Android studio使用lambda表达式

   分三步

　1.引入retrolambda插件：

　　在Project的build.gradle中添加

    apply plugin: 'me.tatarka.retrolambda'

   2. 设置编译选项（必须要写）

　　在Project的build.gradle的android节点中添加如下代码

    compileOptions {        sourceCompatibility JavaVersion.VERSION_1_8        targetCompatibility JavaVersion.VERSION_1_8    }

   3. 引入retrolambda的类路径，

   在Module:app的build.gradle中的buildscript->dependencies节点中添加如下代码

   classpath 'me.tatarka:gradle-retrolambda:3.2.0'

使用范例：

使用前

Observable.create(new Observable.OnSubscribe<Object>() {    @Override    public void call(Subscriber<? super Object> subscriber) {        Drawable drawable = ActionActivity.this.getResources().getDrawable(R.mipmap.ic_launcher);        subscriber.onNext(drawable);        subscriber.onCompleted();    }}).subscribe(new Observer<Object>() {    @Override    public void onNext(Object drawable) {        img.setImageDrawable((Drawable)drawable);    }    @Override    public void onCompleted() {    }    @Override    public void onError(Throwable e) {        Toast.makeText(ActionActivity.this, "Error!", Toast.LENGTH_SHORT).show();    }});
使用后

Observable.create(subscriber -> {    Drawable drawable = ActionActivity.this.getResources().getDrawable(R.mipmap.ic_launcher);    subscriber.onNext(drawable);    subscriber.onCompleted();}).subscribe(o -> img.setImageDrawable((Drawable) o), throwable -> Toast.makeText(ActionActivity.this, "Error!", Toast.LENGTH_SHORT).show(), () -> {});