先建三个module，分别为Butterknife ButterKnife-Annotions ButterKnife-compiler,其中butterknife为Android Module其余的都是Java Module

。

ButterKnife-Annotions：提供注解。

ButterKnife-compiler: 依赖ButterKnife-Annotions,生成代码的module。

Butterknife：应用直接使用的库。

Butterknife-Annotions添加注解

@Retention(CLASS)

@Target(FIELD)

public @interface BindView {

int value();

}

ButterKnife-compiler添加依赖

dependencies {

implementation fileTree(include: ['*.jar'], dir: 'libs')

implementation 'com.google.auto.service:auto-service:1.0-rc3'

implementation 'com.squareup:javapoet:1.9.0'

implementation project(':ButterKnife-Annotions')

}

写一个生成代码的类ButterKnifeProcessor继承AbstractProcessor

public class ButterKnifeProcessor extends AbstractProcessor {

@Override

public boolean process(Set extends TypeElement> annotations, RoundEnvironment roundEnv) {

return false;

}

}

我们的步骤是:

添加注解@AutoService(Processor.class)

确定好我们需要生成代码的JAVA版本

确定生成代码

生成代码

import com.zzw.butterknife_annotions.BindView;

import java.lang.annotation.Annotation;

import java.util.LinkedHashSet;

import java.util.Set;

import javax.annotation.processing.AbstractProcessor;

import javax.annotation.processing.RoundEnvironment;

import javax.lang.model.SourceVersion;

import javax.lang.model.element.TypeElement;

//1. 添加注解 @AutoService(Processor.class)

@AutoService(Processor.class)

public class ButterKnifeProcessor extends AbstractProcessor {

//2. 指定处理的版本 >1.7

@Override

public SourceVersion getSupportedSourceVersion() {

//最高版本

return SourceVersion.latestSupported();

}

//3. 指定处理的注解

@Override

public Set getSupportedAnnotationTypes() {

Set types = new LinkedHashSet<>();

for (Class extends Annotation> annotation : getSupportedAnnotations()) {

types.add(annotation.getCanonicalName());

}

return types;

}

//4. 在这执行生成类

@Override

public boolean process(Set extends TypeElement> annotations, RoundEnvironment roundEnv) {

return false;

}

private Set> getSupportedAnnotations() {

Set> annotations = new LinkedHashSet<>();

annotations.add(BindView.class);

return annotations;

}

}

我们确定一下这个环境编译是否是正确的

Butterknife里面添加ButterKnife-compiler依赖

api project(':ButterKnife-compiler')

app添加Butterknife依赖和compiler生成代码依赖

implementation project(':Butterknife')

annotationProcessor project(':ButterKnife-compiler')

在app的MainActivity添加注解

@BindView(R.id.text_view)

TextView textView;

这个时候运行程序报错了提示

C:\Users\Swartz\Desktop\githubdemo\AptDemo\ButterKnife-compiler\src\main\java\com\zzw\butterknife_compiler\ButterKnifeProcessor.java

Error:(21, 20) 错误: 编码GBK的不可映射字符

Error:(25, 12) 错误: 编码GBK的不可映射字符

Error:(25, 17) 错误: 编码GBK的不可映射字符

Error:(29, 20) 错误: 编码GBK的不可映射字符

Error:(39, 20) 错误: 编码GBK的不可映射字符

Error:Execution failed for task ':Butterknife:javaPreCompileDebug'.

> Annotation processors must be explicitly declared now. The following dependencies on the compile classpath are found to contain annotation processor. Please add them to the annotationProcessor configuration.

- ButterKnife-compiler.jar (project :ButterKnife-compiler)

Alternatively, set android.defaultConfig.javaCompileOptions.annotationProcessorOptions.includeCompileClasspath = true to continue with previous behavior. Note that this option is deprecated and will be removed in the future.

See https://developer.android.com/r/tools/annotation-processor-error-message.html for more details.

这个是因为我们在ButterKnifeProcessor这个类使用了中文，所以我们在ButterKnife-compiler中指定编码集

tasks.withType(JavaCompile){

options.encoding='UTF-8'

}

这个时候我们在ButterKnifeProcessor里面process函数添加打印

System.out.print("11111");

然后随便修改一下MainActivity的代码，重新编译在Gradle Console里面就可以看到打印了。这里需要修改MainActivity代码是因为我们是编译时生成，as为了节省时间是重新编译修改了的类，如果不修改的话可以能会不编译。

环境ok了，这下我们就需要重点放在生成代码这块了，这块又分为以下步骤:

因为这getSupportedAnnotationTypes添加的所有注解都会走到process函数，所以我们要将注解按照类来分离。比如AActivity对应那些有那些注解，BActivity里面有那些注解。

生成代码

package com.zzw.butterknife_compiler;

import com.google.auto.service.AutoService;

import com.squareup.javapoet.ClassName;

import com.squareup.javapoet.JavaFile;

import com.squareup.javapoet.MethodSpec;

import com.squareup.javapoet.TypeSpec;

import com.zzw.butterknife_annotions.BindView;

import java.io.IOException;

import java.lang.annotation.Annotation;

import java.util.ArrayList;

import java.util.LinkedHashMap;

import java.util.LinkedHashSet;

import java.util.List;

import java.util.Map;

import java.util.Set;

import javax.annotation.processing.AbstractProcessor;

import javax.annotation.processing.Filer;

import javax.annotation.processing.ProcessingEnvironment;

import javax.annotation.processing.Processor;

import javax.annotation.processing.RoundEnvironment;

import javax.lang.model.SourceVersion;

import javax.lang.model.element.Element;

import javax.lang.model.element.Modifier;

import javax.lang.model.element.TypeElement;

import javax.lang.model.util.Elements;

//1. 添加注解 @AutoService(Processor.class)

@AutoService(Processor.class)

public class ButterKnifeProcessor extends AbstractProcessor {

//决定生成的文件在哪个文件夹

private Filer mFiler;

//决定生成的生成包名用

private Elements mElementUtils;

@Override

public synchronized void init(ProcessingEnvironment processingEnv) {

super.init(processingEnv);

mFiler = processingEnv.getFiler();

mElementUtils = processingEnv.getElementUtils();

}

//2. 指定处理的版本 >1.7

@Override

public SourceVersion getSupportedSourceVersion() {

//最高版本

return SourceVersion.latestSupported();

}

//3. 指定处理的注解

@Override

public Set getSupportedAnnotationTypes() {

Set types = new LinkedHashSet<>();

for (Class extends Annotation> annotation : getSupportedAnnotations()) {

types.add(annotation.getCanonicalName());

}

return types;

}

//4. 在这执行生成类

@Override

public boolean process(Set extends TypeElement> annotations, RoundEnvironment roundEnv) {

//4.1 注解分类

//拿到所有的注解标记的元素

Set extends Element> elements= roundEnv.getElementsAnnotatedWith(BindView.class);

//分类集合

Map> elementMap= new LinkedHashMap<>();

//进行分类

for (Element element : elements) {

//拿到属于哪个类

Element enclosingElement = element.getEnclosingElement();

List viewBindElements = elementMap.get(enclosingElement);

if(viewBindElements ==null){

viewBindElements = new ArrayList<>();

elementMap.put(enclosingElement,viewBindElements);

}

viewBindElements.add(element);

}

//4.2 生成代码

for (Map.Entry> entry : elementMap.entrySet()) {

Element enclosingElement = entry.getKey();

List viewBindElements = entry.getValue();

//类信息

// public final class xxxActivity_ViewBinding implements Unbinder

final String activityNameStr = enclosingElement.getSimpleName().toString();

ClassName activityClassName = ClassName.bestGuess(activityNameStr);

TypeSpec.Builder classBuilder = TypeSpec.classBuilder( activityNameStr +"_ViewBinding")

.addModifiers(Modifier.FINAL,Modifier.PUBLIC)

//添加实现

.addSuperinterface(ClassName.get("com.zzw.butterknife","Unbinder"))

//添加属性

.addField(activityClassName,"target",Modifier.PRIVATE);

//方法信息

//实现unbinder方法

MethodSpec.Builder unbindMethodBuilder = MethodSpec.methodBuilder("unbind")

.addAnnotation(Override.class)

.addModifiers(Modifier.PUBLIC);

unbindMethodBuilder.addStatement("$T target = this.target",activityClassName);

unbindMethodBuilder.addStatement("if (target == null) throw new IllegalStateException(\"Bindings already cleared.\");");

//构造函数

MethodSpec.Builder constructorMethodBuilder = MethodSpec.constructorBuilder()

.addModifiers(Modifier.PUBLIC)

.addParameter(activityClassName,"target");

constructorMethodBuilder.addStatement("this.target = target");

//findViewById

for (Element viewBindElement : viewBindElements) {

//target.textView1 = Utils.findViewById(target,R.id.text_view1);

String filedName = viewBindElement.getSimpleName().toString();

ClassName utilsClassName = ClassName.get("com.zzw.butterknife","Utils");

int resId = viewBindElement.getAnnotation(BindView.class).value();

constructorMethodBuilder.addStatement("target.$L = $T.findViewById(target,$L)",filedName,utilsClassName,resId);

unbindMethodBuilder.addStatement("target.$L = null" ,filedName);

}

//添加构造函数到类里面

classBuilder.addMethod(constructorMethodBuilder.build());

//添加unbinder方法到类里面

classBuilder.addMethod(unbindMethodBuilder.build());

try {

//拿到包名

String packageName =mElementUtils.getPackageOf(enclosingElement).getQualifiedName().toString();

JavaFile.builder(packageName,classBuilder.build())

.addFileComment("butterknife 自动生成")//注释

.build()

.writeTo(mFiler);

} catch (IOException e) {

e.printStackTrace();

System.out.print("异常");

}

}

return false;

}

private Set> getSupportedAnnotations() {

Set> annotations = new LinkedHashSet<>();

annotations.add(BindView.class);

return annotations;

}

}

生成的代码如下：

// butterknife 自动生成

package com.zzw.app;

import com.zzw.butterknife.Unbinder;

import com.zzw.butterknife.Utils;

import java.lang.Override;

public final class MainActivity_ViewBinding implements Unbinder {

private MainActivity target;

public MainActivity_ViewBinding(MainActivity target) {

this.target = target;

target.textView1 = Utils.findViewById(target,2131165301);

target.textView2 = Utils.findViewById(target,2131165302);

}

@Override

public void unbind() {

MainActivity target = this.target;

if (target == null) throw new IllegalStateException("Bindings already cleared.");;

target.textView1 = null;

target.textView2 = null;

}

}

我们可以自动生成代码了，这个时候我们可以通过这个来实现findViewById

我们在Butterknife module里面建Butterknife这个类

package com.zzw.butterknife;

import android.app.Activity;

import java.lang.reflect.Constructor;

/**

* Des:

* Created by zzw on 2018/1/29.

*/

public class Butterknife {

public static Unbinder bind(Activity activity){

//xxxActivity_ViewBinding viewBinding = new xxxActivity_ViewBinding(activity);

try{

Class extends Unbinder> bindClass= (Class extends Unbinder>) Class.forName(activity.getClass().getName()+"_ViewBinding");

Constructor extends Unbinder> bindConstructor= bindClass.getDeclaredConstructor(activity.getClass());

return bindConstructor.newInstance(activity);

}catch (Exception e){

e.printStackTrace();

return Unbinder.EMPTY;

}

}

}

MainActivity

package com.zzw.app;

import android.os.Bundle;

import android.support.v7.app.AppCompatActivity;

import android.widget.TextView;

import com.zzw.aptdemo.R;

import com.zzw.butterknife.Butterknife;

import com.zzw.butterknife.Unbinder;

import com.zzw.butterknife_annotions.BindView;

public class MainActivity extends AppCompatActivity {

@BindView(R.id.text_view1)

TextView textView1;

@BindView(R.id.text_view2)

TextView textView2;

private Unbinder mUnbinder;

@Override

protected void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

mUnbinder = Butterknife.bind(this);

textView1.setText("你好 大哥");

}

@Override

protected void onDestroy() {

super.onDestroy();

mUnbinder.unbind();

}

}

该文中Butterknife module用到的类:

import android.support.annotation.UiThread;

/**

* Des:

* Created by zzw on 2018/1/29.

*/

public interface Unbinder {

@UiThread

void unbind();

Unbinder EMPTY = new Unbinder() {

@Override public void unbind() { }

};

}

package com.zzw.butterknife;

import android.app.Activity;

import android.view.View;

/**

* Des:

* Created by zzw on 2018/1/29.

*/

public class Utils {

public static T findViewById(Activity activity,int viewId){

return activity.findViewById(viewId);

}

}