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diff --git a/src/com/android/uiautomator/core/UiWatcher.java b/src/com/android/uiautomator/core/UiWatcher.java
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+++ b/src/com/android/uiautomator/core/UiWatcher.java
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+/*
+ * Copyright (C) 2012 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 com.android.uiautomator.core;
+
+/**
+ * See {@link UiDevice#registerWatcher(String, UiWatcher)} on how to register a
+ * a condition watcher to be called by the automation library. The automation library will
+ * invoke checkForCondition() only when a regular API call is in retry mode because it is unable
+ * to locate its selector yet. Only during this time, the watchers are invoked to check if there is
+ * something else unexpected on the screen.
+ * @since API Level 16
+ */
+public interface UiWatcher {
+
+    /**
+     * Custom handler that is automatically called when the testing framework is unable to
+     * find a match using the {@link UiSelector}
+     *
+     * When the framework is in the process of matching a {@link UiSelector} and it
+     * is unable to match any widget based on the specified criteria in the selector,
+     * the framework will perform retries for a predetermined time, waiting for the display
+     * to update and show the desired widget. While the framework is in this state, it will call
+     * registered watchers' checkForCondition(). This gives the registered watchers a chance
+     * to take a look at the display and see if there is a recognized condition that can be
+     * handled and in doing so allowing the current test to continue.
+     *
+     * An example usage would be to look for dialogs popped due to other background
+     * processes requesting user attention and have nothing to do with the application
+     * currently under test.
+     *
+     * @return true to indicate a matched condition or false for nothing was matched
+     * @since API Level 16
+     */
+    public boolean checkForCondition();
+}