android {viewBinding {enabled = true}
}

public final class ActivityMainBinding implements ViewBinding {@NonNullprivate final ConstraintLayout rootView;@NonNullpublic final Button tv;private ActivityMainBinding(@NonNull ConstraintLayout rootView, @NonNull Button tv) {this.rootView = rootView;this.tv = tv;}@Override@NonNullpublic ConstraintLayout getRoot() {return rootView;}@NonNullpublic static ActivityMainBinding inflate(@NonNull LayoutInflater inflater) {return inflate(inflater, null, false);}@NonNullpublic static ActivityMainBinding inflate(@NonNull LayoutInflater inflater,@Nullable ViewGroup parent, boolean attachToParent) {View root = inflater.inflate(R.layout.activity_main, parent, false);if (attachToParent) {parent.addView(root);}return bind(root);}@NonNullpublic static ActivityMainBinding bind(@NonNull View rootView) {// The body of this method is generated in a way you would not otherwise write.// This is done to optimize the compiled bytecode for size and performance.String missingId;missingId: {Button tv = rootView.findViewById(R.id.tv);if (tv == null) {missingId = "tv";break missingId;}return new ActivityMainBinding((ConstraintLayout) rootView, tv);}...}
}

> Task :app:dataBindingMergeDependencyArtifactsDebug UP-TO-DATE
> Task :app:dataBindingMergeGenClassesDebug UP-TO-DATE
> ...
> Task :app:dataBindingGenBaseClassesDebug

public boolean processResources(final ResourceInput input, boolean isViewBindingEnabled) throws ParserConfigurationException, SAXException, XPathExpressionException,IOException
{...// 文件处理 callbackProcessFileCallback callback = new ProcessFileCallback(){...// 是否是增量编译if (input.isIncremental()) {// 增量编译文件处理processIncrementalInputFiles(input, callback);} else {// 全量编译文件处理processAllInputFiles(input, callback);}...}

 private static void processAllInputFiles(ResourceInput input, ProcessFileCallback callback)throws IOException, XPathExpressionException, SAXException, ParserConfigurationException {...for (File firstLevel : input.getRootInputFolder().listFiles()) {if (firstLevel.isDirectory()) {// ①、判断 firstLevel.getName() 的 startWith 是否为 layoutif (LAYOUT_FOLDER_FILTER.accept(firstLevel, firstLevel.getName())) {// ②、创建 subPath callback.processLayoutFolder(firstLevel);// ③、遍历 firstLevel 目录下面的所有文件，满足 toLowerCase().endsWith(".xml");for (File xmlFile : firstLevel.listFiles(XML_FILE_FILTER)) {// ④、处理布局文件callback.processLayoutFile(xmlFile);}} else {...}

 public boolean processSingleFile(@NonNull RelativizableFile input, @NonNull File output,boolean isViewBindingEnabled) throws ParserConfigurationException, SAXException, XPathExpressionException,IOException {// ①、解析 xmlfinal ResourceBundle.LayoutFileBundle bindingLayout = LayoutFileParser.parseXml(input, output, mResourceBundle.getAppPackage(), mOriginalFileLookup,isViewBindingEnabled);...// ②、缓存起来mResourceBundle.addLayoutBundle(bindingLayout, true);return true;
}

 @Nullable
public static ResourceBundle.LayoutFileBundle parseXml(@NonNull final RelativizableFile input,@NonNull final File outputFile, @NonNull final String pkg,@NonNull final LayoutXmlProcessor.OriginalFileLookup originalFileLookup,boolean isViewBindingEnabled){...return parseOriginalXml(RelativizableFile.fromAbsoluteFile(originalFile, input.getBaseDir()),pkg, encoding, isViewBindingEnabled);
}

private static ResourceBundle.LayoutFileBundle parseOriginalXml(@NonNull final RelativizableFile originalFile, @NonNull final String pkg,@NonNull final String encoding, boolean isViewBindingEnabled)throws IOException {...// ①、是否是 databindingif (isBindingData) {data = getDataNode(root);rootView = getViewNode(original, root); } else if (isViewBindingEnabled) { // ②、viewBinding 是否开启data = null;rootView = root;// xml 的根元素} else {return null;}...// 生成 bundleResourceBundle.LayoutFileBundle bundle =new ResourceBundle.LayoutFileBundle(originalFile, xmlNoExtension, original.getParentFile().getName(), pkg,isMerge, isBindingData, getViewName(rootView));final String newTag = original.getParentFile().getName() + '/' + xmlNoExtension;// viewBinding 不会 解析 dataparseData(original, data, bundle);// ③、解析表达式parseExpressions(newTag, rootView, isMerge, bundle);return bundle;

// xml 的输出目录
public void writeLayoutInfoFiles(File xmlOutDir) throws JAXBException {writeLayoutInfoFiles(xmlOutDir, mFileWriter);
}
public void writeLayoutInfoFiles(File xmlOutDir, JavaFileWriter writer) throws JAXBException {// ①、遍历收集的 layout filefor (ResourceBundle.LayoutFileBundle layout : mResourceBundle.getAllLayoutFileBundlesInSource()) {writeXmlFile(writer, xmlOutDir, layout);}...
}
private void writeXmlFile(JavaFileWriter writer, File xmlOutDir,ResourceBundle.LayoutFileBundle layout)throws JAXBException {// ②、生成文件名String filename = generateExportFileName(layout);// ③、写文件writer.writeToFile(new File(xmlOutDir, filename), layout.toXML());}

<?xml version="1.0" encoding="utf-8" standalone="yes"?>
<Layout directory="layout" filePath="/Users/codelang/project/app/src/main/res/layout/activity_main.xml"isBindingData="false"isMerge="false" layout="activity_main" modulePackage="com.codelang.viewBinding"rootNodeType="androidx.constraintlayout.widget.ConstraintLayout"><Targets><Target tag="layout/activity_main_0"view="androidx.constraintlayout.widget.ConstraintLayout"><Expressions /><location endLine="31" endOffset="51" startLine="1" startOffset="0" /></Target><Target id="@+id/tv" view="Button"><Expressions /><location endLine="16" endOffset="51" startLine="8" startOffset="4" /></Target></Targets>
</Layout>

@Suppress("unused")// used by tools
class BaseDataBinder(val input : LayoutInfoInput) {init {input.filesToConsider.forEach {it.inputStream().use {// 又将上面收集的 layout，将 xml 转成 LayoutFileBundleval bundle = LayoutFileBundle.fromXML(it)// 缓存进 ResourceBundleresourceBundle.addLayoutBundle(bundle, true)}}...}

@Suppress("unused")// used by android gradle plugin
fun generateAll(writer : JavaFileWriter) {// 拿到所有的 LayoutFileBundle，并根据文件名进行分组排序val layoutBindings = resourceBundle.allLayoutFileBundlesInSource.groupBy(LayoutFileBundle::getFileName)// 遍历 layoutBindingslayoutBindings.forEach { layoutName, variations ->// 将 LayoutFileBundle 信息包装成 BaseLayoutModelval layoutModel = BaseLayoutModel(variations)val javaFile: JavaFileval classInfo: GenClassInfoLog.GenClass// 当前是否是 databindingif (variations.first().isBindingData) {...} else {// ①、不是的话，按照 ViewBinding 处理val viewBinder = layoutModel.toViewBinder()// ②、生成 java file 文件javaFile = viewBinder.toJavaFile(useLegacyAnnotations = !useAndroidX)...}writer.writeToFile(javaFile)...}

// ①、最终会调用到 JavaFileGenerator 的 create 方法
fun ViewBinder.toJavaFile(useLegacyAnnotations: Boolean = false) =JavaFileGenerator(this, useLegacyAnnotations).create()private class JavaFileGenerator(private val binder: ViewBinder,private val useLegacyAnnotations: Boolean) {// 最终会调用生成 javaFile 方法，生成的类信息主要看 typeSpec 方法fun create() = javaFile(binder.generatedTypeName.packageName(), typeSpec()) {addFileComment("Generated by view binder compiler. Do not edit!")}

private fun typeSpec() = classSpec(binder.generatedTypeName) {addModifiers(PUBLIC, FINAL)val viewBindingPackage = if (useLegacyAnnotations) "android" else "androidx"addSuperinterface(ClassName.get("$viewBindingPackage.viewbinding", "ViewBinding"))// TODO determine if we can elide the separate root field if the root tag has an ID.addField(rootViewField())addFields(bindingFields())addMethod(constructor())addMethod(rootViewGetter())if (binder.rootNode is RootNode.Merge) {addMethod(mergeInflate())} else {addMethod(oneParamInflate())addMethod(threeParamInflate())}addMethod(bind())
}