Android背锅侠Android开发Android技术知识

告别onActivityResult

2018-09-09  本文已影响46人  小枫

一、背景和目标

我们先来看下正常情况下启动Activity和接收回调信息的方式:

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // 启动Activity
        startActivityForResult(new Intent(this, TestActivity.class), 1);
    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        // 接收Activity回调
        if (requestCode == 1) {
            // 处理回调信息
        }
    }

这样看起来似乎也简洁,但是会有两个问题:

那么我们希望的是,可不可以像按钮点击事件一样通过回调的方式接收页面跳转的回调信息呢?在哪调用的跳转,就在哪接收回调,这样看起来就会爽多了,提高代码可读性,也有利于模块的封装和隔离。类似于下面这样:

// 启动Activity
startActivityForResult(TestActivity.class, new Callback() {
    @Override
    public void onActivityResult(int resultCode, Intent data) {
        // 处理回调信息
    }
});

这样看起来是不是更加简洁呢~~~

二、探索与实现

1. 先介绍一种比较直接容易想到的方法:
通过一个代理类ActivityLauncher,封装一下startActivityForResultonActivityResult方法。

public class ActivityLauncher {
    private FragmentActivity mActivity;
    private SparseArray<Callback> mCallbacks = new SparseArray<>();

    private ActivityLauncher(FragmentActivity activity) {
        mActivity = activity;
    }

    public void startActivityForResult(Intent intent, int requestCode, Callback callback) {
        // 保存下Callback
        mCallbacks.put(requestCode, callback);
        mActivity.startActivityForResult(intent, requestCode);
    }

    public void onActivityResult(int requestCode, int resultCode, Intent data) {
        // 取出对应Callback
        Callback callback = mCallbacks.get(resultCode);
        if (callback != null) {
            callback.onActivityResult(requestCode, resultCode, data);
        }
    }

    public interface Callback {
        void onActivityResult(int requestCode, int resultCode, Intent data);
    }
}

如何使用:

    private ActivityLauncher mActivityLauncher;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // 启动Activity
        Intent intent = new Intent(this, TestActivity.class);
        mActivityLauncher = new ActivityLauncher(this);
        mActivityLauncher.startActivityForResult(intent, 1, new ActivityLauncher.Callback() {
            @Override
            public void onActivityResult(int resultCode, Intent data) {
                // 接收Activity回调
                if (requestCode == 1) {
                    // 处理回调信息
                }
            }
        });
    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        mActivityLauncher.onActivityResult(requestCode, resultCode, data);
    }

这种方式看似简单,但是实际用起来会有点问题。这里的onActivityResult仍然需要外部ActivityonActivityResult来手动调用,显得很麻烦,调用者很容易忘记,而且这样也没有做到真正的跟Activity隔离,其实本质上跟原始的方式没太大区别。

其实这种方式,只解决了上面提到的第二个问题,把onActivityResult中的很多不同跳转的回调逻辑分散到了各自调用跳转的地方,看起来会清爽一些。但是第一个问题还是没解决,我们需要把调用跳转的地方和接收回调的地方真正的绑定在一起,不需要其他多余的耦合。

2. 利用java反射和hook技术
既然需要跟外部ActivityonActivityResult解耦,我们能想到的就是,如果上面的那种方法,可以自动帮我们调用onActivityResult那该多好。我们能想到的一种方法就是利用java的反射机制,把ActivityonActivityResult调用流程反射出来,并且注入我们自己改造后的代码,替换原来的流程,实现自动调动onActivityResult的目的。
这里贴一段网上找到的实现hook的方案,有兴趣的同学可以拿来研究下:

public class ActivityThreadCallbackHook {
    // Copy from ActivityThread.mH Handler
    public static final int SEND_RESULT = 108;

    public static void hook() {
        try {
            ActivityThread activityThread = ActivityThread.currentActivityThread();
            // 由于ActivityThread一个进程只有一个,我们获取这个对象的mH
            Field mHField;
            mHField = ActivityThread.class.getDeclaredField("mH");
            mHField.setAccessible(true);
            Handler mH = (Handler) mHField.get(activityThread);

            // 设置它的回调, 根据源码:
            // 我们自己给他设置一个回调,就会替代之前的回调;

            //        public void dispatchMessage(Message msg) {
            //            if (msg.callback != null) {
            //                handleCallback(msg);
            //            } else {
            //                if (mCallback != null) {
            //                    if (mCallback.handleMessage(msg)) {
            //                        return;
            //                    }
            //                }
            //                handleMessage(msg);
            //            }
            //        }

            Field mCallBackField = Handler.class.getDeclaredField("mCallback");
            mCallBackField.setAccessible(true);
            // 塞入我们的 hook 对象
            mCallBackField.set(mH, new MyHandlerCallback(mH));
            Log.d("hook","success");
        } catch (Exception e) {
            // hook 失败,整个 callback 就 gg了
            e.printStackTrace();
        }
    }

    private static class MyHandlerCallback implements Handler.Callback {
        private Handler mOldHandler;
        public MyHandlerCallback(Handler mOldHandler) {
            this.mOldHandler = mOldHandler;
        }

        @Override
        public boolean handleMessage(Message msg) {
            // 不干扰系统分发逻辑
            mOldHandler.handleMessage(msg);

            // 通知 ResultManager
            if (msg.what == SEND_RESULT) {
                Object obj = msg.obj;
                try {
                    // step 1 reflect to get activity
                    Object token = ReflectUtils.on(obj).get("token");
                    ArrayMap mActivities = (ArrayMap) ReflectUtils.on(ActivityThread.currentActivityThread()).get("mActivities");
                    Object activityClientRecord =  mActivities.get(token);
                    Activity activity = (Activity) ReflectUtils.on(activityClientRecord).get("activity");

                    // step2 reflect to get ResultInfo
                    // 注意这里的分发,无法分发到 Fragment 内部,所以采用动态塞入一个 Fragment 是最稳定的方案
                    ArrayList<ResultInfo> results = (ArrayList<ResultInfo>) ReflectUtils.on(obj).get("results");
                    for (ResultInfo result : results) {
                        OnResultManager.getInstance().trigger(activity, result.mRequestCode, result.mResultCode, result.mData);
                    }
                } catch (RuntimeException e) {
                    e.printStackTrace();
                }
            }

            //  default
            return true;
        }
    }
}

3. 还有另一种实现注入onActivityResult的方法,就是是利用AOP技术,通过android-aspectjx插件,可以实现面向切片编程。
直接看代码:

@Aspect
public class OnResultAspect {
    private static final String TAG = "OnResultAspect";

    @After("execution(* android.app.Activity.onActivityResult(..))")
    public void onActivityResultAfter(JoinPoint joinPoint) throws Throwable {
        Object[] args = joinPoint.getArgs();
        int requestCode = (int) args[0];
        int resultCode = (int) args[1];
        Intent data = (Intent) args[2];
        Activity activity = (Activity) joinPoint.getTarget();

        OnResultManager.getInstance().trigger(activity, requestCode, resultCode, data);
    }
}

直接在每次系统调用onActivityResult的时候,插入我们自己的onActivityResult方法自动调用。

方法2方法3,基本思路是一样的,都是通过注入代码的方式实现自动调用我们自己的onActivityResult方法,但是都有不尽人意的地方:
方法2通过反射的方式,兼容性和稳定性都较差,而且容易和其他第三方插件产生冲突,出现问题也很难排查。而且,这两种方法都会对所有页面的onActivityResult都产生注入,而实际使用中可能并不需要对所有页面都生效,可控性较差。

4. 下面介绍一种既简单又稳定的方法,来实现自动调用onActivityResult
安卓系统中,Fragment有着跟Activity一样的生命周期,却比Activity更轻量级。我们可以利用一个空的无界面的Fragment来监听onActivityResult方法,并通过回调形式返回给调用者。由于FragmentonActivityResult是系统自动调用的,所以我们就可以从此简单轻松的告别onActivityResult了,而且这个都是系统自带的方法,稳定又可靠。

下面简单贴下实现代码:

public class ActivityLauncher {
    private static final String TAG = "ActivityLauncher";
    private Context mContext;
    private RouterFragment mRouterFragment;

    public static ActivityLauncher init(FragmentActivity activity) {
        return new ActivityLauncher(activity);
    }

    private ActivityLauncher(FragmentActivity activity) {
        mContext = activity;
        mRouterFragment = getRouterFragment(activity);
    }

    private RouterFragment getRouterFragment(FragmentActivity activity) {
        RouterFragment routerFragment = findRouterFragment(activity);
        if (routerFragment == null) {
            routerFragment = RouterFragment.newInstance();
            FragmentManager fragmentManager = activity.getSupportFragmentManager();
            fragmentManager
                    .beginTransaction()
                    .add(routerFragment, TAG)
                    .commitAllowingStateLoss();
            fragmentManager.executePendingTransactions();
        }
        return routerFragment;
    }

    private RouterFragment findRouterFragment(FragmentActivity activity) {
        return (RouterFragment) activity.getSupportFragmentManager().findFragmentByTag(TAG);
    }

    public void startActivityForResult(Class<?> clazz, Callback callback) {
        Intent intent = new Intent(mContext, clazz);
        startActivityForResult(intent, callback);
    }

    public void startActivityForResult(Intent intent, Callback callback) {
        mRouterFragment.startActivityForResult(intent, callback);
    }

    public interface Callback {
        void onActivityResult(int resultCode, Intent data);
    }
}
public class RouterFragment extends Fragment {

    private SparseArray<ActivityLauncher.Callback> mCallbacks = new SparseArray<>();
    private Random mCodeGenerator = new Random();

    public RouterFragment() {
        // Required empty public constructor
    }

    public static RouterFragment newInstance() {
        return new RouterFragment();
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setRetainInstance(true);
    }

    public void startActivityForResult(Intent intent, ActivityLauncher.Callback callback) {
        int requestCode = makeRequestCode();
        mCallbacks.put(requestCode, callback);
        startActivityForResult(intent, requestCode);
    }

    /**
     * 随机生成唯一的requestCode,最多尝试10次
     *
     * @return
     */
    private int makeRequestCode() {
        int requestCode;
        int tryCount = 0;
        do {
            requestCode = mCodeGenerator.nextInt(0x0000FFFF);
            tryCount++;
        } while (mCallbacks.indexOfKey(requestCode) >= 0 && tryCount < 10);
        return requestCode;
    }

    @Override
    public void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);
        ActivityLauncher.Callback callback = mCallbacks.get(requestCode);
        mCallbacks.remove(requestCode);
        if (callback != null) {
            callback.onActivityResult(resultCode, data);
        }
    }
}

如何调用:

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // 启动Activity
        ActivityLauncher.init(this)
                .startActivityForResult(TestActivity.class, new ActivityLauncher.Callback() {
                    @Override
                    public void onActivityResult(int resultCode, Intent data) {
                        // 处理回调信息
                    }
                });
    }

基本上实现了我们文章开头的预期。上面是我简化过后的代码,只支持FragmentActivity调用,具体可以看我的Github地址,里面实现了对FragmentFragmentActivityActivity的支持。

欢迎大家star和点赞哈~~

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