AdapterViewProtocol.java

package com.google.android.apps.common.testing.ui.espresso.action;

import static com.google.common.base.Preconditions.checkNotNull;
import com.google.common.base.Optional;

import android.view.View;
import android.widget.Adapter;
import android.widget.AdapterView;

import javax.annotation.Nullable;

/**
 * A sadly necessary layer of indirection to interact with AdapterViews.
 * <p>
 * Generally any subclass should respect the contracts and behaviors of its superclass. Otherwise
 * it becomes impossible to work generically with objects that all claim to share a supertype - you
 * need special cases to perform the same operation 'owned' by the supertype for each sub-type. The
 * 'is - a' relationship is broken.
 * </p>
 *
 * <p>
 * Android breaks the Liskov substitution principal with ExpandableListView - you can't use
 * getAdapter(), getItemAtPosition(), and other methods common to AdapterViews on an
 * ExpandableListView because an ExpandableListView isn't an adapterView - they just share a lot of
 * code.
 * </p>
 *
 * <p>
 * This interface exists to work around this wart (which sadly is copied in other projects too) and
 * lets the implementor translate Espresso's needs and manipulations of the AdapterView into calls
 * that make sense for the given subtype and context.
 * </p>
 *
 * <p><i>
 * If you have to implement this to talk to widgets your own project defines - I'm sorry.
 * </i><p>
 *
 */
public interface AdapterViewProtocol {

  /**
   * Returns all data this AdapterViewProtocol can find within the given AdapterView.
   *
   * <p>
   * Any AdaptedData returned by this method can be passed to makeDataRenderedWithinView and the
   * implementation should make the AdapterView bring that data item onto the screen.
   * </p>
   *
   * @param adapterView the AdapterView we want to interrogate the contents of.
   * @return an {@link Iterable} of AdaptedDatas representing all data the implementation sees in
   *         this view
   * @throws IllegalArgumentException if the implementation doesn't know how to manipulate the given
   *         adapter view.
   */
  Iterable<AdaptedData> getDataInAdapterView(AdapterView<? extends Adapter> adapterView);

  /**
   * Returns the data object this particular view is rendering if possible.
   *
   * <p>
   * Implementations are expected to create a relationship between the data in the AdapterView and
   * the descendant views of the AdapterView that obeys the following conditions:
   * </p>
   *
   * <ul>
   * <li>For each descendant view there exists either 0 or 1 data objects it is rendering.</li>
   * <li>For each data object the AdapterView there exists either 0 or 1 descendant views which
   *   claim to be rendering it.</li>
   * </ul>
   *
   * <p> For example - if a PersonObject is rendered into: </p>
   * <code>
   * LinearLayout
   *   ImageView picture
   *   TextView firstName
   *   TextView lastName
   * </code>
   *
   * <p>
   * It would be expected that getDataRenderedByView(adapter, LinearLayout) would return the
   * PersonObject. If it were called instead with the TextView or ImageView it would return
   * Object.absent().
   * </p>
   *
   * @param adapterView the adapterview hosting the data.
   * @param descendantView a view which is a child, grand-child, or deeper descendant of adapterView
   * @return an optional data object the descendant view is rendering.
   * @throws IllegalArgumentException if this protocol cannot interrogate this class of adapterView
   */
  Optional<AdaptedData> getDataRenderedByView(
      AdapterView<? extends Adapter> adapterView, View descendantView);

  /**
   * Requests that a particular piece of data held in this AdapterView is actually rendered by it.
   *
   * <p>
   * After calling this method it expected that there will exist some descendant view of adapterView
   * for which calling getDataRenderedByView(adapterView, descView).get() == data.data is true.
   * <p>
   *
   * </p>
   * Note: this need not happen immediately. EG: an implementor handling ListView may call
   * listView.smoothScrollToPosition(data.opaqueToken) - which kicks off an animated scroll over
   * the list to the given position. The animation may be in progress after this call returns. The
   * only guarantee is that eventually - with no further interaction necessary - this data item
   * will be rendered as a child or deeper descendant of this AdapterView.
   * </p>
   *
   * @param adapterView the adapterView hosting the data.
   * @param data an AdaptedData instance retrieved by a prior call to getDataInAdapterView
   * @throws IllegalArgumentException if this protocol cannot manipulate adapterView or if data is
   *   not owned by this AdapterViewProtocol.
   */
  void makeDataRenderedWithinAdapterView(
      AdapterView<? extends Adapter> adapterView, AdaptedData data);


  /**
   * Indicates whether or not there now exists a descendant view within adapterView that
   * is rendering this data.
   *
   * @param adapterView the AdapterView hosting this data.
   * @param adaptedData the data we are checking the display state for.
   * @return true if the data is rendered by a view in the adapterView, false otherwise.
   */
  boolean isDataRenderedWithinAdapterView(
      AdapterView<? extends Adapter> adapterView, AdaptedData adaptedData);


  /**
   * A holder that associates a data object from an AdapterView with a token the
   * AdapterViewProtocol can use to force that data object to be rendered as a child or deeper
   * descendant of the adapter view.
   */
  public static class AdaptedData {

    /**
     * One of the objects the AdapterView is exposing to the user.
     */
    @Nullable
    public final Object data;

    /**
     * A token the implementor of AdapterViewProtocol can use to force the adapterView to display
     * this data object as a child or deeper descendant in it. Equal opaqueToken point to the same
     * data object on the AdapterView.
     */
    public final Object opaqueToken;

    @Override
    public String toString() {
      return String.format("Data: %s (class: %s) token: %s", data,
          null == data ? null : data.getClass(), opaqueToken);
    }

    private AdaptedData(Object data, Object opaqueToken) {
      this.data = data;
      this.opaqueToken = checkNotNull(opaqueToken);
    }

    public static class Builder {
      private Object data;
      private Object opaqueToken;

      public Builder withData(@Nullable Object data) {
        this.data = data;
        return this;
      }

      public Builder withOpaqueToken(@Nullable Object opaqueToken) {
        this.opaqueToken = opaqueToken;
        return this;
      }

      public AdaptedData build() {
        return new AdaptedData(data, opaqueToken);
      }
    }
  }
}