Service——AIDL

原文(英文)地址

AIDL（Android 接口定义语言）与您可能使用过的其他 IDL 类似。您可以利用它定义客户端与服务端使用进程间通信 (IPC) 进行相互通信时都认可的编程接口。在 Android 上，一个进程通常无法访问另一个进程的内存，所以，进程需要将其原对象分解成操作系统能够识别的原语，进而将原对象编组成可跨越边界的对象。编写执行这一编组操作的代码是一项繁琐的工作，因此 Android 会使用 AIDL 来处理。

注：只有当即允许处于其他应用中的客户端用 IPC 方式访问你的Service，并且想要在Service中处理多线程时，才有必要使用 AIDL。如果您不需要执行跨越不同应用的并发 IPC，就应该通过实现一个 Binder 创建接口；或者，如果您想执行 IPC，但根本不需要处理多线程，则使用 Messenger 类来实现接口。无论如何，在实现 AIDL 之前，请您务必理解绑定Service。

在您开始设计 AIDL 接口之前，要注意 AIDL 接口的调用是直接调用函数(direct function calls)。您不应该猜想发生调用的线程到底是哪一个，因为调用是来自本地进程中的线程和来自远程进程中的线程是两种不同的情况，特别是：

来自本地进程的调用会在发起调用的相同线程中执行。如果该线程是您的 UI 线程，则该线程继续在 AIDL 接口中执行。如果该线程是其他线程，则其便是在Service中执行您的代码的线程。因此，只有在本地线程访问Service时，您才能完全控制哪些线程在Service中执行（但如果真是这种情况，您根本不应该使用 AIDL，而是应该通过实现 Binder 类创建接口）。
来自远程进程的调用将从平台在您自己的进程内维护的线程池中调度。您必须为来自未知线程的传入调用做好准备，同时发生多个调用。换句话说，AIDL接口的实现必须完全是线程安全的。从同一远程对象上的一个线程进行的调用按顺序到达接收器端。
oneway 关键字用于修改远程调用的行为。使用该关键字时，远程调用不会阻塞；它只是发送事务数据并立即返回。接口的实现最终接收此调用时，是以正常远程调用形式将其作为来自 Binder 线程池的常规调用进行接收。如果 oneway 用于本地调用，则不会有任何影响，调用仍是同步调用。

定义 AIDL 接口

您必须使用 Java 编程语言语法在 .aidl 文件中定义 AIDL 接口，然后将它保存在托管Service的应用以及任何其他绑定到Service的应用的源代码（src/ ）目录内。

您开发每个包含 .aidl 文件的应用时，Android SDK 工具都会生成一个基于该 .aidl 文件的 IBinder 接口，并将其保存在项目的 gen/ 目录中。Service必须视情况实现 IBinder 接口。然后客户端应用便可绑定到该Service，并调用 IBinder 中的方法来执行 IPC。

如需使用 AIDL 创建绑定Service，请执行以下步骤：

创建 .aidl 文件

此文件定义带有方法签名的编程接口。
实现接口

Android SDK 工具基于您的 .aidl 文件，使用 Java 编程语言生成一个接口。此接口具有一个名为 Stub 的内部抽象类，用于扩展 Binder 类并实现 AIDL 接口中的方法。您必须继承 Stub 类并实现方这些法。
向客户端公开该接口

实现 Service 并重写 onBind() 以返回 Stub 类的实现。

注意：在 AIDL 接口首次发布后对其进行的任何更改都必须保持向后兼容性，以避免中断其他应用对您的Service的使用。也就是说，因为必须将您的 .aidl 文件复制到其他应用，才能让这些应用访问您的Service的接口，因此您必须保留对原始接口的支持。

创建 .aidl 文件

AIDL 的语法很简单，它使您能通过可带参数和返回值的一个或多个方法来声明接口。参数和返回值可以是任意类型，甚至可以是其他 AIDL 生成的接口。

您必须使用 Java 编程语言构建 .aidl 文件。每个 .aidl 文件都必须定义单个接口，并且只需包含接口声明和方法签名。

默认情况下，AIDL 支持下列数据类型：

Java 编程语言中的所有原语类型（如 int、long、char、boolean 等等）
String
CharSequence
List

List 中的所有元素都必须是以上列表中支持的数据类型、其他 AIDL 生成的接口或您声明的可打包类型。可选择将 List 用作“通用”类（例如，List<String>）。另一端实际接收的具体类始终是 ArrayList，但生成的方法使用的是 List 接口。
Map

Map 中的所有元素都必须是以上列表中支持的数据类型、其他 AIDL 生成的接口或您声明的可打包类型。不支持通用 Map（如 Map<String,Integer> 形式的 Map）。另一端实际接收的具体类始终是 HashMap，但生成的方法使用的是 Map 接口。

您必须为以上未列出的每个附加类型加入一个 import 语句，即使这些类型是在与您的接口相同包中定义的。

定义Service接口时，请注意：

方法可带零个或多个参数，返回值或空值。
所有非原语参数都需要指示数据走向的方向标记。可以是in、out或者inout（见以下示例）。

原语默认为 in，不能是其他的方向。

注意：您应该将方向限定为真正需要的方向，因为编组参数的开销极大。
.aidl 文件中包括的所有代码注释都包含在生成的 IBinder 接口中（import 和 package 语句之前的注释除外）
可以在aidl接口中定义String和int类型的常量，比如const int VERSION=1
方法的调用由transact（）进行调度，该代码通常基于接口中的方法索引。因为这会使版本控制变得困难，所以您可以手动将事务代码分配给方法：void method（）= 10;。
使用@nullable注释可为空的参数或返回类型。

以下是一个 .aidl 文件示例：

// IRemoteService.aidl
package com.example.android;

// Declare any non-default types here with import statements

/** Example service interface */
interface IRemoteService {
    /** Request the process ID of this service, to do evil things with it. */
    int getPid();

    /** Demonstrates some basic types that you can use as parameters
     * and return values in AIDL.
     */
    void basicTypes(int anInt, long aLong, boolean aBoolean, float aFloat,
            double aDouble, String aString);
}

只需将您的 .aidl 文件保存在项目的 src/ 目录内，当您build应用时，SDK 工具会在项目的gen/ 目录中生成 IBinder 接口文件。生成的文件名与 .aidl 文件名一致，只是使用了.java 扩展名（例如，IRemoteService.aidl 生成的文件名是 IRemoteService.java）。

如果您使用 Android Studio，增量编译（incremental build）几乎会立即生成 Binder 类。如果您不使用 Android Studio，则 Gradle 工具会在您下一次build应用时生成 Binder 类(您应该在编写完 .aidl 文件后立即用 gradle assembleDebug （或 gradle assembleRelease）编译项目，以便您的代码能够链接到生成的类）。

实现接口

当您开发应用时，Android SDK 工具会生成一个以 .aidl 文件命名的 .java 接口文件。生成的接口包括一个名为 Stub 的子类，这个子类是其父接口（例如，YourInterface.Stub）的抽象实现，用于声明 .aidl 文件中的所有方法。

注：Stub 还定义了几个helper method，其中最引人关注的是 asInterface()，该方法有一个 IBinder参数（通常便是传递给客户端 onServiceConnected() 回调方法的参数）并返回stub interface的实例。如需了解如何进行这种转换的更多详细信息，请参见调用 IPC 方法一节。

如需实现 .aidl 生成的接口，请继承生成的 Binder 接口（例如，YourInterface.Stub）并实现从 .aidl 文件继承的方法。

以下是一个使用匿名实例实现名为 IRemoteService 的接口（由以上 IRemoteService.aidl示例定义）的示例：

kotlin

private val binder = object : IRemoteService.Stub() {

    override fun getPid(): Int =
            Process.myPid()

    override fun basicTypes(
            anInt: Int,
            aLong: Long,
            aBoolean: Boolean,
            aFloat: Float,
            aDouble: Double,
            aString: String
    ) {
        // Does nothing
    }
}

java

private final IRemoteService.Stub binder = new IRemoteService.Stub() {
    public int getPid(){
        return Process.myPid();
    }
    public void basicTypes(int anInt, long aLong, boolean aBoolean,
        float aFloat, double aDouble, String aString) {
        // Does nothing
    }
};

现在，mBinder 是 Stub 类的一个实例（一个 Binder），用于定义Service的 RPC 接口。在下一步中，将向客户端公开该实例，以便客户端能与Service进行交互。

在实现 AIDL 接口时应注意遵守以下这几个规则：

由于不能保证在主线程上执行传入调用，因此您一开始就需要做好多线程处理准备，并将您的Service正确地编译为线程安全的Service。
默认情况下，RPC 调用是同步调用。如果您明知Service完成请求的时间不止几毫秒，就不应该从 Activity 的主线程调用Service，因为这样做可能会使应用挂起（Android 可能会显示“Application is Not Responding”对话框），您通常应该从客户端内的单独线程调用Service。
您引发的任何异常都不会回传给调用方。

向客户端公开该接口

您为Service实现该接口后，就需要向客户端公开该接口，以便客户端进行绑定。要为您的Service公开该接口，请继承 Service 并实现 onBind()，以返回一个类实例，这个类实现了生成的Stub（见前文所述）。以下是一个向客户端公开 IRemoteService 示例接口的Service示例。

kotlin

class RemoteService : Service() {

    override fun onCreate() {
        super.onCreate()
    }

    override fun onBind(intent: Intent): IBinder {
        // Return the interface
        return binder
    }


    private val binder = object : IRemoteService.Stub() {
        override fun getPid(): Int {
            return Process.myPid()
        }

        override fun basicTypes(
                anInt: Int,
                aLong: Long,
                aBoolean: Boolean,
                aFloat: Float,
                aDouble: Double,
                aString: String
        ) {
            // Does nothing
        }
    }
}

java

public class RemoteService extends Service {
    @Override
    public void onCreate() {
        super.onCreate();
    }

    @Override
    public IBinder onBind(Intent intent) {
        // Return the interface
        return binder;
    }

    private final IRemoteService.Stub binder = new IRemoteService.Stub() {
        public int getPid(){
            return Process.myPid();
        }
        public void basicTypes(int anInt, long aLong, boolean aBoolean,
            float aFloat, double aDouble, String aString) {
            // Does nothing
        }
    };
}

现在，当客户端（如 Activity）调用 bindService() 以连接此Service时，客户端的 onServiceConnected() 回调会接收Service的 onBind() 方法返回的 mBinder 实例。

客户端还必须具有对 interface 类的访问权限，因此如果客户端和Service在不同的应用内，则客户端的应用 src/ 目录内必须包含 .aidl 文件（它生成 android.os.Binder 接口 — 为客户端提供对 AIDL 方法的访问权限）的副本。

当客户端在 onServiceConnected() 回调中收到 IBinder 时，它必须调用YourServiceInterface.Stub.asInterface(service) 以将返回的参数转换成YourServiceInterface 类型。例如：

kotlin

var iRemoteService: IRemoteService? = null

val mConnection = object : ServiceConnection {

    // Called when the connection with the service is established
    override fun onServiceConnected(className: ComponentName, service: IBinder) {
        // Following the example above for an AIDL interface,
        // this gets an instance of the IRemoteInterface, which we can use to call on the service
        iRemoteService = IRemoteService.Stub.asInterface(service)
    }

    // Called when the connection with the service disconnects unexpectedly
    override fun onServiceDisconnected(className: ComponentName) {
        Log.e(TAG, "Service has unexpectedly disconnected")
        iRemoteService = null
    }
}

java

IRemoteService iRemoteService;
private ServiceConnection mConnection = new ServiceConnection() {
    // Called when the connection with the service is established
    public void onServiceConnected(ComponentName className, IBinder service) {
        // Following the example above for an AIDL interface,
        // this gets an instance of the IRemoteInterface, which we can use to call on the service
        iRemoteService = IRemoteService.Stub.asInterface(service);
    }

    // Called when the connection with the service disconnects unexpectedly
    public void onServiceDisconnected(ComponentName className) {
        Log.e(TAG, "Service has unexpectedly disconnected");
        iRemoteService = null;
    }
};

如需查看更多示例代码，请参见 ApiDemos 中的 RemoteService.java 类。

通过 IPC 传递对象

通过 IPC 接口把某个类从一个进程发送到另一个进程是可以实现的。不过，您必须确保该类的代码对 IPC 通道的另一端可用，并且该类必须支持 Parcelable 接口。支持 Parcelable 接口很重要，因为 Android 系统可通过它将对象分解成可编组到各进程的原语。

如需创建支持 Parcelable 协议的类，您必须执行以下操作：

让您的类实现 Parcelable 接口。
实现 writeToParcel，它会获取对象的当前状态并将其写入 Parcel。
为您的类添加一个名为 CREATOR 的静态字段，这个字段是一个实现Parcelable.Creator 接口的对象。
最后，创建一个声明可打包类的.aidl文件（按照下文Rect.aidl文件所示步骤）。

如果您使用的是自定义编译进程，切勿在您的编译中添加 .aidl 文件。此 .aidl 文件与 C 语言中的头文件类似，并未编译。

AIDL 在它生成的代码中使用这些方法和字段将您的对象编组和取消编组。

例如，以下这个 Rect.aidl 文件可创建一个可打包的 Rect 类：

package android.graphics;

// Declare Rect so AIDL can find it and knows that it implements
// the parcelable protocol.
parcelable Rect;

以下示例展示了 Rect 类如何实现 Parcelable 协议。

kotlin

import android.os.Parcel
import android.os.Parcelable

class Rect() : Parcelable {
    var left: Int = 0
    var top: Int = 0
    var right: Int = 0
    var bottom: Int = 0

    companion object CREATOR : Parcelable.Creator<Rect> {
        override fun createFromParcel(parcel: Parcel): Rect {
            return Rect(parcel)
        }

        override fun newArray(size: Int): Array<Rect> {
            return Array(size) { Rect() }
        }
    }

    private constructor(inParcel: Parcel) : this() {
        readFromParcel(inParcel)
    }

    override fun writeToParcel(outParcel: Parcel, flags: Int) {
        outParcel.writeInt(left)
        outParcel.writeInt(top)
        outParcel.writeInt(right)
        outParcel.writeInt(bottom)
    }

    private fun readFromParcel(inParcel: Parcel) {
        left = inParcel.readInt()
        top = inParcel.readInt()
        right = inParcel.readInt()
        bottom = inParcel.readInt()
    }

    override fun describeContents(): Int {
        return 0
    }
}

java

import android.os.Parcel;
import android.os.Parcelable;

public final class Rect implements Parcelable {
    public int left;
    public int top;
    public int right;
    public int bottom;

    public static final Parcelable.Creator<Rect> CREATOR = new Parcelable.Creator<Rect>() {
        public Rect createFromParcel(Parcel in) {
            return new Rect(in);
        }

        public Rect[] newArray(int size) {
            return new Rect[size];
        }
    };

    public Rect() {
    }

    private Rect(Parcel in) {
        readFromParcel(in);
    }

    public void writeToParcel(Parcel out, int flags) {
        out.writeInt(left);
        out.writeInt(top);
        out.writeInt(right);
        out.writeInt(bottom);
    }

    public void readFromParcel(Parcel in) {
        left = in.readInt();
        top = in.readInt();
        right = in.readInt();
        bottom = in.readInt();
    }

    public int describeContents() {
        return 0;
    }
}

Rect 类中的编组相当简单。看一看 Parcel 上的其他方法，了解您可以向 Parcel 写入哪些其他类型的值。

**警告：**别忘记从其他进程接收数据的安全影响。在本例中，Rect 从 Parcel 读取四个数字，但要由您来确保无论调用方目的为何这些数字都在相应的可接受值范围内。如需了解有关如何防止应用受到恶意软件侵害、保证应用安全的更多信息，请参见安全与权限。

调用 IPC 方法

调用类必须执行以下步骤，才能调用使用 AIDL 定义的远程接口：

在项目 src/ 目录中加入 .aidl 文件。
声明一个 IBinder 接口实例（基于 AIDL 生成）。
实现 ServiceConnection。
调用 Context.bindService()，以传入您的 ServiceConnection 实现。
在您的 onServiceConnected() 实现中，您将收到一个 IBinder 实例（名为 service）。调用 *YourInterfaceName*.Stub.asInterface((IBinder)*service*)，以将返回的参数转换为 YourInterface 类型。
调用您在接口上定义的方法。您应该始终捕获 DeadObjectException 异常，它们是在连接中断时引发的；这将是远程方法引发的唯一异常。
如需断开连接，请使用您的接口实例调用 Context.unbindService()。

有关调用 IPC Service的几点说明：

对象是跨进程计数的引用。
您可以将匿名对象作为方法参数发送。

如需了解有关绑定到Service的详细信息，请阅读绑定Service文档。

以下这些示例代码摘自 ApiDemos 项目的远程Service示例代码，展示了如何调用 AIDL 创建的Service。

kotlin

private const val BUMP_MSG = 1

class Binding : Activity() {

    /** The primary interface we will be calling on the service.  */
    private var mService: IRemoteService? = null

    /** Another interface we use on the service.  */
    internal var secondaryService: ISecondary? = null

    private lateinit var killButton: Button
    private lateinit var callbackText: TextView
    private lateinit var handler: InternalHandler

    private var isBound: Boolean = false

    /**
     * Class for interacting with the main interface of the service.
     */
    private val mConnection = object : ServiceConnection {

        override fun onServiceConnected(className: ComponentName, service: IBinder) {
            // This is called when the connection with the service has been
            // established, giving us the service object we can use to
            // interact with the service.  We are communicating with our
            // service through an IDL interface, so get a client-side
            // representation of that from the raw service object.
            mService = IRemoteService.Stub.asInterface(service)
            killButton.isEnabled = true
            callbackText.text = "Attached."

            // We want to monitor the service for as long as we are
            // connected to it.
            try {
                mService?.registerCallback(mCallback)
            } catch (e: RemoteException) {
                // In this case the service has crashed before we could even
                // do anything with it; we can count on soon being
                // disconnected (and then reconnected if it can be restarted)
                // so there is no need to do anything here.
            }

            // As part of the sample, tell the user what happened.
            Toast.makeText(
                    this@Binding,
                    R.string.remote_service_connected,
                    Toast.LENGTH_SHORT
            ).show()
        }

        override fun onServiceDisconnected(className: ComponentName) {
            // This is called when the connection with the service has been
            // unexpectedly disconnected -- that is, its process crashed.
            mService = null
            killButton.isEnabled = false
            callbackText.text = "Disconnected."

            // As part of the sample, tell the user what happened.
            Toast.makeText(
                    this@Binding,
                    R.string.remote_service_disconnected,
                    Toast.LENGTH_SHORT
            ).show()
        }
    }

    /**
     * Class for interacting with the secondary interface of the service.
     */
    private val secondaryConnection = object : ServiceConnection {

        override fun onServiceConnected(className: ComponentName, service: IBinder) {
            // Connecting to a secondary interface is the same as any
            // other interface.
            secondaryService = ISecondary.Stub.asInterface(service)
            killButton.isEnabled = true
        }

        override fun onServiceDisconnected(className: ComponentName) {
            secondaryService = null
            killButton.isEnabled = false
        }
    }

    private val mBindListener = View.OnClickListener {
        // Establish a couple connections with the service, binding
        // by interface names.  This allows other applications to be
        // installed that replace the remote service by implementing
        // the same interface.
        val intent = Intent(this@Binding, RemoteService::class.java)
        intent.action = IRemoteService::class.java.name
        bindService(intent, mConnection, Context.BIND_AUTO_CREATE)
        intent.action = ISecondary::class.java.name
        bindService(intent, secondaryConnection, Context.BIND_AUTO_CREATE)
        isBound = true
        callbackText.text = "Binding."
    }

    private val unbindListener = View.OnClickListener {
        if (isBound) {
            // If we have received the service, and hence registered with
            // it, then now is the time to unregister.
            try {
                mService?.unregisterCallback(mCallback)
            } catch (e: RemoteException) {
                // There is nothing special we need to do if the service
                // has crashed.
            }

            // Detach our existing connection.
            unbindService(mConnection)
            unbindService(secondaryConnection)
            killButton.isEnabled = false
            isBound = false
            callbackText.text = "Unbinding."
        }
    }

    private val killListener = View.OnClickListener {
        // To kill the process hosting our service, we need to know its
        // PID.  Conveniently our service has a call that will return
        // to us that information.
        try {
            secondaryService?.pid?.also { pid ->
                // Note that, though this API allows us to request to
                // kill any process based on its PID, the kernel will
                // still impose standard restrictions on which PIDs you
                // are actually able to kill.  Typically this means only
                // the process running your application and any additional
                // processes created by that app as shown here; packages
                // sharing a common UID will also be able to kill each
                // other's processes.
                Process.killProcess(pid)
                callbackText.text = "Killed service process."
            }
        } catch (ex: RemoteException) {
            // Recover gracefully from the process hosting the
            // server dying.
            // Just for purposes of the sample, put up a notification.
            Toast.makeText(this@Binding, R.string.remote_call_failed, Toast.LENGTH_SHORT).show()
        }
    }

    // ----------------------------------------------------------------------
    // Code showing how to deal with callbacks.
    // ----------------------------------------------------------------------

    /**
     * This implementation is used to receive callbacks from the remote
     * service.
     */
    private val mCallback = object : IRemoteServiceCallback.Stub() {
        /**
         * This is called by the remote service regularly to tell us about
         * new values.  Note that IPC calls are dispatched through a thread
         * pool running in each process, so the code executing here will
         * NOT be running in our main thread like most other things -- so,
         * to update the UI, we need to use a Handler to hop over there.
         */
        override fun valueChanged(value: Int) {
            handler.sendMessage(handler.obtainMessage(BUMP_MSG, value, 0))
        }
    }

    /**
     * Standard initialization of this activity.  Set up the UI, then wait
     * for the user to poke it before doing anything.
     */
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        setContentView(R.layout.remote_service_binding)

        // Watch for button clicks.
        var button: Button = findViewById(R.id.bind)
        button.setOnClickListener(mBindListener)
        button = findViewById(R.id.unbind)
        button.setOnClickListener(unbindListener)
        killButton = findViewById(R.id.kill)
        killButton.setOnClickListener(killListener)
        killButton.isEnabled = false

        callbackText = findViewById(R.id.callback)
        callbackText.text = "Not attached."
        handler = InternalHandler(callbackText)
    }

    private class InternalHandler(
            textView: TextView,
            private val weakTextView: WeakReference<TextView> = WeakReference(textView)
    ) : Handler() {
        override fun handleMessage(msg: Message) {
            when (msg.what) {
                BUMP_MSG -> weakTextView.get()?.text = "Received from service: ${msg.arg1}"
                else -> super.handleMessage(msg)
            }
        }
    }
}

java

public static class Binding extends Activity {
    /** The primary interface we will be calling on the service. */
    IRemoteService mService = null;
    /** Another interface we use on the service. */
    ISecondary secondaryService = null;

    Button killButton;
    TextView callbackText;

    private InternalHandler handler;
    private boolean isBound;

    /**
     * Standard initialization of this activity.  Set up the UI, then wait
     * for the user to poke it before doing anything.
     */
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.remote_service_binding);

        // Watch for button clicks.
        Button button = (Button)findViewById(R.id.bind);
        button.setOnClickListener(mBindListener);
        button = (Button)findViewById(R.id.unbind);
        button.setOnClickListener(unbindListener);
        killButton = (Button)findViewById(R.id.kill);
        killButton.setOnClickListener(killListener);
        killButton.setEnabled(false);

        callbackText = (TextView)findViewById(R.id.callback);
        callbackText.setText("Not attached.");
        handler = new InternalHandler(callbackText);
    }

    /**
     * Class for interacting with the main interface of the service.
     */
    private ServiceConnection mConnection = new ServiceConnection() {
        public void onServiceConnected(ComponentName className,
                IBinder service) {
            // This is called when the connection with the service has been
            // established, giving us the service object we can use to
            // interact with the service.  We are communicating with our
            // service through an IDL interface, so get a client-side
            // representation of that from the raw service object.
            mService = IRemoteService.Stub.asInterface(service);
            killButton.setEnabled(true);
            callbackText.setText("Attached.");

            // We want to monitor the service for as long as we are
            // connected to it.
            try {
                mService.registerCallback(mCallback);
            } catch (RemoteException e) {
                // In this case the service has crashed before we could even
                // do anything with it; we can count on soon being
                // disconnected (and then reconnected if it can be restarted)
                // so there is no need to do anything here.
            }

            // As part of the sample, tell the user what happened.
            Toast.makeText(Binding.this, R.string.remote_service_connected,
                    Toast.LENGTH_SHORT).show();
        }

        public void onServiceDisconnected(ComponentName className) {
            // This is called when the connection with the service has been
            // unexpectedly disconnected -- that is, its process crashed.
            mService = null;
            killButton.setEnabled(false);
            callbackText.setText("Disconnected.");

            // As part of the sample, tell the user what happened.
            Toast.makeText(Binding.this, R.string.remote_service_disconnected,
                    Toast.LENGTH_SHORT).show();
        }
    };

    /**
     * Class for interacting with the secondary interface of the service.
     */
    private ServiceConnection secondaryConnection = new ServiceConnection() {
        public void onServiceConnected(ComponentName className,
                IBinder service) {
            // Connecting to a secondary interface is the same as any
            // other interface.
            secondaryService = ISecondary.Stub.asInterface(service);
            killButton.setEnabled(true);
        }

        public void onServiceDisconnected(ComponentName className) {
            secondaryService = null;
            killButton.setEnabled(false);
        }
    };

    private OnClickListener mBindListener = new OnClickListener() {
        public void onClick(View v) {
            // Establish a couple connections with the service, binding
            // by interface names.  This allows other applications to be
            // installed that replace the remote service by implementing
            // the same interface.
            Intent intent = new Intent(Binding.this, RemoteService.class);
            intent.setAction(IRemoteService.class.getName());
            bindService(intent, mConnection, Context.BIND_AUTO_CREATE);
            intent.setAction(ISecondary.class.getName());
            bindService(intent, secondaryConnection, Context.BIND_AUTO_CREATE);
            isBound = true;
            callbackText.setText("Binding.");
        }
    };

    private OnClickListener unbindListener = new OnClickListener() {
        public void onClick(View v) {
            if (isBound) {
                // If we have received the service, and hence registered with
                // it, then now is the time to unregister.
                if (mService != null) {
                    try {
                        mService.unregisterCallback(mCallback);
                    } catch (RemoteException e) {
                        // There is nothing special we need to do if the service
                        // has crashed.
                    }
                }

                // Detach our existing connection.
                unbindService(mConnection);
                unbindService(secondaryConnection);
                killButton.setEnabled(false);
                isBound = false;
                callbackText.setText("Unbinding.");
            }
        }
    };

    private OnClickListener killListener = new OnClickListener() {
        public void onClick(View v) {
            // To kill the process hosting our service, we need to know its
            // PID.  Conveniently our service has a call that will return
            // to us that information.
            if (secondaryService != null) {
                try {
                    int pid = secondaryService.getPid();
                    // Note that, though this API allows us to request to
                    // kill any process based on its PID, the kernel will
                    // still impose standard restrictions on which PIDs you
                    // are actually able to kill.  Typically this means only
                    // the process running your application and any additional
                    // processes created by that app as shown here; packages
                    // sharing a common UID will also be able to kill each
                    // other's processes.
                    Process.killProcess(pid);
                    callbackText.setText("Killed service process.");
                } catch (RemoteException ex) {
                    // Recover gracefully from the process hosting the
                    // server dying.
                    // Just for purposes of the sample, put up a notification.
                    Toast.makeText(Binding.this,
                            R.string.remote_call_failed,
                            Toast.LENGTH_SHORT).show();
                }
            }
        }
    };

    // ----------------------------------------------------------------------
    // Code showing how to deal with callbacks.
    // ----------------------------------------------------------------------

    /**
     * This implementation is used to receive callbacks from the remote
     * service.
     */
    private IRemoteServiceCallback mCallback = new IRemoteServiceCallback.Stub() {
        /**
         * This is called by the remote service regularly to tell us about
         * new values.  Note that IPC calls are dispatched through a thread
         * pool running in each process, so the code executing here will
         * NOT be running in our main thread like most other things -- so,
         * to update the UI, we need to use a Handler to hop over there.
         */
        public void valueChanged(int value) {
            handler.sendMessage(handler.obtainMessage(BUMP_MSG, value, 0));
        }
    };

    private static final int BUMP_MSG = 1;

    private static class InternalHandler extends Handler {
        private final WeakReference<TextView> weakTextView;

        InternalHandler(TextView textView) {
            weakTextView = new WeakReference<>(textView);
        }

        @Override
        public void handleMessage(Message msg) {
            switch (msg.what) {
                case BUMP_MSG:
                    TextView textView = weakTextView.get();
                    if (textView != null) {
                        textView.setText("Received from service: " + msg.arg1);
                    }
                    break;
                default:
                    super.handleMessage(msg);
            }
        }
    }
}

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