onActivityResult简单使用

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, AActivity.class), 1);
    }

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

正常情况下，我们都会这样写，但会有两个问题：

1.onActivityResult必须在原始Activity中才能接收，如果想在非Activity中调用startActivityForResult，那么调用和接收的地方就不在同一个地方，代码可读性较差。
2.onActivityResult中所有页面跳转回调结果处理都会在该方法中，需要通过对resultCode进行if...else...判断才能区分，如果跳转比较多的话，代码可读性较差。

我们在写点击事件的时候，都知道其通过回调的方式接收点击回调信息？那么能不能将onActivityResult封装成，在哪调用的跳转，就在哪接收回调呢？答案是肯定的，类似于下面这样：

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

一种简单稳定的方法来实现onActivityResult的自动调用：

相信大家对Fragment都很熟悉，其依赖于Activity，有着一样的生命周期，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Fragment的onActivityResult是系统自动调用的，所以可以简单轻松的告别onActivityResult了，而且这个方法是系统自带的，稳定性得到保障。

/**
 * 把OnActivityResult方式转换为Callback方式的空Fragment（V4兼容包）
 *
 */
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
     *
     * @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);
        }
    }
}

/**
 * Activity跳转封装类，把OnActivityResult方式改为Callback方式
 *
 */
public class ActivityLauncher {

    private static final String TAG = "ActivityLauncher";
    private Context mContext;
    /** V4兼容包下的Fragment */
    private RouterFragment mRouterFragment;

    public static ActivityLauncher init(Fragment fragment) {
        return init(fragment.getActivity());
    }

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

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

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

    private ActivityLauncher(Activity 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) {
        if (mRouterFragment != null) {
            mRouterFragment.startActivityForResult(intent, callback);
        } else {
            throw new RuntimeException("please do init first!");
        }
    }

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

使用方式如下:

        // 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
                    }
                });