ViewAction.java

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

import android.view.View;

import org.hamcrest.Matcher;

/**
 * Responsible for performing an interaction on the given View element.<br>
 * <p>
 * This is part of the test framework public API - developers are free to write their own ViewAction
 * implementations when necessary. When implementing a new ViewAction, follow these rules:
 * <ul>
 * <li>Inject motion events or key events via the UiController to simulate user interactions.
 * <li>Do not mutate the view directly via setter methods and other state changing methods on the
 * view parameter.
 * <li>Do not throw AssertionErrors. Assertions belong in ViewAssertion classes.
 * <li>View action code will executed on the UI thread, therefore you should not block, perform
 * sleeps, or perform other expensive computations.
 * <li>The test framework will wait for the UI thread to be idle both before and after perform() is
 * called. This means that the action is guaranteed to be synchronized with any other view
 * operations.
 * <li>Downcasting the View object to an expected subtype is allowed, so long as the object
 * expresses the subtype matches the constraints as specified in {@code getConstraints}.
 * </ul>
 */
public interface ViewAction {

  /**
   * A mechanism for ViewActions to specify what type of views they can operate on.
   *
   *  A ViewAction can demand that the view passed to perform meets certain constraints. For example
   * it may want to ensure the view is already in the viewable physical screen of the device or is
   * of a certain type.
   *
   * @return a {@link Matcher} that will be tested prior to calling perform.
   */
  public Matcher<View> getConstraints();

  /**
   * Returns a description of the view action. The description should not be overly long and should
   * fit nicely in a sentence like: "performing %description% action on view with id ..."
   */
  public String getDescription();

  /**
   * Performs this action on the given view.
   *
   * @param uiController the controller to use to interact with the UI.
   * @param view the view to act upon. never null.
   */
  public void perform(UiController uiController, View view);
}