Android-Accessibility（Android 8.

作者: Dufre | 来源:发表于2018-10-09 20:35 被阅读24次

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。

在这里插入图片描述

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

在这里插入图片描述

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;

@Override
protected 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()and setShowingHintText()
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：

@Override
public 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:

@Override
public 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

@Override
public 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。

Android-Accessibility（Android 8.

Accessibility Overview

Impact of Accessibility

Build accessibility services

Manifest declarations and permissions

Accessibility service declaration

Accessibility service configuration

Accessibility service methods

Register for accessibility events

Accessibility volume

Accessibility shortcut

Accessibility button

Fingerprint gestures

Multilingual text to speech

Take action for users

Listen for gestures

Continued gestures

Use accessibility actions

Use focus types

Gather information

Get event details

Process text

Standardized one-sided range values

Build an accessibility service

Create your accessibility service

Configure your accessibility service

Respond to accessibility events

Query the view hierarchy for more context

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