Android LiveData使用需要注意的地方

/**
* 事件包装器，明确地管理事件是否已经被处理
* @param <T> ViewModel中的数据，比如： 
* MutableLiveData<LiveEventWrapper<String>>()
*/
public class LiveEventWrapper<T> {

  private T content;
  private boolean hasBeenHandled;

  public LiveEventWrapper(T content) {
    this.content = content;
  }

  /**
   * Returns the content and prevents its use again.
   */
  public T getContentIfNotHandled() {
    if (hasBeenHandled) {
      return null;
    } else {
      hasBeenHandled = true;
      return content;
    }
  }

  /**
   * Returns the content, even if it's already been handled.
   */
  public T peekContent() {
    return content;
  }

  public boolean isHasBeenHandled() {
    return hasBeenHandled;
  }

}

import androidx.annotation.NonNull;
import androidx.lifecycle.LifecycleOwner;
import androidx.lifecycle.LiveData;
import androidx.lifecycle.Observer;

public class CleanLiveData<T> extends LiveData<T> {
  private boolean hasModified = false;

  @Override
  public void observe(@NonNull LifecycleOwner owner, @NonNull final Observer<? super T> observer) {
    super.observe(owner, new Observer<T>() {
      private boolean hasIntercept = false;

      @Override
      public void onChanged(T t) {
        if (!hasModified || hasIntercept) {
          observer.onChanged(t);
        }
        hasIntercept = true;
      }
    });
  }

  @Override
  public void observeForever(@NonNull final Observer<? super T> observer) {
    super.observeForever(new Observer<T>() {
      private boolean hasIntercept = false;

      @Override
      public void onChanged(T t) {
        if (!hasModified || hasIntercept) {
          observer.onChanged(t);
        }
        hasIntercept = true;
      }
    });
  }

  @Override
  public void setValue(T value) {
    super.setValue(value);
    hasModified = true;
  }

  @Override
  public void postValue(T value) {
    super.postValue(value);
    hasModified = true;
  }

}