Android开发之手把手教你写ButterKnife框架（二）

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http://blog.csdn.net/johnny901114/article/details/52664112
本文出自:【余志强的博客】

系列文章目录导读：

Android开发之手把手教你写ButterKnife框架（一）

Android开发之手把手教你写ButterKnife框架（二）

Android开发之手把手教你写ButterKnife框架（三）

上一篇博客Android开发之手把手教你写ButterKnife框架（一）我们讲了ButterKnife是什么、ButterKnife的作用和功能介绍以及ButterKnife的实现原理。

本篇博客主要讲在android studio中如何使用apt。

一、新建个项目, 然后创建一个module名叫processor

新建module的时候一定要选择 Java Library 否则在后面会找不到AbstractProcessor。

分别在app和processor 的文件夹下的build.gralde添加如下配置：

compileOptions {   sourceCompatibility JavaVersion.VERSION_1_7   targetCompatibility JavaVersion.VERSION_1_7}

二、然后在建一个module名叫annotation，主要用来保存项目用到的annotation.

import java.lang.annotation.Retention;import java.lang.annotation.Target;import static java.lang.annotation.ElementType.FIELD;import static java.lang.annotation.RetentionPolicy.CLASS;@Retention(CLASS) @Target(FIELD)public @interface BindView {    int value();}

三、新建MainActivity 字段上加上注解，如下：

public class MainActivity extends AppCompatActivity {    @BindView(R.id.text_view)    TextView textView;    @BindView(R.id.view)    TextView view;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);    }}

三、在processor module下新建一个ButterKnifeProcessor 继承AbstractProcessor.

@SupportedAnnotationTypes("com.chiclaim.processor.annotation.BindView")@SupportedSourceVersion(SourceVersion.RELEASE_7)public class ButterKnifeProcessor extends AbstractProcessor {    @Override    public boolean process(Set<? extends TypeElement> annotations, RoundEnvironment roundEnv) {        StringBuilder builder = new StringBuilder()                .append("package com.chiclaim.processor.generated;\n\n")                .append("public class GeneratedClass {\n\n") // open class                .append("\tpublic String getMessage() {\n") // open method                .append("\t\treturn \"");        // for each javax.lang.model.element.Element annotated with the CustomAnnotation        for (Element element : roundEnv.getElementsAnnotatedWith(BindView.class)) {            String objectType = element.getSimpleName().toString();            // this is appending to the return statement            builder.append(objectType).append(" says hello!\\n");        }        builder.append("\";\n") // end return                .append("\t}\n") // close method                .append("}\n"); // close class        try { // write the file            JavaFileObject source = processingEnv.getFiler().createSourceFile("com.chiclaim.processor.generated.GeneratedClass");            Writer writer = source.openWriter();            writer.write(builder.toString());            writer.flush();            writer.close();        } catch (IOException e) {            // Note: calling e.printStackTrace() will print IO errors            // that occur from the file already existing after its first run, this is normal        }        return true;    }}

@SupportedAnnotationTypes(…) 里面的参数是我们需要处理的注解

四、在processor module主目录下resources目录

然后新建META-INF目录，然后在META-INF下新建services 然后新建一个文件名为 javax.annotation.processing.Processor, 里面的内容就是刚刚新建的ButterKnifeProcessor的qualified name ：

com.chiclaim.butterknife.processor.ButterKnifeProcessor

当然也可以用新建这么多文件夹，只需要加入google AutoService，这样就会自动完成上面的操作。

@SupportedSourceVersion(SourceVersion.RELEASE_7)@AutoService(Processor.class)//AutoService自动生成文件(in processor.jar): META-INF/services/javax.annotation.processing.Processorpublic class ButterKnifeProcessor extends AbstractProcessor

五、添加android-apt支持

在全局的build.gradle添加添加apt支持，com.neenbedankt.gradle.plugins:android-apt:1.8,如下所示：

buildscript {    repositories {        jcenter()    }    dependencies {        classpath 'com.android.tools.build:gradle:2.2.0'        classpath 'com.neenbedankt.gradle.plugins:android-apt:1.8'        // NOTE: Do not place your application dependencies here; they belong        // in the individual module build.gradle files    }}ext {    sourceCompatibilityVersion = JavaVersion.VERSION_1_7    targetCompatibilityVersion = JavaVersion.VERSION_1_7}allprojects {    repositories {        jcenter()    }}task clean(type: Delete) {    delete rootProject.buildDir}

分别在app module的build.gradle添加 apply plugin 如下所示：

apply plugin: 'com.android.application'apply plugin: 'com.neenbedankt.android-apt'

六、添加module之间的依赖

dependencies {    compile fileTree(include: ['*.jar'], dir: 'libs')    androidTestCompile('com.android.support.test.espresso:espresso-core:2.2.2', {        exclude group: 'com.android.support', module: 'support-annotations'    })    compile 'com.android.support:appcompat-v7:24.2.1'    testCompile 'junit:junit:4.12'    compile project(':annotation')    compile project(':processor')    compile project(':butterknife')}//把processor module生成的jar拷贝到app libs目录//task processorTask(type: Exec) {//    commandLine 'cp', '../processor/build/libs/processor.jar', 'libs/'//}task processorTask(type: Copy) {      from '../processor/build/libs/processor.jar' into 'libs/'}//build processor 生成processor.jarprocessorTask.dependsOn(':processor:build')preBuild.dependsOn(processorTask)

如下图所示：

会在app module的build的目录下生成代码，如：

public class GeneratedClass {    public String getMessage() {        return "button says hello!\nimageView says hello!\ntextView says hello!\nview says hello!\n";    }}

据此，在android studio 使用apt就介绍完毕了。

具体的可以查看github代码：https://github.com/chiclaim/study-butterknife

下一篇将介绍如何实现ButterKnife注入初始化View功能。

参考文档

http://blog.stablekernel.com/the-10-step-guide-to-annotation-processing-in-android-studio