使用annotationProcessor打造编译时的注解（二）

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使用annotationProcessor打造编译时的注解（一）

参数对象方法说明

public boolean process(Set set, RoundEnvironment roundEnvironment) {
return false;
}

参数Set set：表示使用了支持处理注解的节点集合，此处只支持了BindView，所以此处set集合中只有一个元素
RoundEnvironment roundEnvironment：表示当前或是之前的运行环境,可以通过该对象查找找到的注解
return 返回true为表示后续处理器不会再处理(已经处理)

下面为process方法，相关的字段都已经注释好了

private Map> classMap = new HashMap<>();

   @Override
    public boolean process(Set set, RoundEnvironment roundEnvironment) {
        messager.printMessage(Diagnostic.Kind.NOTE, "process============");
        for (TypeElement typeElement : set) {
            messager.printMessage(Diagnostic.Kind.NOTE, "typeElement: " + typeElement.toString());
          //typeElement就相当于com.cool.butterknife.annoation.BindView
          //通过roundEnvironment来获取所有被BindView注解注解了的字段
            Set elementsAnnotatedWith = roundEnvironment.getElementsAnnotatedWith(typeElement);
            for (Element element : elementsAnnotatedWith) {
                //如果在MainActivity中有这段代码 @BindView(R.id.textView)TextView textView;
               //此处的element就是TextView节点元素
                //element.getEnclosingElement()为获取其父节点元素，即MainActivty
                Element enclosingElement = element.getEnclosingElement();
                TypeMirror classTypeMirror = enclosingElement.asType();
                //className为MainActivty的全类名
                String className = classTypeMirror.toString();
                //上面只是拿MainActivty举个例子，但是真实的使用注解的可能还有SecondActivity等等，所有需要以类名为键保存里面所有使用了BindView注解的节点
                List elements = classMap.get(className);
                if (elements == null) {
                    elements = new ArrayList<>();
                    elements.add(element);
                    classMap.put(className, elements);
                }else {
                    elements.add(element);
                }
            }

            Set>> entries = classMap.entrySet();
            for (Map.Entry> entry : entries) {
                String key = entry.getKey();
                List value = entry.getValue();
              //生成java代码
                generateViewBinding(key,value);
            }

        }
        return false;
    }

generateViewBinding方法

首先看一下生成的2个类中的代码

public class MainActivity_ViewBinding implements Unbinder {
  private MainActivity target;

  @UiThread
  public MainActivity_ViewBinding(final MainActivity target, View source) {
    this.target = target;
    target.textView = source.findViewById(2131165320);
    target.textView2 = source.findViewById(2131165321);
  }

  public void unbind() {
    MainActivity target = this.target;
    this.target = null;
    target.textView = null;
    target.textView2 = null;
  }
}

public class SecondActivity_ViewBinding implements Unbinder {
  private SecondActivity target;

  @UiThread
  public SecondActivity_ViewBinding(final SecondActivity target, View source) {
    this.target = target;
    target.button = source.findViewById(2131165219);
  }

  public void unbind() {
    SecondActivity target = this.target;
    this.target = null;
    target.button = null;
  }
}

生成代码使用了 javapoet,没用过不懂的可以参考其github主页上的例子

private void generateViewBinding(String key, List values) {
        //生成类元素节点 此处key为com.cool.butterknife.MainActivity或者com.cool.butterknife.SecondActivity
        TypeElement classTypeElement = elementUtils.getTypeElement(key);
        //生成参数 final MainActivity target
        ParameterSpec targetParameterSpec = ParameterSpec
                .builder(ClassName.get(classTypeElement), "target", Modifier.FINAL)
                .build();
        //生成参数  View source
        ParameterSpec viewParameterSpec = ParameterSpec.builder(ClassName.get("android.view", "View"), "source")
                .build();
        MethodSpec constructor = null;

        //生成构造函数
        MethodSpec.Builder constructorMethodBuilder = MethodSpec.constructorBuilder()
                .addParameter(targetParameterSpec)
                .addParameter(viewParameterSpec)
                .addAnnotation(ClassName.bestGuess("android.support.annotation.UiThread"))
                .addModifiers(Modifier.PUBLIC);

        //  构造函数中添加代码块
        constructorMethodBuilder.addStatement("this.target = target");
        for (Element element : values) {
            BindView bindView = element.getAnnotation(BindView.class);

            int id = bindView.value();
            Name simpleName = element.getSimpleName();
            constructorMethodBuilder.addStatement("target.$L = source.findViewById($L)", simpleName.toString(), id);
        }
        constructor = constructorMethodBuilder.build();

        //生成unbind方法
        MethodSpec.Builder unbindMethodSpec = MethodSpec.methodBuilder("unbind")
                .addModifiers(Modifier.PUBLIC);
        unbindMethodSpec.addStatement("$T target = this.target", ClassName.get(classTypeElement));
        unbindMethodSpec.addStatement("this.target = null");

        for (Element element : values) {
            Name simpleName = element.getSimpleName();
            unbindMethodSpec.addStatement("target.$L = null", simpleName.toString());
        }

        //生成MainActivity_ViewBinding类
        TypeSpec typeSpec = TypeSpec.classBuilder(classTypeElement.getSimpleName() + "_ViewBinding")
                .addField(ClassName.get(classTypeElement), "target", Modifier.PRIVATE)
                .addMethod(constructor)
                .addMethod(unbindMethodSpec.build())
                .addSuperinterface(ClassName.bestGuess("com.cool.butterknife.core.Unbinder"))
                .addModifiers(Modifier.PUBLIC)
                .build();

        //获取包名
        String packageName = elementUtils.getPackageOf(classTypeElement).getQualifiedName().toString();
        messager.printMessage(Diagnostic.Kind.NOTE, "packageName: " + packageName.toString());
        JavaFile javaFile = JavaFile.builder(packageName, typeSpec)
                .build();

        try {
            //写入java文件
            javaFile.writeTo(filer);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

看完，你可能会有点身体不适，但是这个难点在于如何拼接类，有点繁琐，一不小心就容易出错，而且出错之后问题比较难找，唯有静下心来慢慢的看，一定要仔细。

到处，点击make就可以生成类了，接下来使用刚刚生成的类

/**
 * Created by cool on 2018/7/3.
 */
public class Butterknife {

    static final Map, Constructor> BINDINGS = new LinkedHashMap<>();

    @NonNull
    @UiThread
    public static Unbinder bind(@NonNull Activity target) {
        View sourceView = target.getWindow().getDecorView();
        return createBinding(target, sourceView);
    }

    private static Unbinder createBinding(Activity target, View sourceView) {
        Class targetClass = target.getClass();
        Constructor constructor = findBindingConstructorForClass(targetClass);
        if (constructor == null) {
            return Unbinder.EMPTY;
        }
        try {
            return constructor.newInstance(target, sourceView);
        } catch (IllegalAccessException e) {
            throw new RuntimeException("Unable to invoke " + constructor, e);
        } catch (InstantiationException e) {
            throw new RuntimeException("Unable to invoke " + constructor, e);
        } catch (InvocationTargetException e) {
            Throwable cause = e.getCause();
            if (cause instanceof RuntimeException) {
                throw (RuntimeException) cause;
            }
            if (cause instanceof Error) {
                throw (Error) cause;
            }
            throw new RuntimeException("Unable to create binding instance.", cause);
        }
    }

    private static Constructor findBindingConstructorForClass(Class targetClass) {
        Constructor constructor = BINDINGS.get(targetClass);
        if (constructor != null) {
            return constructor;
        }

        String targetClassName = targetClass.getName();
        try {
            Class viewBindingClass = Class.forName(targetClassName + "_ViewBinding");
            constructor = (Constructor) viewBindingClass.getConstructor(targetClass, View.class);
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (NoSuchMethodException e) {
            e.printStackTrace();
        }
        BINDINGS.put(targetClass, constructor);

        return constructor;
    }
}

呃呃，这个就不解释类，比较简单，接下来是使用

public class MainActivity extends AppCompatActivity {

    @BindView(R.id.textView)
    TextView textView;

    @BindView(R.id.textView2)
    TextView textView2;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Butterknife.bind(this);
        textView.setText("ButterKnife Test");
    }

    @OnClick(R.id.bt_click)
    public void onClick(View view){
        Toast.makeText(this,"点击",Toast.LENGTH_SHORT).show();
    }
}

最后贴一下BindViewProcessor.java完整版

package com.cool.butterknife.compiler;

import com.cool.butterknife.annoation.BindView;
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.ParameterSpec;
import com.squareup.javapoet.TypeSpec;

import java.io.IOException;
import java.util.ArrayList;
import java.util.HashMap;
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.Messager;
import javax.annotation.processing.ProcessingEnvironment;
import javax.annotation.processing.Processor;
import javax.annotation.processing.RoundEnvironment;
import javax.annotation.processing.SupportedAnnotationTypes;
import javax.annotation.processing.SupportedSourceVersion;
import javax.lang.model.SourceVersion;
import javax.lang.model.element.AnnotationMirror;
import javax.lang.model.element.AnnotationValue;
import javax.lang.model.element.Element;
import javax.lang.model.element.ExecutableElement;
import javax.lang.model.element.Modifier;
import javax.lang.model.element.Name;
import javax.lang.model.element.TypeElement;
import javax.lang.model.element.VariableElement;
import javax.lang.model.type.TypeMirror;
import javax.lang.model.util.Elements;
import javax.tools.Diagnostic;

@AutoService(Processor.class)
@SupportedAnnotationTypes("com.cool.butterknife.annoation.BindView")
@SupportedSourceVersion(SourceVersion.RELEASE_7)
public class BindViewProcessor extends AbstractProcessor {

    private Messager messager;
    private Filer filer;
    private Elements elementUtils;
    private Map> classMap = new HashMap<>();

    @Override
    public synchronized void init(ProcessingEnvironment processingEnvironment) {
        super.init(processingEnvironment);
        filer = processingEnvironment.getFiler();
        messager = processingEnvironment.getMessager();
        elementUtils = processingEnvironment.getElementUtils();
        messager.printMessage(Diagnostic.Kind.NOTE, "=========init============");
    }

    @Override
    public boolean process(Set set, RoundEnvironment roundEnvironment) {
        messager.printMessage(Diagnostic.Kind.NOTE, "=======process============");
        for (TypeElement typeElement : set) {
            messager.printMessage(Diagnostic.Kind.NOTE, "typeElement: " + typeElement.toString());
            //typeElement就相当于com.cool.butterknife.annoation.BindView
            //通过roundEnvironment来获取所有被BindView注解注解了的字段
            Set elementsAnnotatedWith = roundEnvironment.getElementsAnnotatedWith(typeElement);
            for (Element element : elementsAnnotatedWith) {
                //如果在MainActivity中有这段代码 @BindView(R.id.textView)TextView textView;
                //此处的element就是TextView节点元素
                //element.getEnclosingElement()为获取其父节点元素，即MainActivty
                Element enclosingElement = element.getEnclosingElement();
                TypeMirror classTypeMirror = enclosingElement.asType();
                //className为MainActivty的全类名
                String className = classTypeMirror.toString();
                //上面只是拿MainActivty举个例子，但是真实的使用注解的可能还有SecondActivity等等，所有需要以类名为键保存里面所有使用了BindView注解的节点
                List elements = classMap.get(className);
                if (elements == null) {
                    elements = new ArrayList<>();
                    elements.add(element);
                    classMap.put(className, elements);
                } else {
                    elements.add(element);
                }
            }

            Set>> entries = classMap.entrySet();
            for (Map.Entry> entry : entries) {
                String key = entry.getKey();
                List value = entry.getValue();
                //生成java代码
                generateViewBinding(key, value);
            }

        }
        return false;
    }

    private void generateViewBinding(String key, List values) {
        //生成类元素节点 此处key为com.cool.butterknife.MainActivity或者com.cool.butterknife.SecondActivity
        TypeElement classTypeElement = elementUtils.getTypeElement(key);
        //生成参数 final MainActivity target
        ParameterSpec targetParameterSpec = ParameterSpec
                .builder(ClassName.get(classTypeElement), "target", Modifier.FINAL)
                .build();
        //生成参数  View source
        ParameterSpec viewParameterSpec = ParameterSpec.builder(ClassName.get("android.view", "View"), "source")
                .build();
        MethodSpec constructor = null;

        //生成构造函数
        MethodSpec.Builder constructorMethodBuilder = MethodSpec.constructorBuilder()
                .addParameter(targetParameterSpec)
                .addParameter(viewParameterSpec)
                .addAnnotation(ClassName.bestGuess("android.support.annotation.UiThread"))
                .addModifiers(Modifier.PUBLIC);

        //  构造函数中添加代码块
        constructorMethodBuilder.addStatement("this.target = target");
        for (Element element : values) {
            BindView bindView = element.getAnnotation(BindView.class);

            int id = bindView.value();
            Name simpleName = element.getSimpleName();
            constructorMethodBuilder.addStatement("target.$L = source.findViewById($L)", simpleName.toString(), id);
        }
        constructor = constructorMethodBuilder.build();

        //生成unbind方法
        MethodSpec.Builder unbindMethodSpec = MethodSpec.methodBuilder("unbind")
                .addModifiers(Modifier.PUBLIC);
        unbindMethodSpec.addStatement("$T target = this.target", ClassName.get(classTypeElement));
        unbindMethodSpec.addStatement("this.target = null");

        for (Element element : values) {
            Name simpleName = element.getSimpleName();
            unbindMethodSpec.addStatement("target.$L = null", simpleName.toString());
        }

        //生成MainActivity_ViewBinding类
        TypeSpec typeSpec = TypeSpec.classBuilder(classTypeElement.getSimpleName() + "_ViewBinding")
                .addField(ClassName.get(classTypeElement), "target", Modifier.PRIVATE)
                .addMethod(constructor)
                .addMethod(unbindMethodSpec.build())
                .addSuperinterface(ClassName.bestGuess("com.cool.butterknife.core.Unbinder"))
                .addModifiers(Modifier.PUBLIC)
                .build();

        //获取包名
        String packageName = elementUtils.getPackageOf(classTypeElement).getQualifiedName().toString();
        messager.printMessage(Diagnostic.Kind.NOTE, "packageName: " + packageName.toString());
        JavaFile javaFile = JavaFile.builder(packageName, typeSpec)
                .build();

        try {
            //写入java文件
            javaFile.writeTo(filer);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

onClick在写这篇文章时没做实现，到时实现放在第3篇吧
查看源码
使用annotationProcessor打造编译时的注解（三)

使用annotationProcessor打造编译时的注解（二）

参数对象方法说明

下面为process方法，相关的字段都已经注释好了

generateViewBinding方法

到处，点击make就可以生成类了，接下来使用刚刚生成的类

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