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Containing the common interfaces of mosby mvp

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/*
 * Copyright 2015 Hannes Dorfmann.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.hannesdorfmann.mosby.mvp;

import android.support.annotation.Nullable;
import java.lang.ref.WeakReference;

/**
 * A base implementation of a {@link MvpPresenter} that uses a WeakReference for referring
 * to the attached view.
 * 
 * You should always check {@link #isViewAttached()} to check if the view is attached to this
 * presenter before calling {@link #getView()} to access the view.
 * 
 *
 * @param  type of the {@link MvpView}
 * @author Hannes Dorfmann
 * @see MvpNullObjectBasePresenter
 * @since 1.0.0
 */
public class MvpBasePresenter implements MvpPresenter {

  private WeakReference viewRef;

  @Override public void attachView(V view) {
    viewRef = new WeakReference(view);
  }

  /**
   * Get the attached view. You should always call {@link #isViewAttached()} to check if the view
   * is
   * attached to avoid NullPointerExceptions.
   *
   * @return null, if view is not attached, otherwise the concrete view instance
   */
  @Nullable public V getView() {
    return viewRef == null ? null : viewRef.get();
  }

  /**
   * Checks if a view is attached to this presenter. You should always call this method before
   * calling {@link #getView()} to get the view instance.
   */
  public boolean isViewAttached() {
    return viewRef != null && viewRef.get() != null;
  }

  @Override public void detachView(boolean retainInstance) {
    if (viewRef != null) {
      viewRef.clear();
      viewRef = null;
    }
  }
}