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】

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.Processor
public 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/'
}
//build processor 生成processor.jar
processorTask.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。