[译][Google工程师] 刚刚发布了 Fragment 的新特性 “Fragment 间传递数据的新方式” 以及源码分析

FragmentManager.setFragmentResultListener(
    requestKey,
    lifecycleOwner,
    FragmentResultListener { requestKey: String, result: Bundle ->
        // Handle result
    })

parentFragmentManager.setFragmentResultListener(...)

childFragmentManager.setFragmentResultListener(...)

parentFragmentManager.setFragmentResult(
    requestKey, // Same request key FragmentA used to register its listener
    bundleOf(key to value) // The data to be passed to FragmentA
)

@Test
fun shouldReceiveData() {
    val scenario = FragmentScenario.launchInContainer(FragmentA::class.java)
    // Pass data using the parent fragment manager
    scenario.onFragment { fragment ->
        val data = bundleOf(KEY_DATA to "value")
        fragment.parentFragmentManager.setFragmentResult("aKey", data)
    }
    // Verify data is received, for example, by verifying it's been displayed on the UI
   onView(withId(R.id.textView)).check(matches(withText("value"))) 
}

@Test
fun shouldSendData() {
    val scenario = FragmentScenario.launchInContainer(FragmentB::class.java)
    // Register result listener
    var receivedData = ""
    scenario.onFragment { fragment ->
        fragment.parentFragmentManager.setFragmentResultListener(
            KEY,
            fragment,
            FragmentResultListener { key, result ->
                receivedData = result.getString(KEY_DATA)
            })
    }
    // Send data
    onView(withId(R.id.send_data)).perform(click())
    // Verify data was successfully sent
    assertThat(receivedData).isEqualTo("value")
}

FragmentManager.setFragmentResultListener(
    requestKey,
    lifecycleOwner,
    FragmentResultListener { requestKey: String, result: Bundle ->
        // Handle result
    })

parentFragmentManager.setFragmentResult(
    requestKey, // Same request key FragmentA used to register its listener
    bundleOf(key to value) // The data to be passed to FragmentA
)

private final ConcurrentHashMap<String, LifecycleAwareResultListener> mResultListeners =
        new ConcurrentHashMap<>();
@Override
public final void setFragmentResultListener(@NonNull final String requestKey,
                                            @NonNull final LifecycleOwner lifecycleOwner,
                                            @Nullable final FragmentResultListener listener) {
    // mResultListeners 是 ConcurrentHashMap 的实例，用来储存注册的 listener
    // 如果传递的参数 listener 为空时，移除 requestKey 对应的 listener
    if (listener == null) {
        mResultListeners.remove(requestKey);
        return;
    }
    // Lifecycle是一个生命周期感知组件，一般用来响应Activity、Fragment等组件的生命周期变化
    final Lifecycle lifecycle = lifecycleOwner.getLifecycle();
    // 当生命周期处于 DESTROYED 时，直接返回
    // 避免当 Fragment 处于不可预知状态的时，可能发生未知的问题
    if (lifecycle.getCurrentState() == Lifecycle.State.DESTROYED) {
        return;
    }
    // 开始监听生命周期
    LifecycleEventObserver observer = new LifecycleEventObserver() {
        @Override
        public void onStateChanged(@NonNull LifecycleOwner source,
                                   @NonNull Lifecycle.Event event) {
            // 当生命周期处于 ON_START 时开始处理数据
            if (event == Lifecycle.Event.ON_START) {
                // 开始检查受到的数据
                Bundle storedResult = mResults.get(requestKey);
                if (storedResult != null) {
                    // 如果结果不为空，调用回调方法
                    listener.onFragmentResult(requestKey, storedResult);
                    // 清除数据
                    setFragmentResult(requestKey, null);
                }
            }
            // 当生命周期处于 ON_DESTROY 时，移除监听
            if (event == Lifecycle.Event.ON_DESTROY) {
                lifecycle.removeObserver(this);
                mResultListeners.remove(requestKey);
            }
        }
    };
    lifecycle.addObserver(observer);
    mResultListeners.put(requestKey, new FragmentManager.LifecycleAwareResultListener(lifecycle, listener));
}

private final ConcurrentHashMap<String, Bundle> mResults = new ConcurrentHashMap<>();
private final ConcurrentHashMap<String, LifecycleAwareResultListener> mResultListeners =
        new ConcurrentHashMap<>();
@Override
public final void setFragmentResult(@NonNull String requestKey, @Nullable Bundle result) {
    if (result == null) {
        // mResults 是 ConcurrentHashMap 的实例，用来存储数据传输的 Bundle
        // 如果传递的参数 result 为空，移除 requestKey 对应的 Bundle
        mResults.remove(requestKey);
        return;
    }
    // Check if there is a listener waiting for a result with this key
    // mResultListeners 是 ConcurrentHashMap 的实例，用来储存注册的 listener
    // 获取 requestKey 对应的 listener
    LifecycleAwareResultListener resultListener = mResultListeners.get(requestKey);
    if (resultListener != null && resultListener.isAtLeast(Lifecycle.State.STARTED)) {
        // 如果 resultListener 不为空，并且生命周期处于 STARTED 状态时，调用回调
        resultListener.onFragmentResult(requestKey, result);
    } else {
        // 否则保存当前传输的数据
        mResults.put(requestKey, result);
    }
}