Android 基于MediatorLiveData实现红点的统一管理

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public class MediatorLiveData<T> extends MutableLiveData<T> {
  private SafeIterableMap<LiveData<?>, Source<?>> mSources = new SafeIterableMap<>();

  
  public <S> void addSource(@NonNull LiveData<S> source, @NonNull Observer<? super S> onChanged) {
    //使用Source包一下
    Source<S> e = new Source<>(source, onChanged);
    Source<?> existing = mSources.putIfAbsent(source, e);
    if (hasActiveObservers()) {
      e.plug();
    }
  }

  private static class Source<V> implements Observer<V> {
    final LiveData<V> mLiveData;
    final Observer<? super V> mObserver;
    int mVersion = START_VERSION;

    Source(LiveData<V> liveData, final Observer<? super V> observer) {
      mLiveData = liveData;
      mObserver = observer;
    }

    void plug() {
      mLiveData.observeForever(this);
    }

    void unplug() {
      mLiveData.removeObserver(this);
    }

    @Override
    public void onChanged(@Nullable V v) {
      if (mVersion != mLiveData.getVersion()) {
        mVersion = mLiveData.getVersion();
        mObserver.onChanged(v);
      }
    }
  }
｝

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/**
 * 基于MediatorLiveData，实现树形红点管理
 */
class RedPointManager : IRedPointManager {

  companion object {
    val TAG = "RedPointManager"

    @JvmStatic
    val instance: IRedPointManager by lazy(mode = LazyThreadSafetyMode.SYNCHRONIZED) {
      RedPointManager()
    }
  }

  override val liveDataA = MediatorLiveData<Boolean>()
  override val liveDataB1 = MediatorLiveData<Boolean>()
  override val liveDataB2 = MutableLiveData<Boolean>()
  override val liveDataC1 = MutableLiveData<Boolean>()
  override val liveDataC2 = MutableLiveData<Boolean>()

  init {
    Log.d(TAG, "RedPointManager init")
    /**
     * 构建树型关系。按路径层级，进行观察。一般外部只需要改动最低层的红点对应的LiveData，顶部的LiveData就会自动改变
     */
    liveDataA.addSource(liveDataB1, Observer {
      liveDataA.postValue(liveDataB1.isTrue() || liveDataB2.isTrue())
    })
    liveDataA.addSource(liveDataB2, Observer {
      liveDataA.postValue(liveDataB1.isTrue() || liveDataB2.isTrue())
    })

    liveDataB1.addSource(liveDataC1, Observer {
      liveDataB1.postValue(liveDataC1.isTrue() || liveDataC2.isTrue())
    })
    liveDataB1.addSource(liveDataC2, Observer {
      liveDataB1.postValue(liveDataC1.isTrue() || liveDataC2.isTrue())
    })
  }

  override fun testChangeDataC1(show: Boolean) {
    liveDataC1.postValue(show)
    Log.d(TAG, "testChangeDataC1: $show")
  }
}

/**
 * 定义接口
 * 提供只读的属性，提供修改liveData的方法
 */
interface IRedPointManager {
  val liveDataA: LiveData<Boolean>
  val liveDataB1: LiveData<Boolean>
  val liveDataB2: LiveData<Boolean>
  val liveDataC1: LiveData<Boolean>
  val liveDataC2: LiveData<Boolean>

  fun testChangeDataC1(show: Boolean)
}

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private fun testRedPointManager() {
    RedPointManager.instance.liveDataA.observe(this, Observer {
      Log.d(TAG, "liveDataA: $it")
    })
    RedPointManager.instance.liveDataB1.observe(this, Observer {
      Log.d(TAG, "liveDataB1: $it")
    })
    RedPointManager.instance.liveDataB2.observe(this, Observer {
      Log.d(TAG, "liveDataB2: $it")
    })
    RedPointManager.instance.liveDataC1.observe(this, Observer {
      Log.d(TAG, "liveDataC1: $it")
    })
    RedPointManager.instance.liveDataC2.observe(this, Observer {
      Log.d(TAG, "liveDataC2: $it")
    })
    RedPointManager.instance.testChangeDataC1(true)
  }
  
 //从输出日志可以发现，底层的liveDataC1发生改变，触发顶层的liveDataB1发生改变。liveDataB1的变化，也触发了liveDataA发生改变。
RedPointManager init
testChangeDataC1: true
liveDataC1: true
lveDataB1: true
liveDataA: true