content: /*
   * Copyright (C) 2014 The Android Open Source Project
   *
   * 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 androidx.test.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.
     *
     * <p>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 <a href="http://hamcrest.org/JavaHamcrest/javadoc/1.3/org/hamcrest/Matcher.html">
     *     <code>Matcher</code></a> 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);
  }
  