看不懂.

绕来要去, Activity最终通过ServiceConnection获得一个Service实例的引用(Binder持有)
为什么不直接实例化Service得到其引用?

而且代码里还循环依赖, Service持有Binder的引用, Binder又持有Service的引用.

//----------------------Service代码------------------------------

public class MyService extends Service {
    private static final String TAG = "zjy";
    // 第4步，实例化一个MyBinder对象
    private MyBinder mBinder = new MyBinder(this);

    @Nullable
    @Override
    public IBinder onBind(Intent intent) {
        return mBinder;//第4步，返回这个mBinder对象
    }


//-------------------Binder代码-------------------------------
public class MyBinder extends Binder {
    private static final String TAG = "zjy";
    private MyService mService;
    private OnTestListener mListener;

    public MyBinder(MyService service) {
        this.mService = service;
    }
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