - 1;
final String strippedValue = value.substring(startIndex, endIndex);
Location attrLocation = new Location(attr);
Location valueLocation = new Location();
// offset to 0 based
valueLocation.startLine = attr.attrValue.getLine() - 1;
valueLocation.startOffset = attr.attrValue.getCharPositionInLine() +
attr.attrValue.getText().indexOf(strippedValue);
valueLocation.endLine = attrLocation.endLine;
valueLocation.endOffset = attrLocation.endOffset - 2; // account for: "}
bindingTargetBundle.addBinding(escapeQuotes(attr.attrName.getText(), false),

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compilerCommon/src/main/java/android/databinding/tool/store/LayoutFileParser.java
public class LayoutFileParser {
// ...
private void parseData(File xml, XMLParser.ElementContext data,
ResourceBundle.LayoutFileBundle bundle) {
if (data == null) {
return;
}
for (XMLParser.ElementContext imp : filter(data, "import")) {
final Map attrMap = attributeMap(imp);
String type = attrMap.get("type");
String alias = attrMap.get("alias");
Preconditions.check(StringUtils.isNotBlank(type), "Type of an import cannot be empty."
+ " %s in %s", imp.toStringTree(), xml);
if (Strings.isNullOrEmpty(alias)) {
alias = type.substring(type.lastIndexOf('.') + 1);
}
bundle.addImport(alias, type, new Location(imp));
}
for (XMLParser.ElementContext variable : filter(data, "variable")) {
final Map attrMap = attributeMap(variable);
String type = attrMap.get("type");
String name = attrMap.get("name");
Preconditions.checkNotNull(type, "variable must have a type definition %s in %s",
variable.toStringTree(), xml);
Preconditions.checkNotNull(name, "variable must have a name %s in %s",
variable.toStringTree(), xml);
bundle.addVariable(name, type, new Location(variable), true);

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Gradle Plugin
おまけ

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ドキュメントに書いてないオプション
dataBinding {
enabled true
version "2.3.3"
addDefaultAdapters false
enabledForTests true
}

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Annotation Processor

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• https://android.googlesource.com/platform/
frameworks/data-binding/+/gradle_3.0.0/
compiler/

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• Bindingクラス生成
• BRクラス生成
• DataBinderMapperクラス生成
kotlinが使われてる

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compiler/src/main/java/android/databinding/annotationprocessor/ProcessDataBinding.java
@SupportedAnnotationTypes({
"android.databinding.BindingAdapter",
"android.databinding.InverseBindingMethods",
"android.databinding.InverseBindingAdapter",
"android.databinding.InverseMethod",
"android.databinding.Untaggable",
"android.databinding.BindingMethods",
"android.databinding.BindingConversion",
"android.databinding.BindingBuildInfo"}
)
/**
* Parent annotation processor that dispatches sub steps to ensure execution order.
* Use initProcessingSteps to add a new step.
*/
public class ProcessDataBinding extends AbstractProcessor {
private List mProcessingSteps;
private DataBindingCompilerArgs mCompilerArgs;
@Override
public boolean process(Set extends TypeElement> annotations, RoundEnvironment roundEnv) {
if (mProcessingSteps == null) {
readArguments();
initProcessingSteps();
}
if (mCompilerArgs == null) {
return false;
}
DataBindingInfo
のアノテーション

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• Viewへの反映を行うクラス
• レイアウトやアノテーションから生成される
Bindingクラス生成

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public class ActivityMainBinding extends ViewDataBinding {
@Nullable
private static final IncludedLayouts sIncludes;
@Nullable
private static final SparseIntArray sViewsWithIds;
static {
sIncludes = null;
sViewsWithIds = null;
}
@NonNull
private final LinearLayout mboundView0;
@NonNull
public final TextView textView1;
@Nullable
private ViewModel mViewModel;
public ActivityMainBinding(@NonNull DataBindingComponent bindingComponent, @NonNull View root) {
super(bindingComponent, root, 2);
final Object[] bindings = mapBindings(bindingComponent, root, 2, sIncludes, sViewsWithIds);
this.mboundView0 = (LinearLayout) bindings[0];
this.mboundView0.setTag(null);
this.textView1 = (TextView) bindings[1];
this.textView1.setTag(null);
setRootTag(root);
// listeners
invalidateAll();
}
@Override
public void invalidateAll() {
synchronized(this) {
mDirtyFlags = 0x4L;
}

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• レイアウトファイルをパースしたXMLファイル 
からBindingクラスを生成

isMerge="false"
layout="activity_main" modulePackage="com.star_zero.debugdatabinding">
type="com.star_zero.debugdatabinding.ViewModel">

view="android.support.constraint.ConstraintLayout">

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• import文の生成
• からプロパティ生成
• android:idがあるViewのフィールド作成
• @{}の式をパース
• 式のパースにはANTLR v4が使われている
• EventListenerの実装
• Viewに反映する処理
• BindingAdapterアノテーション
• set + XMLの属性名のメソッド

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compiler/src/main/kotlin/android/databinding/tool/writer/LayoutBinderWriter.kt
class LayoutBinderWriter(val layoutBinder : LayoutBinder) {
// ...
fun executePendingBindings() = kcode("") {
nl("@Override")
block("protected void executeBindings()") {
val tmpDirtyFlags = FlagSet(mDirtyFlags.buckets)
tmpDirtyFlags.localName = "dirtyFlags";
for (i in (0..mDirtyFlags.buckets.size - 1)) {
nl("${tmpDirtyFlags.type} ${tmpDirtyFlags.localValue(i)} = 0;")
}
block("synchronized(this)") {
for (i in (0..mDirtyFlags.buckets.size - 1)) {
nl("${tmpDirtyFlags.localValue(i)} = ${mDirtyFlags.localValue(i)};")
nl("${mDirtyFlags.localValue(i)} = 0;")
}
}
model.pendingExpressions.filter { it.needsLocalField }.forEach {
nl("${it.resolvedType.toJavaCode()} ${it.executePendingLocalName} = ${if (it.isVariable())
it.fieldName else it.defaultValue};")
}
L.d("writing executePendingBindings for %s", className)
do {
val batch = ExprModel.filterShouldRead(model.pendingExpressions)
val justRead = arrayListOf()
L.d("batch: %s", batch)
while (!batch.none()) {
val readNow = batch.filter { it.shouldReadNow(justRead) }
if (readNow.isEmpty()) {
throw IllegalStateException("do not know what I can read. bailing out $
{batch.joinToString("\n")}")
}
L.d("new read now. batch size: %d, readNow size: %d", batch.size, readNow.size)

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BRクラス生成
• @BindableからBRクラスを生成する
• notifyPropertyChangedで使う
public class BR {
public static final int _all = 0;
public static final int text = 1;
public static final int viewModel = 2;
}

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BRクラス生成
compiler/src/main/kotlin/android/databinding/tool/writer/BRWriter.kt
class BRWriter(properties: Set, val useFinal : Boolean) {
val indexedProps = properties.sorted().withIndex()
fun write(pkg : String): String = "package $pkg;${StringUtils.LINE_SEPARATOR}$klass"
val klass: String by lazy {
kcode("") {
val prefix = if (useFinal) "final " else "";
annotateWithGenerated()
block("public class BR") {
tab("public static ${prefix}int _all = 0;")
indexedProps.forEach {
tab ("public static ${prefix}int ${it.value} = ${it.index + 1};")
}
}
}.generate()
}
}

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DataBinderMapperクラス生成
• レイアウトとBindingクラスのマッピング
class DataBinderMapper {
final static int TARGET_MIN_SDK = 19;
public DataBinderMapper() {
}
public ViewDataBinding getDataBinder(DataBindingComponent bindingComponent,
View view,
int layoutId) {
switch(layoutId) {
case R.layout.activity_main:
return ActivityMainBinding.bind(view, bindingComponent);
}
return null;
}
// …
}

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DataBinderMapperクラス生成
compiler/src/main/kotlin/android/databinding/tool/writer/BindingMapperWriter.kt
class BindingMapperWriter(var pkg : String, var className: String,
val layoutBinders : List,
val compilerArgs: DataBindingCompilerArgs) {
// ...
fun write(brWriter : BRWriter) = kcode("") {
nl("package $pkg;")
nl("import ${compilerArgs.modulePackage}.BR;")
val extends = if (generateAsTest) "extends $appClassName" else ""
annotateWithGenerated()
block("class $className $extends") {
nl("final static int TARGET_MIN_SDK = ${compilerArgs.minApi};")
if (generateTestOverride) {
nl("static $appClassName mTestOverride;")
block("static") {
block("try") {
nl("mTestOverride = ($appClassName)
$appClassName.class.getClassLoader().loadClass(\"$pkg.$testClassName\").newInstance();")
}
block("catch(Throwable ignored)") {
nl("// ignore, we are not running in test mode")
nl("mTestOverride = null;")
}
}
}
nl("")

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コード生成・実行

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• notifyPropertyChanged
• executeBindings
• mDirtyFlags
• EventListener
• @BindingAdapter
• Two-way binding

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notifyPropertyChanged
• Viewへの変更通知を行う
public class ViewModel extends BaseObservable {
private String text;
@Bindable
public String getText() {
return text;
}
public void setText(String text) {
this.text = text;
notifyPropertyChanged(BR.text);
}
}

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• Activity
public class MainActivity extends AppCompatActivity {
private ActivityMainBinding binding;
private ViewModel viewModel = new ViewModel();
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
binding = DataBindingUtil.setContentView(
this, R.layout.activity_main);
binding.setViewModel(viewModel);
// ...
}
}

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• Bindingクラス
// ...
public void setViewModel(@Nullable ViewModel ViewModel) {
updateRegistration(2, ViewModel);
this.mViewModel = ViewModel;
mDirtyFlags |= 0x4L;
}
notifyPropertyChanged(BR.viewModel);
super.requestRebind();
}
}
通知できる状態をつくる

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• setViewModelをした状態（簡易版）
ActivityMainBinding(ViewDataBinding)
WeakListener
ViewModel
参照
参照

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• notifyPropertyChangedを実行
ActivityMainBinding(ViewDataBinding)
WeakListener
ViewModel
参照
参照
notifyProperty
Changed
View更新
executeBindings

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• executeBindings
• mDirtyFlags
• EventListener
• @BindingAdapter
• Two-way binding

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executeBindings
// …
@Override
protected void executeBindings() {
long dirtyFlags = 0;
dirtyFlags = mDirtyFlags;
mDirtyFlags = 0;
}
java.lang.String viewModelText = null;
ViewModel viewModel = mViewModel;
if ((dirtyFlags & 0x7L) != 0) {
if (viewModel != null) {
viewModelText = viewModel.getText();
}
}
TextViewBindingAdapter.setText(this.textView, viewModelText);
}
}
// …
}

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executeBindings
1. プロパティ変更通知
2. mDirtyFlagsをセット
3. Choreographer.postFrameCallback実行
4. 3のコールバックからexecuteBindings実行

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executeBindings
• Choreographer.postFrameCallbackによって 
次フレームで実行される
• https://developer.android.com/reference/android/view/
Choreographer.html#postFrameCallback(android.view.Choreographer.FrameCallback)

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executeBindings
• RecyclerView.ViewHolder
• 次のフレームで実行されるので、間違った
データでViewサイズの計算が行われる可能性
がある
• これを防ぐには直接executeBindingsを呼んで
即時反映させる
• https://medium.com/google-developers/android-data-binding-
recyclerview-db7c40d9f0e4

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• executeBindings
• mDirtyFlags
• EventListener
• @BindingAdapter
• Two-way binding

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mDirtyFlags
• プロパティの変更ビットフラグ
@Override
public void invalidateAll() {
mDirtyFlags = 0x10L;
}
requestRebind();
}
private boolean onChangeViewModelText1(ObservableField ViewModelText1, int fieldId) {
if (fieldId == BR._all) {
mDirtyFlags |= 0x1L;
}
return true;
}
return false;
}
@Override
// ...
TextViewBindingAdapter.setText(this.textView1, viewModelText1Get);
}
}
}

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mDirtyFlags
• longのビットフラグ
• プロパティが64を超える場合は新しい変数が 
作られる
• mDirtyFlags_1
• mDirtyFlags_2
• 1番左のビットはすべて変更フラグ
• 変数が複数ある場合は最後の変数の1番左

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• executeBindings
• mDirtyFlags
• EventListener
• @BindingAdapter
• Two-way binding

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EventListener
public class ViewModel {
public void onClick(View view) {
// ...
}
}
android:id="@+id/button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:onClick="@{viewModel::onClick}"
android:text="Button" />

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EventListener
• ViewBindingAdapterに定義
binding/+/gradle_3.0.0/extensions/baseAdapters/
@BindingMethods({
@BindingMethod(type = View.class,
attribute = "android:onClick",
method = "setOnClickListener"),
})
public class ViewBindingAdapter {
}

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EventListener
@Override
OnClickListener listener = null;
listener = new OnClickListenerImpl();
listener.setValue(viewModel);
button.setOnClickListener(listener);
}
public static class OnClickListenerImpl implements OnClickListener{
private ViewModel value;
public OnClickListenerImpl setValue(ViewModel value) {
this.value = value;
return value == null ? null : this;
}
@Override
public void onClick(android.view.View arg0) {
this.value.onClick(arg0);
}
}
}
ViewModelに定義したメソッド
EventListenerをセット
OnClickListenerを定義

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• executeBindings
• mDirtyFlags
• EventListener
• @BindingAdapter
• Two-way binding

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• カスタムセッター
• アノテーションで指定したメソッドが使われる
@BindingAdapter
public class CustomBinding {
@BindingAdapter("intValue")
public static void setIntValue(TextView view, int value) {
view.setText(String.valueOf(value));
}
}
@Override
// …
CustomBinding.setIntValue(this.textView, viewModelValueGet);
// ...
}
}
@BindingAdapterで定義したメソッド

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@BindingAdapter
• インスタンスメソッドも使える
public class SampleBindingAdapter {
private SimpleDateFormat format;
public SampleBindingAdapter(SimpleDateFormat format) {
this.format = format;
}
@BindingAdapter("dateValue")
public void setDate(TextView view, Date date) {
view.setText(format.format(date));
}
}
インスタンスメソッド
android:id="@+id/text"
android:layout_width="match_parent"
app:dateValue="@{viewModel.date}"/>

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@BindingAdapter
• DataBindingComponentというinterafaceが生成
される
package android.databinding;
public interface DataBindingComponent {
SampleBindingAdapter getSampleBindingAdapter();
}

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@BindingAdapter
• DataBindingComponentを実装する
public class MyComponent implements DataBindingComponent {
@Override
public SampleBindingAdapter getSampleBindingAdapter() {
SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd");
return new SampleBindingAdapter(format);
}
}

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@BindingAdapter
• DataBindingUtil.setContentViewに設定
• もしくはsetDefaultComponentでデフォルトを
設定
public class MainActivity extends AppCompatActivity {
private ActivityMainBinding binding;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
binding = DataBindingUtil.setContentView(
this, R.layout.activity_main, new MyComponent());
// デフォルトを指定したい場合
DataBindingUtil.setDefaultComponent(new MyComponent());
// ...
}
}
定義したComponentを指定

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@BindingAdapter
public ActivityMainBinding(
@NonNull DataBindingComponent bindingComponent,
@NonNull View root) {
super(bindingComponent, root, 2);
// ...
}
@Override
// ...
this.mBindingComponent.getSampleBindingAdapter()
.setDate(this.textView, viewModelValueGet);
}
}
setContentViewの
引数に渡したComponent

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• executeBindings
• mDirtyFlags
• EventListener
• @BindingAdapter
• Two-way binding

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Two-way binding
• @={} でTwo-way binding
• TextViewのはTextViewBindingAdapterで定義
binding/+/gradle_3.0.0/extensions/baseAdapters/
android:id="@+id/editText"
android:layout_width="match_parent"
android:text="@={viewModel.text}"/>

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Two-way binding
@BindingAdapter("android:text")
public static void setText(TextView view, CharSequence text) {
final CharSequence oldText = view.getText();
if (text == oldText || (text == null && oldText.length() == 0)) {
return;
}
// ...
view.setText(text);
}

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Two-way binding
private InverseBindingListener textAttrChanged = new InverseBindingListener() {
@Override
public void onChange() {
String callbackArg_0 = TextViewBindingAdapter.getTextString(editText);
// ...
viewModel.setText(callbackArg_0));
}
};
@Override
// …
TextViewBindingAdapter.setText(editText, viewModelText);
TextViewBindingAdapter.setTextWatcher(editText, null, null, null,
textAttrChanged);
}
}

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Two-way binding
@InverseBindingAdapter(attribute = "android:text",
event = "android:textAttrChanged")
public static String getTextString(TextView view) {
return view.getText().toString();
}

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Two-way binding
@Override
// ...
}
};
@Override
// …
textAttrChanged);
}
}
@InverseBindingAdapter
ViewModelに設定

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Two-way binding
@BindingAdapter(value = {"android:beforeTextChanged", "android:onTextChanged",
"android:afterTextChanged", "android:textAttrChanged"},
requireAll = false)
public static void setTextWatcher(TextView view,
final BeforeTextChanged before,
final OnTextChanged on,
final AfterTextChanged after,
final InverseBindingListener textAttrChanged) {
// ...
newValue = new TextWatcher() {
@Override
public void onTextChanged(CharSequence s, int start, int before, int count) {
if (textAttrChanged != null) {
textAttrChanged.onChange();
}
}
// ...
};
// ...
}
@InverseBindingAdapter
のevent
InverseBindingListener
値を反映したいタイミングでonChange

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Two-way binding
@Override
// ...
}
};
@Override
// …
textAttrChanged);
}
}
@BindingAdapter("android:textAttrChanged")

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まとめ

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まとめ
• コードを読むことで仕組みを深く知れる
• ドキュメントに載ってないことも分かる
• コード読むの大変だけどオススメ

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ありがとうございました

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DataBindingのコードを読む - DroidKaigi 2018

DataBindingのコードを読む - DroidKaigi 2018

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