Android-Accessibility（Android(安卓)8.0以上）
Accessibility Overview
Accessible design allows users of all abilities to navigate, understand, and use your UI successfully.Android Accessibility的目的在于让所有的用户都能更方便的使用Android设备，不仅为残障人士提供了便利，更是方便了all users，比如你在开车，在做饭的时候。
说个题外话，看Google I/O 2017或2018开发者大会视频，讲解Accessibility in Android的Product Manager（Patrick Clary）and Technical Program Manager（Victor Tsaran）是两位残障人士，由衷的敬佩。
Impact of Accessibility
- Increase your app’s reach.
- Improve your app’s versatility.
全世界约有15%的残障人士，如果能使你的APP more Accessibility，那么会有更多的人使用；另外Accessibility不仅仅方便了残障人士，也能方便所有人，比如你在开车的时候也能用语音代替手势或点击行为。也有可以做一些外挂，比如微信抢红包什么的。
Build accessibility services
在分析内部的AccessibilityService之前，我们先来看看构建accessibility service基础知识，先有个宏观上的认识，再去分析内部实现。
Manifest declarations and permissions
Accessibility service declaration
Accessibility Service也是一个服务，需要在AndroidManifest.xml中声明，注意这里必须有BIND_ACCESSIBILITY_SERVICE permission，让Android System知道可以绑定。
<application> <service android:name=".MyAccessibilityService" android:permission="android.permission.BIND_ACCESSIBILITY_SERVICE" android:label="@string/accessibility_service_label"> <intent-filter> <action android:name="android.accessibilityservice.AccessibilityService" /> intent-filter> service> application>Accessibility service configuration
Accessibility Service还需要配置信息，指定服务处理时的accessibility events类型和关于服务的附加信息。配置信息可以通过AccessibilityServiceInfo类的setServiceInfo()方法配置。Android4.0后，可以在Manifest中包含 < meta-data> 元素。
For example：
AndroidManifest.xml
<service android:name=".MyAccessibilityService"> ... <meta-data android:name="android.accessibilityservice" android:resource="@xml/accessibility_service_config" />service>< project_dir>/res/xml/accessibility_service_config.xml
<accessibility-service xmlns:android="http://schemas.android.com/apk/res/android" android:description="@string/accessibility_service_description" android:packageNames="com.example.android.apis" android:accessibilityEventTypes="typeAllMask" android:accessibilityFlags="flagDefault" android:accessibilityFeedbackType="feedbackSpoken" android:notificationTimeout="100" android:canRetrieveWindowContent="true" android:settingsActivity="com.example.android.accessibility.ServiceSettingsActivity"/>属性的解释
Accessibility service methods
自己写的Accessibility Service必须从AccessibilityService继承，然后再重写里面的方法，这些方法都是被Android System调用。
- start service：
onServiceConnected() - running service：
onAccessibilityEvent(), onInterrupt() - close service：
onUnbind()
Register for accessibility events
Accessibility service configuration一个很重要的功能是告诉指定Accessibility Service可以处理哪些Accessibility Event，这些event可以靠两种方式判别：
- Package Names
- Event Types
Android Framework可能会把AccessibilityEvent分发给多个Accessibility Service，前提是这些Accessibility Service有不同的Feedback Types。如果多个Accessibility Service的Feedback Types相同，只有第一个注册的Accessibility Service会接收到这个Accessibility Event。
Accessibility volume
Android 8.0 (API level 26) 及以上，包含了STREAM_ACCESSIBILITYvolume category，可以独立于设备上其他的声音，只控制accessibility service的声音输出。通过调用AudioManager实例的 adjustStreamVolume()方法调节accessibility service的音量。
For example：
import static android.media.AudioManager.*;public class MyAccessibilityService extends AccessibilityService { private AudioManager mAudioManager = (AudioManager) getSystemService(AUDIO_SERVICE); @Override public void onAccessibilityEvent(AccessibilityEvent accessibilityEvent) { AccessibilityNodeInfo interactedNodeInfo = accessibilityEvent.getSource(); if (interactedNodeInfo.getText().equals("Increase volume")) { mAudioManager.adjustStreamVolume(AudioManager.STREAM_ACCESSIBILITY, ADJUST_RAISE, 0); } }}Accessibility shortcut
用户可以通过长按两个音量键来启用和禁用他们喜欢的Accessibility Service。
Accessibility button
导航栏的右侧包括一个Accessibility button。当用户按下这个按钮时，可以根据屏幕上显示的内容调用几个启用的Accessibility Service。Accessibility Service需要add FLAG_REQUEST_ACCESSIBILITY_BUTTONflag（android:accessibilityFlags），然后调用registerAccessibilityButtonCallback()。
For example：
private AccessibilityButtonController mAccessibilityButtonController;private AccessibilityButtonController .AccessibilityButtonCallback mAccessibilityButtonCallback;private boolean mIsAccessibilityButtonAvailable;@Overrideprotected void onServiceConnected() { mAccessibilityButtonController = getAccessibilityButtonController(); mIsAccessibilityButtonAvailable = mAccessibilityButtonController.isAccessibilityButtonAvailable(); if (!mIsAccessibilityButtonAvailable) { return; } AccessibilityServiceInfo serviceInfo = getServiceInfo(); serviceInfo.flags |= AccessibilityServiceInfo.FLAG_REQUEST_ACCESSIBILITY_BUTTON; setServiceInfo(serviceInfo); mAccessibilityButtonCallback = new AccessibilityButtonController.AccessibilityButtonCallback() { @Override public void onClicked(AccessibilityButtonController controller) { Log.d("MY_APP_TAG", "Accessibility button pressed!"); // Add custom logic for a service to react to the // accessibility button being pressed. } @Override public void onAvailabilityChanged( AccessibilityButtonController controller, boolean available) { if (controller.equals(mAccessibilityButtonController)) { mIsAccessibilityButtonAvailable = available; } } }; if (mAccessibilityButtonCallback != null) { mAccessibilityButtonController.registerAccessibilityButtonCallback( mAccessibilityButtonCallback, null); }}Fingerprint gestures
Accessibility Service可以响应另一种输入机制，即在设备的指纹传感器上进行定向滑动（向上、向下、左、右）。配置一个Service来接收这些交互的回调，需要完成以下步骤：
- 声明
USE_FINGERPRINTpermission 和CAPABILITY_CAN_REQUEST_FINGERPRINT_GESTUREScapability. - 设置
FLAG_REQUEST_FINGERPRINT_GESTURESflag（android:accessibilityFlags）. - 注册函数
registerFingerprintGestureCallback().
For example:
AndroidManifest.xml
<manifest ... > <uses-permission android:name="android.permission.USE_FINGERPRINT" /> ... <application> <service android:name="com.example.MyFingerprintGestureService" ... > <meta-data android:name="android.accessibilityservice" android:resource="@xml/myfingerprintgestureservice" /> service> application>manifest>myfingerprintgestureservice.xml
<accessibility-service xmlns:android="http://schemas.android.com/apk/res/android" ... android:accessibilityFlags=" ... |flagRequestFingerprintGestures" android:canRequestFingerprintGestures="true" ... />MyFingerprintGestureService.java
import static android.accessibilityservice.FingerprintGestureController.*;public class MyFingerprintGestureService extends AccessibilityService { private FingerprintGestureController mGestureController; private FingerprintGestureController .FingerprintGestureCallback mFingerprintGestureCallback; private boolean mIsGestureDetectionAvailable; @Override public void onCreate() { mGestureController = getFingerprintGestureController(); mIsGestureDetectionAvailable = mGestureController.isGestureDetectionAvailable(); } @Override protected void onServiceConnected() { if (mFingerprintGestureCallback != null || !mIsGestureDetectionAvailable) { return; } mFingerprintGestureCallback = new FingerprintGestureController.FingerprintGestureCallback() { @Override public void onGestureDetected(int gesture) { switch (gesture) { case FINGERPRINT_GESTURE_SWIPE_DOWN: moveGameCursorDown(); break; case FINGERPRINT_GESTURE_SWIPE_LEFT: moveGameCursorLeft(); break; case FINGERPRINT_GESTURE_SWIPE_RIGHT: moveGameCursorRight(); break; case FINGERPRINT_GESTURE_SWIPE_UP: moveGameCursorUp(); break; default: Log.e(MY_APP_TAG, "Error: Unknown gesture type detected!"); break; } } @Override public void onGestureDetectionAvailabilityChanged(boolean available) { mIsGestureDetectionAvailable = available; } }; if (mFingerprintGestureCallback != null) { mGestureController.registerFingerprintGestureCallback( mFingerprintGestureCallback, null); } }}Multilingual text to speech
text-to-speech (TTS) service可以在一个文本块识别和使用多种语言，要启用这种功能，需要将LocaleSpan对象中的所有字符串封装起来
For example：
TextView localeWrappedTextView = findViewById(R.id.my_french_greeting_text);localeWrappedTextView.setText(wrapTextInLocaleSpan("Bonjour!", Locale.FRANCE));private SpannableStringBuilder wrapTextInLocaleSpan( CharSequence originalText, Locale loc) { SpannableStringBuilder myLocaleBuilder = new SpannableStringBuilder(originalText); myLocaleBuilder.setSpan(new LocaleSpan(loc), 0, originalText.length() - 1, 0); return myLocaleBuilder;}Take action for users
从Android 4.0起，Accessibility Service可以代替用户做出Action，比如改变焦点（焦点就是当前正在处理事件的位置，比如有多个text输入框，同一时间内只能有一个输入框可以输入），模拟点击，模拟手势等等。
Listen for gestures
Accessibility Service可以监听特定的手势，然后代替用户做出反应。需要设置flags FLAG_REQUEST_TOUCH_EXPLORATION_MODE
public class MyAccessibilityService extends AccessibilityService { @Override public void onCreate() { getServiceInfo().flags = AccessibilityServiceInfo.FLAG_REQUEST_TOUCH_EXPLORATION_MODE; } ...}Continued gestures
可以通过Path表示手势的路径，然后用GestureDescription.StrokeDescription构造手势。
For example：
// Simulates an L-shaped drag path: 200 pixels right, then 200 pixels down.private void doRightThenDownDrag() { Path dragRightPath = new Path(); dragRightPath.moveTo(200, 200); dragRightPath.lineTo(400, 200); long dragRightDuration = 500L; // 0.5 second // The starting point of the second path must match // the ending point of the first path. Path dragDownPath = new Path(); dragDownPath.moveTo(400, 200); dragDownPath.lineTo(400, 400); long dragDownDuration = 500L; GestureDescription.StrokeDescription rightThenDownDrag = new GestureDescription.StrokeDescription(dragRightPath, 0L, dragRightDuration, true); rightThenDownDrag.continueStroke(dragDownPath, dragRightDuration, dragDownDuration, false);}Use accessibility actions
可以通过getSource()得到node，然后调用performAction做出Action。
public class MyAccessibilityService extends AccessibilityService { @Override public void onAccessibilityEvent(AccessibilityEvent event) { // get the source node of the event AccessibilityNodeInfo nodeInfo = event.getSource(); // Use the event and node information to determine // what action to take // take action on behalf of the user nodeInfo.performAction(AccessibilityNodeInfo.ACTION_SCROLL_FORWARD); // recycle the nodeInfo object nodeInfo.recycle(); } ...}Use focus types
可以用AccessibilityNodeInfo.findFocus()查找node有哪些元素具有Input Focus or Accessibility Focus，还可以使用focusSearch()选择Input Focus。最后使用performAction(AccessibilityNodeInfo.ACTION_SET_ACCESSIBILITY_FOCUS)设置Accessibility Focus。
Gather information
Accessibility services also have standard methods of gathering and representing key units of user-provided information, such as event details, text, and numbers.
Get event details
AccessibilityEvent.getRecordCount()或getRecord(int)AccessibilityEvent.getSource()- 返回一个AccessibilityNodeInfo对象
Process text
Hint text
isShowingHintText()andsetShowingHintText()getHintText()
Locations of on-screen text characters
refreshWithExtraData()
Standardized one-sided range values
一些AccessibilityNodeInfo对象用AccessibilityNodeInfo.RangeInfo的实例表示UI元素的范围值。
- For ranges with no minimum,
Float.NEGATIVE_INFINITYrepresents the minimum value. - For ranges with no maximum,
Float.POSITIVE_INFINITYrepresents the maximum value.
Build an accessibility service
这一部分会介绍构建一个accessibility service的flow，从应用程序接收到的信息，然后该信息反馈给用户。
Create your accessibility service
create class
package com.example.android.apis.accessibility;import android.accessibilityservice.AccessibilityService;import android.view.accessibility.AccessibilityEvent;public class MyAccessibilityService extends AccessibilityService {... @Override public void onAccessibilityEvent(AccessibilityEvent event) { } @Override public void onInterrupt() { }...}AndroidManifest.xml
<application ...>...<service android:name=".MyAccessibilityService"> <intent-filter> <action android:name="android.accessibilityservice.AccessibilityService" /> intent-filter> . . .service>...application>Configure your accessibility service
告诉Android System，你想怎么运行，何时运行，你想对何种AccessibilityEvent做出回应，Service是否要监听所有Application，还是特定的Application，使用哪种feedback types。
有两种方法，一种是setServiceInfo(android.accessibilityservice.AccessibilityServiceInfo)，然后重写onServiceConnected()。
For example：
@Overridepublic void onServiceConnected() { // Set the type of events that this service wants to listen to. Others // won't be passed to this service. info.eventTypes = AccessibilityEvent.TYPE_VIEW_CLICKED | AccessibilityEvent.TYPE_VIEW_FOCUSED; // If you only want this service to work with specific applications, set their // package names here. Otherwise, when the service is activated, it will listen // to events from all applications. info.packageNames = new String[] {"com.example.android.myFirstApp", "com.example.android.mySecondApp"}; // Set the type of feedback your service will provide. info.feedbackType = AccessibilityServiceInfo.FEEDBACK_SPOKEN; // Default services are invoked only if no package-specific ones are present // for the type of AccessibilityEvent generated. This service *is* // application-specific, so the flag isn't necessary. If this was a // general-purpose service, it would be worth considering setting the // DEFAULT flag. // info.flags = AccessibilityServiceInfo.DEFAULT; info.notificationTimeout = 100; this.setServiceInfo(info);}另一种方法是使用xml方法
For example：
<accessibility-service android:accessibilityEventTypes="typeViewClicked|typeViewFocused" android:packageNames="com.example.android.myFirstApp, com.example.android.mySecondApp" android:accessibilityFeedbackType="feedbackSpoken" android:notificationTimeout="100" android:settingsActivity="com.example.android.apis.accessibility.TestBackActivity" android:canRetrieveWindowContent="true"/>同时在AndroidManifest.xml中添加< meta-data>，假设XML file 在res/xml/serviceconfig.xml
<service android:name=".MyAccessibilityService"> <intent-filter> <action android:name="android.accessibilityservice.AccessibilityService" /> intent-filter> <meta-data android:name="android.accessibilityservice" android:resource="@xml/serviceconfig" />service>Respond to accessibility events
当监听有AccessibilityEvent时，使用onAccessibilityEvent(AccessibilityEvent)方法做出回应。用getEventType()获取AccessibilityEvent Type，getContentDescription()提取与触发事件的视图有关的标签文本。
For example:
@Overridepublic void onAccessibilityEvent(AccessibilityEvent event) { final int eventType = event.getEventType(); String eventText = null; switch(eventType) { case AccessibilityEvent.TYPE_VIEW_CLICKED: eventText = "Clicked: "; break; case AccessibilityEvent.TYPE_VIEW_FOCUSED: eventText = "Focused: "; break; } eventText = eventText + event.getContentDescription(); // Do something nifty with this text, like speak the composed string // back to the user. speakToUser(eventText); ...}Query the view hierarchy for more context
有时候，需要得到视图的相关信息，可以查看视图的层次关系，为了做到这一点，需要现在xml中配置。
android:canRetrieveWindowContent="true"使用getSource()获得AccessibilityNodeInfo对象，当接收到一个AccessibilityEvent时，它会做以下事情：
1.抓住该事件视图的父节点。
2.在该视图（父节点）寻找label and check box作为子视图。
3.如果它找到了它们，就创建一个字符串来向用户报告，指示标签，以及是否检查了它。
4.如果在遍历视图层级时返回null（不管什么时候），那么该方法就会放弃。
For example：
// Alternative onAccessibilityEvent, that uses AccessibilityNodeInfo@Overridepublic void onAccessibilityEvent(AccessibilityEvent event) { AccessibilityNodeInfo source = event.getSource(); if (source == null) { return; } // Grab the parent of the view that fired the event. AccessibilityNodeInfo rowNode = getListItemNodeInfo(source); if (rowNode == null) { return; } // Using this parent, get references to both child nodes, the label and the checkbox. AccessibilityNodeInfo labelNode = rowNode.getChild(0); if (labelNode == null) { rowNode.recycle(); return; } AccessibilityNodeInfo completeNode = rowNode.getChild(1); if (completeNode == null) { rowNode.recycle(); return; } // Determine what the task is and whether or not it's complete, based on // the text inside the label, and the state of the check-box. if (rowNode.getChildCount() < 2 || !rowNode.getChild(1).isCheckable()) { rowNode.recycle(); return; } CharSequence taskLabel = labelNode.getText(); final boolean isComplete = completeNode.isChecked(); String completeStr = null; if (isComplete) { completeStr = getString(R.string.checked); } else { completeStr = getString(R.string.not_checked); } String reportStr = taskLabel + completeStr; speakToUser(reportStr);}以上基本是Android官网的学习资料，下一篇会学习AccessibilityService的源码，看看内部是怎么实现的。
请看Android 9.0源码学习-AccessibilityManager
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